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Full text of "Operations analysis of airport surface traffic control (ASTC) system at O'Hare International Airport"

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in 2012 with funding from 

CARLI: Consortium of Academic and Research Libraries in Illinois 



http://www.archive.org/details/operationsanalys02dale 



21- 









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OPERATIONS ANALYSIS OF 

AIRPORT SURFACE TRAFFIC CONTROL (ASTC) 

SYSTEM AT O'HARE INTERNATIONAL AIRPORT 




VOLUME II 
SECTIONS 5 THROUGH 8 

F. D'Alessandro, W. Heiser, G. Knights, P. Monteleon, 
R. Reffelt, R. Rudmann, W. Wolff 



.iLl^Vs. 




NOVEMBER 1974 



WORKING PAPER 



Prepared for 

DEPARTMENT OF TRANSPORTATION 

TRANSPORTATION SYSTEMS CENTER 

Cambridge, Massachusetts 02142 




Technical Report Documentation Page 



1. Report No. 



2. Government Accession No. 



4. Title and Subti tl« 



Operations Analysis of Airport Surface Traffic Control 

(ASTC) System at O'Hare International Airport (Working 

Paper) Volume I - Sections 1 through 4 
Volume II- Sections 5 through 8 



7. A«A.,',) w>Heiser>Gt Knights, R. Reffelt, W. Wolff, 
F. D'Alessandro, R. Rudmann, P. Monteleon 



3. Recipient'* Cotoloq No. 



5. Report Dote 

November 1974 



6. Performing Otgonnolion Code 



8. Performing Organization Report No. 

CSC-TR-74-4410 
CSC-TR-74-4411 



9. Preforming Organization Nam© and Addrei* 

Computer Sciences Corporation 
670 Winters Avenue 
Paramus, New Jersey 07652 



10. Work Unit No. (TRAIS) 



II. Contract or Grant Nc 

DOT-TSC-678 



I 2. Sponsoring Agency Name and Addresi 

Department of Transportation 
Transportation Systems Center 
Cambridge, Massachusetts 02142 



13. Type ol Report und Period Covered 



Working Paper 



14. Sponsoring Agency Code 



15. Supp I ementor y Notes 



16. Abstract 



This working paper examines the air traffic control, airline operations, and airport 
management procedures at the busiest airport in the world. Detailed analysis of air 
traffic flow (based on ASDE film data) and the associated delays are presented for 
ramp, ground control, and local control (runway management) areas. Runway con- 
figurations are examined and surface traffic routing is presented. Congestion loca- 
tions are identified and analyzed. ATC procedures employed by FAA controllers are 
examined through a detailed analysis of communications taking place between pilots 
and controllers. Controller activity and work flow procedures are set forth. The 
results of extensive interviews with pilots and controllers are given to indicate the 
constraints of such factors as aircraft type, visibility, display limitations, and 
special events. Safety aspects are also examined. Based upon the delays and con- 
troller workload results a cost effectiveness analysis is presented to show the pos- 
sible benefits which can be obtained from improvements in the surface traffic control 
system. 



i7. Keywords Airport Operations, Effective- 
ness Measures, Airport Configurations, 
Airline Operations, Tower Cab Operations, 
Environmental Conditions, Runway Config- 
urations, Cost Effectiveness 



18. Distribution Stotement 



19. Security Clossif. (o) thi 

Unclassified 



20. Security dossil, (ol this poqe) 



21. No. of Pages 

Vol. 1-228 
Vol. 11-300 



22. PriCf 



Form DOT F 1700.7 (8-72) 



Reproduction of completed page authorized 



(I. S r.CH'VnNMI- VT I'iUNTfNfi OFFICF : 117 3 72S-Stu/1?fl 



PREFACE 

This report presents the preliminary findings of the first 
phase of the Advanced Airport Surface Traffic Control 
(ASTC) Systems Concept Formulation Study. The overall 
study is a part of the ASTC program of the Department of 
Transportation, Transportation Systems Center (TSC). 
The program is sponsored by the Department of Trans- 
portation, Federal Aviation Administration (FAA), Sys- 
tems Research and Development Service. The TSC ASTC 
program office has contracted with Computer Sciences 
Corporation to perform the study. 

The report is a working paper. It is not the final report 
of the study and is not intended for formal Government 
publication. Its purpose is to permit review, comment 
and correction (if required) by the FAA and other agen- 
cies involved prior to incorporating the findings into the 
final report. The report has been reviewed by TSC and 
does incorporate their comments. In addition, all of 
the theoretical analysis of local area capacity presented 
in Section 5. 3.3. 1 was done by Messrs. Paul Rempfer 
and Lloyd Stevenson of TSC. 



in 



TABLE OF CONTENTS - VOLUME I 

Page 

Section 1 - Introduction 1-1 

1.1 General 1-1 

1.2 Overview of Study 1-1 

1. 3 Description of Operations Analysis 1-4 

Section 2 - Operations Analysis Approach 2-1 

2.1 General 2-1 

2.2 Establishing the Basis for Analyses 2-1 

2.3 O'Hare Operations Effectiveness Analysis Approach 2-8 

2.3.1 General 2-8 

2.3.2 Fuel Consumption Assessment 2-9 

2.3.3 Pollution Emission Assessment 2-11 

2.3.4 Operating C ost 2-12 

2.3.5 Passenger Inconvenience Assessment 2-13 

2.3.6 Accident Risk Assessment 2-15 

2.3.7 Summary of Effectiveness Measures 2-17 
2. 4 Methodology for Functional Analysis of ASTC System Operation 2-19 
2.4. 1 Controller Task Analysis 2-19 

2.4.2 Aircraft Flow Analysis 2-28 

2.4.3 Airline Operations Analysis 2-39 

2.4.4 Airport Management Operations Analysis 2-43 

2. 5 Projection of the Future Operating Environment at 

O'Hare Airport 2-44 

Section 3 - Airport Configuration Description 3-1 

3. 1 General 3-1 

3.2 Runway Configuration Description 3-1 

3.2.1 Runway Descriptions 3-1 

3.2.2 Runway Configuration Usage 3-6 

3.3 Taxi Flow Patterns 3-23 

3.3.1 Configuration 1 3-24 

3.3.2 Configuration 2 3-32 

3.3.3 Configurations 3-34 

3.3.4 Configuration 4 3-36 

3.3.5 Configurations 3-38 

3.3.6 Configuration 6 3-40 



TABLE OF CONTENTS (Continued) 



Page 

3.3.7 Configuration 7 3-40 

3.3.8 Configurations 3-43 

3.3.9 Configuration 9 3-45 

3.3.10 Configuration 10 3-47 

3.3.11 Configuration 11 3-47 
3.4 Terminal Configuration Description 3-51 
3.4. 1 Terminal Gate Layout 3-51 

3.4.2 Aircraft Docking at the Gates 3-54 

3.4.3 Aircraft Movements and Control 3-54 

3. 4. 4 Impact of Terminal Configuration on ASTC System Operation 3-55 

Section 4 - Functional Description of the O'Hare ASTC System 4-1 

4. 1 General 4-1 

4.2 FAA Airport Traffic Control Tower (ATCT) Functions 4-1 

4.2.1 General Responsibilities 4-1 

4.2.2 Tower Cab 4-2 

4.2.3 TRACON 4-69 

4.3 Airline Functions 4-74 

4.3.1 General Responsibilities 4-74 

4.3.2 Airline Terminal Operations 4-75 

4.3.3 Flight Deck (Cockpit) Operations 4-84 

4.4 Airport Management Functions 4-88 

4.4.1 General Responsibilities 4-88 

4.4.2 Airport Personnel Position Descriptions 4-88 

4.4.3 Functional Operations Descriptions 4-92 

4.4.4 Emergency Operations 4-97 



VI 



TABLE OF CONTENTS - VOLUME II 

Page 

Section 5 - Operational/Functional Activity Analyses 5-1 

5.1 General 5-1 

5.2 Traffic Operations Environment for Data Analysis Periods 5-1 
5. 2. 1 Selection of Operational Periods for Study 5-2 

5.3 Aircraft Flow Analysis 5-7 

5.3.1 Ramp Area 5-9 

5.3.2 Ground Controllers' Area 5-30 

5.3.3 Local Controllers' Area 5-77 

5.4 Controller Activity (Workload) Analysis 5-140 

5.4.1 Controller Communications Activity Analysis 5-141 

5.4.2 Controller Non-Communications Activity Analysis 5-169 

5.4.3 Traces of Individual Flights Through the ASTC System 5-186 

5.4.4 Other Observations of Tower Cab Activities 5-194 

5.5 Cockpit Crew Activity (Workload) Analysis 5-201 

5. 5. 1 Crew Activities During Departure and Arrival 5-201 

5.5.2 Cockpit Workload Analysis 5-207 

5.5.3 Cockpit Observations 5-211 

Section 6 - ASTC System Operations Effectiveness Analysis 6-1 

6. 1 General 6-1 

6.2 System Effectiveness Criteria Measures 6-1 

6.3 Current O'Hare ASTC System Effectiveness 6-3 

6.3.1 Traffic Delay Effectiveness 6-4 

6.3.2 Controller Communications Workload 6-6 

6.3.3 Fuel Consumption Effectiveness 6-7 

6.3.4 Pollution Emission Effectiveness 6-10 

6.3.5 Operating Cost Effectiveness 6-14 

6.3.6 Passenger Inconvenience 6-16 

6.3.7 Accident Risk Evaluation 6-19 

6.3. 8 Qualitative Analysis of Accident Risk Potential 6-25 

6.4 Future O'Hare ASTC System Effectiveness Assessment 6-32 
6.4. 1 Projected Future Operating Environment 6-32 
6.4.2 Assessment of the ASTC System Effectiveness in the Projected 

Future Operating Environment 6-34 



Vll 



TABLE OF CONTENTS (Continued) 



Section 7 - Findings and Conclusions 7-1 

7. 1 General 7-1 

7.2 Summary of Findings 7-1 

7.2. 1 Functional Responsibilities of Operational Personnel 7-1 

7. 2. 2 Current O'Hare Operating Configuration 7-5 

7.2.3 Future O'Hare A STC System 7-9 

7.3 Conclusions 7-11 

7.3.1 Capacity and Delay 7-11 

7.3.2 System Effectiveness Assessment 7-18 

7.3.3 General Observations 7-20 

7. 3. 4 Summary 7-22 

7.4 Recommendations 7-23 

Section 8 - References 8-1 



Vlll 



LIST OF ILLUSTRATIONS 



Figu re 



1-1 Task Breakdown and Study Flow 1-2 

1-2 Simplified O'Hare Operations Analysis Flow Diagram 1-5 

2-1 Departure Flight Operations Flow 2-3 

2-2 Arrival Flight Operations Flow 2-4 

3-1 O'Hare International Airport 3-2 

3-2 Location of Departure Queues and Ground Control Handoff 

Areas at O'Hare 3-25/3-26 

3-3 Aircraft Route at O'Hare — Hangar, Cargo, and Air Force 

Areas 3-27/3-28 

3-4 Main Service Vehicle Roads at O'Hare Airport 3-29/3-30 

3-5 Configuration 1 3-31 

3-6 Configuration 2 3-33 

3-7 Configuration 3 3-35 

3-8 Configuration 4 3-37 

3-9 Configuration 5 3-39 

3-10 Configuration 6 3-41 

3-11 Configuration 7 3-42 

3-12 Configuration 8 3-44 

3-13 Configuration 9 3-46 

3-14 Configuration 10 3-48 

3-15 Configuration 11 3-49 

3-16 Gate Assignments 3-52 

4-1 O'Hare Control Tower Floor Plan 4-3 

4-2 Tower Cab Detail 4-4 

4-3 Tower Cab Photographs 4-10 

4-4 Visual Surveillance Limitations 4-30 

4-5 Radar Coverage 4-32 

4-6 Functional Flow of Major Flight Data Tasks 4-34 

4-7 Functional Flow of Clearance Delivery Tasks 4-39 

4-8 Functional Flow of Major Outbound Ground Tasks 4-45 

4-9 Functional Flow for Major Inbound Ground Tasks 4-56 

4-10 Functional Flow of Major Local Control Tasks 4-61 

4-11 TRACON Room - O'Hare International Airport 4-70 

4-12 United Airlines Gate Plan for O'Hare Airport 4-77 

4-13 VHF Radios in Cockpit 4-85 

4-14 Chicago - O'Hare International Airport Organization Chart 4-89 

5-1 Aircraft Flow Between Movements Analysis Areas 5-7 

5-2 Gate Assignments 5-10 

5-3 Distribution of Ramp Service Times for "Arrivals" 5-18 

5-4 Distribution of Ramp Service Times for "Departures" 5-20 



IX 



LIST OF ILLUSTRATIONS (Continued) 



Figure Page 

5-5 Distribution of Operation Durations 5-21 

5-6 Distribution of Gate Occupancy Times 5-23 

5-7 Timing Relationships - Ground Controllers' Area (Arrivals) 5-31 

5-8 Timing Relationships - Ground Controllers' Area 

(Departures) 5-32 

5-9 Penalty Box Delays 5-52 

5-10 Aircraft Delay in Ground Control Area 5-54 

5-11 Intersection Numbering - O'Hare (CSC Assigned) 5-56 
5-12 Time Line Plot of Ideal Single Runway Operation Saturated 

In Arrival and Departure Demand (80 Operations/Hour) 5-79 
5-13 Time Line Plot of Actual Single Runway Operation Saturated 

In Arrival and Departure Demand in Good Visibility 

Conditions (64 Operations /Hour) 5-79 
5-14 Arrival Runway Occupancy Time for Two One-Hour Periods 

(Total Mean 46 Seconds) 5-81 
5-15 Departure Runway Occupancy Time for Two One-Hour Periods 

(Total Mean 40 Seconds) 5-81 
5-16 Interarrival Spacing for Six One-Hour Periods of Varying 

Demand 5-82 

5-17 Interarrival Spacing for Two One-Hour Busy Periods 5-83 

5-18 Departure Capacity Estimate for Single Runway Operation 5-86 

5-19 Strategy Curves for Various Runway Configurations 5-88 
5-20 Position of Arrival Pairs at the Time of Departure Release 

for Two Runway Configurations 5-96 
5-21 Initial Heading Mix of Departures for Quasi -Independent 

Runway Operation Over 50 Minutes of Heavy Demand 5-98 

5-22 Potential Payoffs for Metering and Spacing 5-104 
5-23 Timing Relationships - Local Controllers' Area 

(Departures) 5-107 

5-24 Correlation of Delay and Capacity Estimates 5-126 

5-25 Local Control Delay - North Side (East Arrivals) 5-128 

5-26 Local Control Delay - South Side (East Arrivals) 5-129 

5-27 Local Control Delay - North Side (West Arrivals) 5-130 

5-28 Local Control Delay - South Side (West Arrivals) 5-131 

5-29 Inbound Ground Channel Occupancy Vs Traffic Volume 5-149 
5-30 Channel Occupancy Vs Aircraft Handled for Both Ground 

Control Positions 5-154 

5-31 Local Control Hourly Occupancy Time Vs Aircraft Handled 5-160 



LIST OF ILLUSTRATIONS (Continued) 



Figure Page 

5-32 Analysis of Short Term Communication Saturation Effects 5-163 

5-33 Ground Control Communication Saturation 5-165 

5-34 Local Control Communication Saturation 5-167 

5-35 Gate Delay Curves 5-183 

5-36 Flight Strip for UA 247 5-187 

5-37 Flight Strip for General Aviation N309VS 5-190 

5-38 Illustration of In-Cockpit Flight Trace 2 5-219 

6-1 Cockpit Communications Workload Calculation 6-22 

6-2 Projected Future Operating Environment at O'Hare 6-33 

7-1 Current O'Hare Layout 7-8 

7-2 Projected Future Operating Environment at O'Hare 7-10 



XI 



LIST OF TABLES 



Table Page 

2-1 Summary of Effectiveness Measures 2-18 

2-2 Examination of Aircraft Flow Variables 2-30 

2-3 Movement Events Measured for ASDE Film Analysis 2-33 

3-1 Classification of Crossing Runway Configurations 3-3 

3-2 Runway Landing Aids at O'Hare 3-5 

3-3 Primary Runway Configurations Identified by ATCT 3-8 

3-4 Runway Usage Minimums Under Low Visibility Conditions 3-11 

3-5 O'Hare Runway Utilization - CY-71 3-13 

3-6 Seasonal Runway Configuration Usage (Jan. and Feb. 1973) 3-15 

3-7 Seasonal Runway Configuration Usage (April and June 1973) 3-16 

3-8 Profile of Runway Configurations Used in Clear and Calm 

Weather 3-19 
3-9 Profile of Runway Configurations Used in the Clear and/or 

Windy Weather 3-20 
3-10 Relative Usage of Various Runway Configuration Classes 

at O'Hare 3-22 

3-11 Gate Assignments Vs Ramp Areas at O'Hare 3-53 

4-1 Responsibilities and Duties of the Flight Data Position 4-16 

4-2 Responsibilities and Duties of the Clearance Delivery 

Position 4-17 
4-3 Responsibilities and Duties of the Outbound Ground 

Position 4-19 

4-4 Responsibilities and Duties of the Inbound Ground Position 4-21 

4-5 Responsibilities of Local Control Position 4-23 

4-6 Clearance Delivery Gate Marking 4-41 

4-7 Predominantly Preferred Checkpoints for Position Reporting 

During Low Visibility Conditions 4-50 
4-8 Specific Points or General Area at Which Turnover to Local 

Control May be Made by Outbound Ground 4-53 

4-9 Responsibilities and Duties of the Approach Control Position 4-71 

4-10 Responsibilities and Duties of the Departure Control Position 4-72 

4-11 Responsibilities and Duties of Parallel Approach Monitor (2) 4-73 
4-12 Authorized Aircraft Parking - O'Hare Passenger Terminal - 

American Airlines 4-80 
5-1 Summary of Operational Environments for Data Periods 

Selected for Detailed Analysis 5-5 

5-2 Ramp Usage Data 5-12 

5-3 Peak Traffic Flow — Ramp Area 5-15 

5-4 Aircraft Flow Data - Ramp Area 5-16 

5-5 Arrival and Departure Hold Analysis 5-24 



xn 



LIST OF TABLES (Continued) 



Table Page 

5-6 Selected Ramp Area Activity (Run #33 - 16:45-17:45) 5-26 

5-7 Ramp Activity by 10-Minute Periods (Run #33) 5-26 

5-8 Sample Data Sheet 5-33 

5-9 Sample Data Reduction Sheet 5-35 

5-10 Summary of Ground Control Aircraft Flow 5-38 

5-11 Summary - Aircraft Flow Statistics - Ground Control 5-51 

5-12 Summary of Analyzed Runs 5-53 

5-13 Breakdown of Holds by Location and Cause 5-57 

5-14 Summary of Holds by Reason 5-70 

5-15 Delay Time by Category 5-70 

5-16 Operating Strategies for Capacity Estimation 5-87 

5-17 Predicted Capacity of Various Runway Configurations 5-89 
5-18 Single Runway Mixed Operations in Good Visibility with 

Continuous Double Departure Demand 5-91 

5-19 Near-Near Runway Configuration in Good Visibility 5-92 

5-20 Near-Far Runway Configuration in Good Visibility 5-94 

5-21 Far-Far Runway Configuration (1 of 2 Cases) 5-95 

5-22 Practical Estimated Runway Capacity 5-99 
5-23 Single Runway Mixed Operations in Bad Cab Visibility 

Conditions With Continuous Double Departure Demand 

and ASDE-2 in Use 5-100 
5-24 Single Runway Mixed Operations in Bad Cab Visibility 

Conditions With Continuous Double Departure Demand 

Without ASDE-2 in Use 5-102 

5-25 Effect of Bad Visibility on Single Runway Mixed Operations 5-102 

5-26 Sample Data Reduction Sheet 5-108 

5-27 Summary of Local Control Aircraft Flow 5-110 

5-28 Summary - Aircraft Flow Statistics - Local Control 5-122 

5-29 Average Delay for the Primary Arrival Modes 5-123 
5-30 North Side/South Side Delay for the Primary Arrival Modes 

in Good Cab Visibility Conditions 5-124 
5-31 Delay and Percent Predicted Capacity for Good Cab Visibility 

Conditions 5-125 
5-32 Distribution Statistics of Local Control Delays (Arrivals 

from West) 5-134 
5-33 i Distribution Statistics of Local Control Delays (Arrivals 

from East) 5-135 

5-34 Summary of Current O'Hare Capacity in Good Visibility 5-137 
5-35 Summary of ASTC Improved O'Hare Capacity in Good 

Visibility Without Metering and Spacing 5-138 



XI 11 



LI ST OF TABLES (Continued) 



Table Page 

5-36 Summary of Clearance Delivery Transactions 5-144 

5-37 Summary of Inbound Ground Communications Transactions 5-147 
5-38 Intersection Control Instruction Approach Vs Visibility 

Conditions - Inbound Ground 5-150 

5-39 Summary of Outbound Ground Communications Transactions 5-152 
5-40 Intersection Control Instruction Approach Vs Visibility 

Conditions - Outbound Ground 5-155 

5-41 Summary of Local Control Communications Transactions 5-159 

5-42 Communication Channel Saturation Estimates 5-164 

5-43 Flight Data Activities Measurement 5-173 

5-44 Clearance Delivery Activities Measurement 5-174 

5-45 Departure Ground Activities Measurement 5-175 

5-46 Inbound Ground Activities Measurement 5-176 

5-47 Local Control Activities Measurement 5-177 

5-48 Summary of Non- Communications Activity Workload 5-185 

6-1 Distribution of Aircraft Types at O'Hare 6-2 

6-2 Weighted Average Gallons of Fuel per Idle Aircraft 

Minute at O'Hare 6-9 
6-3 Typical Pollution Emissions Vs Fuel Consumption Rate 

at Idle Engine Speed 6-11 
6-4 Estimated Average Pollutants per Idle Aircraft Minute 

at O'Hare 6-12 
6-5 Weighted Average Operating Cost Per Idle Aircraft 

Minute at O'Hare 6-15 

6-6 Weighted Passenger Loading for Aircraft at O'Hare 6-17 

6-7 Accident Risk Evaluation 6-20 

7-1 Primary Runway Configuration Identified by ATCT 7-7 

7-2 Average Delay Summary in Good Visibility Conditions 7-16 

7-3 Summary of Aircraft Load (Density) 7-17 



xi v 



SECTION 5 - OPERATIONAL/ FUNCTIONAL ACTIVITY ANALYSIS 

5. 1 GENERAL 

The purpose of this section is to present the results of the quantitative 
analyses of the O'Hare ASTC System operations. The operations environments for 
the periods selected for detailed analysis of the ASDE films and controller commu- 
nications recording are described. Following this, results of the data analyses are 
presented for the areas of: 

1. Aircraft flow analysis, including traffic flow statistics for the 
ramp, ground taxi, and local control areas. 

2. Controller workload analysis, both communications and non- 
communications. 

3. Cockpit crew workload analysis, both communications and non- 
communi cations . 

5. 2 TRAFFIC OPERATIONS ENVIRONMENTS FOR DATA ANALYSIS 

PERIODS 

As noted in several earlier portions of this report the airport operating 
mode and the runway configuration in use are the primary determinants in the direc- 
tion of ground traffic flow and, therefore, can be expected to influence taxi times 
and delays. In addition, the nature of the runway configuration could be expected 
to influence traffic flow for departures after reaching the runway queue as well as 
arrival operations. For these reasons it was decided that the data analysis would 
be performed in a manner that allowed examination of the differences in airport op- 
erations as a function of runway configuration and operating mode (i. e. , Arrivals 
from the East or Arrivals from the West). Thus, various traffic operations peri- 
ods represented in the ASDE films and controller communications recordings made 
by TSC and CSC were selected for detailed study to derive a data base for the 

1. Analysis of traffic flow statistics 

2. Controller workload statistics 



5-1 



3. Pilot workload analysis 

4. ASTC system effectiveness assessment 

5. 2. 1 Selection of Operational Periods for Study 

The following guidelines and criteria were generally employed in the 
selection of the various operational periods for detailed analysis: 

1. The runway configuration met the general definition of the two op- 
erating modes; that is, during a sample time period of one hour it 
was possible to identify one primary arrival runway among the 
northside and southside runways to which approaches were made 
from generally the same direction, east or west. This did not 
rule out occasional arrivals on another runway. 

2. There was no runway configuration change during the sample 
period. Because runway configuration influences the ground taxi 
flow pattern, changes in configuration would result in differing 
taxi operations for which ground movements data could not be con- 
sidered from the same statistical sample for analysis purposes. 

In addition, such changes tend to introduce additional influences 
on traffic movement delays which would be difficult to distinguish 
in the ASDE films. 

3. The sample time periods of interest were restricted to weekdays 
and, more specifically, to hours of normal traffic, i.e., between 
0800 and 2100 local time. 

4. Periods representing normal visual operations in either east or 
west mode would constitute the primary samples for analysis. 
The basis for this criteria was the decision that the data derived 
should support the following study analyses of ASTC functional 
performance and design definition. Since future ASTC systems 
would function and be of primary value during normal operating 
traffic volumes, if these volumes are to increase as predicted, 
the supporting data should be drawn primarily from such opera- 
tional periods. 

5. Sample periods representing other than normal visual operations 
would be selected if they 

a. met criteria 1-3 above; 



5-2 



b. exhibited a "normal" constraint on airport operations due to 
reduced visibility. 

6. Satisfactory ASDE films and controller communications record- 
ings were available to permit the analysis of traffic flow statistics 
and controller communications activities, particularly under re- 
duced visibility conditions. 

7. The traffic operations volume (i. e. , total number of operations) 
represented a moderate to heavy level of traffic. 

Using these criteria, the operations environments represented in the 
40 TSC data runs (80 hours of operations) and the quality of the data available for 
analysis were reviewed. The potential runs for analysis were first narrowed down 
to twelve that met criteria 1 through 5. Runway occupancy counts were made from 
the ASDE films on these runs to verify the runway configuration and to measure the 
total traffic volume. Based on these results, the choice of eight runs (four for each 
mode of operation) for analysis was made. These runs all represented normal vis- 
ual operations periods.* For the various TSC runs involving non-visual conditions, 
several were definitely eliminated because they did not satisfy criteria 5a or 5b. 
The decision was deferred for a few of these runs, pending the availability of suit- 
able non-visual operations periods from the CSC data collection, because they did 
not satisfy criteria 6 (i. e. , no ASDE films were available or interference between 
ground control channels did not permit investigation of the effects of these condi- 
tions on controller communications activity). 

These same selection criteria were applied to CSC data resulting in the 
choice of five runs for analysis. Three of the runs represented operations under 
Category I and Category II conditions. The choice of two of these runs holds spe- 
cial significance. The first of these runs includes Category I conditions for the 
first hour of the collection period and deterioration of conditions to Category II 



*The analysis for one of these runs was terminated because of difficulties with the 
ASDE film. 



5-3 



early in the second hour. Thus, the data derived from this run allows examina- 
tion of the transition for Category I to Category II operations. The second of these 
runs was made later in the same day, also under Category I conditions, and exhib- 
its the effects on airport operations resulting from the extreme disruption caused 
by the preceding Category II situation. 

The operational environments represented in the selected data periods 
are summarized in Table 5-1. From the table it may be seen that a total of 14 
operational periods were analyzed, including five "Arrival from the East" mode 
and four "Arrival from the West" mode under good visibility conditions, and five 
"Arrival from the West" mode under low visibility conditions (which is the normal 
mode for such conditions). Traffic volumes ranging from approximately 100 to 
140 operations per hour, excluding Run CSC #8b, were observed. In addition, 
both Dual (i.e. , independent intersecting arrivals) and Parallel (i.e. , indepen- 
dent parallel arrivals) approach modes of runway operation were covered. 



5-4 



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5-6 



5.3 



AIRCRAFT FLOW ANALYSIS 



A major part of the operational analysis at O'Hare has consisted of an 
examination of the aircraft flow statistics for the three main areas of interest, 
namely, the Ramp (or Carrier) area, the Ground Controllers' area, and the Local 
Controllers' area. The Ramp area has been defined for the purposes of this anal- 
ysis as that inside the concourse fingers. The Ground Controllers' area has been 
defined to include the remainder of the airport surface excluding the departure 
queue and active runways. These latter two areas have been defined as the Local 
Controllers' area which is of interest to the ASTC program. Each aircraft moves 
through these three areas irrespective of its flight phase (i. e. , arrival or depar- 
ture). The examination of these three areas has taken into account the operational 
differences between them, wherein the north and south side runways at O'Hare are 
handled by separate Local Controllers. On the other hand, the Ground Controllers' 
operation is based not on geographic separation but rather on aircraft flight phase-- 
one controller for arrivals and another for departures. Each of the eight ramp 
areas, of course, handles both arrivals and departures so that both Ground Con- 
trollers must consider the impact of ramp area operations on their respective 
traffic. Figure 5-1 illustrates the flow of aircraft through these areas. 



GATES 



r 

8 
L 



GROUND CONTROL 
AREAS 



RAMP 
AREA 



RAMP 
AREA 




ARRIVALS 



DEPARTURES 



LOCAL CONTROL 
AREAS 



£ 




LOCAL CONTROL 
NORTH 



LOCAL CONTROL 
SOUTH 



t 

Figure 5-1. Aircraft Flow Between Movements Analysis Areas 



-A 



5-7 



The traffic flow in each of these areas is analyzed to derive statistical 
parameters for nominal movement times and delays in relation to the volume of 
traffic flowing in the area during the period. In addition, queuing analysis models 
are employed to derive an average density (Q) or number of aircraft flowing in 
each of the movement areas at any time. 

The aircraft delays which occur in the several parts of the surface 
traffic control system are influenced by parameters unique to the particular move- 
ment area. Delays in the ramp areas are more influenced by airline scheduling 
than by runway operations levels. Departure delays in the Local Control area will 
be highly influenced by arrival traffic. To establish a common basis for combin- 
ing the various delays, all values were normalized to an average delay per opera- 
tion. This permits a comparison of delays at various points in the total system. 
The simple model to be used for comparison and/or addition of the various delays 
contains the following components: 

Ramp Area Delay 
Penalty Box Delay 
Ground Control Delay 
Local Control Delay 

Other possible delays may be experienced while the aircraft is at the 
gate or while the aircraft is under approach control. Neither of these has been 
evaluated in this analysis. Delays at turnoff for arrivals have been investigated 
and occur so seldom that they will not be considered as a significant component 
of the overall delay model. 

Descriptions of the data analysis and results for each of the three 
movement areas are presented in the following paragraphs. 



5-8 



5. 3. 1 Ramp Area 

5. 3. 1. 1 Data Collection 

During the period January 16 to 18 and January 23 to 25, 1974, visual 
observations were made at Chicago's O'Hare Airport terminal area to determine 
aircraft movement characteristics within the ramp area. During this period, ap- 
proximately 350 individual aircraft movements were recorded within several ramp 
areas for both arriving and departing aircraft. TSC ASDE film data taken during 
February and March 1973 was also used for determining activity in the various 
ramp areas. 

The principal parameters of interest for arrival flights consisted of 
total taxi time and hold time, if any. For departing aircraft the time intervals of 
interest were separated as follows: 

1. Pushback operation 

2. Engine start time (waiting period between end of pushback to start 
of taxi) 

3. Taxi time 

4. Hold time 

The techniques used for obtaining these parameters were described in 
Section 2. 

The concourse configurations together with gate numbering schemes 
are shown in Figure 5-2 to aid in the identification of the location of the ramp 
areas described in this report. With the exception of the K ramp (Gates 1-11), 
all ramp areas are described in this report by two alpha- characters which relate 
to a specific area enclosed between two adjacent concourses. 

VFR conditions generally prevailed throughout most of the visual ob- 
servation period. The first of two exceptions occurred on 17 January around 0900 
when the visibility was somewhat reduced due to fog and haze. The data collected 



5-9 



3t^r , 0N4L ® 



IO B m m / \ 






LEGEND 




• 


Jetway 




A 


Stairs 




a 


Stairs and Lower Jetway 


■ 


Abbreviated 


Jetway 


• 


Helicopter 




LL 


Lower Level 





AIRLINES 



AAL 


American 


EAL 


Eastern 


AC 


Air Canado 


NOR 


North Central 


AL 


Allegheny 


NWA 


North West Orient 


BNF 


Broniff 


OZA 


Ozork 


CAL 


Continental 


TWA 


Trans World 


DAL 


Delta 


UAL 


United 



Figure 5-2. Gate Assignments 



5-10 



during this period was not indicative of any perceptual difference in aircraft move- 
ment within the ramp area and is, therefore, included in this report. 

The second exception occurred on the morning of 18 January. An at- 
tempt was made to record data on the K and HK ramp areas. Visibility conditions, 
however, deteriorated steadily throughout the observation interval with reported 
RVRs of 1000 or less due to patchy fog which occasionally obscured the outer edge 
of the concourses. Also, ceilings were, at times, below 100 feet which had a sig- 
nificant impact on overall airport operations both during these morning hours and 
later on in the day when conditions had improved. Many flights were subsequently 
canceled. Since conditions outside of the ramp area were considered to be abnor- 
mal (lack of arrivals, delayed departures and long queues) with the result that al- 
most no activity existed at the gate, this ramp area data has not been included in 
this report. 

5. 3. 1. 2 Data Results 

Table 5-2 provides ramp usage data for TSC Runs 35, 33, 20, 29, and 
37 on both a numerical and percentage basis. The numbers represent aircraft 
movement either in or out of the specific ramp area from or to the identified run- 
ways as collected from the ASDE films. The letter "A" following the runway num- 
ber indicates arrival aircraft that proceeded to a specific ramp area while the 
letter "D" indicates departing aircraft that left a ramp area and proceeded to a 
specific runway. Ramp areas FG and GH appear to be uniformly the most active 
with movements of 20-22 aircraft per hour. Note, however, that in three of the 
runs the general aviation area (Butler) experienced comparable traffic. 



5-11 



Table 5-2. Ramp Usage Data (1 of 2) 



Ramp Area 


A-C 


CD 


DE 


EF 


FG 


GH 


HK 


K 


Other 


Total 


Run #35 10:07-11:07 


2 


5 


4 


1 


6 


3 


4 


3 


1 




RW 32R D 


32L A 


1 


4 


4 


2 


4 


6 


2 


1 


1 




27L D 




1 


5 


3 


6 


5 


3 


2 


1 




32L D 










1 












27R D 


1 




















22R A 


1 












1 








27R A 


6 


3 


1 


1 


4 


5 




1 






Total 


11 


13 


14 


7 


21 


19 


10 


7 


3 


105 


Percent 


10 


12 


13 


7 


20 


18 


9 


7 






Run #33 16:45-17:45 


1 


3 


4 


1 


4 


6 


4 


3 


1 




RW 22L D 


32R D 


4 


3 


5 


5 


5 


6 


2 


2 






32L D 


4 


2 




1 










1 




27L D 








2 


1 












22R A 


6 












2 








27R A 


6 


5 


4 




6 


4 


1 


2 


1 




27L A 


2 


4 


3 


7 


3 


6 


4 


4 


1 




Total 


23 


17 


16 


16 


19 


22 


13 


11 


4 


142 


Percent 


16 


12 


11 


11 


14.5 


15 


9 


8 






Run #20 8:40-9:40 


7 


4 


3 


5 


3 


3 


2 


3 


3 




RW 22R A 


27L A 


2 


2 


8 


5 


6 


4 


6 


1 


1 




27R A 


2 




















27R D 


1 


2 




2 


3 


3 


1 


1 


1 




27L D 


5 


3 


4 


4 


4 


3 


7 


4 


2 




32R D 


2 


1 


6 


2 


4 


3 


2 


3 






Total 


19 


12 


21 


18 


20 


16 


18 


12 


7 


143 


Percent 


13 


8 


15 


13 


14 


11 


13 


8 


5 





5-12 



Table 5-2. Ramp Usage Data (2 of 2) 



Ramp Area 


A-C 


CD 


DE 


EF 


FG 


GH 


HK 


K 


Other 


Total 


Run #29 18:02-19:02 






















RW 9R A 


2 


3 




6 


5 


5 


2 


2 


4 




14L A 




2 


3 


2 


3 


5 


3 


4 






4L D 




3 


1 


2 


2 


3 


4 


4 


1 




4R D 


3.8 


1.8 


5.8 


4.8 


3.8 


3.8 


1.8 


1.7 


0.7 




Total 


5.8 


9.8 


9.8 


14.8 


13.8 


16.8 


10.8 


11.7 


5.7 


99.0 


Percent 


5.9 


9.9 


9.9 


14.9 


13.9 


17.0 


10.9 


11.8 


5.8 




Run #37 15:36-16:36 


9 


2 


2 




2 


3 


6 


6 






RW 14L A 


14R A 


2 


6 


6 


6 


7 


4 


2 


2 






22R A 


2 




















9L D 


10 


2 


2 




3 


6 


1 


3 






4L D 












1 










9R D 


1 


6 


5 


5 


7 


6 


2 


1 


1 




Total 


24 


16 


15 


11 


19 


20 


11 


12 


1 


129 


Percent 


19 


12 


12 


9 


15 


16 


9 


9 


1 





5-13 



From the data given in Table 5-2, the estimated "Break Point"* for 
the eight ramp areas is as follows: 



Run # 


35 


33 


20 


29 


37 


Est. Break Point Location 


FG 


F 


F 


FG 


F 



A summary of peak traffic flow as extracted from Table 5-2 is given 
in Table 5-3. From this table it appears that O'Hare is running about 1. 4 opera- 
tions/hour/gate for the jetway terminal areas during their peak periods. Ramp 
parking increases this capability greatly in AC and EF giving a weighted mean of 
about 1.6 operations/hour/gate. With a mean service time of about 45 minutes/ 
turnaround (see paragraph 5.3.1.3) measured at O'Hare, this gives an average 
gate utilization (i.e. , percent gates occupied at any instant) of 60 percent. 



Operations/Hour _ Operations/ Turnaround (2) x Gate Utilization 

Gate ' Hours of Service/Turnaround (. 75) 



This 60 percent is consistent with the results of preliminary requirements at 
O'Hare (Reference 8). It will be seen in paragraph 5. 3. 2. 3 that there exists sub- 
stantial gate delays during peak periods and, therefore, 1. 6 operations/hour/gate 
can be considered a peak capacity estimate. This would result in an overall peak 
gate capacity of 150 operations/hour at O'Hare (with 94 gates). 



*Break Point is the physical median for traffic origination and destination, i. e. , 
50 percent of the traffic originates before this point. This impacts on controller 
decision-making with respect to routing of traffic. 



5-14 



Table 5-3. Peak Traffic Flow — Ramp Area 



Ramp Area 


A-C 


CD 


DE 


EF 


FG 


GH 


HK 


K 


Peak AM 


19.0 


13.0 


21.0 


18.0 


21.0 


19.0 


18.0 


12.0 


Peak PM 


24.0 


17.0 


16.0 


16.0 


19.0 


22.0 


13.0 


12.0 


Gates 


8.0 


13.0 


15.0 


9.0 


14.0 


16.0 


10.0 


9.0 


Peak Operations/ 
Hour /Gate 


3.0 1 


1.3 


1.4 


2.0 2 


1.5 


1.4 


1.8 


1.4 



General aviation ramp parking gives many effective gates. 

2 
Ozark ramp parking gives 13 effective gates. 

A summary of pertinent visual ramp observation data is given in 
Table 5-4. The data is grouped into three categories: 



1. 



Run Identification 



This grouping contains a run number, the ramp area identifica- 
tion, and the date of observation. These run numbers are for the 
visual ramp measurements only and should not be correlated with 
other CSC run numbers given in this report. 

Overall Ramp Activity Summary 

Included in this grouping are the starting and ending times of the 
observation period, the number of arriving and departing aircraft 
and the operations rate per hour (arrivals and departures) during 
the total observation period. 

Average Aircraft Flow Durations 

The data provided here are average values calculated on individ- 
ual runs and include all information for the total observation 
period. Runs 3 and 5 and runs 4 and 6 have been combined and 
the data tabulated in the rows corresponding to runs 3 and 4, 
respectively. The duration for each element is in seconds with 
the exception of Gate Occupancy time, which is shown in minutes. 



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5-16 



5. 3. 1. 3 Supporting Data Analysis for Visual Observations 

As indicated previously, the entries provided in Table 5-4 are average 
values obtained from the data for specific observation periods. While these values 
do have some significance in certain applications, they are restrictive since they 
do not convey any information as to the spread of values observed between differ- 
ent samples. In order to demonstrate the variations that were observed, cumula- 
tive distributions of the various parameters were prepared by combining the data 
collected during all of the runs shown in the table. 

The reason for combining the data, instead of presenting it on an indi- 
vidual run basis, is due to the relatively small number of samples contained in 
any given run. For example, the maximum number of samples in either depar- 
tures or arrivals is twenty-one, so that any sample period represents approxi- 
mately five percent of the total sample population. Thus, the weighting of any 
sample period is too large for any reasonable presentation of a distribution. 

Figure 5-3 demonstrates the variability of Ramp Service Time for 
arrivals as a percentage of total observations. The plot is relatively linear for 
cumulative percentages up to 90 percent and has a shallow slope indicating a rela- 
tively uniform distribution of the amount of time required from the time of entry 
to docking. This is consistent with the fact that the gates are located at various 
distances from the end of the concourse where the timing history of each aircraft 
first begins and indicates that 90 percent of the arrivals experienced no ramp 
delays. 

The remaining 10 percent of the traffic exhibited increasingly longer 
arrival durations which were the result of holds or a slow down in taxi speed caused 
by various activities in the ramp area. These activities include such factors as: 

1. Gate area not clear of ground vehicles 

2 . Pushbacks of other aircraft 

3. Jetway operator not on station 

4. Vehicles moving about in ramp area 



5-17 



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5-li 



Figure 5-4 depicts the cumulative distribution of Ramp Service Time 
for departures as measured from the time pushback started until the aircraft 
cleared the outer edge of the concourse. Since this time duration includes four 
separate intervals, i. e. , pushback, engine start, taxi, and holds, the variability 
can be expected to be, and is indeed shown to be, significantly greater than that 
observed for arrival durations. The plotted data appears to be broken into three 
segments: up to 50 per cent, between 50 per cent and 85 per cent, and beyond 85 
percent. Starting with the lower percentile segment, each segment exhibits an 
increased slope from that of the previous segment. This characteristic is dis- 
cussed further in relation to the data shown in Figure 5-5. 

Cumulative distributions as well as the calculated average values of 
the taxi, engine start, and pushback time intervals are shown in Figure 5-5 as 
curves A, B, and C, respectively. Curve A exhibits an essentially uniform slope 
throughout the entire range. This is considered to be due to the fact that in virtu- 
ally all cases the pilot of the aircraft is in a position to evaluate the situation in 
the ramp area between himself and the outer edge of the concourse during the in- 
terval between the end of the pushback operation and the start of the taxi operation. 
Consequently, if he determines a conflict exists he will either delay the start of 
the taxi operation or else he will taxi slowly in anticipation of a resolution of the 
conflict before he would be required to hold. Approximately 68 per cent of the 
samples completed the taxi operation in less than or equal to the average value of 
54 seconds. 

Curve B, which depicts the distribution of sample intervals between 
the completion of pushback and start of taxi, i. e. , "engine start" time, demon- 
strates a considerably greater variation in the amount of time required. Factors 
which contribute to this variability are the "pilot conflict resolutions" discussed 
above and differences in time required for aircraft checkout procedures, engine 
startup, etc. The average value of "engine start" time was 64 seconds. 



5-19 



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5 10 20 30 40 50 60 70 80 90 95 

PERCENTAGE OF "DEPARTURES" WHOSE RAMP SERVICE 
TIME WAS EQUAL TO OR LESS THAN ORDINATE 



98 99 






Figure 5-4. Distribution of Ramp Service Times for "Departures" 



5-20 

























































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5-21 



The variability of pushback times around the average value of 73 sec- 
onds is shown in Curve C. Basically, the amount of time required for this opera- 
tion is a function of the size of the aircraft, the relative location of the gate from 
which the aircraft departed, other activities in the immediate vicinity of ramp area 
utilized (vehicle movements, other aircraft pushbacks, etc. ) and the specific check- 
out procedures required for the nose-wheel assembly of different aircraft. With 
respect to the latter operation, it was of interest to note that the time required 
for checkout of the DC-8 was observed to be somewhat longer than for comparable 
or smaller size aircraft. It was subsequently learned that previous experience 
with this aircraft has necessitated a more comprehensive examination of this 
mechanical assembly at the completion of the pushback operation. 

The data plotted in Figure 5-6 show the variability in Gate Occupancy 
times for aircraft which arrived and departed within the observation intervals of 
each run. These values represent the actual elapsed time between docking as an 
arrival and start of pushback as a departure. It should be noted that the upper 
limit (maximum time possible) is dictated by the length of the longest observation 
period (160 minutes). Obviously, aircraft that were already at gates at the start 
of an observation period as well as aircraft arriving towards the end of an obser- 
vation period are automatically excluded from this presentation. The average of 
the 82 gate occupancy measurements was 46 minutes with the 10 per cent and 90 
percent points of the distribution at 24 minutes and 58 minutes, respectively. 

5. 3. 1. 4 Analysis of Arrival and Departure Holds 

A summary of the results of the ramp area hold analysis is given in 
Table 5-5. The actual number of arrivals and departures is repeated from Table 
5-4 to permit a comparison between the number of holds and the total number of 
operations for each observation interval (run). The ratio of aircraft encountering 
holds to the total number of aircraft observed (arrivals or departures) is expressed 
in percentages. In addition, the average duration of each type of hold is also given. 



5-22 



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5 10 20 30 40 50 60 70 80 90 95 

PERCENTAGE OF OBSERVATIONS WHOSE DURATION 
WAS EQUAL TO OR LESS THAN ORDINATE 



98 99 






Figure 5-6. Distribution of Gate Occupancy Times 



5-23 



Table 5-5. Arrival and Departure Hold Analysis 





No. of 




No. of 




Run No. 


Arrivals 


No. of Holds 


Departures 


No. Holds 


1 


15 





12 





2 


20 


2 


16 





3&5 


7 





13 





4&6 


17 


1 


17 


5 


7 


11 





11 


4 


8 


21 


1 


20 





9 


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6 


20 


4 


10 


21 


3 


23 


5 


11 


15 


1 


18 


1 


12 


21 





20 


3 


166 


14 


170 


22 


Ratio "Holds" to 








Arrivals or De- 


8.4% 


13% 




partures 








Average "Hold" 
Duration 


90 sec 


67 sec 





5-24 



The majority of the arrival holds were observed to be caused by activi- 
ties related directly to the aircraft's assigned gates (gate blocked by parked vehi- 
cles, gate not lighted or incorrectly positioned, etc. ). In a few instances the delay 
was attributed to pushback operations of other aircraft or "exiting" aircraft. Since 
arriving aircraft timing did not commence until the outer edge of the concourse 
was passed, a considerable number of arrival holds on the inner circular taxiway 
or between the outer and the inner circular taxiways are not included in these 
statistics. However, these delays are included as part of the ground control anal- 
ysis. 

Departure holds could, in most instances, be attributed to near simul- 
taneous departure operations by other aircraft in the ramp area. In a few cases, 
aircraft departing from one of the lower numbered gates (those closest to the main 
terminal building) were held for arriving aircraft which were to dock at one of the 
higher numbered gates. 

5. 3. 1. 5 Scheduling Effects 

To determine possible effects of airline scheduling on ramp area activ- 
ity, the ramp areas FG and GH were examined in more detail for TSC Run #33. 
Table 5-6 presents the time sequence of operations in these two areas. The aver- 
age interval between ramp movements was 200 seconds for the FG ramp area and 
171 seconds for the GH area. Table 5-7 presents summaries of the number of op- 
erations in each ramp area using the same data organized into 10-minute blocks 
between 16:45 and 17:45. A large traffic peak in the vicinity of 5 p. m. is appar- 
ent with 21 operations occurring in the 2 ramp areas in the 20-minute period from 
16:55 to 17:15. Individual ramp usage rates as high as 0. 7 aircraft/minute may be 
noted in both ramp areas. 

The ramp operation is such that several departures are often in the 
pushback mode at the same time. Notice the pairs of departures at 17:09 in area 
FG and 17:11 and 17:27 in area GH. This "batch" method of operation appears to 



5-25 



Table 5-6. Selected Ramp Area Activity (Run #33) 16:45 - 17:45 



RAMP AREA - FG 


RAMP AREA - GH 


Time of Entry 


Time Interval 


Time of Entry 


Time Interval 


or Exit 


(Seconds) 


or Exit 


(Seconds) 


16:47:47 D 




16:46:36 D 




17:01:06 D 


199 


16:52:37 D 


360 


17:01:36 D 


30 


16:54:12 D 


95 


17:02:21 D 


45 


16:56:08 A 


116 


17:05:30 D 


189 


16:58:52 D 


164 


17:08:16 A 


166 


16:59:12 A 


20 


17:09:22 D 


76 


17:00:25 A 


73 


17:09:55 D 


33 


17:04:37 A 


252 


17:10:09 A 


14 


17:04:51 A 


14 


17:11:38 D 


89 


17:04:57 D 


6 


17:14:08 A 


150 


17:05:58 A 


61 


17:16:09 A 


121 


17:07:09 A 


71 


17:23:45 A 


456 


17:10:59 D 


230 


17:28:01 A 


256 


17:12:00 D 


61 


17:28:58 D 


57 


17:16:34 A 


274 


17:29:30 A 


32 


17:18:27 D 


113 


17:33:07 A 


217 


17:27:20 D 


533 


17:36:50 A 


223 


17:28:45 D 


85 


17:40:49 D 


239 


17:33:17 D 


272 






17:42:28 D 


551 






17:43:09 A 


41 






17:44:44 A 


95 



19 A/C (Avg Interval = 200 sec) 22 A/C (Avg Interval = 171 sec) 
Table 5-7. Ramp Activity by 10-minute Periods (Run #33) 





Ramp FG 


Ramp GH 






Operations 


Operations 


Total 


16:45 - 16:55 


1 


3 


4 


16:55 - 17:05 


3 


7 


10 


17:05 - 17:15 


7 


4 


11 


17:15 - 17:25 


2 


2 


4 


17:25 - 17:35 


4 


3 


7 


17:35 - 17:45 


2 


3 


5 



5-26 



offer advantages in reducing ramp area delays for departures. However, it may 
result in increased Local and/or Ground Control delays, since it tends to have 
aircraft move in "platoons" rather than individually. 

5. 3. 1. 6 Ramp Area Occupancy 

Aircraft movement in an active ramp area may also be described in 
terms of an occupancy factor. This occupancy factor is defined in terms of the 
number of aircraft serviced and the ramp service time required. Therefore, it 
pertains only to the ramp area through which aircraft physically move and specif- 
ically excludes aircraft after they have docked as well as any empty gate areas. 
The relationship for obtaining an average occupancy factor is given as: 

Q = X T +A J T, 
a ca d cd 

where 

Q = The average Occupancy factor 

X , X = The number of arrivals and departures, respectively, to or 
from the ramp area within a specific time period 

T T . = The average ramp service times for arrivals and departures, 

Ca > Cd 4.- 1 C \-U 4. 

respectively, for that ramp area 

Using the average ramp service times given in Table 5-4 (T = 75 sec and T 
= 200 sec) and assuming \ = X = 11 operations per hour, 

{11^75) + (11)(200) 
^ 3600 3600 

Short term (5-10 minute) peaks of twice this value will occur often. 
Because of the approximately 3 to 1 difference in service times between departures 
and arrivals, short term variations in the former will play the more significant 
role in influencing ramp density. 



5-27 



5. 3. 1. 7 Summary of Ramp Area 

It appears that the gate structure at O'Hare will and does support a 
traffic flow of 1. 6 operations /hour /gate. This is consistent with a 60 percent gate 
utilization (i.e., 60 percent of the gates occupied at any one instant) and a mean turn 
turnaround time of 45 minutes. This translates to 150 operations /hour overall 
when considering O'Hare' s 94 gates and is just in excess of their current quota. 

Approximately 90 percent of all arrivals encounter no delay while taxi- 
ing in the ramps. The remaining 10 percent experience holds with an average 
duration of about 1. 5 minutes primarily due to the gate not being ready, other 
pushbacks or service vehicle movement in the ramp area. 

Approximately 10 percent of the departures experience holds with an 
average duration of one minute. In most instances the holds can be attributed to 
near simultaneous departures or waits for arrivals to dock. Once a departure is 
rolling, it experiences no slow downs. 

The aircraft flow measurements made in the ramp area represent 
values obtained under VFR conditions and were primarily taken in the more active 
ramp areas. Significant values obtained from the 350 aircraft movements are as 
follows: 





Arrivals 


Departures 




(sees) 


(sees) 


Ramp Service Time 


75 


200 


% of Aircraft "Held" in 
Ramp Area 


8.4% 


13% 


Average Duration of "Hold" 


90 


67 


Pushback Duration (Avg) 


- 


73 


Engine Start Duration (Avg) 


- 


64 


Taxi Duration (Avg) 


- 


54 



5-28 



While the maximum value of the ramp movement rate was less than 
0. 5 aircraft/minute (i. e. , 22 aircraft in one hour were observed in Run #10) peak 
values over short intervals (5-10 minutes) showed movement rates of almost one 
aircraft per minute. On numerous occasions several aircraft have been observed 
exiting or entering behind each other. 

It should be noted that "delays" at the gate are not included in the above 
parameters. 

Gate occupancy time exhibited an average value of 46 minutes based 
upon 82 measurements and had a 10 percent to 90 percent spread from 24 minutes 
to 58 minutes. 



5-29 



5. 3. 2 Ground Controllers' Area 

5. 3. 2. 1 Data Base Generation for Flow Statistics 

Figures 5-7 and 5-8 illustrate the timing relationships and definitions 
used for "Arrivals" and "Departures" which are handled by two separate control- 
lers. The Ground Controllers' area of responsibility has been taken as that exter- 
nal to the Ramp Area but excluding active runways (except for crossing) and the 
turnoffs thereof. 

To determine the operations level and associated delays the following 
procedure was used. For each runway a time history sheet of "Arrivals" and 
"Departures" was prepared as shown in sample data sheets of Table 5-8 using the 
aircraft flow events previously referenced. Next, a time period of one hour was 
selected; aircraft were included in the statistical sample based upon their entrance 
time into the Ground Controllers' area of responsibility. For departures, the cri- 
teria was that aircraft "LR" (Leave Ramp) time was within the hour while for ar- 
rivals "TO" (Turnoff R/W) time was used. For each aircraft observed in the 
selected hour, the following parameters were determined as shown in the sample 
Data Reduction sheets of Table 5-9 for departures and arrivals respectively. * 

1. Departures : T - GC Service Time 

T _ Hold Time 

gdh 

T Jt - Taxi (Movement) Time 
gdt 

2. Arrivals: T - Entrance Delay 
gaw 

T - GC Service Time 

ga 

T , - Total Hold Time 
gah 

T - Taxi (Movement) Time 

gat 

T - Penalty Box Hold Time 

caw 

T , - Taxi Hold Time 
gah 



*The complete set of data reduction sheets for the Ground Controllers' area is 
provided in the Operational Analysis Data Supplement. 



5-30 



AIRCRAFT 
SOURCES 

R/WX (North)' 

R/W Y( South)- 

Hangar/Cargo • 
Areas 



TO 



STT 



'gaw 



HI SI 



go 



HP 



SP H2 S2 ER 



AIRCRAFT 
DESTINATIONS 



^WAIT^ 









-»-Ramp Areas (8) 
■** Cargo/Hangar 
Areas 




where 



T = STT - TO 

gaw 



ga 



gat 

T u 

gah 



Entrance Delay at Turnoff 
GC Service Time (Arrivals) 
GC Taxi (Movement) Time 
2 (SI- HI) + (S2-H2) + + (SP-HP) Total Hold Time 



= T + T' , = ER-STT 
gat gah 

= T - T ' 

ga gah 



= T +T , 

caw gah 



where 



T = SP-HP 
caw 

T = T ' - 
gah gah 



caw 



Penalty Box Hold Time 
Non-Penalty Box Hold Time 



NOTES 



1. The Hold in Penalty Box, of duration SP-HP, represents a delay due to gate 
unavailability rather than to taxiway congestion and is experienced by only 
some of the aircraft. 

2. Subscript code - g = Ground Controllers' area 

a = Arrivals entering Ground Controllers' area 

w = Entrance delays 

h = Holds 

t = Taxiing (movement) times 

p = Penalty Box 

c = Carrier Area (Ramp Area) 

Figure 5-7. Timing Relationships - Ground Controllers' Area - Arrivals 



5-31 



AIRCRAFT 
SOURCES 

• Ramp Areas (8) 

• Cargo/Hangar Areas- 



RTT 



LR 



WAlf' 



/INC 
RAMP- 
/'AREA. 



— T, 



gdw 



H2 S2 



gd 



: Tg dh + Tg dt 



AIRCRAFT 
EDQ DESTINATIONS 

•ToR/W X(North)Dep.Q 

-To R/W Y(South)Dep. Q 

^■To Hangar 



where 



T , = LR - RTT 
gdw 



gd 



gdh 



= T + T 
gdt gdh 

= EDQ - LR 

= 2 (Sl-Hl) + (S2-H2) + 



T = T - T 

gdt gd gdh 



Entrance Delay (Occurs in Ramp Area) 
GC Service Time (Departures) 

Total Hold Time 

GC Taxi (Movement) Time 



NOTES 

1. T , cannot be determined from ASDE films and was measured as part of 

ramp survey effort. 

2. Subscript code - g = Ground Controllers' area 

d = Departures entering Ground Controllers' area 

w = Entrance delays 

h = Holds 

t = Taxiing (movement) time 



Figure 5-8. Timing Relationships - Ground Controllers' Area - Departures 



5-32 






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5-34 






Table 5-9. Sample Data Reduction Sheet (1 of 2) 



RUN NO. 2 DATE "5-1-73 GROUND CONTROLLER ANALYSIS 



RUNWAY 27 'R 



DEPARTURES 



L.-R 8;40 - ( X^Q 



No, 


EDQ-LR 
T edt +T ? dh 


Total Hold Time 
T erdh 


Taxi Time 
T edt 


1 


204 




204 


2 


2*56 


- 


256 


"5 


259 


- 


259 


4 


260 


- 


260 


5" 


239 


- 


259 


<p 


166 


- 


168 


•7 


297 


107 


190 


8 


157 


50 


127 


9 


160 


- 


160 


10 


45 


— 


4b 


11 


194 


— 


194 


12 


221 


- 


221 


15 


i^o 


— 


130 


14 


411 


117 


294 


15 


166 


- 


188 














































































2T gdh 254 


2T gdt 2917 




No. Holds 3 


N a 15 






T gdt 194 



5-35 



Table 5-9 . Sample Data Reduction Sheet (2 of 2) 



RUN NO. 20 



DATE 3-1-70 



GROUND CONTROLLER ANALYSIS 



RUNWAY 2_T L. 



ARRIVALS 



T. o. 8'4o io S;4o 



No. 


Wait Time 
T Kaw =SST-TO 


ER-STT 
1 eah +i eat 


Arrival Holds 
T? gah 


Taxi service Time 
T gat 


penalty box 
Holds T C aw 


Taxi Hold rime 
T gatr T ' e ah~ T caw 


'26 


~ 


Z9i) 


171 


1Z8 


171 


— 


29 


— 


19'7 


- 


197 


— 


— 


30 


~ 


2.4 2 


115 


127 


.._ 


115 


31 


— 


268 


- 


26b 


— 


— 


52 


— 


149 


29 


120 


— 


29 


53 


— 


249 


^16 


aoi 


— 


Ad 


34 


— 


154 


5c 


104 


— 


SO 


55 


— 


166 


- 


166 


_ 


- 


36 


— 


411 


216 


195 


2,16 


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ST 
gaw 




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2080 


ZT 


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1456 


ZT , 




No. Waits 


No. Holds 

20 


N 
a 

53 


No. PB Holds 
6 












T gat 152. 







Taxi Queue Time (T ) = 



5-36 



Next in the data reduction process was to sum the individual aircraft param- 
eters for each runway. For departures, the following parameters were obtained: 

N — Number of departure aircraft 



Y T „ — Summation of all hold time 

L> gfdh 



gdh 
Number of Holds 



T — Average taxi (movement) time 

For arrivals the following summation values were obtained: 

N — Number of arrival aircraft 

a 

y T 1 — Summation of all hold time 

L. gah 

Number of all Holds 



T , — Average taxi (movement) time 

gat 

y T — Summation of all "Penalty Box" hold time 

L-> caw 

Number of Penalty Box Holds 

V T — Summation of all hold time excluding Penalty Box 

hold time 

These runway summation values were next used to develop a composite 
picture/summary of the aircraft flow within the total ground control (GC) area. 
Table 5-10 shows the results of the analyzed runs. In addition to the parameters 
previously discussed, these sheets present such parameters as average duration of 
Penalty Box "Holds" and other holds as well as the average time (T ) of the air- 
craft in the GC area as previously defined. From this parameter and the number 
of aircraft entering the GC area, the average hourly aircraft density, Q, may be 
determined as 

/N + N, 



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5-49 



5. 3. 2. 2 Summary of Results of Ground Control Analysis 

Table 5-11 summarizes the results of the various runs which have been 
analyzed. These runs have been separated into either an "Arrival from the West" 
or "Arrival from the East" mode of runway operation. This table presents average 
taxi (movement) time for arrivals, departures, and all aircraft as well as delay 
statistics. The latter includes the number of arrival waits at runway turnoffs and 
the number of non-penalty box holds as well as penalty box holds. The average 
delay time associated with each of the last two delays is also presented. 

Data compiled from the individual run sheets are presented in the sum- 
mary table. Also included is the average time of an aircraft in the ground system 
(i. e. , from ramp exit to departure queue entrance or from turnoff to ramp en- 
trance) and the hourly average aircraft density (Q). The average delay times have 
been normalized to the number of operations per hour to permit addition of delays 
occurring in the several portions of the surface area (ramp, ground control, local). 
The data from the summary table have been used to develop a graphical presenta- 
tion of the results of this analysis. 

5. 3. 2. 3 Penalty Box Delay 

The normalized penalty box delay time per operation has been plotted 
vs operations level in Figure 5-9. There does not appear to be any difference be- 
tween East and West mode of operation. There is a general upward trend with 
operations/hour. At 140 operations /hour an average of eight aircraft would be 
sent to the box (over 10 percent of the arrivals) for over three minutes each, a 
substantial delay. The delay does appear to depend upon the ratio of arrivals to 
departures. More arrivals than departrues should tend to clog up the gates. In 
Figure 5-9 all the points above the curve have an excess of arrivals and all the 
points below the curve (except CSC #5 for which arrivals are about equal to depar- 
tures) have an excess of departures. 



5-50 



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5-52 



5. .2.4 Non-Penalty Box Delay 

The normalized non-penalty box delay time per operation has been 
pic ted vs operations level in Figure 5-10. The substantial difference in the two 
rui way configuration modes is readily apparent. The "Arrivals from the West" 
mode appears to have almost a minute longer taxi time. This is due simply to the 
longer taxi routes in this mode especially for the North side arrivals from 14L. In 
addition, the West mode has almost a minute more delay being experienced at high 
operations levels (135 operations /hour). 



In examining the differences in delay each of the runs were analyzed in 



det ail . 



In all, twelve runs were analyzed, each consisting of one hour of air- 
port operations. Table 5-12 summarizes the runs included in the analysis and 
gives the number of flights and number of holds observed in each. 

Table 5-12. Summary of Analyzed Runs 



Run 


Direction 


No. of Flights 


No. of Holds 


TSC 








15 


West 


100 


40 


20 


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136 


50 


29 


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110 


62 


33 


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142 


44 


35 


East 


106 


8 


37 


West 


130 


82 


39 


West 


140 


83 


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138 


35 


7 


West 


110 


50 


8 


West 


104 


43 


9 


West 


116 


46 


10 


East 


116 


12 



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150 



Figure 5-10. Aircraft Delay in Ground Control Area 



5-54 






For the purpose of the analysis a "hold" was defined as any stop while 
taxiing excluding penalty box and departure queues. Holds were categorized as 
follows based on observation of the traffic conditions apparent on the ASDE films: 

1. Competing Traffic - Aircraft stops due to other traffic on taxi- 
ways such as another aircraft crossing its path, stopped traffic 
ahead, merging traffic, etc. 

2. Runway Crossing - Aircraft stops prior to crossing a runway 
whether or not the runway is active. 

3. Ramp Congestion - Aircraft stops due to ramp operations or to 
await a gate. This does not include penalty box holds. 

4. Unknown - Stops for which no reason is apparent. 

5. Other - Any holds for reasons not included in the above categories. 

In addition to ascertaining the reason for each hold, the location of 
each was also noted so that high incidence areas could be identified. For ease in 
indicating the location of holds, certain significant intersections in the taxiway 
system were assigned numbers as shown on the diagram in Figure 5-11. Numbers 
from 1 to 10 indicate intersections on the Outer Circular, 21 to 34 are intersec- 
tions between runways and taxiways, 41 to 63 are taxiway/taxiway intersections, 
and 70 is the intersection of runways 4L/22R and 9L/27R. Locations along the 
Inner Circular and adjacent ramp entrances are indicated by the ramp letter des- 
ignations (i. e. , A to K). 

The hold data from each of the twelve runs is given in Table 5-13. Ar- 
rival and departure runways in both north and south portions of the field are shown 
and the total number of flights related to each and the number of holds observed for 
those flights. In each column under specific hold reasons, the location of each hold 
is given by the appropriate designation from Figure 5-11. When holds were observed 
between designated intersections and/or ramp areas, two letters or numbers sepa- 
rated by a slash are used, e. g. , if a hold occurred between intersections 3 and 4 on 
the Outer Circular the designation 3/4 is used. Similarly, holds in the area of the Inner 
between Ramps G and H are entered as G/H. 



5-55 




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5-68 



Table 5-18 presents a summary breakdown of holds observed for ar- 
rival and departure flights by East and West Arrival modes. Of the 1448 flights 
observed, 810 were in the west mode of operations and these had 406 holds, or a 
. 50 hold-per-flight ratio. The 638 flights in the east mode had 149 holds or a .23 
hold-per-flight ratio which is approximately half that for the west. The higher 
ratio for the west mode is directly attributed to the higher incidence of run- 
way crossing holds. These were caused by the use of Runway 4R for departures 
with 9R for arrivals (55 holds), 9R for departures with 14R for arrivals (56 holds), 
and the use of 9L for departures with 14L for arrivals (29 holds). To examine the 
impact of the runway crossings on the delay curve in Figure 5-10, the two high 
delay points (TSC #39 and TSC #37) are broken down by category of delay in 
Table 5-15. As expected, the major element is due to runway crossing. 

If the runway crossing is subtracted from the total for the two cases 
and the adjusted points plotted on Figure 5-10, they fall close to the curve for the 
East arrival mode. It is presumed that a similar adjustment to all the West mode 
points would produce a common delay curve showing 10 seconds to 30 seconds of 
delay per aircraft at the higher operations rates (135 operations /hour). The total 
delay is similar to that for penalty box holds; however, its impact is not as dra- 
matic since it is distributed over more aircraft (i.e., an average of 48 non-penalty 
box holds vs 8 penalty box holds). 

In considering why the runway crossing delays increase sharply at 
130 to 140 operations /hour, it is necessary to consider runway capacity. Para- 
graph 5.3.3 will show that the current quota (135 operations /hour) is quite con- 
sistent with the capacity of the runways. Operations (e. g. , TSC #37 and TSC #39) 
for which departures must cross an active arrival runway and which are near 
capacity building a queue, should tend to experience increased crossing delays as 
the controller (Ground Control) loses the incentive to be prompt in his crossing 
command. In this case, runway crossing delay is simply more runway delay in a 
two segment queue (i. e. , one on each side of the active runway). In addition, 



5-69 



Table 5-14. Summary of Holds by Reason 





West 


East 


Combined 




Number 


%of 


Number 


%of 


Number 


%of 




of Holds 


Holds 


of Holds 


Holds 


of Holds 


Holds 


Competing Traffic 


145 


36 


80 


54 


225 


40 


Runway Crossing 


140 


35 


8 


5 


148 


27 


Ramp Congestion 


78 


19 


34 


23 


112 


20 


Unknown 


37 


9 


23 


15 


60 


11 


Other 


6 


1 


4 


3 


10 


2 


Total 


406 


100 


149 


100 


555 


100 



Table 5-15. Delay Time by Category 









Delay Per 




Percent 


Operation 




Traffic Held 


(seconds) 




Runway Crossing 


32 


35 




Competition 


18 


7 


TSC 37 


Ramps 


9 


5 




Not Identified 


4 


3 


TOTAL 


63 


50 




Runway Crossing 


27 


36 




Competition 


16 


11 


TSC 39 


Ramps 


10 


15 




Not Identified 


6 


8 


TOTAL 


59 


70 



5-70 



creating two queues on the terminal side of the arrival runway can facilitate moving 
aircraft into the departure queue in an advantageous sequence. 

5.3.2.5 Review of Individual Runs 

The following brief summaries present some salient features observed 
in each of the runs analyzed. 

TSC Run 15 

Although this is an "Arrivals from the West" run, the departure run- 
way in the south part of the field is 22L rather than 4R which is more often used in 
this configuration. This results in the elimination of the runway crossing holds 
normally encountered for flights departing on 4R when 9R is used for arrivals (e. g. , 
Runs 29 and 39). Several runway crossing holds were observed in the north side 
of the field for flights arriving on 14L and having to cross departure runway 9L. 
About half of the holds (21 out of 40) were due to competing traffic with arrivals on 
9R stopping mostly on the Outer and departures on 9L encountering stops on the 
Inner or in crossing the Outer. Ramp congestion holds occurred throughout the 
terminal area and several holds were observed along the cargo taxiway for flights 
arriving on 14L and going to the cargo area and for departures going to 22 L. 

TSC Run 20 

In this run both arrivals and departures in the south use 27L. Most of 
the holds recorded for flights using this runway occur on or crossing the outer 
taxiway between the penalty box area and the junction of the Outer with the cargo 
taxiway. It is not clear that any relationship exists between these two observa- 
tions. Ramp congestion in the FG area caused holds on or crossing the Outer 
while some flights exiting between H and K were held at the Inner for reasons which 
are not obvious but which may be associated with departure sequencing. 

TSC Run 29 

The use of 4R for departures in this run causes most flights using that 
runway to hold before crossing Runway 9R which is used for arrivals. These holds 



5-71 



occur at the intersections of the 14R/32L parallel with the 9R/27L parallel or 9R. 
Many other holds are due to competing traffic on or crossing the Outer from the 
area of the penalty box to the junction of the Outer with the cargo taxiway. Most 
ramp congestion holds occurred in the area of Ramps F, G, and H. 

TSC Run 33 

The 142 flights in this run were observed to have 44 holds. Approxi- 
mately 60 percent of these were attributed to competing traffic. No definite pat- 
tern to these holds was apparent although several flights arriving on 27 L encoun- 
tered traffic at the south side of the terminal area at Outer opposite the FG and 
GH ramps and the intersection of the north-south and 9R/27L parallel taxiways. 
About one-third of the holds were in the categories of "Ramp Congestion", "Un- 
known", or "Other" and these too had no significant pattern. No runway crossing 
holds occurred in the southern part of the field where 22L was the major depar- 
ture runway and 27L was used for arrivals. In the north, the primary runways 
were 32R for departures and 27R for arrivals. Several flights landed on 22R re- 
sulting in three runway crossing holds at the intersection of 22R and 27R. 

TSC Run 35 

Only 8 holds were observed in the 106 flights in this run. Five of these 
occurred south of the terminal area for flights arriving on runway 32L, at the same 
points noted for 27L arrivals in Run 33. The lower number of holds in this run as 
compared to Run 33 which also involved "Arrivals from the East" may have been 
due to fewer operations (106 in Run 35 to 142 in Run 33) and/or to a difference in 
the runway usage in the southern portion of the airport. In Run 33, 22L was the 
major departure runway in the South and 27 L was the arrival runway while in Run 
35 the major departure runway was 27L and the arrival runway was 32L. Opera- 
tions in the North were similar for both runs. 



5-72 



TSC Run 37 

Most flights departing on 9R had to hold one or more times before 
crossing 14R which was being used for arrivals. These holds occurred in the 
area of the intersection of taxiway T-l with the Outer, 14R/32L parallel, and 
14R, and on the 9R/27L parallel at intersection with the north-south, 14R/32L 
parallel, and 14R. Although arrivals on 14L had to cross departure Runway 9L 
to get to the terminal area, relatively few (5 out of 32) had to hold before crossing 
9L. This may be due to the spacing of these flights relative to the time intervals 
associated with runway operations in contrast to the more random distribution of 
departure flights leaving the terminal and having to cross a runway to get to the 
departure runway. Ramp congestion and competing traffic holds were distributed 
throughout the terminal area on both the Inner and Outer during this run. 

TSC Run 39 

With 83 holds for 140 flights this run had considerably more holds than 
Run 33 which had slightly more operations (142 flights with 44 holds). The differ- 
ence may be directly attributed to the 37 flights which had to stop prior to crossing 
arrival Runway 9R in order to use Runway 4R for departure. Many holds in this 
run were caused by Ramp Congestion and heavy traffic in the southeast portion of 
the terminal area in the vicinity of Ramps H and K. This resulted in delays inside 
the Bridge for flights arriving on 14L. Several holds were observed for flights 
arriving on 9R in the same areas noted for 27L arrivals in Run 33 and 32L arriv- 
als in Run 35. 

CSC Run 5 

This run had a similar runway configuration as Run 35 but substantially 
more flights (138 to 106). While Run 35 had only 8 holds, this run had 35 holds, 
most of which were attributed to Ramp Congestion and competing traffic on the 
Outer Circular. Ramp Congestion holds occurred throughout the terminal area. 



5-73 



Most of the holds on the Outer Circular were observed between T-3 and the north- 
south taxiway. Almost all holds in these categories involved arrival flights and 
were about equally divided between aircraft landing on runways 27R in the north 
and 32L in the south. 

CSC Run 7 

The runways used in this run were the same as in TSC Run 37. Al- 
though there were fewer flights (110 in Run 7 and 130 in Run 37) and fewer holds 
(50 to 82) there are several similarities in the occurrence of holds. In both runs 
most departures on 9R experienced one or more holds in crossing 14R which was 
used for arrivals while only a few flights arriving on 14L stopped before crossing 
departure runway 9L. In this run most of the competing traffic holds were due to 
an extremely long departure queue for runway 9L. At times during the run this 
queue extended down the Outer past the penalty box causing congestion along the 
Outer and at T-l and T-3. 

CSC Run 8 

This run is similar in runway usage to Runs 37 and 7; the significant 
difference is that, instead of using 9R for the departure runway in the south, 14R 
was used for both departures and arrivals. This, of course, eliminated the run- 
way crossing holds experienced by 9R departures. Another difference was that in 
Run 8 a far greater number of arrival flights on 14L had runway crossing holds at 
9L. The number of Ramp Congestion and Competing Traffic holds in this run was 
comparable to Runs 37 and 7; however, 14R arrivals were not affected by the 9L 
departure queue as in Run 7. The 104 flights in Run 8 were observed to have 43 
holds. 

CSC Run 9 

The runway configuration in this run is similar to Runs 37, 7, and 8 
except that the departure runway in the south was 27L instead of 9R or 14R. The 
number of Ramp Congestion and Competing Traffic holds were comparable in all 



5-74 



these runs. However, in Run 9 most Ramp Congestion holds were observed on 
both the Inner and Outer in the area of Ramps H and K while most competing traf- 
fic holds were on the Outer in the western half of the terminal area. In this run 
only a few flights landing on 14L stopped before crossing 9L. The penalty box was 
heavily used in this run and several holds, whose reasons could not be definitely 
determined, may have been caused by the use of other areas in lieu of the penalty 
box. 

CSC Run 10 

The runway usage in this run was similar to Runs 35 and 5. As in Run 
35 a fairly low number of holds was observed (12 holds for 116 flights). Most of 
the holds were due to competing traffic on the Outer both at the intersection with 
T-3 and opposite Ramp H. 

5.3.2.6 Ground Control Area Summary 

1. Penalty box delay time does tend to increase with operations /hour. 
The mean curve (Figure 5-9) passed through the 150 operations/ 
hour point at 18 seconds per aircraft. This appears very low com- 
pared with the runway delays; however, at this operations rate 
about 10 arrivals (see Table 5-11, TSC #33) comprise the delay. 
This amounts to over 4 minutes/aircraft held. On this basis, the 
150 operations /hour capacity estimate appears reasonable. 

2. Non-penalty box delay time tends to increase with operations /hour. 
Delays in the West Arrival mode are much higher (mean delay of 

a minute at 140 operations/hour) due to runway crossing delays in 
that mode. Excluding runway crossing delays, the average delay 
per operation in either mode is about 20 seconds per aircraft. 
This is similar to the penalty box delay but remains distributed 
over a much larger number of aircraft. In addition, of the 20 sec- 
onds delay in the taxiway, as much delay is associated with ramp 
congestion (again gate related problems) as competing taxiway 
traffic (see Table 5-15). On this basis, it does not appear that the 
basic taxiways are operating near saturation- -but rather quite 
smoothly. 



5-75 



3. Only 9 Arrival aircraft of the approximately 700 observed experi- 
enced entrance waits before taxiing after runway turnoff. This 
may be an indication of the small percentage of time that conflicts 
arise between aircraft at turnoff s and other taxiing aircraft. Thus, 
although during peak hours the Ground channels can reach satura- 
tion (see paragraph 5.4. 1. 6), its impact on aircraft delay is not 
currently showing up as substantial. Pilot interviews indicate 
they tend to taxi while waiting for clearance from Ground. This 
may be why so few waits were detected. 

4. Excessive runway crossing hold times (about a minute/aircraft) in 
the West mode in the 130 to 140 operations/hour region can be 
attributed to runway saturation with long departure queues on the 
outside of the arrival runway and the lack of controller incentive 
to hasten to cross the aircraft into a queue. In addition, creating 
two departure queues on the inside of the arrival runway can facil- 
itate moving aircraft into the departure queue in an advantageous 
sequence. 

5. The average time of other "holds" ranges from 60 to 90 seconds. 

6. With the exception of Run #35, the number of holds (including pen- 
alty box holds) ranged from 42 to almost 80. Since each hold will 
probably require two control instructions, this would represent 
80-160 control instructions per hour or almost one per minute per 
controller. 

7. While most hourly surface density values (aircraft only) ranged 
from 6 to 10. 4, Run #39 had a value of 15. 4. We attribute this 

to the large departure Q for runway 4R in the south, and the delays 
associated with moving aircraft into the departure Q in the proper 
order. 

8. The total non-penalty box delay time ranged from about 2 percent 
to 10 percent of non-delay taxi (movement) time for the east mode 
of operation but from 10 percent to 23 percent for the west mode 
of operation. 



5-76 



5. 3. 3 Local Controllers [ Area 

Two Local Controllers are on duty during most of the day at O'Hare. 
The split is between the North side and South side. This section describes the 
controllers operation in a quantitative way beginning with his capacity to handle 
traffic (paragraph 5.3.3.1), then correlating that capacity with observed delays 
(paragraph 5.3.3.2). 

5. 3. 3. 1 Local Control Area Capacity 

The local control area capacity is dependent on many external factors. 
These factors include weather, visibility conditions, terminal ATC procedures, 
runway configurations, traffic demand, demand mix (i. e. , arrivals versus depar- 
tures), aircraft type mix, aircraft weight mix and aircraft service mix (i. e. , IFR 
versus VFR). This analysis does not examine all of these factors and those con- 
sidered are done so with a limited amount of data. Its purpose is to derive some 
understanding of what the Local Controller is faced with for typical O'Hare condi- 
tions and to estimate the potential capacity increase which new local controller 
aids might provide. Any generalization to other airports or even to O'Hare oper- 
ating in a mode not examined here (e. g. , high VFR operations in a low air carrier 
demand period) requires careful examination of the impact of each factor. That 
examination is not made here. The factors which were in effect for this analysis 
are 

1. Good braking action, 

2. Winds varying from to 15 knots with gusts to 25 knots, 

3. Visibility either excellent, permitting visual approaches, or very 
poor such that the cab could not see the entire airport, 

4. O'Hare, a Group I TCA airport, 

5. Aircraft type mix as given in Table 6-1, and 

6. Aircraft service mix with IFR representing over 90 percent of 
all aircraft. 



5-77 



Each Local Controller at O'Hare controls a mixed arrival/departure 
operation, either a single runway with mixed operations or intersecting runways. 
His job is basically (1) to assure a clear arrival runway for the next arrival, and 
(2) to clear departures out between arrivals. His ability to do this depends on the 
runway configuration, his visibility of the operation and the distributions of vari- 
ous parameters over which he has little control. To illustrate the nature of these 
parameters consider Figures 5-12 and 5-13. 

5. 3. 3. 1. 1 Parameter Distributions 

Figure 5-12 illustrates an ideal single runway operation. Every 90 
seconds an arrival sets down on the runway, rolls out and clears off in 45 seconds. 
Every 90 seconds, just following the arrivals setting down, a departure gets on, 
waits for the arrival to clear and takes off, becoming airborne in 45 seconds. 
Figure 5-13 illustrates an actual single runway operation. The slopes of the ar- 
rival time lines are not uniform. The arrival runway on time is dependent on the 
aircraft type, exit ramp type and location, touchdown (velocity, rate of descent, 
crab angle, roll angle, and position) and roll out deceleration. The slopes of the 
departure time lines are not uniform. Departure on time is dependent on aircraft 
type and load. The inter-arrival spaces are not uniform. The spaces depend on 
the ability of the Approach Controller to deliver perfectly spaced arrivals to the 
outer marker and the final approach velocity profile. The non-uniformity of these 
parameters and the controller's ability to estimate these parameters 

1. Cause controller misjudgments resulting in aborted departures 
(i.e., departure cleared on and then directed off) as for departure 2, 

2. Cause unused inter-arrival spaces (i.e. , space too small so a 
departure is held) as for inter-arrival space 11-12, 

3. Permit double departures as for departures 3 and 4. 

The actual operations rate observed is 64 operations/hour versus the 
ideal of 80 operations/hour, a substantial reduction due to the distributions of the 
parameters. 



5-78 



Arrival ( 


ON 
OFF 


1 


OFF 


Departure / 


STO 
ON 




IN QUEUE 



I 2 3 4 5 6 7 8 

I 2 3 4 5 6 7 




3 6 

MINUTES 



Figure 5-12. Time Line Plot of Ideal Single Runway Operation Saturated 
In Arrival and Departure Demand (80 Operations /Hour) 



ARRIVAL 



[Z \ WW W\ 



DEPARTURE 



OFF 

STO 

ON 

IN QUEUE 




MINUTES 



ARRIVAL 



£ \ WWW W 



DEPARTURE 



OFF 
STO 
ON 
IN QUEUE 




20 25 

MINUTES 



Figure 5-13. Time Line Plot of Actual Single Runway Operation Saturated 

In Arrival and Departure Demand in Good Visibility Conditions 
(64 Operations /Hour) (R/W- 27L) 



5-79 



Figure 5-14 illustrates the distribution of arrival "on" times for two one- 
hour periods. The total distribution is also shown and will be used as a general 
arrival on time distribution for the subsequent capacity estimates. It should bo 
noted that this distribution is for good braking conditions. 

Figure 5-15 illustrates the distribution of departure "on" times for two 
one-hour periods. Again they are very similar and display a smaller variance 
than do the arrivals. The on times only involve the roll out time. Delays prior to 
initiating takeoff are not included. As with the arrivals, the total distribution will 
be used as a general departure on time distribution for subsequent capacity esti- 
mates. 

Figure 5-16 illustrates the distribution of inter-arrival time as arrival 
demand increases. The times are taken over the runway threshold. With a mod- 
est number of arrivals (TSC #35N) the distribution is not sharply peaked and only 
one space falls in the 70-second bin. At a common approach speed of 160 knots at 
the outer marker (Approach Control to Local hand-off) 67 seconds is 3 nautical 
miles, the minimum separation standard. At a common touchdown speed of 130 
knots, the 70-second bin represents 2. 5 nautical miles separation at the threshold. 
As the demand increases the distribution's mean (shown by the solid triangle) shifts 
to the left, while the 60-second bin remains empty (i. e. , the 3 nautical mile sepa- 
ration is adhered to at the outer marker) until at 37 arrivals the leading edge of the 
distribution slips into the 60-second bin (2. 7 nautical miles at the outer marker 
and 2. 2 nautical miles at the threshold). At this point the probability of double 
runway occupancy begins to increase (see Figure 5-14) as the main body of the 
arrival on time distribution begins to overlap the inter-arrival distribution. For 
the purposes of capacity estimation the sum of the two runs prior to TSC #37S 
(i.e. , TSC #20S and CSC #5S) will be used to represent a general saturated demand 
inter-arrival distribution. The total is shown in Figure 5-17. 

The inter-arrival spacings in Figure 5-17 depict a distribution which 
peaks at about 95 seconds and is evenly distributed about the peak with a standard 



5-80 



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Total (61 Arrivals) 



10 20 30 40 '•^O 60 70 80 90 

ARRIVAL OCCUPANCY TIME (SECONDS) 



100 



Figure 5-14. Arrival Runway Occupancy Time for Two One-Hour 
Periods (Total Mean 46 Seconds) 



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DEPARTURE OCCUPANCY TIME (SECONDS) 



Figure 5-15. Departure Runway Occupancy Time for Two One-Hour 
Periods (Total Mean 40 Seconds) 



5-81 



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Figure 5-16. Interarrival Spacing for Six One-Hour 
Periods of Varying Demand 



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5-83 



deviation of 10 seconds except for a set of trailing inter-arrivals beginning at 2 
minutes. By listening to voice communication tape recordings these trailing 
spaces have been determined as primarily heavy spacings. These trailers repre- 
sent 17 percent of the spaces which is consistent with the percent of the heavies 
operated in general at O'Hare. 

5. 3. 3. 1. 2 Predicted Capacity (Theoretical) 

Given the three distributions and a single runway operating strategy, 
an operations rate can be predicted. The single runway operating strategy used 
here is as follows: 

To clear a departure following an arrival the previous arrival should 
be initiating his turnoff (not necessarily clear) and the next arrival should be at 
least 40 seconds from threshold (about 2 miles). 

For mixed operations on a single runway the runway entrance time 
(i. e. , the time needed for the aircraft to move from the Local Control Departure 
Q to "in-place" on the runway) becomes a significant parameter in developing an 
operating strategy. This factor, however, has not been treated in this analysis 
since it is not significant in multiple runway operations. 

To clear a departure following a departure the previous departure 
should be off the runway and the next arrival should be at least 40 seconds from 
threshold (about 2 miles). 

The rationale for the strategy is that (1) except for predictable circum- 
stances (e. g. , a heavy on a reverse high speed) the maximum clear time from turn 
initiation observed was 15 seconds and the minimum time for a departure to pass 
the common turnoffs was 30 seconds, leaving 15 seconds of margin following an 
arrival; (2) an arrival 15 seconds out at departure release will catch the depar- 
ture so that using 40 seconds leaves 5 seconds pilot delay and 20 seconds of mar- 
gin; (3) an arrival 40 seconds out will minimize (not eliminate) double runway 



5-84 



occupancy; and (4) a previous departure off will permit an immediate turn clearing 
the runway for the next departure. 

The resulting operations rate may be estimated graphically with Fig- 
ure 5-18. The dotted curve represents the probability of a controller being unable 
to successfully release a single departure as a function of inter-arrival spacing. 
The curve is obtained by taking the arrival on-time distribution, which represents 
the minimum time that the departure must wait to be released after the arrival has 
touched down, and adding 40 seconds (the minimum time the next arrival must be 
from the threshold to permit a release) to obtain the distribution of minimum inter- 
arrival spaces required for a departure, and taking the inverse accumulation (i. e. , 
integration) of that distribution. Similarly, the dashed line represents the proba- 
bility that a controller would be unable to release two departures as a function of 
inter-arrival spacing. The curve, in this case, is obtained by taking the convolu- 
tion of the arrival on-time distribution with the departure on-time distribution, 
which represents minimum time that the second departure must wait to be released 
after the arrival has touched down, and adding 40 seconds (again, the minimum 
time the next arrival must be from threshold to permit a release) to obtain the dis- 
tribution of minimum inter-arrival spaces required for double departures, and tak- 
ing the inverse accumulation of that distribution. 

The departure rate estimate is obtained by "playing" these strategy 
curves against the saturated demand inter-arrival distribution (e. g. , 30 percent 
of the 20 percent inter-arrival spaces between 80 and 90 seconds will not permit 
a departure — 70 percent will). The results are 34 arrivals/hour, 27 single depar- 
tures/hour and 6 extra departures for a total of 67 operations/hour. 

With rationale similar to that used for single runway operations, oper- 
ating strategies were developed for dependent intersecting runways. All strate- 
gies used are summarized in Table 5-16. The resulting strategy curves are shown 
in Figure 5-19; and the resulting capacity estimates are shown in Table 5-17. As 
evidenced by Figure 5-19, all crossing runways are predicted to clear at least one 



5-85 





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5-86 



Table 5-16. Operating Strategies for Capacity Estimation 



Configuration 


Previous Arrival 


Next Arrival 


Previous Departure 


Single 
(Mixed) 


Initiating turn-off 


40 seconds out 
from threshold 
(2 miles) 


Off and turning 


Near-Near 
Crossing 


Clear through 
intersection 


40 seconds out 
from threshold 
(2 miles) 


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Near-Far 
Crossing 


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from intersection 
(at threshold) 


50 seconds out 
from threshold 
(2-1/2 miles) 


Off and turning 


Far-Far 
Crossing 


15 seconds out 
from intersection 
(1000 feet) 


50 seconds out 
from threshold 
(2-1/2 miles) 


Off and turning 



5-87 



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DEMAND 




20% 








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INTER-ARRIVAL TIME (SECONDS) 



Figure 5-19. Strategy Curves for Various Runway Configurations 



5-88 



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5-89 



departure for every inter-arrival space. The ability to get double departures 
varies. Near-Near crossing runways do best since the second departure clears 
the critical intersection quickly. The Near-Far crossing runways do poorer since 
the second departure takes longer to clear the critical intersection. The Far- Far 
crossing runways do poorest since a large variance in first arrivals clearing the 
intersection plus the longer time to clear the critical intersection impact on the 
operation. It may also be noted that the data presented to the Local Controller 
gives him no predictive capabilities for either arrivals or departures. 

5. 3. 3. 1. 3 Predicted Capacity (Actual) 

The actual operation at O'Hare is compared with the predicted capac- 
ity in Tables 5-18 to 5-21. The single runway operation is rare at O'Hare and 
O'Hare traffic volumes place a good deal of strain on the operation. In this in- 
stance (Table 5-18) the controller got off 27 single departures versus 30 theoret- 
ically predicted (for this inter-arrival distribution) and all six predicted extra 
departures. Measured against the operating strategy previously given, the con- 
troller did nearly perfect. That he was straining his capabilities to do this, how- 
ever, is also evident from Table 5-18. Of the 20 single departures released for 
spaces between 70 and 110 seconds, 10 were released perfectly (within 5 seconds) 
according to the strategy, 2 were released more than 5 seconds early (one of them 
16 seconds before the preceding departure committed to clear) and 1 was released 
more than 5 seconds late (the next arrival only 32 seconds out). This resulted in 
5 cases where the runway was occupied by 2 aircraft for more than 5 seconds. La 
addition, in one instance an aircraft was cleared on and then directed off due to 
the proximity of the next arrival. It would appear that the theoretical capacity 
should not be expected or demanded of the controller. As mentioned previously, 
this is a rare operation at O'Hare. 

The Near-Near operation is shown in Table 5-19. Although the depar- 
ture queue exceeded 10 aircraft for much of the hour, at one point it was only 1 
aircraft and hence a double departure demand did not exist. To account for this 



5-90 



Table 5-18. Single Runway Mixed Operations in Good Visibility With 
Continuous Double Departure Demand 



TSC 20 South 


Operations Per Time Interval 


70/ 
80 


80/ 
90 


90/ 
100 


100/ 
110 


110/ 
120 


120/ 
130 


130/ 
140 


140/ 
150 


150/ 
160 


160/ 
170 


170/ 
180 


Predicted Percent 
Single Departures 


23 


70 


92 


100 


100 


100 


100 


100 


100 


100 


100 


Predicted Percent 
Double Departures 








2 


14 


26 


70 


86 


95 


100 


100 


100 


Inter arrivals 


2 


7 


10 


5 


1 


1 


2 


1 


2 


1 





Single Departures 


2 


5 


8 


5 





1 


2 


1 


2 


1 





Extra Departures 

















1 


2 


1 


1 


1 





Withheld Departures 





1 


2 





1 




















Departure Late by 
Over 5 Sees 








1 


























Departure Early by 
Over 5 Sees 


1 


1 





























Runway Double Occu- 
pancy Over 5 Sees 


1 


2 


2 


























Departures/Arrival 
Aborted 





1 





























Perfect Departure ±5 
Sees Early /Late 


1/2 


3/1 


5/3 


1/0 
























5-91 



Table 5-19. Near-Near Runway Configuration in Good Visibility 



TSC 33 North 
(40 minutes) 


Operations Per Time Interval 


80/90 


90/100 


100/110 


110/120 


120/130 


130/140 


140/150 


Predicted Percent 
Single Departures 


100 


100 


100 


100 


100 


100 


100 


Predicted Percent 
Double Departures 


18 


75 


98 


100 


100 


100 


100 


Interarrivals 


4 


3 


5 


4 


2 


1 


3 


Single Departure 
Demand 


4 


3 


5 


4 


2 


1 


3 


Single Departures 


4 


3 


5 


4 


2 


1 


3 


Double Departure 
Demand 


4 


3 


5 


3 


2 


1 


3 


Double Departures 














1 





2 


Withheld Departures 























Departure Release 
Late by Over 5 Sees 























Departure Release 
Early by Over 5 Sees 























Double Runway Occu- 
pancy by Arrivals 























Perfect Release ±5 
Sees Early /Late 


1/0 


0/0 


1/0 


0/0 


2/0 


0/0 


1/0 



5-92 



the two rows, Single Departure Demand and Double Departure Demand, are added 
to the table format. These represent inter-arrival spaces for which the departure 
queue was at least 1 and 2, respectively. Predicted percent departures must be 
"played" against these demand rows instead of the inter-arrival row as for the 
single runway case. 

The Near-Near operation results in 100 percent of all predicted singles 
but only 3 of 16 predicted (for its inter-arrival distribution) extra departures. As 
with the previous case (single runway case), the departure queue exceeded 10 air- 
craft so the loss of extra departures was not due to low demand. The high degree 
of success for single departures would be expected due to the simple strategy. 
The loss of extra departures remains to be explained. 

The Near- Far operation (Table 5-20) results in 90 percent of all pre- 
dicted single departures and as with the Near- Near only 20 percent of all double 
departures. The 10 percent loss of singles is explained by some reluctance on the 
controller's part to put in the 15 seconds "lead" (i. e. , clear departure 15 seconds 
prior to the arrivals clearing the intersection) hypothesized in the strategy. How- 
ever, the perfect releases on the early side indicate that the lead is inserted for 
the most part. 

The Far- Far operation (Table 5-21) results in only 75 percent of the 
predicted single departures and none of the double departures. This 25 percent 
loss in singles is due to even more reluctance on the controllers' part to put in the 
15 seconds lead especially for the tight inter-arrival spaces. The complete loss 
of double departures combined with the 80 percent loss for the other two cases 
prompts the special examination of Quasi- Independent intersecting runways (an 
effective departure only independent runway. ) 

Figure 5-20 depicts the relative position of the two arrivals at the 
time a departure is released between them. In accordance with the Near-Near 
strategy, at the time of departure all first arrivals are clear of the intersection 
and all second arrivals are more than 40 seconds out. However, for the 



5-93 



Table 5-20. Near-Far Runway Configuration in Good Visibility 



CSC 5 South 


Operations Per Time Inter va 




60/ 
70 


70/ 
80 


80/ 
90 


90/ 
100 


100/ 
110 


110/ 
120 


120/ 
130 


130/ 
140 


140/ 
150 


150/ 
160 


160/ 
170 


170/ 
180 


Predicted Percent 
Single Departures 


100 


100 


100 


100 


100 


100 


100 


100 


100 


100 


100 


100 


Predicted Percent 
Double Departures 








2 


18 


76 


98 


100 


100 


100 


100 


100 


100 


Interarrivals 


1 


4 


6 


8 


7 


3 


2 


1 








1 


2 


Single Departure 
Demand 


1 


2 


6 


7 


4 


3 


2 


1 








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Figure 5-20. Position of Arrivals Pairs at the Time of Departure 
Release for Two Runway Configurations 



5-96 






Quasi- Independent configuration, no such clear strategy is evident. Departures 
are released with arrival pairs in any position although the preference is to guar- 
antee that the first arrival is down all right (i. e. , between 20 and 40 seconds into 
roll out) and the second arrival is over 30 seconds out. Thus, departures should 
represent a nearly independent departure only runway. 

In accordance with the strategies thus far, a departure only runway 
sould be capable of a departure every 45 seconds or so (a capacity of 80 departures/ 
hour!). The Quasi-Independent example ran 44 departures /hour. The missing 
factor is departure separation standards. These standards are summarized as: 

• One minute when each departure diverges immediately by more 
then 45 degrees, 

• Two minutes when each departure diverges within 5 minutes by 
more than 45 degrees, and 

• Three minutes when departures will remain on the same course 
longer than 5 minutes. 

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which depends on where those departures are bound and how they have been se- 
quenced by Local Control with the help of Departure Ground Control. 

Figure 5-21 shows the initial heading mix for the Quasi- Independent 
example. If the aircraft going out on the same heading are assumed to diverge 
within five minutes, their spacing is two minutes. If this is considered the norm 
at O'Hare then "extra" departures could add as many as 30 more departures 
through a perfect initial heading mix. What actually occurred was, 11 favorable 
heading changes out of 37 departures. Had separation standards been strictly ad- 
hered to this would have represented 37 departures in 62 minutes or 36 departures/ 
hour realizing 20 percent of the potential "extra" departures. Instead, for this 
Quasi- Independent case, the 37 departures were done in 50 minutes for 44 depar- 
tures/hour. However, the 20 percent figure corresponds well to the two near end 
crossing cases and therefore (1) the 100 percent double departures of the single 
runway case will be considered exceptional due to the high pressure situation it 



5-97 



Departure Sent to 
Wrong Runway 




15 20 25 

DEPARTURE SEQUENCE NUMBER 



30 



35 



40 



Figure 5-21. Initial Heading Mix of Departures for Quasi -Independent 
Runway Operation Over 50 Minutues of Heavy Demand 

represents; and (2) for capacity prediction 20 percent of theoretical double depar- 
tures will be used. 

Table 5-22 shows the effect of using 20 percent of possible doubles on 
the capacity estimates. In addition, the Practical column represents the added 
loss in capacity that either occurred (departures withheld) or should have occurred 
(departures in violation of strategy) in practice when applied to the peak inter- 
arrival distribution. 

5. 3. 3. 1. 4 Bad Cab Visibility Effects 

When the cab loses visibility of the runways the Local Controller uses 
pilot position reports and ASDE-2 radar, when functioning. Even when using 
ASDE-2, the controller does not have complete coverage of the flight path. ASDE 
covers only the airport surface and the ARTS BRITE display blanks out arrivals 
prior to reaching the runway and departures until they are well off the runway (see 
Figure 4-5). The result is that initial turn position reports from departures are 
required and the position of arrivals in the final seconds of their approach must be 
estimated. These factors influence runway capacity. 

Table 5-23 shows a single runway mixed operation in Category II con- 
ditions. Demand is high with the departure queue always exceeding five aircraft 
and averaging 16 for 20 minutes. The arrival demand was fairly high, 21 in 40 



5-98 



Table 5-22. Practical Estimated Runway Capacity 







Perfect 

Split 

(Table 5-17) 


20 Percent 
Split 


Practical 


Single 
Mixed 


Departures 


33 


28 


23 


Operations 


67 


62 


57 


Near-Near 
Crossing 


Departures 


54 


37 


37 


Operations 


87 


71 


71 


Near- Far 
Crossing 


Departures 


47 


36 


29 


Operations 


81 


70 


63 


Far-Far 
Crossing 


Departures 


45 


35 


27 


Operations 


79 


69 


61 


Quasi- 
Independent 


Departures 


60 


36 


36 


Operations 


94 


70 


70 



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5-100 



minutes or 31 arrivals/hour. In this case, it is evident from voice communication 
recordings that ASDE-2 is being used. Missed approaches (pilot initiated) broke 
up the arrival stream as indicated from the inter-arrival spaces before and after 
the three missed approaches. The controller did pretty well in the operation suf- 
fering a 25 percent loss over predicted for singles but getting 40 percent of all 
possible doubles. The high percent of doubles might be explained by the fact that 
this was the only runway in operation at O'Hare at the time and a favorable initial 
heading split was more likely than normal. 

Table 5-24 shows a single runway mixed operation in which voice com- 
munication recordings indicate the controller cannot see the runway and is not us- 
ing ASDE-2. In place of ASDE-2 he uses reports from the number 1 departure in 
the runup pad to determine arrival on time (and so to clear the next departure on) 
and reports from the arrival aircraft on runway turnoff initiation (to permit clear- 
ing the departure for takeoff). The impact of the completely blind operation is 
evident. Practically no inter-arrival spaces less than two minutes in duration were 
used in release of departures. The three that were used had the departure cleared 
early (before the arrival began its turn but after the pilot said he would) to leave a 
very safe margin between it and the next arrival. In this instance, the inter- 
arrival distribution did not peak sharply in the 90-110 second period as is normally 
the case and so 65 percent of the predicted single operations were achieved. Had 
the more normal peak occurred, this would have dropped to about 30 percent. The 
more normal 15 percent extra departures were released during the long inter- 
arrival spaces. Unlike the Category II case, both sides of the airport were run- 
ning. As in the Category II case, departure demand was high with a queue averag- 
ing 11 for 20 minutes. 

The effect of bad visibility is estimated in Table 5-25 by applying the 
strategies of the two bad visibility cases to the peak hour inter-arrival spacing. 
This essentially normalizes all the capacity estimates to a peak arrival demand. 
Case CSC #8, however, is an example of how arrivals can be traded (in some 
fashion) for departures. For this case, only 28 arrivals were taken permitting 



5-101 



Table 5-24. Single Runway Mixed Operations in Bad Cab Visibility 
Conditions With Continuous Double Departure Demand 
Without ASDE-2 In Use 



CSC 8A (West) 
No Cab Visibility 


Operations Per Time Interval 


70/ 
80 


80/ 
90 


90/ 
100 


100/ 
110 


110/ 
120 


120/ 
130 


130/ 
140 


140/ 
150 


150/ 
160 


160/ 
170 


170/ 
180 


180/ 
190 


Predicted Percent 
Single Departures 


23 


70 


92 


100 


100 


100 


100 


100 


100 


100 


100 


100 


Predicted Percent 
Double Departures 








2 


14 


26 


70 


86 


95 


100 


100 


100 


100 


Interarrivals 


2 


3 


1 


4 


3 


3 


3 


2 


2 


1 


1 


2 


Single Departures 











1 


2 


2 


3 


2 


2 


1 


1 


2 


Double Departures 


























1 








1 


Withheld Departures 


2 


3 


1 


3 


1 


1 




















Departure Late by 
Over 5 Sees 






































Departure Early by 
Over 5 Sees 











1 








1 

















Perfect Departure ±5 
Sees Early /Late 














2/0 
























Table 5-25. Effect of Bad Visibility on Single Runway Mixed Operations 





• 


Theoretical 


Good 

Visibility 


Bad 
Visibility 
With ASDE 


Bad 
Visibility 
Without ASDE 


Current 
Analysis 


Arrivals 
Departures 


34 

28 


34 
23 


34 
20 


34 
9 


Total 


62 


57 


54 


43 


Percent of Ideal 


- 


92 


87 


69 


Preliminary 
Analysis 


Total 


60 


54 


43 


40 


Percent of Ideal 


- 


90 


72 


67 



5-102 



19 valid departures for a total of 47 versus the 43 predicted for the unbalanced 
operation. Therefore, the arrival/departure mix juggling between the cab and 
Approach Control can have a beneficial effect on total operations and (1) the depar- 
ture capacity estimates should be considered as problem indicators rather than 
exact estimates and (2) the total capacity estimates should be considered conserva- 
tive. 

Also included in Table 5-25 are the results of the preliminary analy- 
sis done in Reference 8. The comparison with the current results is fairly good 
in good visibility conditions and bad visibility conditions without ASDE-2. How- 
ever, the Category II case indicates that a controller can do better with an ASDE 
than originally thought, adding increased weight to the ASDE deployment recom- 
mended in Reference 8. 

5. 3. 3. 1. 5 Capacity Improvements 

The first area of potential improvement concerns the distributions of 
the three basic parameters: arrival on time, departure on time, and inter-arrival 
spacing. Of the three, the only one which impacts each configuration is inter- 
arrival spacing. The potential payoffs associated with narrowing the spacing dis- 
tributions are substantial and are the driving force behind the current Metering 
and Spacing program. If the current distribution could be converted to one more 
nearly like that shown in Figure 5-22, the arrival rate would rise from 34 per 
hour to 45 per hour (within 20 percent heavies). In addition, if the arrivals on 
time could be shortened and the distribution narrowed, the inter-arrival distribu- 
tion could be moved to the left (i. e. , separation standards could be reduced), fur- 
ther increasing capacity. 

The next area of potential improvement concerns the lost departure 
release opportunities, particularly in the 60 to 100 second inter-arrival bins. The 
potential improvement is runway configuration dependent, ranging (in good visibil- 
ity) from none for the Near-Near crossing runways to 25 percent for the Far-Far 
crossing runways. In addition, when Metering and Spacing is deployed, it will 



5-103 



60- 



40 



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Current Distribution 




60 80 100 120 140 160 180 200 



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Potential Distribution 



A 



X 



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Figure 5-22. Potential Payoffs for Metering and Spacing 



5-104 



place most of the traffic in the critical 60 to 100 second bins where Local Control 
currently has the most problems. Its effect will be to increase arrival capacity 
while choking off departures unless some assistance is provided to Local Control. 

A third area of potential improvement concerns the last departure re- 
leases under poor cab visibility conditions. The single runway mixed operation 
cases herein indicate that the critical 60 to 100 second inter-arrival spaces are 
largely ignored when cab visibility is lost and only position reporting is used (i.e. , 
no ASDE). In this instance Metering and Spacing improvements could not be used 
to their full potential. ASDE does help the situation but falls short of good visibil- 
ity capacity and will not permit Metering and Spacing to realize its full potential. 
At hard pressed airports such as O'Hare, something more is required. 

The last area of potential improvement concerns the lost double depar- 
tures due to unfavorable mixing of initial departure directions of flight. It is pos- 
sible that some assistance to Departure Ground Control, who initially sets up the 
departure sequence, might tap some of this potential improvement. 

5. 3. 3. 2 Local Control Area Delays 

For arrival aircraft, no queueing or delay time was defined from the 
ASDE film. Any arrival delays prior to landing would occur while the aircraft 
was being handled by Approach Control in the TRACON. Delays associated with 
aircraft movements after clearing the runway were treated in the previous Ground 
Controllers' Area analysis. This is not completely in agreement with the opera- 
tional procedures described in Section 4. 2 for Local Control to retain aircraft un- 
til clear of the last active runway for which he is responsible. However, this divi- 
sion significantly eased the ASDE film analysis in that it was not necessary to make 
the distinction as to whether the aircraft was or was not under Ground Control for 
the various configurations. 



5-105 



Departure aircraft, for the purposes of this analysis, have been con- 
sidered to be in the Local Controller's area of responsibility from the time of 
entrance into the Departure Queue (EDQ) until they leave the runway. The timing 
relationships for departures are shown in Figure 5-10. Initial data reduction ef- 
forts separated the departure delays into the two components of departure queue 
delay and runway "Hold" time. In the remainder of the runs the difference between 

STO and EDQ time was used to obtain a total delay value, i. e. , T, , + T, „ based 

J ' ' ldq ldh' 

upon the assumption (as verified in the initial runs) that the movement time from 
ldq to the runway was approximately 30 seconds. 

Runway occupancy time, as measured from "over threshold" to "turn- 
off" was determined for 210 arrival aircraft. The data samples included all run- 
ways except those requiring a taxi phase because of the absence of turnoffs. The 
average of this parameter varied from 38-52 seconds depending on the runway; 
the standard deviation ranged from 6-19 seconds. This parameter appears sensi- 
tive to both runway and aircraft navigation effects and will influence the operating 
strategies used by the Local Controller (s). 

The basic data for analysis was derived from the departure history 
forms discussed earlier in paragraph 5. 3. 2 (Table 5-7). A sample of the data re- 
duction sheet for Local Control is given in Table 5-12; the remaining data reduction 
sheets for the various runs are given in the Operations Analysis Data Supplement. 
The flights treated as occurring within the sample hour are those whose STO (take- 
off) time was within the observation period. The compilation of data on each run- 
way sheet permitted the following parameters to be obtained for departures: 

N , - Number of Takeoffs in Observation Period 
d 

T. , and V T - Average and total taxi (movement) time 

(only for some runs) 



5-106 



EDQ 



MOVE UP 
DEPQ 



LDQ 



LTR 



STO 



OFF 



MOVE FROM 

DEPQ 

TO R/W 



HOLD ON 
R/W 



RUNWAY 

OCCUPANCY 

TIME 



T, 



dq 



T ldt 
-T/ d 



T, 



dh 



Ido 



where 



Code: 



T., + T. „ - Total "Hold" Time 
Idq Idh 

T. , - Delay in Departure Queue 

T - Delay on Runway 

T - Local Control Taxi (Movement) Time 

T i* = T ,^ + + T u + T ,^- Local Control Service Time 
Id Idt Idq Idh 

T - Runway Occupancy Time 



I = Local Controller 

d = Departures 

t = Taxiing 

h = Runway "Holds" 

q = Departure Queue "Holds" 

o = R/W Occupancy 



Figure 5-23. Timing Relationships - Local Controllers' Area (Departures) 



5-107 



Table 5-26. Sample Data Reduction Sheet 

LOCAL CONTROL - DEPARTURES 

Run # 2.Q Date 6-1-75 Runway 27R 

Start Time 8 : 40 STO End Time 9 : 4 O STO 



AC # 


Time in Dept.Q 

LDQ-EDQ(l) 

T ldq 


Runway Hold Time 

STO-RTR(2) 

T ldh 


Local Control Taxi 

+Delay Time 
STO-EDQ(3)= T 'ld 


Local Control 

Taxi (Movement) Time 

T ldt=3-(2+l) 


i 


385" 


64 


583 


114 


z 


451 


-2.59 


746 


56 


5 


AOG 


61 


499 


32 


4 


&39 


16$" 


635 


39 


o 


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760 


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(o 


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165 


663 


45 


7 


825 


160 


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a 


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24 


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954 


154 


11x30 


72. 


10 


1/2.77 


111 


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61 















































































































































(Nd) 



6665 



ST. 



Idq 

667 

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ldq 



1425" 



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ldh 
143) 

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ldh 



aac 



ST' 
Id 

66X 

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ldt 



54- 



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5-108 



Number of aircraft with 

Departure Q delays > 10 sec 
Runway holds 

Total Delay Times 

a* Vt b) T and c) the sum of the two delays 

' L ldq' ldh, 

The data for the individual runway data reduction sheets was next sum- 
marized for each run to show the delays in the north and south areas respectively. 
This data is presented in Table 5-27. The number of arrival aircraft within the 
observation hour was based on "OL" time. 

The summary data sheets for each run present the total Local Control 
delays [in some cases broken down into Departure Queue and runway hold compo- 
nents)] as well as the average delay per departure for both the north and south areas, 
While average delay per departure for the total airport is also presented in these 
summary sheets, these values are not as meaningful as those for each Local area. 

The data from the individual runs have been summarized in Table 5-28 
which presents the runway configuration used, the total number of arrivals and de- 
partures in the sample hour, the departure queue which existed at the start of the 
hour, the total delay to departing aircraft and the normalized parameters of aver- 
age delay/departure and average delay/operation. Runs CSC #7 and CSC #8 repre- 
sent bad cab visibility conditions. 

Table 5-29 presents the average delay for the two modes of operation. 
The delay associated with the West Arrival Mode is higher than the East Arrival 
Mode (8. 5 minutes versus 6. 2). This is largely due to the two poor cab visibility 
cases included in this set. The good visibility delay differences are examined in 
Table 5-30. 



5-109 



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5-122 



Table 5-29. Average Delay for the Primary Arrival Modes 





Average 
Departures/Hour 


Average Delay/ 
Departure (Minutes) 


East Arrival Mode 


55.2 


6.2 


West Arrival Mode 


57.8 
57.8 

58.0 


8.5 
7.0 

11.6 


Good Visibility 
(from Cab) 

Bad Visibility 
(from Cab) 



From Table 5-30 it is apparent that the East mode of operation bal- 
ances its operations between the North and South side very well, each running at 
about 85 percent of capacity (using paragraph 5. 3. 3. 1 capacity estimates). However, 
when the Arrivals are coming from the West there appears to be substantial differ- 
ences in delay between North and South side operations (8. 5 minutes/departure in 
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West mode cases. 

In order to correlate the delay with runway configuration and its asso- 
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capacity represented by the departures are computed for each case, presented in 
Table 5-31 and plotted in Figure 5-24. For the most part the data falls about a 
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some of the delay is associated with the previous hour), TSC#20S which represents 
the exceptionally fine performance shown previously on a single runway with mixed 



5-123 



Table 5-30. North Side/South Side Delays for the Primary Arrival 
Modes in Good Cab Visibility Conditions 







East Arrivals 
Mode 


West Arrivals 
Mode 


North Side 


Average Observed 
Departure s /Hour 


30.4 


20.6 


Percent of Total 
Departures 


55.0 


36.0 


Average Capacity 
(Departures/Hour) 


35.0 


32.4 


Percent of Capacity 


87.0 


64.0 


Average Delay 
(minutes) 


6.9 


4.4 


South Side 


Average Observed 
Depar tur es /Hour 


24.8 


37.2 


Percent of Total 
Departures 


45.0 


64.0 


Average Capacity 
(Departur e s /Hour) 


29.4 


36.0 


Percent of Capacity 


84.0 


10.3 


Average Delay 
(minutes) 


4.3 


8.5 


Total 


Average Observed 
Departur es /Hour 


55.2 


57.8 


Average Capacity 
( Departur e s /Hour ) 


64.4 


68.4 


Percent of Capacity 


86.0 


85.0 


Average Delay 
(minutes) 


6.2 


7.0 



5-124 






Table 5-31. Delay and Percent Predicted Capacity for 
Good Cab Visibility Conditions 















Delay Per 


Run 


Config- 


Capacity 


Depar- 


Delay 


Percent 


Departure 


Identity 


uration 


Estimate 


tures 


(sees) 


Capacity 


(mins) 


TSC 20N 


F-F 


27 


30 


16718 


130 


9.3 


TSC 20S 


S 


23 


34 


25218 


148 


12.4 


TSC 33N 


N-N 


37 


30 


18412 


81 


10.2 


TSC 33S 


N-N 


37 


38 


3585 


100 


1.6 


TSC 35N 


N-N 


37 


31 


15661 


84 


8.4 


TSC 35S 


N-F 


29 


20 


880 


69 


0.7 


CSC 5N 


N-N 


37 


36 


8512 


97 


3.9 


CSC 5S 


N-F 


29 


29 


4592 


100 


2.6 


CSC ION 


N-N 


37 


25 


3399 


68 


2.3 


CSC 10S 


N-F 


29 


28 


3942 


100 


2.3 


TSC 15N 


QI 


36 


19 


7726 


53 


6.8 


TSC 15S 


QI 


36 


40 


27244 


111 


11.4 


TSC 29N 


F-F 


27 


19 


9177 


70 


8.0 


TSC 29S 


QI 


36 


35 


41491 


97 


19.8 


TSC 37N 


QI 


36 


24 


2151 


67 


1.5 


TSC 37S 


QI 


36 


37 


8756 


100 


3.9 


TSC 39N 


F-F 


27 


22 


5618 


81 


4.3 


TSC 39S 


QI 


36 


37 


8169 


100 


3.7 


CSC 9N 


QI 


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19 


2314 


53 


2.0 


CSC 9S 


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37 


9481 


103 


4.2 



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5-125 



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5-126 



operations, and TSC#29N which represents an extremely conservative operation 
of a far-far end crossing runway (the most difficult to tolerate). In general, the 
data tends to confirm the capacity estimates. 

5. 3. 3. 2 Summary of Results of Local Control Analysis 

The values shown in Table 5-28 have been used to plot delay vs oper- 
ations for the north and south areas for both the Arrival from West and Arrival 
from East modes (Figures 5-25 through 5-28). The format used represents data 
taken from the reference (indicated on the figure) on which the 1973/1974 data re- 
sults have been superimposed (with the exception of southside-west arrivals for 
which no previous survey was performed). 

Considering first the Arrival from the East curves, reasonably good 
agreement exists between the two sets of data which indicate apparent northside 
saturation near 30 departures/hr and southside saturation at between 35 and 40 de- 
partures/hr. The southside appears also capable of operating at the 35-40 depar- 
tures/hr in the Arrival from the West mode. However, the northside appears to 
be appreciably less efficient when operating in the Arrival from the West mode. 
Saturation levels appear to be between 20-25 departures/hr, based on the proposed 
saturation level of 4-minute average departure delay proposed by the FA A Airport 
Capacity Manual developed some years ago. 

5. 3. 3. 3 Delay Analysis 

Official FAA NASCOM delay statistics count only those aircraft expe- 
riencing delays greater than 30 minutes. For operational reasons, statistics on 
delays to Departure aircraft are developed at the tower facilities (ATCT) while 
delays to "Arrivals" are kept at Centers (ARTCCs). A recent study ("FAA Report 
on Airport Capacity"; FAA-EM-74-5, I and II dated Jan 1974} examined delays at 
eight major airports associated with aircraft meeting the above 30-minute criteria. 
This analysis indicated a 2:1 ratio in the number of Arrival aircraft experiencing 
these delays as contrasted to Departure aircraft. It was further concluded that 



5-127 



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5-131 



weather is the major reason for these extensive delays. This reference states that 
at O'Hare approximately 20, 000 aircraft were delayed more than 30 minutes in 
1973. Assuming an average delay of 45 minutes (no exact value is available) the 
total yearly delay for these aircraft would amount to 900, 000 minutes. If the av- 
erage delay per aircraft is the same for both Departure and Arrivals the above 
values would indicate 6, 000 Departures experiencing total delay time of 300, 000 
minutes per year; Arrival delay values would be twice those for Departures. 

These delay statistics, as reported by NASCOM, may be compared 
with those experienced by aircraft not included in the NASCOM figures since they 
do not meet the 30-minute criteria. These "other" aircraft, representing the 
large majority of operations as well as primarily good weather conditions, expe- 
rience delays for a wide variety of reasons. These include: 

Aircraft Equipment Type (Sequencing and Separation Rules) 

Mix of Arrivals/Departure Loads 

Data Inadequacy for Sequencing Purposes 

Controller Differences 

Runway Configurations 

Pilot /Aircraft Differences 

Runway Occupancy Times 

The sensitivity of aircraft delays to these multiple factors during 
"normal" operations has not been determined, although individual studies have 
shown the effects of varying some of the individual parameters, i. e. , the effect 
of "heavies", for example. 

It is in this area of operations that improved data for the controller 
can result in significant delay reductions. The total delay, of course, includes 
both Arrivals and Departures. Since this operations analysis effort is directed 
solely at tower cab operations, only Departures delays (and potential improve- 
ments in this area) can be estimated. 



5-132 



At O'Hare during the 13-hour busy period from 0800-2100, approxi- 
mately 750 "Departures" will be handled. The distribution of Local Control delays 
during the 12 sample hours is presented in Tables 5-32 and 5-33 for the two differ- 
ent arrival modes. The average delay per departure is seen to be 6. 2 minutes for 
the Arrival from the East mode and 8. 48 minutes for the West mode. 

These values include departure aircraft which would be cited in NAS- 
COM statistics as well as those which would not be included. Since the 750 "busy 
hour" departures translate into about 225, 000 departures in a year (300 busy days 
per year with Saturdays and Sundays each treated as a half day), it can be seen 
that only 2. 6 percent (6000 4- 225, 000) of the Departures are actually counted in 
the NASCOM statistics. From the distribution shown in the tables it appears that 
the aircraft included in NASCOM data would be those falling into the 25-30 minute 
"bin". We may therefore adjust the average delay time to exclude these aircraft 
so that the average delay under normal busy conditions and good weather becomes 
7. 93 (8. 48-0. 55) and 5. 75 (6. 2-0. 45) minutes for the two cases. Using a conser- 
vative average delay of 6. 75 minutes for the 97. 4 percent of departures not counted 
in NASCOM data gives rise to a total estimated yearly delay of (. 974 x 225, 000 x 
6. 75 = 1. 48 (10 ) minutes. This value may be contrasted with the 300, 000 minutes 
of delay as reported by NASCOM. A reduction of only 20 percent in delays during 
normal operations would be comparable to all the Departure delays reported by 
NASCOM for O'Hare. At an average aircraft cost of $10. 00 per minute this 20 
percent reduction would translate to $3, 000, 000 per year savings for the carriers. 
Moreover, the potential exists for greater reductions in Departure delays than the 
20 percent assumed above. Delay reductions for Arrival aircraft during "normal" 
operations are a further potential benefit if Metering and Spacing techniques can 
be developed and applied on an integrated basis for the several control positions 
involved, namely the "transitional" sector controller(s) at the center, approach 
control, and local control. 



5-133 



Table 5-32. Distribution Statistics of Local Control Delays 
(Arrivals from West) 



Run 




No 


. of Occurrences with 


Delays 


of 




0-5 


5-10 


10-15 


15-20 


20-25 


25-30 


No. 


Runway 


min. 


min. 


min. 


min. 


min. 


min. 


Total 


TSC 


















15 


9R 






2 


- 


- 








22L 


13 


2 


8 


11 


4 








9L 


9 


4 


4 


2 


- 






29 


4R 


22 


6 


14 


13 


4 












10 


17 






14R 




3 














4L 


4 


8 


7 










37 


9R 


4 


11 


7 


10 


17 






25 


12 












9L 


22 


2 












39 


14R 


47 


14 












3 


_ 


_ 










4L 


14 


7 


1 












4R 


24 


7 


3 










CSC 




41 


14 


4 






















7 


9R 


9 


10 


11 


4 


- 


- 






9L 


6 


- 


- 


11 


11 


8 




8 


9L 


15 


10 


11 


15 


11 


8 




16 


9 












14R 


5 


3 












9 


9L 


21 


12 


1 


5 


6 






16 


3 












27L 


24 


13 












Subtotal - North 


40 


16 












100 


35 


20 


24 


15 


8 


(202) 


Subtotal - South 


90 


48 


17 


19 


23 


- 


(197) 


Total 


190 


83 


37 


43 


38 


8 


(399) 


Percent 


47.5 


20.7 


9.3 


10.8 


9.5 


2 





Avg Delay = . 475(2. 5)+. 207(7. 5)+. 093(12. 5)+. 108(17. 5)+. 095(22. 5)+. 02(27. 5) 
= 1. 18 + 1. 55 + 1. 16 + 1. 9 + 2. 14 + . 55 
= 8.48 minutes 



5-134 



Table 5-33. Distribution Statistics of Local Control Delays 
(Arrivals from East) 



Run 




No. of Occurrences \ 


vith Delays of 




0-5 


5-10 


10-15 


15-20 


20-25 


No. 


Runway 


min. 


min. 


min. 


min. 


min. 


Total 


TSC 
















20 


27R(N) 


- 


3 


4 


2 


1 






27L 


2 


8 


14 


9 


1 






32R(N) 


10 


6 


- 


3 


1 




33 


22L 


12 


17 


18 


14 


3 




25 


1 


_ 


_ 






27L 


3 


- 


- 


- 








32R(N) 


5 


6 


15 


4 








32L 


8 


1 


- 


- 






35 


32R(N) 


41 


8 


15 


4 






12 


4 


7 


4 


3 




27L 


24 














32L 


1 














27R(N) 


1 
















38 


4 


7 


4 


3 




CSC 
















5 


32R(N) 

27L 

36(N) 


15 

25 

9 


12 
3 














49 


15 










CSC 
















10 


27L 
32R(N) 


23 
20 


5 
5 










Subtotal - North 


43 


10 








(152) 


72 


36 


26 


13 


5 


Subtotal - South 


111 


18 


14 


9 


1 


(153) 


Total 


183 


54 


40 


22 


6 


(305) 


Percent 


60 


17.7 


13. 1 


7.3 


2 





Avg Delay = 0. 6(2. 5) + . 177(7. 5) 
= 1.5 + 1.32 + 1.65 + 
= 6.2 minutes 



+ .131(12.5) + 

1.28 + .45 



073(17.5) + .02(22.5) 



5-135 



5. 3. 3. 4 Summary of Local Control Area 

1. The good visibility conditions capacity estimates are tabulated by 
configuration and percent utilization in Table 5-34 along with the 
average capacity as weighted by percent utilization. The estimates 
support a quota of 135 operations /hour evenly split between arriv- 
als and departures, evenly split between the North and South sides 
and with a 20 percent mix of heavy aircraft. However, unbalanced 
operations (between North and South sides), such as those run in 
the West Arrival Mode cases herein, put a severe load on the 
Southside controller even with the 135 operations/hour quota. 

2. The estimate for capacity improvements which could be achieved 
in good visibility conditions by assisting the controller in getting 
departures out in tight inter-arrival spaces is given in Table 5-35. 
The average departure rate increase is just over 10 percent. 
This amounts to about 5 percent of the total operations and would 
lead to a quota of about 140 operations/hour. All of the improve- 
ment lies in the Near-Far, Far- Far and single runway configura- 
tions, an average improvement of over 25 percent. This would be 
very important at other airports with less favorable runway con- 
figurations than O'Hare. 

3. Although the potential for increasing departure capacity in the cur- 
rent system is significant (i. e. , 10 percent at O'Hare and up to 25 
percent at other airports), this potential will increase greatly with 
the deployment of Metering and Spacing. Metering and Spacing 
will be designed to create tight inter-arrival spacings to increase 
the arrival rate. These are precisely the spacings in which the 
unassisted Local Controller has trouble getting off departures. 

4. Since current operations rates can often exceed the current run- 
way capacity in good visibility conditions (i. e. , mean capacity 
over all configurations is 132 operations/hour, the quota is 135 
operations/hour) it would be expected that the departure delays 
would exceed the standard 4-minute delay criteria for acceptable 
(unsaturated) service. The average delay is 6. 2 minutes in the 
East Arrival mode and 7. minutes in the West Arrival mode. 
These measurements are from periods of essentially "no delay" 
as would be reported by the ATCT. 

5. When operating a single runway mixed mode in bad cab visibility 
conditions, a substantial reduction in capacity is experienced, 

(i. e. , 25 percent in total operations). Thus, in Category II con- 
ditions at O'Hare with the two 14s operating an independent mixed 



5-136 



Table 5-34. Summary of Current O'Hare Capacity in Good Visibility 



Runway Configurations 


Departure 
Capacity 


Total 
Capacity 


Percent 
Use 


South 


North 


South 


North 


Near-Far 


Near-Near 


29 


37 


134 


36 


Quasi -Independent 


Far-Far 


36 


27 


131 


24 


Quasi -Independent 


Quasi -Independent 


36 


36 


140 


13 


Quasi-Independent 


Near-Near 


36 


37 


141 


6 


Far-Far 


Quasi -Independent 


27 


36 


131 


2 


Single 


Far-Far 


23 


27 


118 


7 


Near- Far 


Far-Far 


29 


27 


124 


2 


Near- Far 


Single 


29 


23 


120 


2 


Single 


Single 


23 


23 


114 


4 


Single 


Near-Near 


23 


37 


128 


4 


Weighted Mean 


31 


33 


132 


100 



5-137 



Table 5-35. Summary of ASTC Improved O'Hare Capacity in Good 
Visibility Without Metering and Spacing 



Runway Con. 


igurations 


Improved 

Departure 

Capacity 


Improved 

Total 
Capacity 


Percent 
Use 


South 


North 


South 


North 


Near-Far 


Near -Near 


36 


37 


141 


36 


Quasi-Independent 


Far-Far 


36 


35 


139 


24 


Quasi -Independent 


Quasi-Independent 


36 


36 


140 


13 


Quasi-Independent 


Near-Near 


36 


37 


141 


6 


Far-Far 


Quasi -Independent 


35 


36 


139 


2 


Single 


Far-Far 


28 


35 


131 


7 


Near-Far 


Far-Far 


36 


35 


139 


2 


Near-Far 


Single 


36 


28 


132 


2 


Single 


Single 


28 


28 


124 


4 


Single 


Near-Near 


28 


37 


133 


4 


Weighted Mean 


35 


36 


139 


100 



5-138 



operation, the capacity would be 86 operations/hour. The use of 
ASDE appears to provide substantial improvement. The two 14s 
would have a capacity of 108 operations/hour. This is still well 
below quota and will result in delays. 

6. Most bad cab visibility operations are taken in the West Arrival 
Mode. For the two cases examined herein the delay/departure 
averaged 18. 2 minutes reflecting the lost capacity in bad visibility. 

7. When including the bad visibility cases in the West Arrival Mode, 
normalizing the delay per operation and ignoring the operation 
level variations between runs, the average delay per operation 
was 3. 1 minutes (186 seconds) for east arrivals and 4. 25 minutes 
(255 seconds) for west arrivals. These values will be used for 
comparison with delays at other portions of the system. 

8. Departure delays at O'Hare during good weather are estimated at 
five times those reported by NASCOM using a 30 minute minimum 
delay criteria. Reduction of these delays by only 20 percent would 
benefit the airlines by more than $3, 000, 000. 



5-139 



5. 4 CONTROLLER ACTIVITY (WORKLOAD) ANALYSIS 

The second major area of investigation was related to the controller 
functional activity (workload) analysis. The results of the analysis of controller 
responsibilities and procedures were described in Section 4.2. The purpose of 
this section is to present the results of the quantitative analysis of controller 
activities. These activities fall into two general areas, communications and non- 
communications activities. The latter category may be further divided into four 
classes of activities: (1) visual observation and/or use of ARTS Brite or ASDE 
Brite displays; (2) recordkeeping on flight strips, logs, or scratch sheets; (3) han- 
dling of departure flight strips; and (4) coordination between controller positions. 
By virtue of the manner in which these activities were performed by controller 
personnel and could be observed by project analysts, it was not practically pos- 
sible to obtain measurements of the time spent in the performance of visual mon- 
itoring and inter-controller coordination. However, these activities are discussed 
qualitatively later in this section. 

Thus, the quantitative measurements of the activities of various con- 
troller positions presented in this section are limited to their communications 
activities and to their recordkeeping and strip handling activities. 

Before proceeding further, it must be noted that communications 
activity represents the best measure of controller workload. Although record- 
keeping and flight strip handling activities are performed for all aircraft, whether 
arrival or departure, they were observed to be performed almost totally in parallel 
with communications to the aircraft for which the activities were performed. 
Thus, computation of a total workload based upon addition of communications and 
these non-communications activities would result in a higher than true level of 
controller activity time. 

Therefore, statistical analyses of controller recordkeeping and flight 
strip activities are presented in this report for the purpose of completeness and 



5-140 



to serve as a reference in following program activities to develop functional de- 
signs for future ASTC systems. This is based on the premise that future system 
automation should, if anything, decrease the physical activity and should not in- 
crease it. 

In addition to quantitatively describing this physical activity, this 
section presents examples of the handling of selected departure and arrival 
flights referenced to a chronological history of the movement of these aircraft 
through the ASTC system. 

5.4.1 Controller Communications Activity Analysis 

The communications activity data presented in the following para- 
graphs were derived from detailed analysis of controller communications record- 
ings made by TSC and CSC for the various controller positions. The data pre- 
sented for each position includes summaries of the message contents within the 
various communications transactions (CTs) examined, average number of CTs 
per aircraft, average CT duration, and channel occupancy (percent of time within 
the one-hour measurement periods spent in communications). For Ground Con- 
trol and Local Control positions channel occupancy versus traffic volume is ex- 
amined as well. 

5.4. 1. 1 Clearance Delivery 

The Clearance Delivery Controller is responsible for the issuance of 
flight clearance instructions to pilots and the handing over of aircraft ready to 
enter the ground control system to Ground Control, normally the Outbound Ground 
position. 

A typical communication transaction sequence for an air carrier flight 



is: 



1. Pilot contacts Clearance Delivery for his clearance. 
Controller transmits clearance from flight strip. 



5-141 



Pilot repeats clearance instructions. 

Controller affirms that pilot has correctly received clearance and 
may request gate identification. 

Pilot provides gate identification and signs off. 

2. Pilot subsequently calls controller as "Ready to taxi. " 

Controller instructs pilot to monitor the Outbound Ground fre- 
quency 121. 75. 

Transaction sequences vary due to the following typical causes: 

1. Pilot calls for clearance which is not yet available to Controller; 
Controller puts flight "under request" status. 

2. Pilot of flight "under request" may repeat request for clearance 
which is still not available to Controller. 

3. Controller may attempt to contact flight which does not answer. 

4. Pilot may challenge the validity of a provided clearance or seek 
a change. 

5. At times of peak activity the Controller may broadcast "Anyone 
for taxi only ?" or "Anyone for clearance only ?" in order to sort 
a large number of flights attempting to contact him. 

6. It is common for general aviation aircraft to call for flight clear- 
ance and be turned over to Outbound Ground in the same CT. 

A transcripted example of communications for this controller position 
is provided in the Operations Analysis Data Supplement. 

Analysis of the communication transactions indicated that Controller 
activity should be a nearly linear function of the number of aircraft seeking clear- 
ance. Upon traffic volume approaching saturation, abnormal delays will be 



5-142 



encountered by flights requiring clearance. Based on two tape recordings, TSC #33 
and CSC #7, a summary of transaction contents for typical one-hour periods is 
shown in Table 5-36. * 

That the workload is a reasonably linear function of aircraft seeking 
clearance is demonstrated by the occupancy per aircraft contacted and the average 
number of CTs required per aircraft handled shown in the table. However, while 
remaining linear, the nature of the controllers service changed as the operations 
rate changed. In run CSC #7 at a total communication loading of 49 percent, the 
controller was able to initiate clearances prior to pilot request (i. e. , 80 percent 
of clearances were not requested). In run TSC #33 at a total communication load- 
ing of 66 percent, the pilots were forced to get on the frequency and request their 
clearance (i. e. , 75 percent of all clearances were requested). If it is assumed 
that 60 percent channel occupancy is a reasonable limit, then one controller could 
handle about 82 aircraft/hour or 66 departures /hour (based upon handovers/con- 
tacted aircraft of 0. 8 from Table 5-36). This is consistent with the runway capacity 
estimates and the quota. It is also consistent with the fact that in December of 1973 
the O'Hare ATCT had instituted a dual Clearance Delivery procedure for peak 
traffic periods. A "Pre-taxi" position was manned during this period and was 
responsible only for transmission of Center clearances to air carrier departures 
using the spare frequency 126. 9. The Clearance Delivery position retained respon- 
sibility for handling air carriers as well as IFR and VFR general aviation traffic 
when ready to taxi. No data could be obtained on this dual position operation be- 
cause it was terminated in January 1974 when the flight schedule reductions obviated 
the need for it. However, its existence tends to confirm that the current operation 
is near saturation. 



*Only two tape recordings were analyzed for this position. Clearance Delivery 
recordings were made for only a portion of the TSC runs; of the runs selected 
for analysis a tape was available only for TSC #33. Clearance Delivery record- 
ings were available for nearly all CSC runs. However, after the completion of 
CSC #7 and comparison with the results of TSC #33, further analysis of this 
position was terminated. 



5-143 



Table 5-36. Summary of Clearance Delivery Communications Transactions 



Run 


TSC #33 


CSC #7 


2 CTs 


198 


142 


Message Elements* 






180A 


58 


11 


180B 


16 


3 


180 


78 


52 


180S 


1 





150 


3 


1 


210A 


3 


2 


210B 


5 


1 


230 


64 


58 


310 


52 


29 


420 


60 


58 


500 


17 


13 


Total Message Elements 


297 


228 


No. of A/C Handled 


89 


68 


Avg CT Duration (sees) 


12.4 


12.3 


Avg No. of CTs/Aircraft 


2.5 


2.3 


(complete sequences) 


Channel Time Occupancy (%) 


66 


49 


Occupancy per A/C Handled (%) 


0.75 


0.72 


CTs/Aircraft Handled 


2.2 


2. 1 



*Message element definitions were provided in 
Section 2. 4 and are not repeated here. 



5-144 



5.4. 1.2 Inbound Ground Control 

Inbound Ground Control is responsible for the control of aircraft 
movements from the point of handover by Local Control to gate or other airport 
destination (i. e. , Butler Aviation, cargo area, hangar area, military area). The 
point of handover is usually upon exit from the arrival runway or when the air- 
craft has crossed the last active runway under control of the Local Control for 
the south or north area in which it landed. 

In discharging these responsibilities Inbound Ground is observed as 
attempting to exert some form of ramp control at times and appears to monitor 
gate status as far as he is able. When gate delay holds are reported by a pilot, 
he directs the aircraft to the penalty box or any other convenient holding area. 
He also directs aircraft out of these areas upon receiving notification from pilots 
that they have a gate. In addition to coordinating the movement of runway arrival 
aircraft, Inbound Ground coordinates the movement of aircraft between any two 
points on the airport (e.g. , hangar to and from terminal, gate to gate, as well as 
the movement of all vehicles across runways and vehicles assisting aircraft. 

Finally, he coordinates the initial departure of certain aircraft 
(mostly helicopters) and pushbacks for aircraft parked at the end of terminal 
fingers. 

A typical communication transaction sequence for a particular arrival 
flight would be as follows: 

1. Pilot contacts Controller and provides his flight identification, 
destination and his position. Controller provides taxi routing 
control instruction. 

Pilot acknowledges and repeats instruction. 

2. Subsequently, the Controller may provide traffic advisory notice 
or call for a hold or yield to another aircraft. 

Pilot acknowledges and repeats instructions. 



5-145 



3. Controller clears aircraft to the gate. 
Pilot acknowledges. 

Actual transaction sequences vary considerably depending on traffic 
volume, weather conditions, presence of aircraft with mechanical difficulties, 
etc. A transcripted example of communications for this controller position is 
provided in the Operations Analysis Data Supplement. 

Inspection of the communications transactions indicated that controller 
activity was highly variable due to operating conditions but strongly dependent 
on traffic volume. In addition, the tape recordings indicated a fair amount of 
"human adaption" as operating conditions changed, in speed-up of talking rate, 
abbreviation of transactions, addressing multiple aircraft, etc. Due to adjacent 
channel interference, only one TSC recording, Run TSC #33, was analyzed to- 
gether with six CSC-produced tapes — CSC #5, 7, 8A, 8B, 9 and 10. A summary of 
transaction contents for one-hour segments from these tapes is presented in 
Table 5-37. 

Before exploring the ramifications of the above data, further explana- 
tion is required of the conditions under which tape runs TSC #33, CSC #8B and #9 
were made. In the case of TSC #33, the data was difficult to analyze due to 
garbling through adjacent channel interference. Hence the data provided is to be 
judged as a "best estimate. " In particular it is to be noted that the actual noted 
formal clearance of aircraft into the ground system was less than actual due to 
"lost" clearance messages. The number of aircraft handled, as posted, has been 
formed from the number of aircraft contacted and correlated with the ASDE data. 

In the case of CSC #8B, the weather deteriorated rapidly from run 
CSC #8A and dense fog formed. Extremely long departure queues formed and 
departures were routed from runway 14R to runway 14 L. The arrival Ground 
Controller assisted in the movement of some of these aircraft through the hangar 



5-146 



Table 5-37. Summary of Inbound Ground Communications Transactions 



Run 


TSC 


CSC 


#33A 


#33B 


#5 


#7 


#9 


#10 


#8A 


#8B2 


CTs 


222 


199 


157 


170 


203 


173 


132 


158 


CTs Aircraft Only 


220 


197 


156 


165 


196 


173 


132 


153 


Message Elements ■*■ 

110 
111 
112 
120 
140 
150 
160 
230 
310 
311 
410 
420 
470 
500 


82 
18 

1 
31 
24 
56 

7 


11 
20 
20 

7 
37 
13 


57 

15 



8 

25 

75 





9 

36 

20 

1 

34 

7 


41 

20 

7 

27 

7 

62 

6 

3 

2 

49 

24 

5 

3 

3 


37 
12 

1 
15 

8 
49 

7 

1 
54 
42 
16 
10 

5 
20 


63 

12 

18 

28 

32 

62 

1 



14 

53 

12 

3 

28 

19 


46 

16 

6 

8 

22 

75 

2 

1 

7 

66 

12 

6 

8 

9 


23 
11 


18 

3 
48 

3 

1 
79 
39 
11 
14 

2 
14 


43 

3 



23 

8 

12 

3 

4 

77 

24 

22 

10 

6 

20 


2 Message Elements 


325 


287 


259 


271 


353 


284 


266 


255 


No. of A/C Handled 


92 


87 


80 


66 


73 


83 


65 


35 


Avg CT Duration (sees) 


8.0 


9.6 


9.2 


8.3 


11.5 


9.2 


10.2 


8.5 


Avg No. of CTs per 
Arrival A/C Handled 


2.3 


2.6 


2.3 


3.0 


3. 1 


2.3 


2.3 


5.3 


Time Occupancy (%) 


49 


53 


40 


39 


64 


44 


38 


38 



NOTES 

1. Message element definitions were given in Section 2. 4. 

2. Much of controller's time spent in moving aircraft from 14R to 14L and in 
assisting Outbound Ground. 



5-147 



area. Arrival runway operations virtually were halted during the period of the 
recording with the exception of a few flights early in the period and a few midway 
during the period when the fog lifted briefly. As determined from the tape, ASDE-2 
was in use by Ground Control (not by Local). 

In the case of CSC #9, the airport operating conditions under which 
this tape was made were abnormal. That morning (CSC #8B) dense fog virtually 
stopped operations, completely disrupting the system of terminal gate allocations 
upon restoration of "normal operations. " This situation caused the penalty box 
and other holding areas to be completely filled with some aircraft required to 
undergo circular taxiing due to the lack of gates. In addition, a DC-10 had under- 
carriage trouble which required eight transactions to the flight, plus transactions 
to assistance vehicles and lengthy transactions to other aircraft circumventing the 
disabled aircraft. 

The one single parameter that best describes controller communica- 
tions activity is the time occupancy of communication transactions required to 
control aircraft movement. Figure 5-29 demonstrates the apparent relationship 
between the number of aircraft handled and occupancy for the data acquired. It 
appears that the percentage hourly occupancy for normal operations is approxi- 
mately 0. 55 N (where N is the number of aircraft handled per hour). Under 
H H 

abnormal conditions due to heavy fog, interruptions of normal aircraft traffic flow 
develop and the need for the aircraft position reports increases. Thus, com- 
munication transaction channel occupancy rises. 

The requirement for aircraft position reports significantly increases 
under lower visibility conditions. Under normal operating conditions (TSC #33, 
CSC #5 and CSC #10) position reports (message category 310) comprised approx- 
imately 2. 5 percent of all messages. However, under low Category I conditions 
(CSC #7 and #8A), position reports comprised approximately 16.5 percent of 
all messages. Under Category II conditions (CSC #8B), the situation worsened to 
where position reports comprised approximately 30 percent of all messages. 



5-148 



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5-149 



As noted in Section 4. 2, the Ground Controllers use both hold and yield 
instructions to accomplish intersection traffic control. Table 5-38 illustrates the 
relative usage of these types of control philosophy under good and low visibility con- 
ditions. The values shown are the percentage of all communications messages for 
the various runs under various conditions. It may be seen that the use of hold in- 
structions tends to increase as visibility decreases, while the use of yield instruc- 
tions tends to decrease as visibility decreases, but the percentage of communications 
devoted to intersection control is nearly the same for all conditions. 

Table 5-38. Intersection Control Instruction Approach 
Vs Visibility Conditions - Inbound Ground 





Percentage of all Messages 






Holds and 


Visibility Conditions 


Holds 


Yields 


Yields 


Good visibility 


6.4 


6.8 


13.2 


Category I 


6.9 


4.8 


11.7 


Category II 


9.0 


3. 1 


12.1 



In general the data indicates that as airport activity increases, so does 
occupancy. However, the mean CT duration is fairly independent and is probably 
more a function of individual controllers. In normal operations, the number of 
CTs per aircraft is fairly constant. Even in runs CSC #7 and CSC #8A where 
visibility was marginal (the cab could see almost to the runways) position report- 
ing and CTs per aircraft were near normal. However, in run 8B when the cab 
could not see, reliance on position reporting doubled as did CTs per aircraft in 
general. 

5. 4. 1. 3 Outbound Ground Control 

The Outbound Ground position is responsible for the coordination of 
airport departure aircraft movements from the terminal ramp to some conven- 
ient geographical point where the aircraft is handed over to the appropriate Local 



5-150 



Control. The geographical location of handover is one where the aircraft is re- 
moved from the taxi operations associated with terminal operations and has a 
clear taxiway to the runway run-up pad. These locations for various runways 
were identified in Section 4. 2. Outbound Ground only handles aircraft that have 
received flight clearance from Clearance Delivery. 

A typical communication transaction sequence for a departure flight 
under normal visual conditions would be as follows: 

1. Controller contacts pilot and identifies his takeoff runway 
and provides routing instructions, as well as necessary 
sequencing and control instructions. 

Pilot acknowledges and repeats taxi clearance. 

2. Subsequently the controller may provide traffic advisory 
information or call for a hold or yield to another aircraft. 

Pilot acknowledges and repeats instructions. 

3(a). Controller contacts pilot and instructs him to monitor the 
appropriate Local Control frequency. 

Pilot acknowledges. 

3(b). Controller clears aircraft across a runway and instructs 
pilot to monitor the appropriate Local Control frequency 
when across. 

Pilot acknowledges. 

A transcripted example of communications for this controller position 
is provided in the Operations Analysis Data Supplement. 

Examination of the communication transactions for this position in- 
dicated that controller activity was normally straightforward and strongly depend- 
ent on traffic volume. However, controller workload could increase remarkably 
upon the development of departure queues that extended backward across runways 
or into the Outer and Inner taxiway area. Under the latter circumstance a fair 
amount of "human adaption" occurred such as speed-up in talking rate, abbrevia- 
tion of terms, or addressing multiple aircraft. Due to adjacent channel interference, 



5-151 



no TSC recordings were utilized for analysis. Six CSC-produced recording tapes — 
CSC #5, 7, 8A and 8B, 9 and 10 — were analyzed. A summary of transaction con- 
tents for one-hour segments from these tapes is presented in Table 5-39. 

Table 5-39. Summary of Outbound Ground Communications Transactions 





CSC #5 


CSC #7 


CSC #8A 


CSC #8B 


CSC #9 


CSC #10 


2 CTs 


149 


217 


177 


273 


163 


159 


No. of A/C Handled 


66 


67 


58 


49 


59 


59 


Message Elements* 














110 


21 


87 


47 


52 


40 


20 


111 


31 


29 


22 


31 


16 


19 


120 


4 


20 


4 


43 


2 


3 


140 


10 


22 


10 


10 


5 


3 


150 


66 


30 


49 


42 


56 


55 


160 





30 


3 


4 


2 


1 


230 


66 


66 


57 


46 


58 


58 


310 


4 


10 


10 


118 


5 


3 


500 


7 


6 


20 


30 


12 


7 


Misc 


5 


24 


17 


34 


13 


26 


2 Message Elements 


216 


324 


239 


410 


209 


195 


Avg Ct Duration (sees) 


8.7 


7.8 


7.2 


10. 1 


6.3 


7.5 


Time Occupancy (%) 


36 


46 


36 


76 


28 


32 


Avg No. of CTs per 
A/C Handled 


2.3 


3.2 


3. 1 


5.6 


2.8 


2.7 



*Message element definitions were previously given in Section 2.4. 



5-152 



It can be seen from the table that the results for CSC #8B exhibit the 
same expansion of communications activity noted for the Inbound Ground position. 
However, the results for the other runs are quite similar. The greater com- 
munications activity under CSC #7 was caused by a rather large queue for depar- 
tures which extended some distance on the Outer. This caused some difficulties 
for Outbound in clearing departures out of the ramp areas blocked by the queue, 
including repeated requests to the waiting aircraft to avoid blocking the crossing 
taxiways between the Inner and Outer. 

With the number of aircraft handled varying only from 58 to 67 for the 
sample hours, no meaningful relationships could be developed based on this data 
alone that could be used for interpolation, or limited extrapolation, to describe 
the various parameters on an hourly basis. 

However, it was postulated that a similarity should exist between the 
nature of Outbound Ground and Inbound Ground data. To test this hypothesis, the 
Outbound Ground data (excluding the highly unusual data run CSC #8B) was plotted 
with the Inbound data. The results are shown in Figure 5-30 for the relationships 
between mean hourly channel occupancy vs aircraft handled/hour. It can be seen 
that for operations observed the Outbound Ground data fits well with the relation- 
ships developed for Inbound Ground data. The data for run CSC #7 which exhibited 
a long departure queue also appears to fit loosely with "abnormal operation" data 
of Inbound Ground. 

The use of holds versus yields instructions for intersection control 
during various level of visibility as shown in Table 5-40 appears to follow the 
same pattern seen for Inbound Ground; that is, the use of holds tends to increase 
with reduced visibility while the use of yield instructions tends to decrease with 
reduced visibility (if the unusual CSC #7 run is not included for the Category I 
conditions). However, the total amount of intersection control appears to increase 
with reduced visibility for this position where it was approximately the same under 
the varying conditions for Inbound Ground. 



5-153 

















Data 
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tions - 

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Dns 




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Operat 

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Ground 
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Departu 
Norma 
Abnorr 

Arrival 
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5-154 



Table 5-40. Intersection Control Instruction Approach 
Vs Visibility Conditions - Outbound Ground 





Percentage of a 


il Messages 






Holds and 


Visibility Conditions 


Holds 


Yields 


Yields 


Good visibility 


1.7 


3.2 


4.9 


Category I 


3.3 


3.3* 


8.2 


Category II 


10.4 


12.4 


12.9 



*This excludes the unusual conditions observed 
under CSC Run #9. 

The effect of low visibility on Outbound Ground communications is also 
exhibited in the requirement for position reports from aircraft. Under good visi- 
bility conditions such reports occur for only 1. 7 percent of all messages. In addi- 
tion, unlike the Inbound Controller who required position reports for arrivals enter- 
ing his control area out by the runways, the Outbound Controller in runs CSC #7 
and CSC #8A handed off his aircraft before he lost visibility and needed little posi- 
tion reporting. In run #8B, however, he relied heavily on position reports as did 
the Inbound Controller (i. e. , 28. 8 percent). 



5.4.1.4 



Local Control 



The two Local Controllers at O'Hare are responsible for controlling 
runway operations; Local Control #1 controls runway operations in the South and 
Local Control #2 controls runway operations in the North. Departure aircraft 
are handed over to the appropriate Local Control from the Outbound Ground at 
some convenient geographic point when the aircraft has departed the main Ground 
Control problem and has a clear taxiway to the runway run-up pad. From the 
communication tapes it may be determined that Local Control checks that his 
aircraft are in the right order in the departure queue, controls them onto the 
runway, clears them for takeoff, and provides turn headings after takeoff. When 



5-155 



the departure aircraft has begun executing its turn after takeoff, the aircraft is 
handed over to Departure Control. In addition, it may be determined that Local 
Control time spaces successive takeoffs, taking into consideration wake turbulence 
problems when aircraft of vitally different sizes are attempting to take off and 
when a runway is used for mixed operations. 

Arrival aircraft are handed over to Local Control from Approach 
Control from 3-6 miles off the end of the arrival runway. The identity and air- 
craft type are checked, the aircraft cleared to land on short final, and the air- 
craft handed over to Arrival Ground Control upon successfully exiting the runway 
in the South and after clearing all runways in the North. 

The required monitoring of air movements, runway takeoff s and land- 
ings by Local Control, together with the provision of necessary time spacing of 
runway operations, indicates that a successful system is one which requires only 
a moderate amount of communication activity. 

A typical communication transaction sequence for a departure aircraft 
would be as follows: 

1. Local Control contacts pilot and instructs him (typically) to follow 
the aircraft ahead of him in the departure queue. 

Pilot acknowledges. 

The above transaction may be repeated one or more times until 
the aircraft reaches the runway. 

2. Controller instructs aircraft to position and hold on the runway 
and may provide a turn heading and perhaps weather advisory 
information. 

Pilot acknowledges the position and hold and heading instructions. 

3. Controller clears aircraft for takeoff and may provide a turn 
heading if not previously given. 

Pilot acknowledges the clearance and heading and may report that 
the aircraft is rolling. 



5-156 



4. Controller (after noting satisfactory takeoff and turn) instructs the 
pilot to contact Departure Control on the appropriate frequency. 

Pilot acknowledges. 

For arrival aircraft the following typical communication transaction 
sequences ensue: 

1. Pilot contacts controller reporting at (or passing) the outer marker. 
Controller acknowledges and gives the landing runway designation. 

2. Controller clears aircraft to land or advises pilot that he is Num- 
ber 2 to land. 

Pilot acknowledges and may request weather information. 

3. Controller may provide runway turnoff instruction when desired. 
Pilot acknowledges. 

4. Controller (after noting aircraft has cleared the runway) instructs 
pilot to contact Inbound Ground on 121. 9 and may provide limited 
taxi instructions. 

Pilot acknowledges. 

The communication sequences can be seen to be quite straightforward 
but variations may occur due to the following causes: 

1. Aircraft mechanical trouble causing an aborted takeoff. 

2. Aircraft mechanical trouble or runway turnoff not completed by 
previous arrival requiring wave-off of incoming traffic. 

3. Aircraft in departure queue may have to return to gate for various 
reasons. 

4. Visibility conditions may be below airline minimums requiring 
resolution of pilot intentions. 

5. General aviation aircraft are provided with very precise single 
message element instructions. 

6. General aviation aircraft may "pop up" and request to land. 



5-157 



Inspection of the communications transactions indicated that controller 
activity should be a reasonably linear function of the number of aircraft handled. 
Limitations upon communication activity appear to be controlled simply by the 
capability of the airport runway systems. 

Four TSC tape recordings — #29, 33, 35 and 39 — were reduced and 
analyzed for the two Local Control positions. In addition, tape recordings — CSC 
#8A and #8B — were analyzed to depict conditions where heavy fog disrupts airport 
operations. Also included in part to add to the understanding of fog operations is 
48 minutes of run TSC 24. A summary of transaction contents for one hour seg- 
ments from the tapes (except TSC 24) is presented in Table 5-41. The rows for 
TSC 24 have been multiplied by 1.25 to show an equivalent hour. 

Hourly time occupancy (HO) is the parameter which best describes the 

controller communication activity and this parameter has been plotted in Figure 

5-31 against the number of aircraft handled (N ). Each point in the figure is identi- 

H 

fied as to Local Control position and mode of runway arrival (east or west); data 
from runs CSC #8B and TSC 24 (heavy fog) are identified as circled points. Time 
occupancy increased in a reasonably linear fashion for the range of data secured, 
indicating that a rough measure of occupancy (for HO not approach 1. 0) can be ob- 
tained from the relation 

normal conditions HO « 0. 52 N percent 

H 

The average communication transaction duration (T) as measured ap- 
peared to be independent of the traffic volume for the occupancies observed. It can 
be determined from Table 5-41 that an average value of 5. 8 seconds is best descrip- 
tive of the data for normal weather conditions. As with Ground Control, the average 
duration is probably most heavily a function of the controller. 



5-158 



Table 5-41. Summary of Local Control Communications Transactions 



Run 


TSC #29 


TSC #33 


TSC #35 


TSC #39 


CSC #8A 


CSC#8B 


TSC #24 


Local Control 


1 


2 


1 


2 


1 


2 


1 


2 


1 


2 


1 


2 


2 1 


2 CTs 


255 


183 


229 


189 


176 


197 


190 


219 


202 


226 


80 


184 


225 


No. of A/C Handled 


90 


52 


82 


58 


64 


67 


69 


67 


47 


55 


17 


34 


60 


Message Elements 




























110 


164 


147 


210 


120 


78 


143 


113 


166 


70 


80 


28 


57 


- 


120 


48 


24 


34 


34 


1 


41 


22 


27 


10 


35 


6 


1 


- 


151 


40 


22 


40 


25 


27 


42 


35 


22 


18 


27 


4 


22 


- 


152 


37 


30 


33 


41 


34 


25 


34 


45 


24 


24 


1 


9 


- 


160 








3 


6 


31 


4 


14 


9 


29 


32 


5 


34 


- 


230 


79 


52 


76 


52 


53 


56 


57 


53 


44 


54 


17 


34 


- 


310 


59 


10 


23 


32 


27 


12 


40 


32 


76 


48 


24 


46 


- 


450 


28 


6 


23 


21 


9 


2 


9 


15 


19 


29 


6 


30 


- 


500 


12 


8 


7 


25 


7 


14 


3 


32 


9 


10 


5 


18 


- 


Misc 


4 


- 


- 


- 


- 


- 


6 


- 


- 


- 


- 


- 


- 


2 Message Elements 


471 


299 


449 


356 


267 


339 


333 


401 


299 


339 


96 


251 


- 


Avg CT Duration 
(sees) 


6.5 


5.7 


7.0 


6.7 


5.3 


4.9 


5.9 


6. 1 


5.2 


5.3 


7.2 


7.4 


8.1 


Channel Time Occu- 
pancy (%) 


44 


30 


45 


35 


27 


27 


33 


37 


28 


34 


16 


38 


51 


Avg No. of CTs/Air- 


























craft (complete se- 


3.2 


3.4 


2.8 


3.3 


3.0 


3.0 


2.8 


3.2 


- 


- 


- 


_ 


_ 


quences only) 




























Avg No. of CTs per 
A/C Handled 


2.9 


3.5 


2.8 


3.3 


2.8 


2.9 


2.8 


3.3 


4.3 


4. 1 


4.7 


4.2 


3.8 


Ratio of Arrival/De- 
parture A/C Handled 


0.88 


1.36 


0.91 


1. 15 


0.88 


0.59 


0.82 


2.05 


1.04 


0.9 


.42 


.42 


1.17 



Single runway in use. One controller only. 



5-159 



70 



>■ 
o 
■z 
<x 
a. 

<_> 
o 



or 

O 



ro 
0D 






60 



50 



40 



30 



20 



10 



















<§ 


TSC 24 

r 


* 


/ 






.^CSCNo.8B. 




IE /$ 

x /x 

/ IW 


^ 




®i 


Af 

o 2E 
2W« 

• 
2W . 


2W X> 
% / 

/ x 

/ IW 


^- H - 0. 


52 N H 




. CSC No 8BJ 


X / 

iwX 


2E 

X» 
IE 






® 


W / 










r 


• 


' 


i 


1 I 


1 



10 20 30 40 50 60 70 80 90 100 110 120 
NUMBER OF AIRCRAFT HANDLED ( N H ) 

Figure 5-31. Local Control Hourly Occupancy Time 
vs Aircraft Handled 



5-160 



These two findings indicate that in good weather the average number of 
communication transactions per aircraft handled should also be reasonably constant. 
The data tabulation provided indicates the confirmation of this expectation with the 
average result of: 

v- CT 
Local Control #1 ^ TT" = 3. 10 (variation approx. 10 percent 

H for 80 percent of data) 

_ CT 
Local Control #2 ) — = 3.40 (variation approx. 10 percent 

H for 80 percent of data) 

In bad weather the number of CTs is above the good weather average. 
This is due to such transactions as reporting the lights in sight and weather mini- 
mum discussions with aircraft in queue. RVR/visibility is given with landing clear- 
ance and will tend to lengthen the average CT time rather than the number of CTs. 
However, rate of delivery can overcome even this tendency as evidenced by CSC 
#8A. RVR/visibility was required on this run but rapid fire delivery by the con- 
trollers kept the mean CT duration down. 

5. 4. 1. 5 Short Term Aspects of Controller Voice Communications 

In the preceding paragraphs, relationships were developed to permit 
interpolation and limited extrapolation of the measured data on an hourly basis. 
A reasonable question therefore exists as to what the limits of extrapolation are, 
and what are the associated implications on a short term basis. 

For the Clearance Delivery Controller, no aircraft are in motion out- 
side the terminal ramp areas and delays in clearance delivery accrued through 
communication channel congestion occur but are of minor consequence to the 
safety and efficiency of traffic flow. Also, the procedure for clearance delivery 
is relatively fixed, hence it is considered that the data derived for clearance 
delivery can be extrapolated to extremely high levels of hourly occupancy. The 
net effect of such high occupancy will be: (a) controller fatigue; (b) probably some 
confusion among aircraft crews in having to monitor a large numberof other aircraft 



5-161 



transactions in securing their own clearance; and (c) inadvertent jamming and 
difficulty by aircraft crews in obtaining taxi clearance. 

For all other controller positions, however, aircraft are in transit 
into and out of the airport and across the airport. As the hourly channel occupancy 
increases, the probability of communication channel saturation on a short term 
basis (say 5 minutes) increases, rendering control of various aircraft extremely 
difficult. 

A good rule of thumb for most distributions is that the 95 percent 

point of the distribution can be approximated by the mean plus twice the standard 

deviation. Since the occupancy must be equal to or less than 1. 0, and the mean 

hourly occupancy is the mean of the associated 5-minute occupancies, we can 

postulate an arbitrary boundary limitation for the mean 5-minute occupancy and 

its standard deviation as 

q + 2 a < 1. 

where 

q = mean occupancy, o = standard deviation 

In order to permit an assessment for the maximum degree of potential 
extrapolation of the previously derived hourly data relationships, it is necessary 
to know the levels of occupancy causing 5-minute saturation effects. Therefore 
measurements of q and cr for 5-minute periods of occupancy have been plotted as 
shown in Figure 5-32. The data thus obtained has been extrapolated as shown to 
determine the mean value for q for which apparently q + 2 a =1. This value of 
occupancy has also been utilized to define the "aircraft handled" volumes which, 
when approached, indicate that the controller voice channel is saturating in some 
5-minute periods producing problems in traffic control. 

Actual data plots are provided in the figure which indicate that the maxi- 
mum mean hourly occupancy when short term saturation problems occur is approxi- 
mately 60 percent for all controllers. This value of hourly occupancy of 60 percent 
is also indicated as the limit of extrapolation in the previous sections. Sixty percent 



5-162 



0.8 



6 



04 



0.2 



- 0.0 





/is 


Assumed Limit for 
Possible 5 Minute Sotu 
(q + 2 or = 1.0) 


ration 






r 

-y 


<k: 


■ Meon 


Limit Volue 


q = 0.58 






s ° 




>. 














-« 




X«* 

^ x 

\ 




^ 

•^ 






o-CD 
d-061 
x- IGI 
•-LC 








"^ 


^* 






1 



2.0 



4.0 6.0 8.0 10.0 12.0 






Figure 5-32. Analysis of Short Term Communication 
Saturation Effects 



5-163 



was used in capacity estimation in the Clearance Delivery discussion and will now 
be used to discuss Ground and Local Control. 

« 

To estimate the operations /hour capability of the Ground Controllers, 
the data from paragraphs 5. 4. 1. 2 and 5. 4. 1. 3 is plotted with respect to arrivals 
or departures /hour in Figure 5-33. In addition, since only run CSC #8B had bad 
visibility for the ground controllers, the bad visibility data for O'Hare from Ref- 
erence 8 has been added. In all bad visibility cases ASDE was in use. The plot 
shows a range of data for both good and bad visibility conditions. The range is due 
to a combination of traffic problems (e. g. , gate delays due to previous weather 
problems, aircraft equipment problems, and related hold ups in the taxi ways) and 
controller delivery rate. Applying the 60 percent limit to the curves and multiplying 
by 2 to represent the two controller capacity, the estimates shown in Table 5-42 
are arrived at. The estimates indicate that most of the time, in good visibility 
conditions, the controllers are operating with a comfortable loading. However, 
with the current quota (135 operations/hour), the controllers can be expected to 
saturate when traffic problems occur (a fairly frequent occurrence). In bad visi- 
bility, even when things go smoothly, Ground Control can just handle the two 14s 
running as independent single mixed operations (i.e. , 108 operations/hour). Either 
increased operations or traffic problems (which are bound to occur when O'Hare is 
running near its quota for very long) will cause Ground Control serious problems. 

Table 5-42. Communication Channel Saturation Estimates 





Two Controller 
Operations Rates 




Smooth 


Problems 


Ground 
Control 


Good Visibility 


220 


130 


Bad Visibility 
With ASDE 


105 


65 


Local 
Control 


Good Visibility 


220 


180 


Bad Visibility 


195 


115 



5-164 






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o 


o 


jj 


o 


a: 


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+j 




z 


rt 




o 


GO 




o 


C 




Q 


o 




Z 


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Cj 




o 





o 


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00 


o 




o 


g 




^ 


g 




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cr 


o 
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pj 

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Sh 


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5 


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Z 


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3 
fafl 



h 



H3T10U.LN00 ONDOcJO H3d 
9NIQV01 NOIlVOINnWKIOD 39VlN30d3d 



5-165 



To estimate the operations /hour capability of the Local Controller, the 
data from paragraph 5. 4. 1. 4 is plotted with respect to arrivals or departures per 
hour in Figure 5-34. For Local Control, runs CSC #8A, CSC #8B and TSC #24 are 
considered bad visibility. CSC #8A is represented by the lower two points. A brief 
rapid fire delivery is responsible for the low values. The other points are a mix of 
ASDE and no ASDE operations. Apparently ASDE has little impact on Local Control 
communications. 

As for Ground Control, the plot shows a range of data for both good and 
bad visibility conditions. The range is a combination of runway configuration (e.g. , 
runway crossings require added communications) and controller delivery rate. 
Applying the 60 percent limit to the curves and multiplying by 2 to represent the 
two controller capacity, the estimates shown in Table 5-42 are arrived at. The 
estimates indicate that in good visibility the communication channel is not the 
pacing factor. Even with a bad configuration and slow message communication, 
the runways and their control will saturate (at above 142) even in the best configu- 
ration before the communication channel. However, in bad visibility conditions 
this is not the case. With slow message delivery Local Control would be just able 
to handle the two 14s running as independent mixed operation runways. If inter- 
secting runways were in use, short terse commands would be a requirement. 

5. 4. 1. 6 Controller Communications Summary 

1. Due to traffic fluctuations during an hour, if a 60 percent 
mean hourly communications loading limit is used to esti- 
mate channel capacity, it can be expected with about a 95 
percent confidence factor that the channel will reach satu- 
ration (i.e., 100 percent loading) for at least five minutes 
in the hour. This 60 percent is used as the criteria for 
capacity estimation in this section. 

2. The estimated channel capacity for Clearance Delivery is 
66 departures /hour. On an even mix of arrivals to de- 
partures this is consistent with the runway capacity and 
the current quota. Clearance Delivery is just at satura- 
tion with little room for growth. 



5-166 




AONVdnooo BiMii AianoH 



5-167 



3. The estimated channel capacity for Ground Control is dependent 
upon visibility conditions and ASDE usage. For the bad visibility 
cases examined in this section, ASDE was in use. In good visi- 
bility conditions two channels (two Ground Controllers) can easily 
support a smooth operation. However with the current quota 
(135 operations/hour) , when traffic problems occur (which is 
not infrequently) due to weather, gate tie ups, or aircraft 
equipment problems in the taxi ways, the Ground Control chan- 
nels) can be expected to saturate. On this basis Ground Con- 
trol is approaching saturation in good visibility conditions with 
little room for growth. 

In "bad visibility" conditions for Ground Control (i. e. , the con- 
troller cannot see the airport surface) the weather conditions 
are severe and the airport is usually operating the two 14s for 
arrivals. In this mode with a smooth operation, two Ground 
channels (with the controllers using ASDE) can just support the 
single independent mixed operations capacity of the two runways 
(i.e. , about 108 operations/hour). However, this is below the 
current quota and, if operated for prolonged periods, can cause 
traffic tie ups. In this situation Ground Control channels are in 
serious difficulties. On this basis Ground Control is currently 
operating in a saturated fashion in "bad visibility conditions". 

4. The major reason for increased Ground Control channel loading 
in "bad visibility" is the controllers use of pilot position reports, 
even with ASDE in use. This category of communication goes 
from one percent to two percent of all communications in good 
visibility to 30 percent when the Ground Controller cannot see 

(i. e. , approaching or in Category II). 

5. The estimated channel capacity for Local Control is dependent 
upon visibility conditions. In good visibility conditions the 
Local channels are well below saturation. The estimated capa- 
city is 195 operations/hour. In "bad visibility" conditions (i. e. , 
the controller cannot see the runways) a controller who delivers 
his messages in short terse commands will not saturate the chan- 
nel. However, in two cases of the analysis, messages rates were 
observed which would have led to channel saturation had the opera- 
tions rate been as high as 115 ope rations /hour. This would have 
just handled the two 14s as single independent mixed operations. 
For any operations rates in excess of that, short terse commands 
would be a requirement. 



5-168 



6. The major causes for increased Local Control channel loading in 
"bad visibility" are weather reports (RVR and visibility) and posi- 
tion reports (e.g. , lights in sight by the pilot). In the case of 
single runway mixed operations, arrival turn-off negotiations are 
important position reports and have a substantial impact on chan- 
nel loading. 

5.4.2 Controller Non-Communications Activity Analysis 

5. 4. 2. 1 Descriptions of Non-Communications Activities 

As noted in the beginning of this section the primary areas of concen- 
tration for quantitative investigation of controller non-communication activities 
were manual recordkeeping and flight strip handling. The activities studied for 
each position are listed below:* 

1. Flight Data 

a. Retrieve flight strips from printer 

b. Separate strips 

c. Mount strips on flight strip holder 

d. Annotate strips for local restrictions and flight character- 
istics 

e. Post strips on Clearance Delivery Flight Strip Board 

2. Clearance Delivery 

a. Retrieve strip from Flight Strip Board when (air carrier) 
pilot calls for clearance 

b. Record gate number 

c. Replace strip in Flight Strip Board until (air carrier) pilot 
calls for taxi 

e. Record time pilot called for taxi 

f. Pass strip to Ground Control (normally Outbound Ground) 



*These activities were described in detail in Section 4.2. 



5-169 



Outbound Ground 

a. Record departure runway on strip 

b. Position strip in Flight Strip Board (in sequence to the runway) 

c. Pass strip to Local Control #1 or #2 

Inbound Ground 



a. Record flight call sign on scratch pad 

b. Record location where aircraft is holding for a gate on scratch 
pad. 

c. Eliminate flight call sign from scratch pad 

5. Local Control 

a. Mark indication that pilot has been instructed to follow pre- 

ceding aircraft in queue or to position and hold. 

b. Record departure heading on strip. 

c. Position strip in Flight Strip Board in order of takeoff se- 
quence. 

d. Pass strip (down the Flight Strip Tubes) to Departure Control. 

e. Record arrival flight call sign on Arrival Log. 

With the exception of activities 1(a), 4(b), 5(a), and 5(c) the activities 
are performed for all arrival and departure aircraft handled by the ASTC system. 
Thus, the total time spent in these manual activities will be approximately lin- 
early related to the traffic volume. 

In the case of activity 1(a) for Flight Data, flight strips are usually 
printed in batches, usually every 15 minutes. Therefore, the time spent in this 
activity per aircraft must be pro-rated among the aircraft for which strips were 
printed at each output. Although flight strips may be printed for individual air- 
craft, when it becomes necessary to request a clearance for a flight for which a 
strip has not been previously received or when a revised clearance is requested 
by the pilot, these instances occur infrequently and are treated in the computa- 
tions in this analysis. 



5-170 



In the case of activity 4(b) for Inbound Ground the performance of this 
activity is strongly influenced by the traffic situation. Obviously, when heavy 
traffic levels or abnormal operating conditions result in increased gate availability 
problems, the requirement for this activity will increase directly with the number 
of aircraft required to hold for a gate. When there are only a few aircraft holding, 
it may be unnecessary for the controller to record the locations at which they are 
holding, since these locations would be limited to one or two areas, usually based 
upon the particular airline as discussed in Section 4.2. However, as the number 
of aircraft waiting for a gate becomes significant and a number of holding areas 
may have to be used, the requirement for recording of the holding location for in- 
dividual aircraft increases. 

In the case of activity 5(a) for Local Control, the performance of this 
activity appeared to differ between controllers. For some it was performed for 
all aircraft regardless of the traffic level. For others it was influenced by the 
traffic demand for the departure runway; that is, when there were only a few air- 
craft queued for the runway, the controller would not mark the strip but when 
there was a significant number of aircraft in the queue, the strip was marked for 
each flight. For some controllers it was never performed. However, in general 
this activity was performed at least for some departures by most controllers. 

In the case of activity 5(c) for Local Control, the requirement to adjust 
the position of the flight strip in his Flight Board will be influenced by the run- 
ways in use, the operating conditions, and the arrival aircraft sequence. As noted 
in Section 4. 2 Outbound Ground normally attempts to establish the aircraft in a 
reasonable sequence for the runway. Some modest adjustment of this sequence 
may be accomplished by Local Control when necessary or feasible. For example, 
for all runways but 4L there is a run-up pad where such an adjustment can be 
made. In the case of 4L Local Control basically has no option but to work the air- 
craft in the sequence set up by Outbound Ground and adjustment of the strip posi- 
tions would not be performed. In situations where departures are established in 



5-171 



two separate queues by virtue of the use of alternative routing by Outbound Ground, 
adjustment of strip positions is the rule while both queues exist. In some cases 
the nature of aircraft in the arrival sequence may lead Local Control to adjust 
the sequence of aircraft for departure, where this can be accomplished, to avoid 
delays in operation; for example, if heavy aircraft were in arrival sequence, he 
might sequence a heavy for departure ahead of another aircraft to avoid delays 
between these operations or minimize the impact of the turbulence caused by the 
arrival on departure operations. 

The time required to perform each of the task activities for the var- 
ious controller positions was measured. The measured values for each of the 
positions are shown in Tables 5-43 through 5-47 and include the computed average 
duration and standard deviation for each activity. It may be seen from these 
tables that the widest variation in performance times occurred for the Outbound 
Ground and Local Control activities related to the passing of flight strips to 
Local Control or Departure Control, respectively. This variation is anticipated 
based upon the manner in which the flight strips are passed to the succeeding posi- 
tion as described in Section 4.2; that is, the controller checked the flight's move- 
ments in reference to the strip, frequently holding the strip in his hand, while 
accomplishing this activity. The effect of this procedure is most effectively 
demonstrated in Table 5-45 with regard to the passing of the strip from Outbound 
Ground to Local Control #1. During the observation of two controllers, several 
measurements were specifically identified as having been made in the case where 
the controller was watching the movements of aircraft in the vicinity of the inter- 
sections of the Outer, New Scenic, and Bypass taxiways. For these specific in- 
stances the average duration of the activity was 8. 8 seconds. The values shown in 
these tables are used in the following estimation of controller non- communica- 
tions activity workload. 



5-172 



Table 5-43. Flight Data Activities Measurement 



Controller 


Retrieve 


Separate 


Mount 


Annotate 


Post 


Number 


Strip 


Strip 


Strip 


Strip 


Strip 


1 


2.0 


2.5 


3.0 


0.5 


2.5 




2.0 


2.5 


3.5 


3.5 


2.5 




2.5 


2.0 


3.0 


3.0 


2.0 




2.0 


3.0 


3.0 


4.0 


1.5 




2.0 


2.5 


2.5 


3.5 


2.0 




2.0 


2.5 


3.0 


3.0 


3.0 






2.0 


3.0 


4.0 


2.5 






2.5 


4.0 


2.5 


3.0 






3.0 


3.0 


0.5 


3.0 






2.5 


3.0 


3.5 


2.5 


2 


2.5 


3.0 


3.0 


3.5 


2.0 




2.0 


3.0 


3.0 


4.0 


1.5 




2.0 


2.5 


3.5 


4.5 


2.5 




2.0 


2.5 


4.5 


2.5 


3.5 




2.0 


2.5 


3.0 


0.5 


2.5 




2.5 


2.5 


3.0 


3.5 


2.5 




2.5 


2.0 


3.0 


3.5 


2.5 






2.0 


2.5 


3.5 


2.0 






3.0 


3.0 


3.0 


2.5 






3.0 


3.0 


3.5 


2.5 


3 


2.0 


2.5 


3.0 


3.0 


2.5 




2.5 


2.5 


3.0 


3.5 


2.5 




2.5 


2.5 


3.0 


3.5 


2.0 




2.5 


2.5 


4.0 


4.0 


2.0 




3.0 


2.5 


3.5 


4.0 


1.5 






3.0 


3.0 


0.5 


2.5 






3.0 


2.5 


0.5 


1.0 






3.0 


3.0 


3.0 


3.0 






2.0 


3.0 


3.5 


2.5 






2.5 


3.0 


3.5 


2.0 


2T (seconds) 


40.5 


77.0 


93.5 


89.0 


70.0 


Avg Duration 
(seconds) 


2.4 


2.6 


3. 1 


3.0 


2.3 


Std Deviation 
(seconds) 


0. 19 


0.34 


0.39 


0.89 


0.50 



5-173 



Table 5-44. Clearance Delivery Activities Measurement 





Call for Clearance 








Controller 


(A 


Lr Carrier) 




Call for Taxi 


Retrieve 


Record 


Replace 


Retrieve 


Mark 


Pass Strip 


Number 


Strip 


Gate 


Strip 


Strip 


Time 


GC 


1 


1.5 


0.5 


1.5 


1.5 


2.0 


1.0 




2.5 


0.5 


2.0 


2.0 


2.5 


1.0 




2.5 


1.0 


2.0 


2.5 


2.5 


1.5 




2.5 


0.5 


2.0 


2.0 


2.5 


1.0 




3.0 




2.5 


2.5 


3.0 


1.0 




3.5 


0.5 


2.0 


2.0 


3.0 


1.5 




2.0 


0.5 


1.5 


1.5 


3.5 


1.5 




2.5 


1.0 


2.0 


2.0 


2.5 


1.0 




3.0 


0.5 


2.0 


2.0 


2.5 


1.5 




2.0 




2.0 


2.0 


2.0 


1.0 


2 


1.5 


0.5 


2.0 


2.0 


1.5 


1.5 




2.5 


0.5 


2.0 


2.0 


2.0 


1.0 




3.0 


0.5 


3.0 


3.5 


2.0 


1.0 




3.5 


0.5 


2.5 


2.0 


2.5 


1.0 




3.0 


1.0 


1.5 


2.0 


2.5 


1.0 




2.5 




2.5 


2.0 


3.0 


1.5 




2.5 


0.5 


1.5 


1.5 


3.0 


1.5 




3.0 


0.5 


2.0 


2.0 


3.5 


1.0 ' 




1.5 


0.5 


2.0 


2.0 


2.0 


1.0 




2.5 


0.5 


2.0 


2.0 


2.5 


1.0 


3 


2.5 


0.5 


2.0 


2.0 


2.0 


1.5 




2.5 


0.5 


2.5 


2.0 


2.5 


1.0 




3.0 


0.5 


1.5 


2.0 


3.0 


1.0 




3.0 


1.0 


2.0 


2.0 


2.5 


1.0 




1.5 


0.5 


2.0 


2.0 


2.5 


1.5 




2.0 


1.0 


2.0 


2.5 


3.0 


1.5 




2.5 


1.0 


2.0 


3.0 


2.5 


1.0 




2.5 


0.5 


3.0 


2.0 


3.0 


1.0 




2.5 


0.5 


3.0 


1.5 


3.5 


1.0 




2.5 


1.5 


2.0 


2.0 


2.0 


1.0 


ST (seconds) 


75.0 


17.5 


62.5 


62.0 


71.0 


35.0 


Avg Duration 
(seconds) 


2.5 


0.7 


2. 1 


2.1 


2.4 


1.2 


Std Deviation 
(seconds) 


0.53 


0.26 


0.41 


0.41 


0.52 


0.25 



5-174 



Table 5-45. Departure Ground Activities Measurement 



Controller 


Record 


Position 


Pass Strip 


Pass Strip 


Number 


Runway 


Strip 


to LC#1 


to LC #2 


1 


1.0 


1.5 


3.5 


4.5 




1.0 


2.0 


3.0 


5.0 




1.0 


1.0 


3.5 


6.0 




1.0 


1.5 


3.5 


9.5 




1.0 


2.0 


2.5 


4.5 




1.0 


2.5 


2.5 


4.5 




1.5 


1.5 


3.5 


7.5 




1.0 


1.5 


3.5 


5.5 




1.0 


2.0 


2.5 


3.0 




1.0 


1.0 


3.0 


4.0 


2 


1.0 


1.0 


3.0 


3.0 




1.5 


1.0 


2.5 


3.5 




1.0 


1.5 


3.5 


4.5 




1.0 


2.5 


5.0 


16.0 




1.0 


1.5 


3.0 


3.0 




1.5 


1.5 


12.0 


4.5 




1.0 


1.5 


7.0 


3.0 




1.5 


2.0 


15.0 


4.0 




1.0 


1.5 


3.5 


4.5 




1.0 


2.0 


3.5 


3.5 


3 


1.0 


1.5 


3.0 


2.0 




1.5 


1.5 


7.0 


3.0 




1.0 


2.0 


3.0 


3.0 




1.0 


1.5 


6.0 


3.5 




1.0 


1.5 


3.5 


3.5 




1.0 


1.5 


11.5 


4.0 




1.5 


1.0 


7.5 


3.5 




2.0 


1.0 


13.0 


2.5 




1.0 


2.0 


6.0 


3.0 




1.0 


1.5 


6.0 


3.5 


ST (seconds) 


33.5 


47.5 


155.5 


135.0 


Avg Duration 
(seconds) 


1. 1 


1.6 


5.2 


4.5 


Std Deviation 
(seconds) 


0.26 


0.39 


3. 12 


1.55 



5-175 



Table 5-46. Inbound Ground Activities Measurement 



Controller 


Record ID on 


Mark 


Eliminate 


Number 


Scratch Pad 


Noted Point 


ID 


1 


2.5 




0.5 




3.0 




0.5 




3.0 


1.5 


0.5 




3.5 




0.5 




2.0 




0.5 




2.5 




0.5 




3.0 




0.5 




3.0 


1.5 


0.5 




3.0 




0.5 




3.5 




0.5 


2 


3.0 




0.5 




3.0 




0.5 




3.0 




0.5 




3.5 




0.5 




2.0 




0.5 




3.0 


1.5 


0.5 




2.5 




0.5 




3.0 




0.5 




3.0 




0.5 




3.0 




0.5 


3 


2.5 




0.5 




3.0 




0.5 




3.0 




0.5 




3.0 




0.5 




3.5 


1.5 


0.5 




2.5 




0.5 




3.0 




0.5 




3.0 




0.5 




3.0 




0.5 




3.0 




0.5 


ST (seconds) 


87.5 


6.0 


15.0 


Avg Duration 
(seconds) 


2.9 


1.5 


0.5 


Std Deviation 
(seconds) 


0.37 


-0- 


-0- 



5-176 



Table 5-47. Local Control Activities Measurements 



Controller 


Mark 


Record 


Position 


Pass Strip 


Record ID 


Number 


P&H 


Heading 


Strip 


to DC 


on Arrival Log 


1 


0.5 


1.5 


3.0 


3.5 


2.5 




0.5 


0.5 


2.0 


3.5 


2.5 






1.5 


2.5 


12.5 


3.0 




1.0 


1.0 


3.0 


7.0 


3.0 






1.5 


3.0 


3.0 


3.0 




0.5 


1.5 


2.5 


3.0 


4.5 




0.5 


1.5 




2.0 


2.5 






2.0 




3.5 


2.0 




1.0 


3.0 


2.0 


5.0 


3.0 






1.5 




4.0 


2.5 


2 


0.5 


1.5 




2.0 


1.5 






2.0 




2.5 


3.5 




1.0 


1.0 




1.5 


2.0 




0.5 


1.5 


2.0 


7.5 


1.5 






2.0 


2.5 


3.5 


2.0 






2.0 


3.0 


1.5 


2.5 




0.5 


1.5 




2.0 


2.0 






2.0 


2.5 


3.0 


5.0 




0.5 


1.5 




3.5 


3.0 






1.0 




2.5 


2.0 


3 




1.0 




3.0 


3.5 




0.5 


2.0 




2.5 


2.5 






1.5 




4.0 


3.0 






1.5 




3.0 


2.0 






2.0 




5.0 


3.0 




0.5 


3.5 




3.5 


3.5 






2.0 




3.5 


2.5 






1.0 




2.5 


2.0 






2.0 




3.0 


3.0 






1.5 




3.0 


3.0 


ST (seconds) 


8.0 


57.0 


28.0 


105.5 


78.5 


Avg Duration 
(seconds) 


0.6 


1.9 


2.5 


3.6 


2.7 


Std Deviation 
(seconds) 


0.24 


0.53 


0.34 


2.01 


0.78 



5-177 



5. 4. 2. 2 Computation of Non-Communications Activity Workload 



The relationships employed in computing the activity workloads for 
the various controller positions for busy hours are described below: 



where 



where 



FD 



k T „ + T n „ + T„„ + T . „ + T„ 
p RS SS MS AS PS 



x Avg. No. Dep/Hour 



T = avg. time spent by Flight Data/Hour 
FD 

k = pro-rating factor for individual flight 

T = avg. time to retrieve strips from printer 

T = avg. time to separate strip 

T,,^, = a vg. time to mount strip 
MS * 

T = avg. time to annotate strip 

no 

T = avg. time to post strip in Flight Strip Board 

Jr o 



CD 



k(T +k T +T )+T +T +T 

AC V RSC RG RG RS 7 RSC RT PSG 



x 



CD 



AC 



RSC 



RG 



x Avg No. Dep/Hour 

= avg. hourly workload for Clearance Delivery 
= percentage of departures involving air carriers 



RG 



T 



RS 



RST 



= avg. time to retrieve strip for delivery of clearance to 
air carriers 

= percentage of departures requiring recording of gate 

= avg. time to record gate number 

= avg. time required to replace strip in Flight Strip Board 

= avg. time required to retrieve strip for aircraft ready 
to taxi 






5-178 



where 



where 



T = avg. time to record time 
RT 

T = avg. time to pass strip to Ground Control 
PSG & 



OG 



T +T +kT +kT 

RR POS S PLS N PLN 



x Avg. No. Dep/Hour 



T = avg. hourly workload for Outbound Ground 

T = avg. time to record runway 

RR 

T = avg. time to position strip in Flight Strip Board 

k = Percentage of flights using south departure runway 

= avg. time to pass strip to Local Control #1 (south run- 



PLS 



N 



ways) 
= percentage of flights using north departure runway 



T = avg. time to pass strip to Local Control #2 (north run- 

PLN , 

ways) 



IG 



T + k T + T 

RI H RHP EI 



x Avg. No. Arrivals/Hour 



IG 



RI 



"h 



RHP 



T 



EI 



avg. hourly workload for Inbound Ground 

avg. time to record ID on scratch pad 

percentage of flights requiring recording of holding point 

avg. time to record holding point 

avg. time to eliminate ID from scratch pad 



5-179 



where 



where 



T = k T +T +k T + T 

LC |_ PH MPH RDH POS POS PDC 

x Avg. No. Dep/Hour + T x Avg. No. Arrivals/Hour 

rift 1 



T = avg. hourly workload for Local Control 

LC 

k = percentage of strips for which controller will mark that 

position and hold instruction was given 

T = avg. time to mark strip that position and hold instruc- 

tion was given 

T = avg. time to record departure turn heading 

k = percentage of strips which will have to be positioned in 

order other than received from Outbound Ground 

T = avg. time to adjust position of strips 

T = avg. time to pass strip to Departure Control 

PDC 

T . , = avg. time to record arrival ID on Arrival Los; 
RAI & 

6 - a ) T^ = T* + T* + T* + T n (departures) 
' DO FD CD OG LC v F ; 

b) T A _ = T T ^ + T T „ (arrivals) 
; AO IG LC l ; 



T = avg. total hourly workload for all departure operations 

DO 

T = avg. total hourly workload for all arrival operations 

Several general assumptions were made in developing the estimates 
for the non-communications activity workload to simplify the computational proc- 
ess. These are: 

1. An average busy hour traffic volume of 120 operations /hour based 
on scheduled air carrier traffic and traffic levels observed in the 
traffic flow analysis. 



5-180 



2. General aviation (and commuter airline) operations account for 
approximately 15 percent of total busy hour operations (with VFR 
and IFR departures evenly divided). 

3. Equal distribution of departure and arrival traffic within a typical 
busy hour. 

4. Equal distribution of traffic operations between the north and 
south runways. 

5. Normal visual operating conditions (so that the measured times 
for the various activities hold). 

5.4.2.2. 1 Flight Data 

For the Flight Data the parameter k in equation (1) is determined 
from the following estimates. Flight strips are normally printed every 15 minutes. 
The average number of strips printed per hour is equal to the percentage of air 
carrier and general aviation IFR departures or 

(0. 85 + 0. 07) (. 50) 120 * 55 strips 

Thus 

k_ = t^ 1 * 0. 073 

P ^x55 

Using this value T is computed as 

[(0.073) (2.4) +2.6 + 3.1 + 3.0+2.3] 60 = 670.5 seconds 

5.4.2.2.2 Clearance Delivery 

The parameter value k in equation (2) is estimated to be 0. 90 based 
upon Clearance Delivery procedures pertaining to gate recording. This is based 
on the fact that operations from 91. 5 percent of the gate require such recording 
but that operations from other than American, Trans World and United gates 
are at a lower volume than for these airlines. Using this value and other param- 



eters previously defined T is computed as 



(0.85) [2.5 + (0.90) (0.7) +2. l] + 2. 1 +2.4 + 1.2 



60 = 608. 7 sec. 



5-181 



5.4.2.2.3 Outbound Ground 

Based on the general assumptions and parameter values shown in 
Table 5-29 T is computed as 

[l. 1 + 1. 6 + (0. 5) (5. 2) + (0. 5) (4. 5)] 60 = 453 seconds 

5. 4. 2. 2. 4 Inbound Ground 

The determination of a practical value for the parameter k involved 

H 

some additional assumptions since no direct relationship between the aircraft 
experiencing gate holds could be readily discerned from the results of the traffic 
flow analysis described in paragraph 5. 3. 2. An assumption was made that under 
normal conditions (i.e. , no weather disruptions of airline schedules) the require- 
ment for aircraft to hold for a gate could be determined using queueing theory. 
Therefore, using the estimated value of approximately 100 available aircraft 
docking spaces (refer to paragraph 5. 3. 1) the family of curves shown in Fig- 
ure 5-35 was developed for the various gate occupancy times shown at extreme 
right of each curve. The number of gate holds observed in the traffic flow anal- 
ysis for various traffic levels were then plotted. As shown in the figure the data 
appeared to approximate a curve with a gate occupancy time of 0. 635 hour or 
38 minutes. Since the average gate occupancy time measured in the ramp area 
flow analysis was 45 minutes or 0. 75 hour, an interpolation was made between 
the curve for this value and the apparent curve for the observed data yielding an 
approximate number of 3 aircraft/hour requiring a gate hold for (0. 85) 120 opera- 
tions per hour. For the purposes of this analysis it was assumed that the holding 
location was recorded for all aircraft so that 

k = « 06 

H (0.85) (60) 

Using this value and measured activity times for Inbound Ground, T is computed 

IG 



as 



[2.9 + (0. 06) (1. 5) + 0. 5] 60 = 209. 4 seconds 



5-182 




cr 
° o 



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CD 

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U 

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HH/AV13Q 31V9 V 3AVH 01 Q31D3dX3 0/V 30 H38KinN 



5-183 



5.4.2.2.5 Local Control 

The values for the parameters k and k in equation (5) were 
derived from the measurement data as the percentage of the observations for which 
the position and hold marking and strip positioning occurred. Thus, 

k^ TT = ~ * 0. 43 and k ^ CT = -^ « 0. 37 
PH 30 POS 30 

Using these parameter values and measured activity times from Table 5-31, T 
is computed as 

[(0. 43) (0. 6) +1.9 + (0. 37) (2.5)+ 3. 6] 60 + (2. 7) 60 

401 (departures) + 162 (arrivals) = 563 seconds 

However, it should be noted that this workload is for both Local Control positions. 
Therefore, the workload for each Local Controller would be equal to 283. 15 sec- 
onds. 

5.4.2.2.6 Total Manual Workload 

Using equations (6. a) and (6. b) and the values computed above, T 



DO 



and T are computed as 



T = 670. 5 + 608. 7 + 453 + 401 = 2133. 2 seconds 
DO 

T AO = 209, 4 + 162 = 371 - 4 seconds 
5. 4. 2. 3 Summary of Non-Communications Activity Workload 

The results of the preceding computations are summarized in 
Table 5-48. From the table it may be seen that Flight Data is the busiest position 
in terms of non-communications activity relative to traffic operations. Since this 
position has no responsibility for communications with aircraft and only infrequent 
interphone communications with the ARTCC, this level of activity may appear low. 
However, the other task activities of the Flight Data position discussed in Section 
4.2 were not measured because they are not directly related to traffic flow. 



5-184 







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5-185 



The next highest levels of non-communications activities may be ob- 
served for the Clearance Delivery and Outbound Ground positions. As the com- 
munications analysis for these positions showed a modest channel occupancy time, 
they would both appear to be fairly busy positions. 

5.4.3 Traces of Individual Flights Through the ASTC System 

The analyses of traffic flow statistics in Section 5. 3 as well as the 
analyses of controller communications and non-communications activities pre- 
sented above have examined the operation of the ASTC from an overview level. 
To examine the effect of the system operation on an individual aircraft as well as 
the interaction between control positions in handling aircraft, a number of arrival 
and departure flights were traced through the system by observation from the 
tower cab. Two departure and two arrival traces have been selected for presen- 
tation in the following paragraphs. 

5.4. 3. 1 Flight Trace 1 - Air Carrier Departure From Southside Runway 14R 

This flight trace was specifically selected because it incorporates a 
number of key points regarding the ASTC system operation. These include: 

1. Blockage of the movements of aircraft within the ramp area by 
other aircraft. 

2. Use of the joint responsibility philosophy of traffic control, i. e. , 
use of yield type instructions, involving pilot adjustment of air- 
craft movement to comply with controller instruction. 

3. The major problem associated with control of combined arrival 
and departure operations on the same runway; i. e. , the need for 
very close monitoring of relative aircraft movements. 

This flight trace took place during the approximate time period of 
4:45 to 5:45 p. m. (2145 to 2245 GMT). Visibility conditions were normal. The 
flight was UA 247 and the equipment was a B727. Figure 5-36 illustrates the 
completed flight strip and shows the results of the various controller strip 



5-186 



marking activities identified in the previous paragraphs and the flight trace descrip- 
tion. The numbers associated with the various markings correspond to specific 
event numbers in the flight trace. 




UA2U7 23 1 U ORD +C0MM3 DBQ_ 
B727/Ap| P2050 ^\^ ORD DBQ J9U RKS./.SLC 
255 V %\Q-3H- 





Figure 5-36. Flight Strip for UA 247 

1. When the trace was initiated the flight strip had already 
been processed (including annotation) by Flight Data and 
was located in the left hand side of the Clearance Deliv- 
ery Flight Strip Board. 

2. 2043:30 Aircraft called for clearance. Clearance Delivery 

checked clearance, marked the gate (Fl) on the strip 
and put the strip in right side of the Flight Strip Board. 
The complete transaction took about 20 seconds. 

3. 2056: 15 A member of the flight crew was observed physically 

checking the exterior of the aircraft. 

4. 2115:05 The jet way began to pull away from United 247. 

5. 2117:00 United 247 started pushback. 

6. 2117:09 United 247 stopped pushback because a TWA 707 was 

being pushed back from G4. 

7. 2117:54 TWA uncoupled and tug pulled away. 

8. 2117:57 TWA called for taxi instructions while starting a pivot 

to face out of the ramp area. 

9. 2119:50 United 247 resumed pushback. 



5-187 



10. 2121:27 United 247 pushback completed with the nose of the air- 

craft facing the F5-7 gates. 

11. 2122:19 United 247 called for taxi. Clearance Delivery wrote 

the time on the strip and placed it in the Outbound 
Ground Flight Strip Board. The transaction took about 
2 seconds. 

12. 2122:38 TWA was given taxi instructions by Outbound Ground 

and moved out of the ramp area. 

13. 2123:23 United 247 was given taxi instructions to runway 14R 

via the Outer and Bypass and told to "pass behind a 
TWA (not the same as aforementioned) coming from 
the right at the end of the building". Outbound Ground 
marked 14R on the strip. United 247 moved out slowly 
as the TWA passed. 

14. 2123:53 United 247 stopped at the end of the ramp area. 

15. 2124:07 United 247 resumed taxi as the TWA passed. 

16. 2124:30 United 247 was across the inner taxiway. 

17. 2124:37 United 247 started a right turn on the Outer. 

18. 2127:17 Outbound Ground instructed United 247 to "turn left on 

the Bypass, monitor local". While talking, Outbound 
Ground picked up the United 247 strip, along with two 
others, walked over to the Local Control #1 position 
and put the strips in his Flight Strip Board. The trans- 
action took about 10 seconds. 

19. 2130:47 United 247 was on the 14R parallel following an Ozark 

DC-9. 

20. 2131:37 United 247 was fourth in a line of taxiing aircraft. 

21. 2134:45 United 247 had stopped along with other aircraft holding 

position for a 14R arrival. 

22. 2136:15 The Ozark in front of United 247 was instructed to taxi 

into position. 



5-188 



23. 2136:30 United 247 was instructed to hold short of runway. 

24. 2137:13 Ozark cleared for immediate takeoff. 

25. 2137:49 The Local Controller examined United 247's strip. 

26. 2138:02 Arrival touched down on runway. 

27. 2138:23 United 247 instructed to position and hold and be ready 

for immediate takeoff and checkmark made next to run- 
way number. 

28. 2138:44 Local Control instructed "United 247, after departure 

it will be left to heading 130; expedite through 3500. Be 
ready for immediate takeoff when cleared". Heading 
was marked on strip while issuing instruction. This 
transaction took about 7 seconds. 

29. The arrival aircraft on the runway decelerated, appear- 
ing to be able to make the T3 turnoff but did not. In- 
stead, the aircraft moved slowly, appearing to be only 
at taxi speed, to the T2 turnoff. This delayed the 
clearance to roll for United 247 who was presently in 
position on the runway. Another arrival was on final. 

30. 2139:15 Local Control contacted United 247: 

Tower- "Do you have room to clear the runway off your 

left side?" 

Pilot - * 'Affirmative ' ' . 

Tower - "Okay, taxi clear of the runway. Report clear". 

This transaction took about 9 seconds. 

31. 2139:30 United 247 reported clear of runway and was instructed 

"United 247 make a 180. Hold short 14R". 

32. 2141:47 United 247 instructed to position and hold again. 

33. 2141:52 Local Control inquired of current arrival confirming 

his ability to make the T3 turnoff. 

34. 2142:02 Local Control instructed current arrival to expedite 

clearing the runway at T3. 

35. 2142:17 Local Control instructed "United 247, 14R, cleared for 

takeoff. Turn left to 130; expedite through 3500 feet". 
This transaction took about 5 seconds. 



5-189 



36. 2142:58 United 247 was rotated and airborne. 

37. 2143:11 Local Control picked up the strip and dropped it down 

the chute, giving the handoff simultaneously. "United 
247 contact departure. Good day". The entire trans- 
action took about 5 seconds with about 2 seconds of that 
time allocated to verbalization. 

Observation: During this trace the observer was located to the left 
and slightly behind Local Control #1 so that aircraft 
movements could be visually monitored and the ASDE 
Brite could be referenced. It was noted that while 
UA 247's movements at the extreme end of the 14R/32L 
parallel and in turning on to 14R could be visually ob- 
served, these movements could not be similarly ob- 
served on the ASDE screen. 

5.4. 3.2 Flight Trace 2 - General Aviation TCA VFR Departure from Northside 
Runway 27R 

This flight trace was selected because it demonstrates the require- 
ment for preparation of a flight strip for general aviation VFR flights and the 
relative ease with which general aviation aircraft are handled by the ASTC system. 

This flight trace took place during the approximate period of 5:45 p. m. 
to 6:00 p. m. (2245 to 2252 GMT). Visibility conditions were good. The flight 
was N309VS and the equipment was an Aero Commander 68. Figure 5-37 illus- 
trates the completed flight strip and indicates the strip marking in the same 
manner as for the previous trace. 




Figure 5-37. Flight Strip for General Aviation N309VS 



5-190 



1. 2246:54 The aircraft called for taxi and TCA VFR clearance. 

Clearance Delivery prepared a flight strip with the 
following information: Aircraft ID and type, the time 
of the call, VFR, the intended heading and altitude, and 
a beacon code selected from a list of available codes. 
Clearance Delivery then gave the pilot his clearance 
and instructed him to "monitor ground control . 75" 
while placing his strip in the Outbound Ground Flight 
Strip Board. 

2. 2248:09 The Outbound Ground controller marked runway 27R 

(36) on the strip while giving the pilot his taxi instruc- 
tions. Runway 36 was circled to indicate that the air- 
craft would start his roll on runway 27R at the inter- 
section of runway 36. This transaction took about 
2 seconds. 

3. 2249:05 Outbound Ground picked up the strip and dropped it 

down the Flight Strip slide for Local Control #2. This 
transaction took 2 seconds. 

4. 2249:08 Local Control #2 picked up the strip almost immediately 

and took about 1 to 2 seconds to bring it back to his 
position. 

5. 2249:51 The aircraft was at the intersection of runway 36 and 

the 9L/27R parallel. 

6. 2250:49 Local Control #2 moved the strip further down in his 

Flight Strip Board, indicating an earlier takeoff than 
previously anticipated. 

7. 2251:00 The aircraft was holding short of 27R. 

8. 2251:06 The aircraft was moving. 

9. 2251:13 The aircraft was in position at 27R/36 for a 27R take- 

off. Local Control issued takeoff clearance instructing 
pilot that his heading was 220 and his altitude out of 
TCA was 4500 feet while marking "220/4. 5" on the 
strip. 

10. 2251:20 The aircraft started to roll. 



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11. 2251:42 The aircraft was airborne. 

12. 2252:08 Local Control picked up the strip and instructed pilot 

to contact Departure Control. 

13. 2252:13 Local Control dropped the strip down the Flight Strip 

tube to Departure Control. 

5.4.3.3 Flight Trace 3 - Air Carrier Arrival on Southside Runway 32 L 

This flight trace was selected as representative of normal operations 
but illustrates a problem associated with Local Control having to record the flight 
call sign in lieu of an arrival flight strip. 

The flight trace took place during the approximate time period of 
6:45 p.m. to 7:00 p.m. (2345 to 2400 GMT). Visibility conditions were good. 
The flight was UA 490 and the equipment was a B727. 

1. 2349:07 UA 490 was just outside the Outer Marker. Local Con- 

trol #1 looked at the ARTS Brite and in error wrote 
UA 470 on the Arrival Log. 

2. 2349:10 The pilot contacted Local Control to report at the 

Outer Marker. Local Control corrected the flight call 
sign on the Arrival Log. 

3. 2350:39 UA 490's alphanumeric tag dropped off the Brite display. 

4. 2351:30 The aircraft touched down. 

5. 2351:35 Local Control #1 advised the aircraft "contact ground 

when clear". 

6. 2352:00 The aircraft turned off runway. 

7. 2352:09 The pilot contacted Inbound Ground and gave his gate. 

Inbound wrote down "United 490" on his list of aircraft 
arriving on the south runways, while issuing taxi in- 
structions to the gate "via T-3 and right on the outer". 

8. 2353:38 United 490 was entering the outer taxi way. 



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9. 2354:15 The aircraft was starting to turn toward the ramp area. 

10. 2355:15 The aircraft was starting to pull into its gate. 

11. 2355:35 United 490 was stopped at the gate. 

Observation: Local Control #1 had to jump up several times to see 

27L departure aircraft over the heads of the two ground 
positions. 

5.4. 3.4 Flight Trace 4 - Air Carrier Arrival on Northside Runway 14L 

This flight trace was selected as demonstrating operations under re- 
duced visibility and poor weather conditions as well as the effects of aircraft move- 
ments in the ramp area. 

The flight trace took place during the approximate time period of 
4:45 p. m. to 5:05 p. m. (2155 to 2205 GMT). The operating conditions were 
Category I and the surface had a covering of snow from precipitation earlier in 
the day. The flight was Northwest 736 and the equipment was a B727. 

1. 2156:00 NW 736 passed the outer marker at Lima. 

2. 2156:33 The pilot reported crossing the Outer Marker. Local 

Control #2 advised "Northwest 736 clear to land 14 Left. 
Braking action fair to poor. Report the lights in sight". 

3. 2159:30 NW 736 alphanumeric tag dropped off the Brite display. 

4. 2159:45 The pilot reported the lights in sight and was given 

clearance to land by Local Control. 

5. 2200:05 The aircraft touched down on runway 14L. 

6. 2200:21 Local Control advised NW 736 to "turn right at 18 and 

contact ground at .9". 

7. 2201:00 The aircraft was clear of runway 14L. The pilot con- 

tacted Inbound Ground and was cleared directly into his 
gate via the 9L/27R parallel and Inner. 



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8. 2201:19 The aircraft crossed the 14L/32R parallel. 

9. 2201:43 The aircraft was approaching the outer taxiway. 

10. 2202:00 The aircraft entered the Northwest ramp area. 

11. 2202:28 NW 736 was observed taxiing behind a Braniff 727 which 

had entered the ramp. 

12. 2202:46 NW 736 was observed heading to his gate which was 

between two "blocked" DC-lOs. 

13. 2202:53 The aircraft stopped its forward motion and began 

swinging its nose into the gate. The aircraft was in this 
mode for about two seconds. 

14. 2203:38 NW 736 was stopped at his gate. 

Observations: After NW 736 was docked both DC-lOs began to push- 
back. This is the basis for terming these aircraft as 
"blocked" in 12 above. These pushbacks would appear 
to have been blocked by both the Braniff and NW 736 
movements. 

Runway 4L was being used for departures during this 
trace. In this configuration there is no requirement 
for the arrival to cross an active runway when 9L is 
used for departures. Thus, the aircraft was able to 
taxi at a fairly high speed as indicated by the event 
times noted above. 

5.4.4 Other Observations of Tower Cab Activities 

During various periods in the tower cab several interesting observa- 
tions regarding controller non-aircraft communications activities were made 
which are discussed below. 

5. 4. 4. 1 Controller Visual Surveillance Activities 

As noted in previous discussions, visual surveillance of traffic move- 
ments is nearly continuous during good visibility conditions. However, when the 
visibility decreases and the ASDE is employed to aid in visual surveillance, a 
number of interesting observations were made. 



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In one situation the procedure of a controller operating at the Local 
Control #2 position was studied. The locations of equipment used by this position 
relative to the normal working location are as follows: 

1. The ARTS Brite Display is to the left of the position. 

2. The Flight Strip Board containing the departure flight strips is 
directly in front of the normal working location. 

3. The pedestal -mounted Arrival Log is slightly to the right of the 
controller's working location. 

4. The ASDE Brite is at the extreme right of the position equipments. 
The display was set up so as to focus the picture not on the run- 
way touchdown area on 14 L (for which coverage was poor, though 
available on the screen) but on the area covering the normal exit 
points for 14L (22R and 18) and the intersection of those runways 
with 9L, the departure runway. 

The controller was observed to utilize these equipments in a continuing 
scanning operation. Starting from the left he would observe the ARTS Brite for 
5 to 10 seconds, then begin moving his area of vision to the right to visually ob- 
serve movements out of the cab window, dropping his vision to the Flight Strip 
Board momentarily. When his scan reached the ASDE Brite he would observe it 
for about 5 to 10 seconds and then begin scanning back to the left. If, during this 
scanning process, he noted on the ARTS Brite that a flight was approaching the 
Outer Marker, he would record the flight call sign on the Arrival Log as it was 
passed in his scan. 

This operation is strongly contrasted to that of the Local Control #1 
position during the same period. The locations of equipments which may be 
employed by this position are as follows: 

1. The ASDE Brite is too far left of the normal working location of 
the controller. It is actually located adjacent to the Inbound 
Ground position and is too far from his normal working position 
to be used easily without the controller having to walk to the left 
to observe it. 



5-195 



2 . The Flight Strip Board is located slightly to the left of the normal 
working position. 

3. The ARTS Brite is at the normal working location. 

4. The pedestal mounted Arrival Log is to the right of the ARTS 
Brite. 

This controller was observed to rely most heavily on the ARTS Brite 
and visual observation of aircraft movements. The movements of departure air- 
craft at the end of the 14R/32L parallel and 14R could be visually observed. In 
fact, during the period of observation he did not use the ASDE Brite at all. This 
is probably due to the problem of the display's reliability at the end of the parallel 
and runway noted in the flight trace for UA 247 (paragraph 5.4. 3. 1) and the re- 
quirement for the controller to move left from his position to use the display. 

During this observation period and others this ASDE Brite display 
appeared to be more heavily used by the Inbound Ground position. This display 
appeared to be set up to focus the presentation on the area between the normal 
aircraft runway turnoffs for 14R arrivals and the intersection of T-l and T-3 
taxiways with the Outer where these arrivals enter the main ground traffic flow. 
It appeared that the Inbound Ground controller was utilizing the display to verify 
the aircraft's position (or reported position) when the pilot contacts him for taxi 
to the terminal and to observe the aircraft's position as it approached the Outer 
on T-l/T-3 in order to determine what control instructions were necessary to 
take the aircraft across the departure traffic on the Outer and into the traffic 
flow in the Inner coming from the Northside arrival runway. 

5.4.4.2 Coordination Between Control Positions 

Coordination between controllers was observed to take two forms: 
direct conversations between two or more controllers, or by one controller simply 
calling out to another, with the latter being the most frequent. This type of ex- 
change generally occurred between: 



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1. Local controllers when one controller's departure was going to 
cross the airspace controlled by the other; in these cases the first 
controller merely called out to the other that "I've got one going 
west" or other appropriate direction. 

2. Outbound Ground and Local Controllers when an aircraft wanted 
a particular runway for departure. 

3. Between Local Controllers and Inbound Ground or Outbound Ground 
when they wanted particular instructions given to aircraft to facil- 
itate the clearance of aircraft from the runway or to allow a flight 
to cross a runway (normally between Local Control #1 and Out- 
bound Ground). 

4. Between Local Controllers and Outbound Ground when they cannot 
reach a flight on their frequencies and want Outbound Ground to 
contact the flight and instruct him to change frequency now. 

The direct conversation approach generally occurred between the two 
Ground Controllers and on a few occasions between Outbound Ground and the Local 
Controllers. Primary examples of the situation in which this type of coordination 
occurred are briefly described below. 

It was generally observed that, when a controller returned from a 
relief break or came on-shift and was assigned to one of the ground positions, a 
conversation took place between the new ground controller and the controller stay- 
ing in position and occasionally the Ground Controller going off duty. The purpose 
of this conversation was to discuss the current flow pattern and particular rout- 
ings that might be used in instances where departures operations were backing up 
on to the Outer. 

One incident was observed which required direct coordination between 
controllers to change the flow of traffic on the Inner and Outer. In this situation 
the airport was operating in the Arrivals from the West mode with departures 
taxiing clockwise on the Outer and arrivals counterclockwise on the Inner. A 
DC-10 arrival from 14L was taxiing west on the 9L/27R parallel. Instead of turn- 
ing slightly to the left and taking the Inner, the aircraft continued straight ahead 



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and on to the Outer. An immediate conversation took place between Outbound and 
Inbound to "swap" the movements of aircraft on the Outer and Inner from the T-l 
intersection to the New Scenic until the DC-10 turned off the Outer at T-3 (its 
gate was in the ramp area between C and D concourses). 

During one observation period the airport was operating in the Arrival 
from the West mode with 14L and 9L being used for arrivals and departures, 
respectively, and 14R being used for both arrivals and departures. A long queue 
of traffic had built up from the 9L pad, down the New Scenic, and on to the Outer 
because in this configuration all departures follow the Outer on to the New Scenic 
until departures for 14R can turn left at the Bypass to the 14R/32L parallel. To 
attempt to relieve this congestion Local Controller and Outbound Ground held a 
conversation and decided to re-route some of the 9L departure traffic further 
along the Outer to the Old Scenic, left on Old Scenic to the 9L/27R parallel, and 
left on the parallel (in essence creating two queues for 9L departures). This 
approach appeared to be relieving the congestion somewhat until a DC-10 arrival 
on 14 L exited the runway at 22R and taxied down 22R to the intersection with 9L. 
At this point the aircraft's further movement across the runway and to the terminal 
was blocked by the aircraft that had been re-routed. The aircraft stayed in this 
location for at least 2 minutes with no apparent prospect for an end of its blockage 
in the near term. At this point another conversation took place between Outbound 
Ground and Local Control #2. This conversation led to re-routing of a 747 that 
was in the queue on the 9L/27R parallel in a position just to the east of the inter- 
section with the New Scenic. The 747 was turned right on the New Scenic up to 
the Scenic and the 14L/32R parallel for departure on 14L. This allowed aircraft 
on 9L/27R parallel and Old Scenic to move up. Outbound Ground instructed the 
re-routed aircraft which had not yet turned on to the Old Scenic to hold their 
position. Local Control #2 then gave priority to sequencing aircraft on the parallel 
into the 9L pad for departure. After two more departures Local Control #2 was 
able to clear the DC-10 across the runway and turned it over to Inbound Ground 



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for taxi to the 9L/27R parallel. However, no further aircraft were sent to 9L 
by the routing that had led to the problem. 

5.4.4.3 Missed Approaches 

On two occasions multiple missed approaches were observed. In the 
event of a missed approach Local Control normally provides altitude and heading 
(i.e. , runway heading) instructions to the aircraft, turns it over to Departure 
Control, and prepares an abbreviated flight strip which is dropped down the Flight 
Strip Tubes to Departure Control. 

The first observation of multiple missed approaches occurred during 
CSC Run #8 as visibility deteriorated to Category II conditions. The approaches 
for at least three arrivals for 14L, which was being observed, had to be termi- 
nated because visibility had decreased below the permissible minimums for 14L. 
In this situation only one of the arrivals had just been turned over to Local Control. 
Therefore, Approach Control in the TRACON still had its own strip for this flight 
as well as strips for the following flights. Thus, Local Control only had to turn 
the one arrival back to the TRACON which handled the vectoring of the aircraft 
to holding points. 

The second observation occurred as a result of the failure of the ILS 
glide slope for 14L under low Category I conditions. Departures were taking place 
on 4L in the North. There were three arrivals being handled by Local Control 
(one having just reported in at the 14L Outer Marker) and a departure had just 
previously been cleared for takeoff when the failure occurred. The departure had 
been given a heading of "090", which was toward the runway heading which had to 
be followed by the arrivals executing the missed approach. The controller had to 
call for blank strips to prepare the abbreviated strips for the arrivals. As each 
strip was being prepared he requested the altitude of both the departure and the 
particular arrival before instructing the arrival to contact Departure Control and 
dropped the strip down to Departure Control. 



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With the exception of his urgent call for flight strips, the controller 
was observed to work smoothly and rapidly to perform the actions described, 
although it was evident that he was under substantial pressure. 



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5. 5 COCKPIT CREW ACTIVITY (WORKLOAD) ANALYSIS 

The functional responsibilities of the cockpit crew as it pertains to 
ASTC operations were discussed in Section 4.3. This section provides a more 
detailed insight into the workload of the crew during passage through the system. 
Although sufficient cockpit time was not available to perform a comprehensive 
time and motion study, members of the CSC staff did have the opportunity to ride 
the jump seat on a number of flights and record their impressions of the crew's 
activity. These observations and the pilot interviews cited in Section 2. 4 form 
the basis for the following discussions. 

5. 5. 1 Crew Activities During Departure and Arrival 

5. 5. 1. 1 Departure Activities 

The cockpit crew is expected to be on board the aircrat at least 20 min- 
utes prior to the scheduled departure time. Prior to this, the Captain and the 
First Officer have coordinated the flight plan with the company dispatcher and 
have initiated the paperwork necessary for clearance delivery. The Second Officer 
has evaluated the maintenance status of the aircraft and has performed a visual 
inspection of external aircraft mechanisms. * Once on board and seated, the crew 
executes the initial aircraft status check list. Approximately 10 minutes prior to 
scheduled departure, radio contact is established by the First Officer with the 
tower on the Clearance Delivery frequency to obtain their flight clearance. If the 
clearance has not yet been received in the tower or if a modification of the clear- 
ance received is desired, the First Officer will be advised that his "clearance is 
on request" and he "will be advised". If the clearance has not been received from 
the tower when the flight is nearly ready to push back, he will initiate communica- 
tions with Clearance Delivery. 



*If there is only a two-man crew this check will be made by the First Officer. 



5-201 



Having received clearance, all crew activities are directed toward 
preparing the aircraft for pushback. Pre-pushback checks are made by pairs of 
the crew members. The first is made by the First and Second Officers, with the 
First Officer calling out the checks and recording the results and the Second 
Officer making the checks and calling out the results. These checks generally 
include the fuel, power, and electrical systems. The second check is made by 
the Captain and First Officer with the latter again calling out the checks and re- 
cording the results. 

When all checks have been completed, the Second Officer monitors the 
status of all doors — cabin and belly — to determine when they are securely closed. 
At this point the flight is normally ready for pushback and departure. If the doors 
are not closed by the scheduled departure time, the First Officer (or Captain) will 
contact the company to determine the cause of the delay and to obtain a new de- 
parture time. 

When the flight is ready for departure, the First Officer will com- 
municate with the company ramp controller for pushback clearance. The Captain 
will be maintaining contact with the tug operator via the internal public address 
system. The engines are usually started after pushback; however, ignition may 
be initiated prior to or during pushback. During this time, the Captain will be 
issuing commands within the cockpit and will check with the tug operator about the 
condition of the nose gear after the tug is unhooked. 

After pushback is completed, the First Officer will contact Clearance 
Delivery on the ATC frequency of radio set 1 indicating that the flight is ready to 
taxi. The Second Officer will monitor various cockpit instruments and the com- 
pany frequency in case of any last minute ramp control directions from the com- 
pany controller. Upon direction from Clearance Delivery, the pilot (not flying) 
will switch to the Outbound Ground control frequency. While the pilots are await- 
ing instructions from Clearance Delivery to switch frequency or contact from 
Outbound Ground, they will generally maintain the aircraft in the pushback position. 



5-202 



However, if the handoff takes too long and/or if they have to maneuver within the 
ramp area to allow passage of an arriving aircraft, they will start to move and 
may drift as far as the end of the ramp before contact with ground control is 
established; they will not go beyond this point without contact. 

When the ground controller contacts the aircraft, gives the runway 
assignment (taxi route), and any other specific directions for taxi, the pilot (not 
flying) will acknowledge the taxi instructions and the pilot (flying) will release the 
brakes and proceed into the taxiway network. Generally, the pilot (flying) does 
not use the throttle to move the aircraft since the engines' idle thrust is sufficient 
to cause movement. Taxi stops and yields to other traffic are accomplished by 
controlled braking action and turns are accomplished through the use of the nose 
gear steering wheel. Only in the event of an unusually fast acceleration require- 
ment (e.g. , active runway crossing) will the throttle be used during taxi. 

While in transit from the ramp to the departure runway, the cockpit 
crew activity can vary substantially depending on the specific route, traffic con- 
ditions, and the weather. For the most part, the pilot (flying) uses common sense 
in controlling the speed and direction of the aircraft; strict speed limits are not in 
effect. The pilot (flying) uses his judgment to determine the safe speed and separa- 
tion based on the condition of the taxiway surface and the type of leading aircraft. 
Primary aircraft separation considerations are protection against the ingestion of 
foreign matter into the engines (e. g. , melting chunks of ice) and jet exhaust in- 
gestion into the cabin. 

Unless specifically contacted by the controller most intersection con- 
flicts are resolved by pilots us sing common courtesy and the rules of the road 
basis. When it appears to a pilot that his aircraft and another aircraft have equal 
contention for the intersection right of way, he will stop and yield or contact the 
ground controller to resolve the conflict if the situation is more complex, i.e., in- 
volving several aircraft or a serious blockage. Most pilots feel that the controller 
should resolve these conflicts prior to the occurrence rather than during the 



5-203 



occurrence and that this is usually the case at O'Hare. Such contacts are made by 
the pilot (not flying) who handles all communications with the tower. Pilots always 
hold short of runways and await direction from the ground control unless previously 
given clearance to cross. Unfortunately in poor visibility it is not always that 
easy for the pilot to detect when the aircraft is approaching an active runway. 
During the ride to the departure runway, additional check lists are being accom- 
plished within the cockpit. In addition, the Captain usually will talk to the pas- 
sengers, particularly if there are delays anticipated under poor conditions. 

Upon entering an area where no further ground control appears to be 
required, the ground controller will advise the aircraft to switch to the Local 
Control frequency. As the aircraft enters the departure queue (if there is one) 
the Captain may again address the passengers indicating the flight's position in the 
queue and the estimated time until takeoff. At this time the pre-takeoff check list 
is accomplished. In the event that taxiing was accomplished with any engines shut 
down, the complete start-up procedure and check list will be accomplished at this 
time. When the aircraft is next to take off the Local Controller will contact the 
aircraft indicating that the aircraft has clearance to position and hold on the run- 
way or hold short of the runway until further advised. Once the instruction to 
position and hold is given to the cockpit, the aircraft is maneuvered by the pilot 
(flying) on to the center of the runway and he gives the commands to put the air- 
craft into the takeoff configuration and the instruments are monitored. When 
clearance for takeoff is received the throttles are applied, the brakes are released, 
and the aircraft begins to roll. Prior to liftoff the pilot will maintain visual ref- 
erence with the runway surface to ensure proper centering. If at this time he 
detects aircraft crossing the runway in front of him, there is relatively nothing 
he can do to avoid a collision. The Second Officer monitors the engines to ensure 
safe operation and will positively verify engine status. The pilot (not flying) calls 
out the velocity V which is the maximum speed at which the pilot can safely abort 
the takeoff and stop short of the end of the runway. The next velocity called out 



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is V which is the velocity at which the pilot raises the nose of the aircraft (ro- 
R 

tates). Shortly thereafter the main gear will lift off and the aircraft will be air- 
borne at which time the pilots will ensure that a positive rate of climb and the 
initial climb velocity V is maintained. Some time after liftoff, the Local Con- 
troller will contact the aircraft giving the departure heading (if not previously 
given) and direction to switch to departure control for final vectoring for noise 
abatement and handoff to the center. The activities which take place after this 
are not directly applicable to the cockpit workload analysis as it relates to ASTC 
system operation. 

5. 5. 1. 2 Arrival Activities 

Although a preliminary gate assignment may have been received by 
the Second Officer prior to the final approach, (e.g., United Airlines obtains gate 
assignments approximately 50 miles out for all aircraft except the B737), surface 
traffic is not a cockpit consideration until the pilot sets the aircraft into the land- 
ing configuration and sees the runway. This preliminary gate assignment is ob- 
tained by the Second Officer. 

After entering the O'Hare TCA the aircraft is vectored into final 
approach by Approach Control and instructed to switch to the Local Control fre- 
quency. The pilot (flying) will acquire the ILS localizer to establish the aircraft 
on the runway heading. Where an approach is being made to a runway with an 
ILS glide slope the pilot (flying) normally performs an instrument landing with 
primary emphasis placed on throttle control in maintaining the proper glide slope. 
This same emphasis is placed on throttle control to maintain a proper approach 
path when a visual approach is made to a runway without an ILS glide slope. 

When instructed by Approach Control the pilot (not flying) will contact 
Local Control and report at Outer Marker. He will acknowledge the clearance to 
land and any other information conveyed by Local Control. The Second Officer 
will be monitoring the engine status and controlling cabin environment. Prior to 



5-205 



reaching decision height, both pilots are obtaining runway visual reference and are 
making certain that the preceding aircraft is sufficiently clear of the runway and 
that other crossing aircraft will not interfere with the landing and rollout course. 

The clearance to land or subsequent communication from Local Control 
may include an exit ramp advisory in which case the pilot can, to some degree, 
plan his touchdown point to facilitate the accomplishment of that turnoff. Pilots 
interviewed indicated that they would prefer to know the desired exit ramp prior 
to touchdown so they can plan the landing and make a comfortable turnoff. Late 
notification of the desired exit ramp may cause the pilot to slow down too quickly 
for a smooth and continuous rollout or may result in a missed turnoff, both of 
which will reduce runway and taxiway efficiency. 

The pilot (not flying) does not usually report that the aircraft is clear 
of the runway, except when requested to do so. However, he will call Local 
Control if a requested turnoff could not be made for any reason (e. g. , due to poor 
braking action caused by snow or ice on the runway). The final contact with 
Local Control will be acknowledgment of the controller's instruction to switch to 
the (Inbound) ground control when clear of the arrival runway or the last active 
runway under the controller's jurisdiction. 

At this point the pilot (not flying) will switch frequency and contact 
Inbound Ground. Normally, this will include an indication of the arrival runway 
and turnoff (e. g. , "off 32 L at T-6") or the runway crossing (e. g. , "across 9L at 
22R"). Duringthe rollout or normally when clear, the Second Officer will verify 
the aircraft's gate assignment and availability. If this is accomplished before 
contact with Inbound Ground, this information will also be included in the com- 
munication. If the pilot's initial contact did not include gate availability informa- 
tion, the ground controller's first message may include a request for gate status 
which determines whether he will direct the aircraft directly to the ramp area or 
to the penalty box. 



5-206 



Crew activity during arrival taxi is similar to the departure with regard 
to local traffic collision avoidance, runway crossings, and intersection conflicts. 
The crew will also be "cleaning up" the aircraft at this time, i. e. , adjusting flaps 
to the ground configuration. During taxi, one or two engines may be shut down. 
They will also be performing post flight checklists. The Second Officer may also 
be communicating with the company to verify gate status (if there has been a sub- 
stantial taxi delay or penalty box hold) and to determine gates for connecting flights. 
The Captain may also address the passengers for a final time or instruct the flight 
attendants to advise them on the status of connecting flights and gates. If there 
are no gate delays the pilot will maneuver the aircraft directly into the ramp area 
and guide the aircraft into the jetway using guidance lights on the building. No 
further communications with the tower will be made unless there is a conflict at 
the entrance to the ramp area. The ground control activity of the cockpit crew is 
complete after the aircraft is docked at the jetway and the blocks are placed on the 
wheels. The crew then goes through a final shutdown checklist. 

5.5.2 Cockpit Workload Analysis 

5. 5. 2. 1 Cockpit Communications Activity 

The results of the detailed analysis of communications activity for the 
various controller positions described in Section 5. 4 were used to derive the in- 
ferences on cockpit communications activity discussed in the following paragraphs. 

5. 5. 2. 1. 1 Departure Aircraft 

The analysis of Clearance Delivery communications indicated that the 
mean number of communications required per aircraft in securing a flight plan 
clearance and handover to the Departure Ground Controller is approximately 2. 6 
or between 2 and 3 transactions. The mean time between first and last contact 
with the Clearance Delivery Controller averaged 560 seconds. It is presumed that 
the pilot monitors the Clearance Delivery Controller for a few minutes prior to 
first contact and, after securing his flight clearance, does not monitor the 



5-207 



Clearance Delivery Controller again until he is ready to taxi. If it is assumed 
that 5 minutes is spent under this communication activity, then each aircraft pilot 
has to monitor approximately 0. 22 N communication transactions (where N is 
the number of aircraft departing/hour) in order to enter the Departure Ground 
Control system. 

The mean number of communication transactions per aircraft deter- 
mined for Outbound Ground was 2. 8 and the mean time under control approxi- 
mately 4 minutes. Hence each crew has to monitor approximately a mean of 
0. 19 N communication transactions in order to determine when Outbound is 
attempting to communicate with them. 

The mean number of communication transactions per aircraft by 
Local Control was 3.2 and the average time under control was approximately 
3 minutes. Hence each crew has to monitor 0. 16 N communications in order to 
determine when Local Control is attempting to communicate with them. 

This data indicates that an aircraft requires an average of 8. 6 com- 
munication transactions to three controllers in departing O'Hare. A mean of 
about 0. 57 N (or approximately 34 at a departure volume of 60/hour) communica- 
tion transactions have to be monitored in securing these transactions. Observa- 
tions of the standard deviation for these quantities indicate that maximum varia- 
tions can be estimated by doubling these values; that is, the maximum number of 
CTs per aircraft required is about 17 and/or the maximum number of total CTs 
to be monitored could be 1. 14 N 

5. 5. 2. 1. 2 Arrival Aircraft 

The mean number of communication transactions required per aircraft 
by Inbound Ground was approximately 2 . 3 and the mean time under control esti- 
mated at approximately 4 minutes. Hence each aircraft has to monitor a mean of 
approximately 0. 15 N (where N is the number of arrival aircraft per hour) 
communication transactions in responding to the Arrival Ground Controller. 



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However, the variation of time under control was noted to be quite extensive due 
to gate availability problems (up to 30 minute waits noted for the penalty box). 

Requirements for arrival aircraft under Local Control are essentially 
the same as for departure aircraft. 

This data indicates that an aircraft requires a mean of 5. 5 communica- 
tion transactions to two controllers in arriving at O'Hare. A mean of 0. 34 N 
(or approximately 21 at an arrival volume of 60 aire raft /hour) communication 
transactions have to be monitored in securing these transactions. Again, ob- 
servations of the standard deviation for these quantities indicate that typical maxi- 
mum variations can be estimated by doubling; that is, the expected maximum num- 
ber of CTs per aircraft is about 11 and/or the maximum number of total CTs to 

be monitored could be 0. 7 N. . 

A 

5. 5. 2. 1. 3 Interpretation of Cockpit Communications Analysis 

The above data indicates that at normal busy hour traffic volumes of 
about 120 operations a departure flight crew has to monitor on the average of 
34 (and possibly 68) communication transactions and an arrival flight crew has to 
monitor on the average of 21 (and possibly approximately 70) communication trans- 
actions in order to determine when a communication is addressed to them and 
some response (both communication and aircraft control) is required. Thus, it 
would appear that this represents a significantly greater workload than that 
actually associated with the control of the particular aircraft. This data also 
implies a significant potential for missing a contact from the tower or non-inten- 
tional interference between communications. 

5. 5.2. 2 Other Workload Considerations Derived from Pilot Interviews 

It is obvious from the preceding descriptions of cockpit crew activities 
that the cockpit workload is well distributed among the three flight officers. Some 
airlines, however, operate certain aircraft (e.g. , B737 and DC9) without a second 
officer and therefore the individual pilot workloads are increased in this situation. 



5-209 



In addition to the manual adjustment of maneuver controls, the crew 
must collectively monitor instruments, maintain visual reference outside the cock- 
pit, perform checklists within the cockpit, advise flight attendants and passengers 
of pertinent situations as well as monitoring and acknowledging ASTC system con- 
troller instructions and company gate control. The large number of communica- 
tions which must be monitored (referred to as "chatter on the frequency" by pilots) 
to obtain these instructions represents a fundamental distraction in the accomplish- 
ment of the aircraft management functions. Pilots indicated that it would be desir- 
able for future ASTC systems to include features to minimize this cockpit disturb- 
ance while still providing the essential information required to safely and efficiently 
process the traffic. 

However, while it is vital that the future voice communications work- 
load per aircraft be reduced, the optimum techniques for providing the necessary 
cockpit information must be carefully analyzed in terms of other human factors 
affecting the crew. For example, while the possible use of a data link and a 
printer or cockpit display device may reduce "chatter" on the ATC channel, it 
may also present a serious visual distraction to the pilot while he is concentrat- 
ing on visual cues outside the aircraft. Pilots interviewed were very interested in 
the various techniques which could be employed to improve the surface guidance 
available to them. While there did not appear to be distinct preference for any 
specific conceptual approach, all seemed to agree on the following: 

• Some type of automated ground traffic control is definitely desir- 
able. 

• Many pilots would have to have hands-on involvement in the human 
factors evaluation of any new concepts. 

• The processing of ground traffic is the ground controller's function; 
however, any automated system should provide for a redundant 
backup on the taxiway network such that the pilots can react in 
case of a system failure. 



5-210 



• More and better signs, lights, and markings are desirable espe- 
cially in IFR conditions. 

• Less voice communications (chatter) is a must. 

5. 5. 3 Cockpit Observations 

Detailed timing studies on the activities of various cockpit crew mem- 
bers were not performed as in the case of tower controllers. The limited number 
of opportunities available for in-flight observation did not permit a reasonably 
comprehensive study of the activities of all crew members, considering the divi- 
sion of functional responsibilities among the crew members. However, the in- 
formation presented in the following paragraphs provides some further insight into 
cockpit operations. 

5. 5. 3. 1 In-Cockpit Flight Trace 1 - Detailed Timing Study 

This flight trace provides a detailed timing study of the movements 
and control of a flight from the viewpoint of the cockpit. It is particularly sig- 
nificant in that it represents a flight under good visibility conditions which demon- 
strates some of the problems noted in previous discussions in this section (as well 
as others) including: 

1. Delay of flight departures 

2. Pilot unawareness of the delay until it occurs 

3. Missed communications because of "chatter" on the ATC frequency 

The flight was UA 366, with a scheduled departure time of 10:45 a. m. 
from O'Hare to Newark. The equipment was a DC-8-62 (heavy). As noted above, 
the weather and visibility conditions were clear. All times given below are GMT. 

1. 1535 Observers in position in the cockpit. Headsets had 

been provided to permit monitoring of all communica- 
tions. It was noted that the Captain had his flight 
manual on top of his flight bag open to the O'Hare plate. 



5-211 



2. 1537:30 The First Officer contacted the tower for the flight 

clearance. 

3. 1540 The First and Second Officers went through a checklist. 

This took about 1 minute. 

4. 1542 The Captain and First Officer went through another 

checklist. This also took about 1 minute. 

5. 1545 Scheduled departure time. The cockpit crew was ready. 

Lights at the Second Officer's position indicated that the 
belly and cabin doors were still open. Both the Captain 
and First Officer commented that they had no idea what 
was causing the delay. 

6. 1549 The cabin door light went out but the belly door light 

was still on. 

7. 1552 The Captain contacted United ramp control to determine 

the new departure time and the cause of the delay. 

8. 1552:45 Captain advised by ramp controller that new departure 

time was 10:55 (1655) and that baggage was still being 
loaded. 

9. 1555 The belly door light went out. 

10. 1555 Pre-taxi checklist was initiated immediately by Second 

Officer reading checklists to both the Captain and First 
Officer. 

11. 1558 Checklist completed. 

12. 1559 First Officer called United ramp controller for "clear- 

ance to push". Clearance given. 

13. 1559:30 Captain advises tug crew to pushback. Pushback began 

almost immediately. 

14. 1601 Captain advised by tug mechanic that he was ready to go. 

15. 1601:30 First Officer called tower for taxi and was instructed to 

"monitor ground . 75". 



5-212 



16. 1602 Flight given taxi instructions by Outbound Ground. 

"Your runway is 14 L via the Outer, Bridge, and paral- 
lel". First Officer acknowledged while Captain released 
brakes and began taxiing. 

17. 1603 Aircraft out of ramp area. 

18. 1605 Aircraft taxiing on to Bridge at 22 knots. 

19. 1605:45 Aircraft taxiing into 32R pad. 

20. 1606:30 Aircraft crossing 9L/27R. Captain suggests that they 

go through checks enroute. 

21. 1608 Aircraft crossing 18/36. It was observed that there 

was only one aircraft ahead of flight, a North Central 
DC-9. 

22. 1609 Aircraft crossing 4L/22R. 

23. 1609:30 Aircraft entered 14L pad. 

24. 1610:15 Aircraft at end of 14L pad turning in behind NC holding 

short of 14L. 

25. 1610:35 NC into position on runway. UA 366 instructed to 

"hold short. " 

26. 1611:15 NC received takeoff clearance and rolling. 

27. 1611:35 UA 366 cleared into position. First Officer acknowl- 

edged. 

28. 1612:00 Aircraft turning on to 14L. 

29. 1612:30 Aircraft in position. 

30. 1613:15 UA 366 cleared for takeoff and First Officer acknowl- 

edged; rolling almost immediately. 

31. First Officer called V and V to Captain but times were 
missed in recording event 30. 



5-213 



32. 1613:50 Aircraft airborne. 

33. 1614:40 UA 366 given heading instruction and told to contact 

Departure Control. First Officer acknowledged. 

34. 1615:20 First Officer contacted Departure Control. 

35. 1616:20 UA 366 given turn heading; acknowledged by First 

Officer. 

36. 1618:50 UA 366 given climb instructions; First Officer acknowl- 

edged. 

37. 1619:40 UA 366 instructed to contact Chicago Center; First 

Officer acknowledged and changed frequency. 

38. 1619:55 First Officer contacted Chicago Center and was in- 

structed to "report passing 12000. " 

39. 1621:20 First Officer reported "out of 12000. " 

40. 1623:45 UA 366 requested to "report leaving 22000. " 

41. 1624:15 First Officer reported "out of 22000" and was instructed 

to change frequency (new sector). 

42. 1624:30 First Officer contacted new sector. 

43. 1626:00 UA 366 told to "maintain 370. " 

The observers returned to cabin at this time. They returned to cock- 
pit when flight was in arrival descent phase to record the following observations: 

44. 1815:10 Flight at 23, 000 feet and descending. 

45. 1817:40 First Officer contacted N.Y. center (flight at 18,000 feet) 

and was given descent instructions. 

46. 1820:40 UA 366 given instruction to cross a specific fix at 

9000 feet. 

47. 1820:40 First Officer began scanning out window for other air- 

craft. 



5-214 






48. 1822:30 UA 366 instructed to reduce speed. First Officer 

acknowledged and reached down to adjust throttles. 

49. 1824:10 UA 366 requested to report altitude. First Officer 

replied "leaving 10, 000. " 

50. 1824:25 UA 366 instructed to contact Newark Approach Control. 

First Officer acknowledged. 

51. 1824:40 First Officer switched frequency and contacted Newark. 

UA 366 given vector to runway 22L; he acknowledged. 

52. 1825:40 UA 366 instructed to change frequency; First Officer 

acknowledged, and switched frequency, and made contact. 

53. 1825:45 UA 366 given traffic advisory. First Officer and Cap- 

tain scanning for traffic. 

54. 1826:00 UA 366 given instruction to "descend to 4000. " First 

Officer acknowledged. Captain initiated descent. 

55. 1826:45 First Officer reported to Approach Control that they 

"have the traffic (in sight). " 

56. 1827:30 UA 366 given another traffic advisory. Traffic spotted 

by Captain. 

57. 1828:11 UA366 given another traffic advisory. Both Captain and 

First Officer looking for the traffic. 

58. 1829:20 Flight reached 4000 feet and Captain leveled out air- 

craft. 

59. 1830:20 UA 366 given vector. 

60. 1830:40 UA 366 given another traffic advisory. First and Second 

Officers looking for traffic. 

61. 1831:40 UA 366 given vector instruction and told by controller 

that he will "have a descent for you soon. " 

62. Sometime in period between events 61 and 63 the ob- 
servers noted a controller transmission smeared by the 
transmission from another aircraft. 



5-215 



63. 1832:50 The flight was approximately 6-1/2 miles from Outer 

Marker. UA 366 was "cleared for a 22 left approach. " 

64. 1832:55 Second Officer called the company for a gate and gave 

a landing estimate. 

65. 1834:50 UA 366 contacted by Approach Control and altitude was 

requested. First Officer indicated altitude as 4000 feet. 
Approach Control asked "didn't you get my earlier in- 
struction to descend to 2500. " First Officer replied 
"negative. " Controller instructed UA 366 to "expedite 
your descent now. " First Officer acknowledged and 
Captain put aircraft into a rapid descent. 

66. 1835:10 UA 366 instructed to contact Newark Tower. First 

Officer acknowledged and changed frequency. 

67. 1835:20 First Officer contacted Newark Tower. 

68. 1835:55 First Officer reported at Outer Marker. Control 

responded "UA 366 cleared to land 22 left. Hold short 
22 right. " First Officer acknowledged. 

69. 1837:20 Flight touched down. 

70. 1837:40 Flight clear of runway at high speed and holding on 

taxiway Echo at 22R. 

71. 1838:10 Controller instructed "UA 366 cross 22 right. Contact 

ground when across. " First Officer acknowledged. 
Captain accelerated aircraft to cross runway. 

72. 1838:40 Flight across 22R. First Officer changed frequency 

and reported "UA 366 across 22 right at Echo. Going 
to 18. " Controller responded "UA 366 left turn on the 
Inner to your gate. " 

73. 1839:40 Flight turning off Inner into ramp area. 

74. 1841:00 Captain swinging aircraft into gate position. 

75. 1841:15 Second Officer reports "UA 366 docked at gate 18. " 

76. 1842:15 Crew completing shutdown check list. 



5-216 



After check list was completed observers talked with crew members 
for a few minutes about events observed. The Captain indicated that the missed 
descent instruction is not a common occurrence, but occasionally instructions are 
garbled by channel chatter. He was asked if he had ever experienced this at 
O'Hare. He indicated that he had, but could not give an estimate of how many times 
it happened. The Second Officer was asked about the difference in procedures for 
company communications noted for O'Hare and Newark. He indicated that the 
reason for the earlier contact at O'Hare was due to higher volume of traffic at 
O'Hare and transmission of gate information for connecting flights. Verification 
of the gate on arrival at O'Hare was necessary because of the higher potential for 
delay problems. He indicated that the traffic volume at Newark was substantially 
lower, there was basically no interconnection of flights, and gate availability 
problems were rare. Thus, contact with the company was only made once under 
normal conditions when a reliable estimate of landing time could be given. If a 
gate change became necessary for any reason the company would call the flight 
after landing. 

5. 5. 3. 2 In-Cockpit Flight Trace 2 - Effects of Poor Weather/Visibility 

This flight observation provides an excellent example of the effects of 
poor weather visibility conditions on flight ground operations from the point of 
view of the cockpit. The events which occurred included: 

1. Controller loss of or confusion in aircraft position. 

2. Pilot loss of visual reference for taxi. 

3. Interference between aircraft and surface vehicle operations. 

4. Resolution of a nose-to-nose aircraft conflict. 

These events occurred at Newark Airport and thus are not directly 
related to the study of O'Hare operations. However, they do represent situations 
that occur at O'Hare or any other airport under similar conditions. 



5-217 



The flight was UA 142 and the equipment was a DC-10. The sched- 
uled departure time was 2:30 p.m. (1930 GMT). The weather at O'Hare was clear 
and the airport was operating in the Arrivals from the East mode. The weather in 
Newark on landing was heavy blowing snow with Category II conditions. 

Detailed timing of cockpit activities was not performed for this flight. 
Flight movements at Newark and salient aspects of the observations are illustrated 
in Figure 5-38. Thus, the observations are presented in narrative form. 

At 1940 (a ten minute delay from scheduled departure) the flight pushed 
back and engines were started. The flight was called by Outbound Ground almost 
immediately after the frequency change instruction from Clearance Delivery. It 
was cleared to runway 32R via the Outer and Bridge. Traffic appeared light. The 
flight taxied to 32R without any delays and was cleared into position on 32R almost 
immediately after entering the runup pad. The flight held for an arrival on 27R and 
was cleared for takeoff after it had passed. Takeoff roll was started at approxi- 
mately 1947. 

Half way to Newark the flight was advised that John F. Kennedy and 
LaGuardia Airports were closed but that Newark was open. The weather at Newark 
was 700 ft. ceiling and an RVR of 4000 with blowing snow. 

After entering the New York TCA the flight was cleared to hold at 
Budd Lake. The Captain indicated that he anticipated a delay. However, before 
reaching the Budd Lake fix the flight was cleared for an approach. 

The clearance read "Cleared for an Approach Runway 4R, wind 020 
degrees at 10 knots, braking action on runway 4R is poor reported by DC9, touch- 
down RVR 2400, rollout 2200. " 

The Captain intersected and acquired the ILS course on runway 4R. 
He then locked on to the ILS course and set the instruments for a fully automated 
(hands off) landing, including flare out. The flight broke out at 500 ft. and the 
runway lights were visible. The flight appeared to be lined up dead-center to the 



5-218 




QJ 
O 

U 

H 

b£ 
• c—i 



o 
U 

i 



o 
•i-i 

03 

3 



CO 

i 

o 
s-l 

be 

•r— I 



5-219 



runway. The aircraft touched down at approximately taxiway E (refer to Figure 
5-38), but since braking action was poor, it passed taxiway s F and G and turnoff 
was made at taxiway J (high speed turnoff). The Captain taxied the aircraft slowly, 
using the brakes, up to and held short of runway 4L, which was being used for 
departure operations. The Captain was asked by the observer to indicate when 
he believed the aircraft's tail was clear of the runway. He did so and explained 
how he determined it. He explained that he taxis with his landing lights set at 
approximately 45° to the horizontal. When the lights cross the edge line of a taxi- 
way, the taxiway edge lights, or the edge lines of a runway, the aircraft is usually 
clear. In this case he also used the lights to determine when to hold short of 4L. 
At this point, the First Officer advised Local Control that he was clear of runway 
4R and holding short of runway 4L. The flight was then cleared to the gate via 
taxiway J and the Outer and instructed to contact Ground Control on 121. 8. The 
flight proceeded to cross 4L but not before the Captain confirmed with the First 
Officer that it was in fact cleared to cross 4L. 

The First Officer contacted Ground Control and was advised by the 
Ground Controller to "continue on taxiway Pappa and hold short of runway 11/29. " 
It was evident that the Ground Controller did not know where the flight was. 
Reference to Figure 5-38 indicates that taxiway P (Pappa) is past the end of run- 
way 4L/22R and crosses 11/29. The First Officer advised the Ground Controller 
of the aircraft's position. After a long pause the flight was cleared to the inner 
taxiway to the gate. 

The flight turned off taxiway J and proceeded on the Inner. The Captain 
began following the taxiway centerline lights and painted centerline very slowly and 
cautiously. * After taxiing a short distance the flight came to an area where the 
blowing snow had covered the centerline lights and painted center. Thus, visible 



*Newark airport has installed centerline lights along the yellow painted centerline. 
However, there are no taxiway edge lights installed. 



5-220 



reference to the taxiway was lost. As the flight came to an area clear of blown 
snow, the Captain, First Officer, and observer could see a double line indicating 
the boundary of the taxiway surface and the shoulder slightly to the right of the 
aircraft nose. * The Captain then brought the aircraft back to the left and taxied 
even more cautiously until the centerline lights could be seen again. 

As the flight was abreast of the A satellite of terminal 2 the cockpit 
was illuminated by headlights of several surface vehicles apparently caused by 
about six snow removal vehicles clearing the snow on the Inner and approaching 
the flight head-on. The First Officer contacted the Ground Controller to report 
the situation. The Ground Controller indicated that he was not aware of snow 
removal equipment in the area. After a brief discussion on what to do the flight 
was instructed to make a left at the intersection and a right on the Outer. 

As the flight proceeded along the Outer, lights were again observed 
approaching the aircraft. At this point it could be heard that a TWA flight taxiing 
on the Outer reported to Ground Control that an aircraft was approaching it on the 
Outer and asked what the other flight was supposed to do. The Ground Controller 
informed TWA about the status of UA 142. The pilot of the TWA aircraft then 
asked the controller if United is supposed to give way to him or he to United. The 
controller indicated that it would depend on their positions . The TWA pilot then 
contacted the UA flight to ask if there was room for them to hold and allow him to 
turn right (on taxiway S). The UA Captain replied that he did not think so but 
thought he could make the right toward the Inner. The situation was resolved in 
that manner and the flight was cleared to the gate. The aircraft docked at the 
gate at approximately 2142. 

After the final checkout the observer spent some time talking with 
the crew about the arrival events and the objectives of the study. The crew 



Considering the size of a DC-10, the right main gear were probably over the 
grass area. 



5-221 



indicated that under such poor conditions in-cockpit instrumenation for aircraft 
taxi guidance would be very desirable and that some of the problems could be 
avoided if there was better information available to the control tower. 



5-222 



SECTION 6 - ASTC SYSTEM OPERATIONS EFFECTIVENESS ANALYSIS 

6. 1 GENERAL 

The purpose of this section is to present the results of the operations 
effectiveness analysis for the current O'Hare ASTC system and for the projected 
future operating environment at O'Hare. The results for the current system in- 
clude both quantitative and qualitative analysis of the operations observed using 
the data derived from the functional activity analysis of system operation. The 
quantitative analysis is very gross and is included only as an indication of the mag- 
nitudes of delay and associated operating costs, etc. , involved in the operation of 
the ASTC system. That small fraction of delay which new systems and procedures 
can reduce will be estimated as part of the second phase of this study. The results 
for the projected O'Hare environment are described only qualitatively due to the 
uncertainty of that environment. 

6. 2 SYSTEM EFFECTIVENESS CRITERIA MEASURES 

The criteria selected and the computation of criteria measures for the 
ASTC system effectiveness analysis were previously discussed in Section 2.3. The 
effectiveness criteria included both directly measured system performance variables 
and performance variables derived from extrapolation of the directly measured vari- 
ables. The effectiveness criteria employed in this analysis included: 

Indirect Performance 
Directly Measured Variables Variables 

Delay Time Operating Cost 

Controller Communications Workload Fuel Consumption 
Pilot Communications Workload Pollution Emission 

Passenger Inconvenience 1 

Accident Risk 

The computational methodology of the effectiveness scores for these 
performance variables is illustrated in Section 6.3. In the case of the indirect 
performance variables it was necessary to apply weighting factors for the 



6-1 



characteristics of the various aircraft operating atO'Hare. Therefore, the actual 
flight schedules for airlines operating at O'Hare were examined to determine 
the type of equipments employed for the various flights. Each aircraft type as 
well as general aviation aircraft were assigned a class type and frequency of 
occurrence of the operation of aircraft by class type was derived. The results 
of this activity is presented in Table 6-1. It may be seen that the predominant 
number of operations at O'Hare are B727 and DC9 equipments. 

Table 6-1. Distribution of Aircraft Types at O'Hare 



Aircraft 




Frequency of 


Equipment Type 


Class Type 


Operation 


B747 


1 


0.0247 


DC 10 


1 


0. 0465 


L1011 


1 


0. 0046 


B707 


2 


0.0620 


DC8 1 
B727 


2 


0.0912 


3 


0.3359 


B737 


3 


0. 0540 


DC9 


3 


0.2021 


B720 


2 


0. 0023 


CV880 


2 


0.0092 


Other 3 


4 


0. 1675 



Notes 

1. Includes all DC8-50 and DC8-60 (stretch) series 
operations. 

2. Includes all B727-100 and B727-200 (stretch) series 
operations. 

3. Composite of all other air carrier and general aviation 
turbojet, light jet, and propeller equipments. 

The frequency of occurrence values shown in Table 6-1 and the various 

performance characteristics [e.g. , fuel flow (consumption) rate, operating cost 

per minute, average passenger loading] for the aircraft class type were employed 

to derive composite average performance parameters according to the formula: 

n. 
Avg Performance Parameter = /_, — (PC.) 



6-2 



where 

i = aircraft class type 

n. 

— = frequency of occurrence of operation of aircraft in the ith 
class type 

PC. = particular performance characteristic for aircraft in the 
ith class type 

6. 3 CURRENT O'HARE ASTC SYSTEM EFFECTIVENESS 

The following paragraphs present the results of the effectiveness 
analysis of the current O'Hare ASTC system. Several assumptions were made to 
allow practical computations of the effectiveness criteria values. These include: 

1. Average traffic operations rate of 120 operations/hour during 
weekday busy traffic hours 0700 to 2300. 

2. Average traffic operations rate of 40 operations/hour during 
weekday night operations hours 2300-0700. 

3. The arrival/departure ratio = 1 for any hour. 

4. The ratio of northside/southside operations = 1 for any hour. 

5. The ratio of hours of operation in Arrivals from the East mode/ 
Arrivals in the West mode = 1 for the year. 

6. The data derived from the traffic flow and communications analysis 
for the sample periods holds on the average throughout the year. 

7. There are negligible or no delays during night operations hours. 

8. Since minimum data was derived for Category II conditions and 
the hours of such conditions throughout the year is small com- 
pared to total operations, all computations were based upon 
visual operating conditions. 

9. Saturdays and Sundays are equivalent to a single weekday, yielding 
approximately 300 equivalent operations days per year. 

10. All aircraft taxi with all engines operating at idle and engine start- 
up and shutdown takes place at the gate. 



6-3 



6.3.1 Traffic Delay Effectiveness 

Using the above assumptions the traffic delay effectiveness values can 
be derived using the relationships: 

ST 



BE ST^ + HT 

E W 



ST W 

TD 



BW ST + HT 

W W 



TD BT = 0.50 (TD\ + 0.50 /TD BW 



TD 
BW 



where 



AMDR B = — D 



TD = 16 x TO^ (HT 7 + HT 

D y W E, 



ST^, and HT^ (ST TTT and HT TT /\ = the average service time and holding 
E E V w w; .. . ._ . . . b 

time per operation in the Arrival 

from the East mode (Arrival from 

the West mode) 

TO = Average busy hour operations rate 
(120 opns/hr) 

TD (TD ]= Average delay effectiveness for busy 
hour operations in the Arrival from 
the East (West) mode. 

TD = Average busy hour delay effectiveness 
throughout the year. 



AMDR = Average busy hour airport operations 
mode effectiveness ratio 

TD = Total average yearly delay 



6-4 



Using the values for taxi service times and holding times derived in 
Section 5.3, the values for ST and HT are computed as 

ST W = ST Ramp + ST Ground(E) + ST Local(E) 

= '- = 6. 95 minutes/operation 

Tinr = U'T 1 + ffT 1 + HT 

ni W Ramp Ground(W) Local (W) 

— = 5. 37 minutes/operation 



60 



ST = ST + ST + ST 

& E Ramp Ground(E) Local(E) 

= '• = 6. 04 minutes/operation 



TTrp TIT _l_ flT 4- HT 

E " Ramp Ground(E) Local(E) 



!. 1 + 25. 1+ 186 n „ B . , 

— = 3. 65 minutes/operations 



60 
Using these values, the effectiveness measures are computed as 

TD^ = a ft f *°f cr = 0. 623 or 62. 3% effective 
BE 6.04 + 3.65 

6 95 

TD BW " 6.95" + 5. 37 " °- 572 ° r 57 - 2% efte0HVe 

TD^^ = 0. 5(. 623) + 0. 5(572) = 0. 598 or 59. 8% effective 
BY 



0.572 



AMDR B = 0^3- =0 - 918 

TD = 16 x 120 (3.65 + 5.37) = 5, 195,520 minutes or 86,592 hours per year 

From these computations it may be seen that about 40 percent of the time 
an aircraft is on the ground at O'Hare he is in a delay waiting for a gate, a runway, 
other taxiing traffic, or service from the ASTC system. It may also be seen that 



6-5 



the East mode is more effective than the West mode on the average. This is gen- 
erally due to less runway crossing required. If operations under Category II con- 
ditions had been considered, the effectiveness of the West mode and the ratio of 
West/East operations would be slightly less than the values computed above. 



6.3.2 



Controller Communications Workload 



Controller communications workload effectiveness values for busy 
hour operations can be derived using the relationships:* 



CCW 



OG 



°- 50CO (E,OG + - 5CO (W)OG 



60 



CCW. 



IG 



°- 5CO (E)OG + - 5CO (E,OG 



60 x 1. 15 



CCW 



LC 



°- 5CO (E)LC + - 5CO (W)LC 



60 



where 



AMCR 



CO (W)OG + L 15 C °(W)IG + 2 C0 (W)LC 



CO (E)OG + L 15 CO (E)IG + 2 C °(E)LC 



CCW = Average percentage Channel Occupancy for each 
position throughout the year. 



CO 



(W) 



CO 



(E) 



Average Channel Occupancy per operation in Arrival 
from West(East) mode. 



Subscripts OG, IG, and LC stand for Outbound Ground, Inbound Ground, 
and Local Control, respectively. 



AMCR = Average airport operations mode effectiveness ratio 



*Clearance Delivery communications are not considered in this analysis because 
this operation is independent of East or West Mode of operation. 



6-6 



Using the data derived in Section 5. 4 these effectiveness values can 
be computed as: 



CCW__ = [. 5(. 56) + . 5(59)] 60 = 34. 5% Occupancy 
OO 



CCW = [. 5(. 55) + . 5(59)] x 60 x 1. 15 = 39. 3% Occupancy 
IG 



CCW T = [. 5(. 49) + . 5(55)] 60 = 31. 2% Occupancy 
LC 



AMCR = 



0.59 + 1. 15(0.59) + 2(0.55) 
0.56 + 1. 15(0.59) + 2(0.49) 



= 1.07 



From the above data it can be seen that communications workload for 
the Inbound Ground is somewhat higher on the average through the year. In addi- 
tion, it may also be seen that the Arrival from the West mode is again less effec- 
tive on the average than the Arrival from the East mode. 

6.3.3 Fuel Consumption Effectiveness 

The annual fuel consumption for operations at O'Hare is derived from 
the relationship: 



FC = 
Expansion of this equation gives: 



k W FC W + k E FC E ' 30 ° 



1 



FC w = 



16 X TO D X ^ST W + HT W 



+ 8 T0 N X ( ST W 



X 



I 



— FF. 

n ) 



Total Aircraft - mins in 
ASTC system per day 



x 



Avg Aircraft Fuel Flow 
Gallons per aircraft min. 



6-7 



where 



TO = Avg hourly daytime operations rate. 

ST = Avg service time for West arrival mode. 

HT TT7 = Avg holding time for West arrival mode. 
W 

TO = Avg hourly nightime operations rate. 



n. 

— FF. = Weighted average gallons of fuel used per idle 
aircraft minute 



and 



FC E = 



'O d x ( ST + HT £ 






+ 8 TO, T x ST 

N ^ E 



x 



n. 

— FF 
n i 



where 

ST = Avg service time for East arrival mode. 
E 

HT = Avg holding time for West arrival mode. 
E 

The values of TO and TO were given earlier as 120 operations/hour 
and 40 operations/hour, respectively. The value of } n./n FF^ is derived from 
Table 6-2 as 8. 615 gallons/minute/aircraft. 



Thus, 



FC = [(16 x 120 x 12. 32) + (8 x 40 x 6. 95)] x 8. 615 
W 



FC = 222, 940 gallons/day 



FC = [(16 x 120 x 9. 69) + (8 x 40 x 6. 04)] x 8. 615 
E 



FC_ = 176, 930 gallons/day 
h 



6-8 



Table 6-2. Weighted Average Gallons of Fuel per Idle 
Aircraft Minute at O'Hare 









Estimated Idle 




Weighted Fuel 


Air- 






Fuel Engine 




Consumption 


craft 




Freq. of x (gallons/minute/x No. of = 


= (gallons/idle 


Type 


Class 


Occurrence 


engine) 


Engines 


engine minute) 


B747 


1 


0. 0247 


5.24 


4 


0.518 


DC 10 


1 


0. 0465 


3.07 


3 


0.428 


L1011 


1 


0. 0046 


3.07 


3 


0.042 


B707 


2 


0.0620 


3.58 


4 


0.888 


DC 8 


2 


0.0912 


3.58 


4 


1.306 


B727 


3 


0.3359 


3.18 


3 


3.205 


B737 


3 


0.0540 


3.24 


2 


0.350 


DC 9 


3 


0.2021 


3.24 


2 


1.310 


B720 


2 


0. 0023 


3.58 


4 


0.033 


CV880 


2 


0. 0092 


1.70 


4 


0.063 


Other 


4 


0. 1675 


1.41 


2* 


0.472 












8.615 



*Composite mix. 



6-9 



and 

FC = [0. 5 (222, 940) + 0. 5 (176, 930)] 300 



FC = 59, 980, 700 gallons/year 



letting HT and HT = for optimum effectiveness gives: 



FC . = [(16 x 120 x 6.95) + (8 x 40 x 6.95)1 x 8.615 

W min K • n 

= 134, 120 gals/day 
FC E . = [(16 x 120 x 6.04) x (8 x 40 x 6.04)] x 8.615 
= 116,560 gals/day 

FC min = [0 * 5 < 134 ' 120 > +0 - 5 (H6,560)] 300 



Thus, 



= 37,602,000 gals/year 



Fuel Consumption Effectiveness = 37?602?000 = 

59,980,700 



0.627 



From these computations it is estimated that the gasoline consumed by 
aircraft taxiing at O'Hare is roughly that of the gasoline consumed by all the cars, 
buses and trucks in the nearby city of Peoria (population 126, 000). The gasoline 
consumed in delays alone could satisfy nearly 10 percent of the needs of the Dis- 
trict of Columbia or the State of Vermont. 

6.3.4 Pollution Emission Effectiveness 

The annual quantity of pollutants emitted can be calculated using the 
same basic relationships as used for calculating fuel consumption. The only 
major difference is the use of the pollution factor PF. instead of the fuel factor 
FF. in the basic formulas such that: 



= [ k 



PE= |k W PE W + k E PE E 



300 



6-10 



, 



where 



PE = 
W 



16TO D ST W + HT W +8T °N ST W 



x 






and 



PE £ = 



16 TCv / ST + HT^ \ + 8 TO XT / ST^ 

D \ E E ) N E 



x 



n. 

— PF 
n i 



The airport assumptions and delay measurement data are the same 
for the evaluation of this parameter. Therefore, the overall effectiveness score 
will be the same for pollution as for fuel consumption, i.e., 



PE 



min 



PE 



= 0.627 



The annual quantities of various pollutants emitted are determined 
using the formula and the pollution factors (PF) for various aircraft. PE is 
related to the fuel consumption for an idle engine as shown in Table 6-3. 

Table 6-3. Typical Pollution Emissions Vs Fuel Consumption 
Rate at Idle Engine Speed 



Fuel Con- 
sumption 
Rate (gal- 
lons/minute) 


Emissions (grams/minute) 


Air- 
craft 
Class 


Typical Aircraft 
Types 


CO 


NO 

X 


S °2 


Hydro- 
Carbons 


Est. Total 

Pollutants 

of All Types 


3.29 


618 


29.2 


8.2 


175.0 


830.4 


1 


B747, DC10, L1011 


2.59/2.82 


1100 


11.9 


8.3 


91.7 


1211.9 


2 


B707, DC-8 


2. 12 


735 


23.3 


2.2 


72.0 


830.5 


3 


B727, B737, DC-9 


1.41 


500 


10.0 


14.0 


60.0 


584.0 


4 


Others 



6-11 



It is interesting to note that the combustion efficiency in the idle mode 
is very low and that between 15 to 20 percent of the fuel which is consumed at idle 
is converted into dangerous pollution. This conversion factor reduces by a factor 
of 20 at takeoff and cruise-engine speeds. 

Based on the aircraft profile at O'Hare the weighted value of pollutants 
emitted by an aircraft at O'Hare is calculated from Table 6-4. 

Table 6-4. Estimated Average Pollutants per Idle Aircraft Minute at O'Hare 



Air- 
craft 
Type 


Class 


Freq. of 
Occurrence 


Estimated 

Pollutants 

<■ ^ . = 

Emission 

(grams/minute) 


Weighted Pollution 
Emission (grams/ 
idle engine minute) 


B747 

DC 10 

LlOll 

B707 

DC 8 

B727 

B737 

DC9 

B720 

CV880 

Other 


1 
1 
1 

2 
2 
3 
3 
3 
2 
2 
4* 


0.0247 
0. 0465 
0. 0046 
0.0620 
0.0912 
0.3359 
0. 0540 
0.2021 
0.0023 
0.0092 
0. 1675 


830.4 

830.4 

830.4 

1211.9 

1211.9 

830.5 

830.5 

830.5 

1211.9 

1211.9 

584.0 


82.0 
115.8 

11.5 
300. 1 
442.1 
836.9 

89.7 
335.7 

11.2 

44.6 
195.6 


*Assume 


d avg m 


ix. 




2465.2 



Therefore, the annual estimated kilograms of pollutants emitted are 



computed as: 



PE„ 7 = [(16 x 120 x 12. 32) + (8 x 40 x 6. 95)] x 2. 4652 
W 



PE = 63 , 795 kilograms/day 



PE_ = [(16 x 120 x 9. 69) + (8 x 40 x 6. 04)] x 2. 4652 
E 



PE„ = 50,621 kilograms/day 
hi 



6-12 



PE = [0.5 (63,759) + 0.5 (50,621)] 300 



PE = 17,162,400 kilograms/year 



PE , =0.627PE 
mm 

PE . = 10,760,824 kilograms/year 
mm 

An estimation of the short term effect of such levels of pollution 
emission can be derived in terms of the actual concentration of air pollutants in 
parts per million in the area of the airport. This requires an estimation of the 
total volume and air flow characteristics in the vicinity of the airport. If it is 
assumed that the airport surface is 100 million square feet (10,000 x 10,000) 
and that a temperature inversion layer existed at a 1000-foot ceiling and that 
there were no cross winds at lower altitudes, an estimate of the pollution level 
increase as a function of time can be computed. 

Based on examination of the operating environments for the TSC and 
CSC data collection periods , it would appear that the airport most probably would 
be operating in the Arrivals from the West under such conditions. For the West 
arrival mode the hourly pollution emission is: 

63,795 „„„„,.. ,, 

— — — = 2,658 kilograms/hour 

The mass of 10 cubic feet of air is: 

9 
2. 8 x 10 kilograms 

If none of the air in this hypothetical volume is allowed to escape the 
pollution level will increase at a rate of 

2.65 8 x 1 3 n nr . , .„. ., 
— = 0. 95 parts/million/hour 

2. 8 x 10 



6-13 



Obviously there would be even higher pollution levels in close proximity 
to the terminal area. Furthermore, private and commercial surface vehicle 
emissions must be added to this figure. The resulting situation over a period of 
several hours or a day represents a serious health hazard. 



6.3.5 Operating Cost Effectiveness 

This analysis provides an estimate of the operating cost for aircraft 
in the ASTC System at O'Hare. The associated effectiveness score and potential 
cost savings for an optimized system are also computed. The same airport op- 
erating assumptions which were made for the fuel and pollution analyses are used 
in this evaluation; therefore, the overall effectiveness score which is based pri- 
marily on delay ratios is 0. 627. The annual estimated cost for ground operation 
at O'Hare is calculated from the formula. 



OC = 



k W° C W + k E° C E 



300 



where 



OC 



and 



W 



oc E = 



16 TO D ST W + HT W + 8 T °N ST W 



16 TO^ ST + m\ ) + 8 TO, T ST^ 

D V E E / N V E 



x 



X 



^ n. 

y ^cf. 



n. 

— CF. 
n i 



Table 6-5 summarizes the cost factors (CF.) for the various aircraft 
types at O'Hare. The average weighted cost per aircraft minute is $11. 23. 
Substituting this value and the previous delay data gives 



OC = [(16 x 120 x 12. 32) + (8 x 40 x 6. 95)] x $11. 23 
W 



OC = $290,614 per day 



6-14 



OC = [(16 x 120 x 9.69) + (8 x 40 x6.04)] x $11.23 
E 



OC.. = $230,638 per day 
E 



The annual cost is therefore estimated to be 



OC = [0.5 ($290,614) + 0.5 ($230,638)] 300 



OC = $78, 187,800 per year 



The estimated annual costs due to delays on the O'Hare Airport sur- 
face are therefore: 



Annual Operating Cost 
Due to Delays 



= (1 - 0.627) $78,187,800 



$29,164,049 



Table 6-5. Weighted Average Operating Cost per Idle 
Aircraft Minute at O'Hare 



Air- 






Estimated Cost 


Weighted Cost 


craft 




Freq. of > 


: of Operation = 


1 (dollars/minute/ 


Type 


Class 


Occurrence 


(dollars/minute) 


idle aircraft) 


B747 


1 


0. 0247 


29.88 


0.74 


DC 10 


1 


0. 0465 


18.37 


0.85 


L1011 


1 


0.0046 


27. 17 


0. 12 


B707 


2 


0.0620 


13.88 


0.86 


DC8 


2 


0.0912 


15.00 


1.37 


B727 


3 


0.3359 


11.25 


3.78 


B737 


3 


0.0540 


10.30 


0.56 


DC9 


3 


0.2021 


8. 15 


1.65 


B720 


2 


0.0023 


15.67 


0.04 


CV880 


2 


0.0092 


15.67 


0. 14 


Other 


4* 


0. 1675 


6.67* 


1.12 










11.23 



*Assumed avg mix. 



6-15 



6.3.6 



Passenger Inconvenience 



Passenger inconvenience is evaluated by estimating the total passenger 
delay minutes per year and the number of passenger stops. Measured data on the 
total aircraft delay minutes and the number of holds per aircraft are analyzed in 
conjunction with passenger loading statistics at O'Hare. 

Passenger Delay minutes are calculated for the year using the formula 



where 



PD 



k PD + k PD 
W W E E 



PD = 
W 



16 TO D HT W 



x 



300 



n. 



- PL. 
n l 



and 



PD 



E 



16 TCL HT 
D E 



x 



7^ PL. 
L_, n i 



Table 6-6 estimates the average aircraft passenger loading at O'Hare 
to be 58. 939 passengers per aircraft. Using the holding time estimates for the 
east/west modes of operation passenger delay is computed as 



PD„ T = [16 (120) 5. 37] x 58. 939 
w 



PD = 607,685 passenger delay minutes/day 



PD^ = [16 (120) (3.65)] x 58.939 
h 



PD = 413,045 passenger delay minutes/day 
hi 



PD = [0.5 (607,685) +0.5 (413,045)] 300 

> 
PD = 153, 109,500 passenger delay minutes/year 

PD = 219.3 passenger delay years/year 



6-16 



Table 6-6. Weighted Passenger Loading for Aircraft at O'Hare 



Air- 






Estimated Pas- 




craft 




Freq. of x senger Loading = 


= Weighted Pas- 


Type 


Class 


Occurrence 


Capacity 


senger Capacity 


B747 


1 


0.0247 


338 


8.35 


DC10 


1 


0.0465 


234 


10.88 


L1011 


1 


0.0046 


254 


1.17 


B707 


2 


0.0620 


141 


8.74 


DC8 


2* 


0.0912 


157 


14.32 


B727 


3* 


0.3359 


110 


36.95 


B737 


3 


0. 0540 


95 


5. 13 


DC9 


3 


0.2021 


89 


17.99 


B720 


2 


0.0023 


140** 


0.32 


CV880 


2 


0. 0092 


140** 


1.29 


Other 


4* 


0. 1675 


40** 


6.70 






Total Avg Capacity /Aircraft 


111.84 






Avg Passenger Loading Factor 
for Domestic Fits (173) 


52. 7% 






Avg Passengers/Fit at O'Hare 


58.939 



*Assumed avg mix of various models. 
**Data not available - Estimated value. 



6-17 



The passenger delay effectiveness score is based on the ratio of delay 
time to actual transit time measured. Therefore, the effectiveness score will be 
identical to that for fuel consumption, pollution emission, and cost, i. e. , 0. 627. 

In addition to delay, passenger discomfort is an inconvenience which 
is somewhat related to the number of accelerations and decelerations that the 
aircraft makes. This can be partially evaluated in terms of the number of holds 
encountered while traveling on the ground. 

The measurements taken at O'Hare indicate that there are an average 
of 0. 1 holds per aircraft operation in the ramp area and 0. 5 taxiway holds per 
aircraft for the west mode of operation and 0. 23 holds per aircraft in the east 
mode. The annual number of passenger stops plus starts can be calculated from 
the formula 



where 



PC = 



k T PC +k PC! 
W W E E 



PC w = 



16 TCv x 2 NH T 
D W 



300 



n 



V-ipL. 

L^ n l 



and 



PC 



16 



TO^ x 2 NH^ x ) — PL. 

D EJ L-, n l 



Substituting the appropriate values gives 

PC„ r = [16 (120) x 2 (0. 5 + 0. 1)] x 58. 939 
w 

= 135 , 795 passenger starts and stops/day 
PC^ = [16 (120) x 2 (0. 23 + 0. 1)] x 58. 939 

= 74,688 passenger starts and stops/day 
PC = [0.5 (135,795) + 0.5 (74,688)] 300 

= 31,572,450 passenger starts and stops/year 



6-18 



The passenger comfort effectiveness score is best evaluated in terms 
of the average number of starts and stops that a single passenger can expect at 
O'Hare. Since this varies for the east and west mode of operation the scores are: 



Comfort 




Effectiveness Score 


Mode 


0.60 


West 


0.33 


East 


0.465 


Weighted Average 50/50 


0. 0000 


Optimum 



This analysis does not account for starts and stops encountered after 
the aircraft enters the departure queue nor does it include those stops which are 
essential to proper aircraft movement (e.g. , after pushback, during docking). 

6.3.7 Accident Risk Evaluation 

As indicated in Section 2 accident risk potential can be viewed with 
respect to several measured factors. In general, accident risk is increased by 
excessive controller workload, and excessive "chatter" on the ATC frequency. 
These conditions will, in all likelihood, result in an increased number of com- 
munications incidents and hazardous incidents. The factors which contribute to 
the assessment of accident risk appear in Table 6-7 along with the measured 
values at O'Hare. The values for an optimum ASTC system are also shown for 
comparison. 

Controller workload CTW is presented as a direct average for all con- 
troller positions in the tower which will impact safe operation. Therefore, the 
controller workload aspect can be expressed in terms of the average communica- 
tions workload of the Outbound Ground, Inbound Ground and Local Control posi- 
tions as: 



CCW + CCW + 2 CCW 
CTW = — — — 



6-19 



Table 6-7. Accident Risk Evaluation 



Factor/Formula 


Calculated 
for O'Hare 


Optimum Value 


Controller Communications Workload 

v- CT k 
ctw = ) — r x 100 

/ , 60 
k 


0.3405 


«1 


Cockpit Communications Workload 

V CTN 

ccw _ ^ go ^ 

k 


Departures 

22.244 

Arrivals 

9.448 


Departures 

^ 7 

Arrivals 
^3 


Communications Incidents Ratio 
CI (measured data) 


0.0710 





Total CT (measured data) 


Hazardous Incident Ratio 

HI (observed) 
TO (observed) 


0.0073 






6-20 



where 



CTW = the average control tower position workload 



Thus, 



CCW = values are taken from the analysis in paragraph 6.3.2 



34.5 + 39.3 + 2x31.2 



CTW- 

4 








CTW = 34. 05% occupied 





The cockpit communications workload can be estimated from the 
number of communications messages monitored by each aircraft in the system. 
This depends on the number of CTs on each ATC frequency and the time that 
the aircraft is on each frequency. Since the values differ substantially for arrivals 
and departures two values which are averaged for east/west modes are provided 
below: 



CCW - k CCW + k CCW See Figure 6-1 for calculation of 

CCW DW and CCW DE 

= 0.5 (24.9) + 0.5 (19.6) 

avg number of CTs monitored during an aircraft departure 



CCW = 22.2 



CCW A = k TTT CCW A „ 7 + t CCW A „ See Figure 6-1 for calculation of 

A W AW E AE ___. & , __„. 

CCW. TT7 and CCW. _ 
AW AE 

= 0.5 (10.1) + 0.5 (8.7) 

avg number of CTs monitored during an aircraft arrival 



CCW A = 9.4 
A 



If the ASTC Communications System could selectively address aircraft 
without causing other aircraft to hear all CTs the number of CTs monitored 
per aircraft would be equal to the number of CTs intended for that aircraft. The 
ideal ASTC situation would be one in which there were approximately 7 CTs per 



6-21 



DEPARTURES 

-w DW - ccw cD + ccw DGW + ccw LCW - ^(BCK^MS-as^), 

2. 8(60) x [0. 5* (3. 33**) + 0. 99***1 3.25 (60) x (4.25) 
60 60 

= 3.7 + 7.4+13.8 

CCWf T7 = 24. 9 average number of CTs monitored per departure (West mode) 
DW 

ccw DE = ccw CD + cc Wdge + ccw LCE 

2. 2 (60) x [0. 5 (3. 33)1 2.8 (60) X f0.5 (3.33) + 0.418] 
CCW DE "60 60 

+ 3.25(60)x3.1 =37 + 58+101 
60 

CCW = 19. 6 average number of CTs monitored per departure (East mode) 
DE 



ARRIVALS 



CCW = CCW +CCW = 2. 1(69) x [1.25 + 0.991 

LCW AW CLW IGW CCW LCW 60 

3.25 (30) x 2.91 _ . , _ 

+ i — l _ 5.4 + 4.7 

60 
= 10. 1 average number of CTs monitored per arrival (West mode) 

rrw -rr + rrw 2. 1 (69) x (1.25 + 0.418) 

ccw AE - cc IGE + ccw LCE - 6Q 

, 3.25 (30) x2.91 . _ . _ 

+ i — f- = 4.0+4.7 

60 

= 8.7 average number of CTs monitored per arrival (East mode) 



*Assumption: 50 percent of Ramp Area Time under CD and 50 percent under 
DGW 
**Average Time in Ramp Area (West) 
***Average Time in Ground Control Area (West) 

Figure 6-1. Cockpit Communications Workload Calculation 



6-22 



aircraft monitored on departure and 3 CTs per aircraft monitored per arrival. 
This is based on the assumption that ideally departure and arrival flights would 
only require the following CTs: 



Departures 

1. Flight plan clearance from 
Clearancy Delivery 

2. Ready-to-taxi handoff from 
Clearance Delivery 

3. Taxi clearance from Outbound 
Ground 

4. Handoff to Local Control from 
Outbound Ground 

5. Instruction to position and hold 
from Local Control 

6. Takeoff clearance from Local 
Control 

7. Handoff to Departure Control 
from Local Control 



Arrivals 

1. Initial contact/clearance 
to land from Local Con- 
trol 

2. Handoff to Inbound 
Ground from Local 
Control 

3. Taxi clearance from 
Inbound Ground 



The Cockpit Communications Workload Effectiveness may be evaluated 
as the ratio of the number of communications that would ideally be addressed to 
an aircraft to the total number of communications transactions that the crew must 
monitor to receive those communications. Therefore, the effectiveness score for 
cockpit communications workload can be calculated as 



since 



CCE = 



k D CC ID + k A CC !A 
k D CCW D + k A CCW A 



k D = k A = 0.5 



CCE 



CC ID + CC !A 

CCW^+CCW A 
D A 



6-23 



CCE = 



7 + 3 



10 



21.26 + 14. 18 35.44 



CCE = .282 



The communications incidents CIs observed are also a factor in 
evaluating the accident risk potential. While not all CIs are directly related to 
hazardous incidents a large number of CIs indicates that the effectiveness infor- 
mation transfer on the ATC frequency is reduced. The number of CIs observed 
during the test periods for all controller portions is compared with the total 
number of CTs analyzed. 



CI G L __ (187) + (150) _ 337 

CT ~ CT„ + CT T = (2530) + (2215) ~ 4745 



fT 

„ = 0. 0710 



Paragraph 6.3. 8 discusses several potentially hazardous incidents 
which were observed during the ASDE film analysis. Out of an estimated value 
of 1500 total operations observed, it was determined that 11 potentially hazardous 
incidents occurred. The hazardous incident ratio is therefore 



HI 



11 



TO 1500 



= 0.00733 



If there were no hazardous incidents observed during an extended 
test period, it could be assumed that the probability of having an accident is 
extremely low. 



6-24 



6. 3. 8 Qualitative Analysis of Accident Risk Potential 

The Accident Risk Effectiveness treatment in the preceding paragraph 
6. 3. 7 is an attempt to place some quantitative assessment on some of the factors 
that could potentially contribute to accidents in the ASTC system. They are recog- 
nized as being limited in their interpretation. This qualitative treatment of acci- 
dent risk potential is an attempt to provide further insight in the situations that 
could lead to an accident. 

During the study activities, project analysts identified several opera- 
tional situations that offerred potential for accidents. These situations include: 

1. Close sequencing of arrivals and departures on the same runway. 

2. Landings on two arrival runways that intersect close to the arrival 
ends of the airport. 

3. Variability of turnoffs from a runway onto a parallel carrying taxi- 
ing traffic. 

4. Taxiing of traffic on intersecting parallels for runways which are 
both in active use. 

Examples of situations 1-3 actually observed by project analysts are 
described in the following paragraph. This is followed by a qualitative discussion 
of the significance of these. 

6. 3. 8. 1 Accident Risk Observations 

During the data reduction of aircraft movements as seen on the ASDE 
films, nine unusual situations were observed which appeared to be "near misses" 
or conflicts that would have been hazardous in periods of low visibility. These 
examples from the population of approximately 1500 aircraft operations (measured 
over the 12 runs) involved in every case at least one "Arrival" aircraft. Potential 
conflicts at low speeds could not be determined from the ASDE film. For this 
reason, and since detail conflict studies were not made, the quantity of incidents 
observed is less than those which may have actually occurred. 



6-25 



In the following descriptions of the observed incidents the TSC/CSC 
run number and ASDE film time references are included to allow other individuals 
to review these situations. 

6. 3. 8. 1. 1 Arrival/Departure Sequencing on the Same Runway 

This type of safety incident was observed on four occasions and in- 
volved the sequencing or release of a departing aircraft in front of an incoming 
arrival. These cases occurred during two runs; in both runs mixed operations 
were being conducted on the same runway (Runway 27 L in Run 20 and Runway 14L 
in Run 24). In the two incidents observed on Runway 27L, it was necessary to 
evacuate a Departure from the runway to make way for an Arrival; i. e. , the De- 
parture was released from the departure queue prematurely. The two incidents 
on 14L in Run 24 may have involved pilot response time since both exhibited an 
Arrival separated from a Departure by short time intervals so that two aircraft 
were on the runway at the same time. These incidents are described below. 

• CASE A ; TSC Run 20, Runway 27L (69 ops/hr). 

Departure #3 leaves the departure queue at 8:39:30 to enter Run- 
way 27L. This aircraft enters 27L and continues across the Run- 
way without stopping in order to avoid an Arrival aircraft. De- 
parture #3 is clear of the Runway at 8:40:05; Arrival #4 passes 
the point-of- conflict seven seconds later at 8:40:12. This Depar- 
ture aircraft turned around on the 27L/9R parallel and later took 
off on 27L. Weather during the observation period was good. 

• CASE B : TSC Run 20, Runway 27L. 

A situation similar to Case A was observed with Departure #30 
being evacuated and cleared of the Runway at 9:25:49 and Arrival 
#30 passed the point-of-conflict at 9:26:23, 34 seconds later. This 
incident was not considered as an accident risk but rather a control 
incident involving aircraft sequencing. The preceding departure 
had been a heavy and the pilot, once on the runway, expressed a 
desire for 2-minute spacing. 

• CASE C : TSC Run 24, Runway 14 L 

This run was not analyzed in depth so no sequenced aircraft num- 
bers can be applied. A Departure was observed starting takeoff 



6-26 



at 7:12:00. At approximately 7:12:22 (22 seconds later) an arrival 
was seen at the start takeoff point. Both aircraft were observed 
on the Runway at the same time. The lowest observed separation 
was about 3400 feet. The weather during the observation period 
went as low as an indefinite to 200 foot ceiling with visibility as 
low as 3/8 mile. 

• CASE D : TSC Run 24, Runway 14L 

A situation similar to Case C was observed with the Departure 
starting takeoff at 8:01:23 and the Arrival at the start takeoff point 
about 8:01:39 (16 seconds later). Minimum observed separation 
was 1950 feet. 

In the judgments of the project analysts Case A represented an unac- 
ceptable separation of aircraft. Cases C and D, where the time separations of the 
Arrival behind the preceding Departures were 22 and 16 seconds, respectively, 
may be contrasted with normal time separations of from 45-70 seconds. It is be- 
lieved that visibility as well as the distance of the 14L departure queue from the 
tower may well have played major roles in these two incidents. While the risk 
level in these time margins is subject to various interpretations as to the amount 
of risk, it is believed that improved ASTC system equipments for use by tower 
controllers would have prevented the low values observed. 

6. 3. 8. 1. 2 Crossing Arrival Traffic 

While most Arrival operations take place on one Runway, there are, 
in some runway configurations, occasional Arrivals on another runway under the 
control of the same Local Controller. Examples include occasional Arrivals on 
14R when 9R is the primary Arrival runway in the South and occasional Arrivals 
on 22R when 14L is the primary Arrival runway in the North. Case E, described 
below, was recognized well before its occurrence by the Controller who informed 
the pilots of both aircraft. In our judgment, however, it appeared to represent a 
highly undesirable, if not accident risk, situation. 



6-27 



• CASE E ; TSC Run 37, Runways 22R, 14L 

Runway 22R Arrival #2 was over the last lights at about 4:33:05 and 
came to an abrupt halt at 14L at about 4:33:27, 22 seconds later. 

Arrival #33 on 14 L was over the last lights at about 4:33:13 and at 
the point of conflict (the intersection of 14L and 22R) at 4:33:30. 

Analysis of the corresponding communication tape revealed that 
the Local Controller told the 22R Arrival to hold short of 14L 
several miles prior to touchdown. The Controller also advised 
the 14L Arrival that the 22R Arrival would hold short. Weather 
during the observation period was good. It is believed that the 
22R Arrival, an AirWisconsin aircraft, was decelerating at 10- 
15 fps 2 ; the length of runway available up to the intersection is 
about 3000 feet. 

6. 3. 8. 1. 3 Control of Arrival Traffic Exits onto Parallels 

The following two situations are not considered as accident risk prob- 
lems in good weather but could have been if they had occurred under low visibility 
conditions. They are rather indicative of special control problems involving run- 
way turnoff and control of traffic on the parallel. 

• CASE F ; CSC Run 8 - Runway 14R 

Flight Arrival #28 turned off 14R at 9:50:45 and began taxiing 
southwest on the 19R/32L parallel. At 9:51:15 Arrival #28 came 
nose-to-nose with three departure aircraft on the 14R parallel, 
going up to the 14R departure queue. Arrival #28 was forced to 
squeeze around the departures. Prior to this situation, all 14R 
departures had been routed via the bypass to avoid such a situa- 
tion. Case F was substantiated from the corresponding communi- 
cations tape. Weather during the observation period went as low 
as 300 foot indefinite ceiling with visibility as low as 1/2 mile. 

• CASE G : TSC Run #37 - 14R Arrivals 

Another situation was observed involving three consecutive Arriv- 
als. Arrival #14 exited T-5 at 3:57:00 and taxied down the 14R/ 
32L parallel. Arrival #15 exited T-4 at 3:58:07 and met Arrival 
#14 at T-4 and the parallel; both aircraft were forced to hold. 



6-28 



Arrivals #14 and #15 yielded to Arrival #16. Arrival #16 exited 
T-3 at 3:59:30. Runway exits T-3, T-4 and T-5 are all high- 
speed turnoffs. 

• CASE H : TSC Run #39 - 9R Arrivals 

Light Arrival #6 was over the last lights at 8:52:50 and turned off 
onto Runway 32L/14R at 8:54:04 and began taxiing north on the 
runway. Runway 14R was activated for light arrivals at the time. 
Meanwhile, light Arrival #1 on 14R was over the last lights at 
8:53:06 and turned off the Runway at 8:53:46. 

The next available exit for 9R Arrival #6 would have been the 32L 
parallel which was occupied by Departures in taxi to 4R. The 
weather during the observation period was rain and showers with 
a 4600 foot broken ceiling and visibility of 8 miles. 

6. 3. 8. 1. 4 Miscellaneous 

• CASE J: Run #29 - 9R Arrivals 

While analyzing the communication tapes for a situation observed 
on the films, another situation was located which was not illus- - 
trated by the ASDE films. Heavy Arrival #2a, over the last lights at 
7:05:09, protested strongly that a 4R Departure aircraft held on 
the 14R/32L parallel was so close to the runway that the Arrival 
nearly hit him. The hold for the 4R Departure started about 
7:05:00. Weather during the observation period was overcast with 
a 2000-foot ceiling, visibility of 6 miles, with fair braking action 
on the 9R runway. 

6. 3. 8. 2 Discussion of Hazard Potential Situations 

Situations as described in paragraph 6. 3. 8. 1. 1 and for Departure 
Flight Trace 1 in paragraph 5. 4. 3. 1, involving close sequencing of arrivals and 
departures on the same runway, offer an obvious hazard potential. Any delay in 
the clearance of the preceding arrival from the runway or the initiation of takeoff 
by the departure increases the potential for accident or at a minimum insufficient 
separations between the departure and following arrival. This potential increases 
if the possibility of an aborted takeoff by the departure is considered. Although in 
each of the situations observed the Local Controller recognized and acted to 



6-29 



resolve the problem, under reduced visibility conditions such recognition might not 
occur in sufficient time. In addition, under heavier traffic volumes that might be 
expected in the future the possibility of momentary controller distraction or in- 
creased communications channel occupancy could lead to delays in recognizing 
and reacting to the situation. 

Situations, as described in paragraph 6. 3. 8. 1. 2, involving simulta- 
neous arrivals on crossing runways offer the obvious hazard potential where one or 
both of the flights can not be brought to a stop at the intersection of the runways. 
At O'Hare such operations are only permitted under VFR operating conditions 
permitting visual observation of the operations by Local Control and, it is as- 
sumed, mutual observations of the actions of the other aircraft by the pilots of the 
arrivals. However, any momentary distraction of Local Control or either of the 
pilots could result in missing or obtaining too late a visual cue that a serious ac- 
cident potential exists. In addition, this type of operation requires that the pilot 
who will be required to hold short of the crossing runway have good control of his 
aircraft with respect to the point at which the aircraft must touch down to permit 
the hold to be safely accomplished. 

Situations, as described in paragraph 6. 3. 8. 1. 3, involving exits from 
the runway onto a parallel carrying taxiing traffic offer two different levels of haz- 
ard potential. Case F in that paragraph describes a situation in which the early 
turnoff by an aircraft permitted the arrival aircraft to be only moving at taxi speed 
when the conflict occurred. This allowed the pilot to recognize and respond to the 
conflict in sufficient time. In addition, as the flight was a small general aviation 
aircraft it was possible for the flight to squeeze past the other aircraft. If, how- 
ever, the flight were a slightly larger aircraft and exited further down the runway 
into the oncoming traffic a serious accident might have resulted. Also, in the case 
of a larger aircraft it might not be possible for it to squeeze through resulting in a 
serious blockage of the parallel and possibly of normal turnoff s for other arrivals. 



6-30 



Case G in paragraph 6. 3, 8. 1. 3 represents a different, and possibly 
more potentially hazardous, situation. The pilots of aircraft that have exited the 
runway and are taxiing in the parallel toward the terminal can not see the opera- 
tions of succeeding arrivals on the runway until the arrival is abreast or ahead of 
them. Thus, they are limited in their response time if the arrival is still moving 
at a reasonable speed in clearing the runway ahead of them, and the onus for reso- 
lution of the problem is on the landing aircraft. Case G represents a good example 
of this situation which results in blockage of a runway exit forcing the next arrival 
to exit further down the runway, thus reducing the effective separation between it 
and the following arrival. 

The last situation discussed here was not observed during data collec- 
tion activities. However, it was brought to the attention of the analysts in discus- 
sions with ATCT personnel pertaining to taxi flow patterns and in discussions with 
airport management personnel. It was noted that, on occasion, flights may be 
taxied on the 9R/27L and up 14R/32L parallel for departure on 14R. Alternately, 
flights arriving on 14R may be taxied down the 14R/32L and left on the 9R/27L 
parallel to a location where they hold while waiting for a gate. Under reduced vis- 
ibility conditions it is possible for the flights to miss the turns and continue on the 
parallel until they find themselves on the active runway; 14R for the former air- 
craft and 9R for the latter. This represents a highly hazardous situation. It was 
indicated that such events have, in fact, occurred, although no accidents resulted 
from them. 



6-31 



6. 4 FUTURE O'HARE ASTC SYSTEM EFFECTIVENESS ASSESSMENT 

6.4.1 Projected Future Operating Environment 

During this study several attempts were made to determine a reliable 
estimate of the future operating environment of O'Hare. The areas of interest in- 
cluded: 

1. New runway construction and modification of existing runways. 

2. New taxiway construction (which is, for the most part, related to 
new runway construction). 

3. New terminal facilities construction or modification of existing 
facilities. 

4. Traffic projections, including both the volume and mix of traffic. 

5. Revised runway and taxiway operations patterns (which is related 
to areas 1-3 above). 

In discussions with airport management, ATCT, and airline manage- 
ment personnel it was clear that no firm plan existed which could be considered 
reliable. However, based on these discussions certain assumptions were made 
pertaining to airport developments which could be considered reasonable for the 
purposes of this analysis. These assumptions, illustrated in Figure 6-2, include: 

1. Construction of a new runway 9L/27R 

2. Construction of a new runway 4L/22R 

3. Construction of a new segment of taxiway connecting the 14R/32L 
parallel to the current 4L./22R runway 

4. Construction of a new International Terminal complex at the loca- 
tion of the current USAF/Air National Guard area 

5. Development of the area southeast of the intersection of runways 
14R/32L and 9R/27L for a new general aviation terminal. * 



*A strong possible alternative to this is development of an area adjacent to the 
assumed new International Terminal complex for this purpose. 



6-32 



PROPOSED 
RUNWAYS 




NEW INTERNATIONAL 
TERMINAL LOCATION 



NEW 

INNER CIRCULAR 

OUTER CIRCULAR' 



AREA TO BE 
DEVELOPED FOR 
GENERAL AVIATION 



\ T 1 



4/^ 



w* 




Figure 6-2. Projected Future Operating Environment at O'Hare 



6-33 



Based on these assumptions, further assumptions were made relative 
to aircraft taxi flow. These include: 

1. The current runways 4L/22R and 9L/27R would be used as parallel 
taxiways for the new runways 

2. Use of the current Inner Circular taxiway would be discontinued in 
favor of the use of the current Outer Circular for this purpose 

3. The combination of the 9R/27L parallel, 14R/32L parallel, and 
new taxiway segment identified above would be used as the new 
Outer Circular 

However, since no information was available pertaining to the construc- 
tion of taxiways in relation to the new 4L/22R and 9L/27R runways, no assumptions 
could be made relative to any potential changes in traffic taxi patterns for depar- 
tures to or arrivals from these new runways. 

6.4.2 Assessment of the ASTC System Effectiveness in the Projected Future 

Operating Environment 

In the following paragraphs a qualitative assessment of the impact of 
the various changes in the physical operating environment is made based upon the 
understanding of current airport operations. These assessments are based upon 
use of the runways in basically the same primary configurations discussed in 
Section 3.3. In summary, they indicate that the planned facility changes can 
streamline the current ground operations and increase gate capacity, easing the 
current gate limitations, but that the overall capacity will not be affected. If any- 
thing, overall capacity will be reduced as the percent of heavy aircraft increases. 
New ATC equipments and/or procedures are required if capacity is to be increased. 

6. 4. 2. 1 New Runways (9L/27R and 4L/22R) 

The basic benefits derived from adding the new runways would be to 
lengthen the rollout capacity of the heavily used 27R and 22R runways (30 percent 
of all arrivals) and to relieve the departure queue congestion associated with de- 
partures from 4L and 9L in the West arrival mode. For the latter it is assumed 



6-34 



that departures will be from near the new 4L/9L intersection. The benefits are 
achieved while permitting the addition of the proposed taxiway from the current 
4L. 

The benefits would be at the expense of taxi time since the new runways 
are away from the terminal. It does not appear that the runways would increase 
the airport's runway capacity since they will simply be used in lieu of the current 
runways. Thus, without new ATC equipments (e.g. , Metering and Spacing) or 
procedures, the current quota would be expected to continue or be reduced due to 
increases in heavy aircraft operations. 

No reliable quantitative projections could be made for the aircraft mix 
that would operate in the future at O'Hare. However, based on the changes in the 
aircraft mix following the flight schedule reductions in January 1974, it is reason- 
able to assume that future traffic demands will be met in part by the use of higher 
passenger capacity aircraft. This would probably involve use of 727s in place of 
DC9s and increased use of stretched 727 aircraft since these equipments comprise 
about 53 per cent of the current fleet. It could also conceivably involve increased 
use of DC10 and L1011 equipments as well as re-introduction of 747s which have 
been deactivated in the schedule reductions by the major carriers. 

6.4.2.2 New International Terminal Location 

The basic benefit of the new terminal is the addition of gates at an air- 
port which is currently gate limited. International gates currently number 13. If 
only these 13 were moved to the new terminal, the gate capacity estimate would in- 
crease to 170 operations /hour from the current 150 operations/hour (see paragraph 
5. 3. 1. 2). Until new ATC procedures and equipments permitted the runways to 
deliver the increased operations, these gates would tend to reduce the current gate 
delays. 

This benefit will be accomplished at the expense of increased taxi times. 
Examination of Figure 6-2 indicates that for all primary runway configurations in 



6-35 



both airport operating modes there will be a marked increase in the average taxi 
service time (ST) for both arrivals and departures. The only instances of de- 
creased taxi time would occur for arrivals from the north and east on 32R (parallel 
32s - East Arrivals mode) and 4L (parallel 4s - West Arrivals mode). In addition, 
marked increases in the taxi delays (HT) for these operations could be anticipated, 
as explained below. 

In the East Arrivals mode, operations on the northside arrival runways 
27R or 22R would have to cross the active departure runway. Where 22R and 27R 
are being used for arrivals and departures, respectively, the exit point from 22R 
would determine whether 27R has to be crossed. Operations on the southside ar- 
rival runways would have to cross both northside runways as well as the traffic 
around the main terminal. Departures to the southside runways would similarly 
have to cross the northside runways and terminal traffic. 

In the West Arrivals all operations on the southside runways would 
similarly have to cross the airport. Since 14L is the primary arrival runway in 
the north for this mode, or when the 9L arrival/4L departure configuration is used, 
arrivals in the north will not generally have to cross an active runway. However, 
in any of the primary northside configurations, departures in the north will have to 
cross an active arrival runway. 

Asa result it would be anticipated that international traffic would en- 
counter a significant increase in taxi delays at taxiway-taxiway and taxi way- runway 
intersections, particularly as the total traffic volume increases. 

6. 4. 2. 3 Development of New General Aviation Facility 

The development of a new general aviation facility in the area shown in 
Figure 6-2 (or in the alternate area adjacent to the New International Terminal 
Complex) would tend to result in the same type of benefits and problems discussed 
in the preceding paragraph. However, in this case the resultant problems are 
likely to be more pronounced. This is due to the fact that general aviation opera- 
tions (and commuter traffic which currently operates from the general aviation 



6-36 



area) constitute a signficantly higher percentage of the traffic volume than does 
international operations and is likely to continue to do so in the future. The 
change is likely to be more significant in the East Arrivals mode where the general 
aviation traffic rather easily taxies directly from the Butler Terminal to the 9L/27 
parallel for departure on runway 36 or on runway 27R from the 27R/36 intersection. 

6. 4. 2. 4 New Inner and Outer Circular Taxi way 

The purpose of the new proposed taxi way link is to reduce the require- 
ment for using the current inner as a taxiway. The inner cannot take heavy air- 
craft in some areas due to space limitations. In addition, ramp congestion due to 
gate limitations and one-way flows between the fingers would be reduced, ramp 
holds to deal with gate limitations and one-way flows could be more easily employed, 
and pushbacks from the finger ends would be facilitated. 

Its success is examined for the three most used configurations. Con- 
figuration 1 (Figure 3-5, Arrivals from the East) is used 36 percent of the time. 
Its only requirement on the Inner is along concourse A-C. In the ASDE films it 
was seen that occasionally, rather than use the Inner, aircraft were routed up the 
14R parallel and down the By-pass. The new taxiway link would eliminate this re- 
quirement entirely. 

In Configuration 11 (Figure 3-15, Mixed Arrivals) which is used 16 per- 
cent of the time, the traffic can simply be moved out with the New Inner (current 
Outer) counter clockwise and the new Outer clockwise. The heavy traffic currently 
on the Inner (27L departures and almost all arrivals) would be eliminated and put 
on the current Outer which is more suitable. 

In Configuration 6 (Figure 3-10, West Arrival Mode), which is used 10 
percent of the time and in bad weather the traffic can simply be moved out with the 
New Inner (current Outer) counter-clockwise and the New Outer clockwise. The 
benefits are similar to those in Configuration 11. 



6-37 



Therefore, it appears that the benefits of the new section of taxi way 
can be realized. However, the price may be safety. Two situations described as 
potentially hazardous in paragraph 6. 3. 8. 2 will become emphasized by this pro- 
posed change. These are conflicts between arrivals (especially coming off high 
speed exits) and traffic on the parallel taxiway (now the Outer), and conflicts caused 
by aircraft taxiing on a parallel accidentally missing the turn at the intersection 
with an active runway and blundering out onto the runway (e. g. , departures on 
their way to 9R missing the turn at the 14R/27L parallels intersection and blunder- 
ing out onto 14R). Consideration will have to be given to its use in bad weather 
and/or at night. 



6-38 



SECTION 7 - FINDINGS AND CONCLUSIONS 

7. 1 GENERAL 

This section provides a summary of the salient findings of this study 
effort and the conclusions and recommendations derived from these findings. 

7. 2 SUMMARY OF FINDINGS 

7.2.1 Functional Responsibilities of Operational Personnel 

7. 2. 1. 1 Air Traffic Control Tower 

The functional responsibilities for management and control of flight 
operations for O'Hare are divided between the TRACON and Tower Cab. The 
TRACON is responsible for organizing the flow of traffic to arrival runways and 
establishing the aircraft on final before turning them over to the tower; this is 
accomplished by the Approach Control positions. The TRACON is also responsible 
for accepting aircraft from the tower after takeoff (or missed approaches) and 
vectoring them enroute out the TCA; this is accomplished by the Departure Control 
positions. 

Tower Cab is responsible for the traffic operations which are the sub- 
ject of this study. During normally busy periods the following positions are manned 
in the Tower: 

1. Flight Data 

2. Clearance Delivery 

3. Outbound (Departure) Ground 

4. Inbound (Arrival) Ground 

5. Local Control #1 (south runways) 

6. Local Control #2 (north runways) 

7. Watch Supervisor 



7-1 



Flight data has three major functional responsibilities. The first is to 
receive departure Flight Strips from the printer and prepare them for posting on 
the Clearance Delivery Flight Strip Board. The second is to assist Clearance De- 
livery in obtaining flight clearances from the Chicago ARTCC when required and 
in obtaining beacon codes for VFR departures. The third is to update the Auto- 
mated Terminal Information Service (ATIS) when changes in the runway configura- 
tion or weather conditions require. 

Clearance Delivery has two major functional responsibilities. The 
first is to deliver ARTCC clearances to departures and verify that the flights have 
properly received their clearances. In addition, he obtains information on the 
departures gates, where necessary, to assist Outbound Ground in handling the 
traffic. This second responsibility is to receive notification from aircraft that 
they are ready for taxi and turn them over to Outbound Ground for taxi instructions. 
In the case of VFR departures this also includes issuing a clearance (i. e. , direc- 
tion and altitude) out of the TCA. 

Outbound Ground has three major functional responsibilities. The 
first is to issue instructions for aircraft taxi to the appropriate departure runways. 
Although it is not a specified duty of this position, Outbound Ground does, through 
his instructions, attempt to establish a practical sequence of aircraft to each of 
the departure runways. The second responsibility is to maintain the safe and ex- 
peditious flow of departure traffic by issuing control instructions to resolve poten- 
tial conflicts at taxiway intersections or adjust the sequence of aircraft to mini- 
mize delays or gaps in the flow. His third responsibility is to turn departures 
over to the appropriate Local Control position when the aircraft are safely estab- 
lished on the final portion of their route to the runway. In certain operating con- 
figurations this includes responsibility for seeing aircraft across an active runway. 

Inbound Ground has four major functional responsibilities. The first 
is to issue instructions for aircraft taxi, after they are clear of the runways, to 
their gates. This also includes determination of whether the aircraft's gates are 



7-2 



available and, if not, to provide taxi instructions to an appropriate holding area. 
When the gates are available taxi instructions to the gates are then provided. In- 
bound Ground's second responsibility is control of the movements of aircraft be- 
tween facilities on the airport surface; that is, between terminal gates and the 
cargo or hangar areas between terminal gates. The third responsibility, similar 
to Outbound Ground, is to maintain the safe and expeditious flow of aircraft under 
his control by issuing the necessary control instructions. Inbound Ground is also 
responsible for control of the movements of vehicular traffic to, on, or between 
airport taxiways or runways; however, he is not responsible for control of these 
vehicles within areas on taxiways or runways that have been closed to aircraft 
traffic for maintenance operations. 

The two Local Control positions have four major functional responsi- 
bilities. With respect to arrivals they are responsible for issuing clearances to 
land and other advisory information required by the pilots for operation of their 
aircraft and for monitoring the approach to assure that it can be safely made. 
When the operations of other aircraft on the runway or other conditions will re- 
sult in unsafe landing conditions he will issue missed approach instructions to the 
arrivals. He is also responsible for turning the arrivals over to Inbound Ground 
for taxi instructions when the aircraft are clear of the runway or across the last 
active runway under his jurisdiction. With respect to departure, Local Control is 
responsible for establishing the aircraft in the final sequence for optimum use of 
the runways. When it is safe to do so, he will establish the aircraft on the runway 
and issue the necessary takeoff clearance instructions, including departure heading 
and advisory information. He is also responsible for monitoring the takeoff to 
assure that safe separations are maintained and turning the flight over to Depar- 
ture Control when the aircraft is established on its assigned departure heading. 



7-3 



7.2.1.2 Airlines 

The functional responsibilities related to ASTC operations are divided 
between airline terminal operations personnel and the aircraft cockpit crew. Air- 
line gate planning and control personnel are responsible for establishing and mon- 
itoring adherence to the scheduled usage of gate facilities. They are also respon- 
sible for managing aircraft operations from or to these facilities, including con- 
trol of aircraft pushback and advising arriving flights of their assigned gates and 
the availability of these gates. While Ramp or Gate Operations Supervisors are 
responsible for adherence to departure schedules, it was noted that they typically 
do not know whether or not the flight departures will be made on time until the 
scheduled time is reached and the flight has or has not departed. This is primar- 
ily due to the fact that preparation of the aircraft for departure is the function of 
separate working units who do not usually coordinate with one another. These 
units include: gate attendants, fuelers, baggage/cargo loaders, food service load- 
ers, and mechanics. When delays occur, the Gate Operations Supervisors and/or 
Gate Control Operators must contact the various units to determine the status of 
the operations and when completion is expected. Typically, the flight crews are 
not aware of the delays until they occur. 

The flight cockpit personnel are responsible for managing the physical 
operations of the aircraft, establishing and maintaining contact with the ATCT and 
responding to instructions given, and for establishing and maintaining contact with 
airlines gate planning/control personnel. Typically these responsibilities are di- 
vided among the members of the crew; that is, Captain (pilot), First Officer 
(pilot) and Second Officer (flight engineer) for three man crews for 727 and larger 
aircraft. Either of the pilots (i. e. , the pilot flying) will be responsible for the 
physical control of aircraft movements. The other pilot (i. e. , the pilot not flying) 
will be responsible for ATC communications. However, the pilot flying monitors 
these communications so that he can discharge his responsibility for control of the 
aircraft movements. With the exception of obtaining the clearance to pushback 



7-4 



from Gate Control, which is accomplished by the Pilot-Not- Flying, communica- 
tions with the company is the responsibility of the Second Officer. 

7. 2. 1. 3 Airport Management 

The major functional responsibilities of the airport management with 
respect to ASTC operations are maintenance of airport surface and visual guidance 
aid facilities in operating condition, direction of the response to emergency situa- 
tions, and coordination of maintenance and emergency operations with the ATCT. 
These responsibilities are divided between the Airport Operations Office, City of 
Chicago Fire Department, and Construction, Electrical Maintenance, and Auto- 
motive Sections. Operations office personnel make a daily check of the airport 
conditions to determine where surface or visual guidance facilities require main- 
tenance. The maintenance operations are scheduled, usually with an attempt to 
avoid interference with normal airport operations, and scheduled closings of the 
work areas coordinated with the ATCT. When snow removal on taxiway or runway 
surface is required, the Operations Office coordinates these with the ATCT as 
well. The Operations Office maintains a Coordination Center in the old control 
tower to accomplish these activities. The Center will advise the ATCT when 
scheduled maintenance or snow removal operations are about to begin. Center 
personnel visually observe and maintain contact with work crews to monitor the 
status of these operations and provide the ATCT with reports of estimated comple- 
tion and completion of these operations. The Center also monitors the status of 
emergency response operations and keeps the ATCT advised of the progress of 
these operations. 

7.2.2 Current O'Hare Operating Configuration 

O'Hare Airport generally operates in two basic operating modes, Ar- 
rivals from the East (departures to the west) and Arrivals from the West (depar- 
tures to the east). There is also a mixed mode of operations where arrivals in 
the north approach from the west and arrivals in the north approach from the east. 



7-5 



The eleven primary runway configurations identified for these operating modes are 
shown in Table 7-1. An airport map is shown in Figure 7-1. 

It may be seen from the table that these configurations involve two 
basic approach patterns. These are Dual Approaches, where the arrival runways 
(and usually departure runways) have non-parallel headings, and Parallel Ap- 
proaches, where arrivals (and usually departures) use parallel runways. In gen- 
eral, Parallel Approaches are mandatory when operating conditions are below 800- 
foot ceiling and 2 miles visibility. They may also be made when wind velocity and 
direction dictate. 

Based upon examination of runway utilization patterns it is clear that 
Configuration 1 is the predominant runway configuration in the East Arrivals mode 
and the most popular configuration in general. For the West Arrivals mode there 
is no similarly predominant configuration. However, Configuration 6 would appear 
to be the most popular. Under reduced visibility conditions the tendency is for 
operation in Configuration 6 and in Configuration 7 under Category II conditions. 

In general, departures to or arrivals from the north and east of O'Hare 
are operated on the northside runways; those from the west, south, or southwest 
are operated on the southside runways. Occasionally, when operations in either 
the northside or southside are heavy due to short term concentrations of traffic to 
particular directions, some of the traffic for the more heavily loaded runways may 
be shifted to the other runways to even out the load. 

Traffic taxi flow patterns are essentially fixed by the runway configu- 
rations in use. In each configuration the traffic flows on the Inner and Outer cir- 
cular taxiways are in opposing directions. The directions in each configuration 
are essentially constrained by the unidirectional traffic flow over the Bridge from 
or onto the Outer. In general, the Outer is used for departures and the Inner for 
arrivals. However, the constraints of the direction of flow for the Inner and Outer 
may require mixing of traffic on either taxiway. While the taxi routes between the 



7-6 



Applicable Conditions 

[Ceiling (ft) /Visibility (mi)] 

and/or Winds (kts) 


CO 

■§ 

a 

m 

r-l 
V 

T3 

a 

CO 
CM 

O 

o 

00 
A 


<800/2 and/or >15 knots 
from NW 


<800/2 and/or >15 knots 
from W 


CO 

-t-> 

o 

a 

to 

V 

T3 

c 

CO 
CM 

O 
O 
00 
A 


CO 

•s 

a 

lO 

rH 
V 

C 
CO 

CM 

O 

o 

00 
A 


<800/2 (but above Cat. II) 
and/or >15 knots from SW 


»— I 
I— i 

>> 

S-i 

O 

bfl 
CD 
+-> 
CO 

U 


>800/2 (clear) and »15 
knots from E 


<800/2 and >15 knots from 
SW (if 9L not available) 


<800/2 and »15 knots from 

NE 


CO 
+-> 
O 

c 

lO 

V 

C 
cO 

CM 

O 

o 

00 
A 


Runway 

Operations 

(Approach) 

Mode 


*C0 
3 

Q 


"cd 
"co 

co 
Ph 


r-l 

0) 
"cO 

u 

CO 

Ph 


CO 

3 

Q 


•— i 

co 
Q 


"cO 

CO 

Ph 


•— H 

CD 
"cO 

;-. 

CO 
Ph 


*CD 

"cO 
U 

CO 

Ph 


"CD 

"cO 

U 

co 
Ph 




"cO 

3 

Q 


Supplemental 
Runways 


u 

< 
Ph 

> 


22R 

Hold Short 

27R 




22R 

Hold Short 

27R 


14L 

Hold Short 

22R 


22R 

Hold Short 

14L 












14L 

Hold Short 

22R 


< a 
° O 


CD 

eo 


CD 
CO 




















Primary Runways 

(Arrival/ 

Departure) 


J3 

-4-> 
U 

o 

525 


CM 

CO 

CM 


en 

CM 

CO 

CM 

CO 


Ph 

CO 
(N 


Ph* 

CM 

CM 
CM 


i-H 


Ci 

rH 


.J 
•J 

rH 


.J 
OS 


rH* 

rH 


.J 
►J 


22R/9L 
or 14L 


+-> 

3 
O 
CO 


<M 

CM 
CO 


J 

CM 

CM 

CO 


CM 

CO 

c- 

<M 


.J 
CM 
CM 
\ 

CM 


9R/9R 
or 14R 


Ph 
rH 


P4 

Ph 

rH 


PS 


Ph 


P5 

Ci 


■J 

CM 

P5 
T"H 


Airport Operating 

Mode (Arrivals 

From ) 


CO 

CO 

W 


H-> 
CO 

co 
W 


-4-> 
CO 

co 


H-» 
CO 

CO 


CO 

CD 


-4J 
CO 
CD 


CD 


■8 

CD 


CO 
CD 


CO 

CD 


T3 
CD 


Configu- 
ration 
Number 


i-H 


CM 


co 


"tf 


to 


CD 


t- 


00 


a* 


o 

rH 


rH 
rH 



7-7 




Figure 7-1. Current O'Hare Layout 



7-1 



terminals and runways are basically standard for the various runway configura- 
tions, alternate routings are applied by the Ground Controllers under certain con- 
ditions. These include congestion on the basic taxi route, establishment of sepa- 
rate departure queues when flights in a particular direction have in-trail separation 
restrictions, and routing of arrival aircraft to areas where they can hold for gates 
when they are not available for occupancy. 

The terminal configuration in which these gates are located is a series 
of alternating y^ and single corridor concourses. The current terminal 

capacity appears to be limited to approximately 100 aircraft "docking" spaces, in- 
cluding both nose-in and off-gate parking. However, the number of gates available 
for occupancy at any time is influenced by the types of aircraft equipment in use. 
Each of the major carriers and carriers with significant operations volumes at 
O'Hare have plans for utilization of their gates which are based in part on the 
space required by the types of aircraft scheduled. Typically, when the number of 
operations of large-bodied aircraft increases in a given period the number of 
gates available for all operations is effectively reduced. 

7.2.3 Future O'Hare ASTC System 

Several assumptions were made in defining the most probable future 
operating environment for O'Hare. The resulting projected environment includes 
the construction of the runway, taxiways, and terminal facilities illustrated in 
Figure 7-2. Also indicated in the figure is the projected use of the current Outer 
as the new Inner Circular and the combination of the 9R/27L parallel, 14R/32L 
parallel and new taxiway segment as the new Outer Circular. 



7-9 



PROPOSED 
RUNWAYS 




Figure 7-2. Projected Future Operating Environment at O'Hare 



7-10 



7. 3 CONCLUSIONS 

7. 3. 1 Capacity and Delay 

7. 3. 1. 1 Ramp Area Capacity and Delay 

1. It appears that the gate structure at O'Hare will and does support 

a traffic flow of 1. 6 operations /hour /gate. This is consistent with 
a 60 percent gate utilization (i. e. , 60 percent of the gates occupied 
at any one instant) and a mean turn-around time of 45 minutes. 
This translates to 150 operations/hour overall when considering 
O'Hare's 94 gates and is just in excess of their current quota. 

2. Approximately 90 percent of all arrivals encounter no delay inside 
the ramps. The remaining 10 percent experience holds with an 
average duration of about 1. 5 minutes primarily due to the gate 
not being ready, other pushbacks or service vehicle movement in 
the ramp area. 

3. Approximately 10 percent of the departures experience holds with 
an average duration of a minute. In most instances the holds can 
be attributed to near simultaneous departures or waits for arriv- 
als to dock. 

7. 3. 1. 2 Ground Control Area Delay 

1. Penalty box delay time does tend to increase with operations /hour. 
At 150 operations/hour the mean delay is estimated at about 18 
seconds per operation. This appears to be very low compared 
with runway queue delays (see paragraph 7. 3. 1. 3); however, at 
this operations rate the delay is concentrated in about 10 arrivals. 
This amounts to an average hold time of over four minutes per 
arrival held. 

2. Non-penalty box delay time tends to increase with operations/hour. 
Delays in the West Arrival mode are much higher (a mean delay of 
a minute at 140 operations /hour) due to runway crossing delays in 
that mode. Excluding runway crossing delays, the average delay 
per operation in either mode is about 20 seconds per aircraft. 
This is similar to the penalty box delay but remains distributed 
over a much larger number of aircraft. In addition, of the 20 sec- 
onds delay in the taxiways as much delay is associated with ramp 
congestion (again gate related problems) as competing taxiway 
traffic. On this basis, it does not appear that the basic taxiways 
are operating near saturation with the current quota (135 opera- 
tions/hour). 



7-11 



3. Very few arrival aircraft experience entrance waits before taxi- 
ing after runway turnoff. Thus, although during peak hours 
Ground channels can reach saturation (see paragraph 7. 3. 1. 4), 
its impact in delay is not currently showing up as substantial. 
Pilot interviews indicate they tend to taxi while waiting for 
clearance from Ground. This may be why so few waits were 
detected. 

4. Excessive runway crossing hold times (about a minute/aircraft) 
in the West mode in the 130 to 140 operations /hour region can be 
attributed to runway saturation with long departure queues on the 
outside of the arrival runway and the lack of controller incentive 
to hasten to cross the departures into a queue. In addition, creat- 
ing two departure queues on the inside of the arrival runway can 
facilitate moving aircraft into the departure queue in an advanta- 
geous sequence. 

7. 3. 1. 3 Local Control Area Capacity and Delay 

1. In good visibility conditions runway capacity estimates support a 
quota of 135 operations /hour evenly split between arrivals and 
departures, evenly split between the North and South sides and 
with a 20 percent mix of heavy aircraft. However, unbalanced 
operations (between North and South sides) such as those run in 
the West Arrival Mode cases herein put a severe load on the 
South side controller even with the 135 operations/hour quota. 
Since this tendency is natural at O'Hare as it is located in the 
North Central part of the country, even a quota of 135 opera- 
tions/hour is ambitious. In addition, an increase in heavy traf- 
fic should bring a corresponding reduction in the quota. 

2. The estimate for capacity improvements which could be achieved 
in good visibility conditions by assisting the controller in getting 
departures out in tight inter-arrival spaces is just over 10 per- 
cent. This amounts to about five percent of the total operations 
and would lead to a quota of about 140 operations/hour. All of the 
improvement lies in the Near-Far, Far- Far and single runway 
configurations, an average improvement of over 25 percent. This 
would be very important at other airports with less favorable run- 
way configurations than O'Hare. 

3. Although the potential for increasing departure capacity in the 
current system is significant (i. e. , 10 percent at O'Hare and up 
to 25 percent at other airports), this potential will increase 
greatly with the deployment of Metering and Spacing. Metering 



7-12 



and Spacing will be designed to create tight inter-arrival spacings 
to increase the arrival rate. These are precisely the spacings in 
which the unassisted Local Controller has trouble getting off depar- 
tures. 

4. Since current operations rates can often exceed the current run- 
way capacity in good visibility conditions (i. e. , mean capacity 
over all configurations is 132 operations/hour, the quota is 135 
operations/hour), it would be expected that the delays would ex- 
ceed the standard 4- minute delay criteria for acceptable (unsatu- 
rated) service. The average delay is 6. 2 minutes in the East 
Arrival Mode and 7. minutes in the West Arrival Mode. 

5. When operating a single runway mixed mode in bad cab visibility 
conditions, a substantial reduction in capacity is experienced (i. e. , 
25 percent in total operations). Thus, in Category II at O'Hare 
with the two 14s operating an independent mixed operation, the 
capacity would be 86 operations/hour. The use of ASDE provides 
substantial improvement. With ASDE the two 14s have a capacity 
of 108 operations/hour. This is still well below quota and can re- 
sult in delays. If it currently tends to remain manageable at 
O'Hare it is because demand tends to become reduced under Cate- 
gory II conditions; several of the air carriers at O'Hare have not 
yet equipped their aircraft for these conditions. 

6. Most bad cab visibility operations are taken in the West Arrival 
Mode. For the two cases examined herein the delay /departure 
averaged 11. 6 minutes reflecting the lost capacity under poor cab 
visibility. 

7. 3. 1. 4 Controller Communications Channel Capacity 

1. Due to traffic fluctuations during an hour, if a 60 percent mean 
hourly communications loading limit is used to estimate channel 
capacity, it can be expected with about a 95 percent confidence 
factor that the channel will reach saturation (i. e. , 100 percent 
loading) for at least five minutes in the hour. This 60 percent is 
used as the criteria for capacity estimation in this section. 

2. The estimated channel capacity for Clearance Delivery is 66 depar- 
tures/hour. On an even mix of arrivals to departures this is con- 
sistent with the runway capacity and the current quota. Clearance 
Delivery is just at saturation with little room for growth. 



7-13 



3. The estimated channel capacity for Ground Control is dependent 
upon visibility conditions and ASDE usage. For the bad visibility 
cases examined in this section, ASDE was in use. In good visibil- 
ity conditions two channels (two Ground Controllers) can easily 
support a smooth operation. However, with the current quota 
(135 operations/hour), when traffic problems occur (which is not 
infrequently) due to weather, gate tie ups, or aircraft equipment 
problems in the taxiways, the Ground Control channel (s) can be 
expected to saturate. On this basis Ground Control is approach- 
ing saturation in good visibility conditions with little room for 
growth. 

In "bad visibility" conditions for Ground Control (i. e. , the con- 
trollers cannot see the airport surface) the weather conditions are 
severe, and the airport is usually operating the two 14s for arriv- 
als. In this mode with a smooth operation, two Ground channels 
(with the controllers using ASDE) can just support the single inde- 
pendent mixed operations capacity of the two runways (i. e. , about 
105 operations /hour). However, this is below the current quota 
and if operated for prolonged periods will cause traffic tie ups. 
In this situation Ground Control channels are in serious difficulties. 
On this basis Ground Control is currently operating in a saturated 
fashion in bad visibility conditions. 

4. The major reason for increased Ground Control channel loading in 
"bad visibility" is the controller's use of pilot position reports, 
even with ASDE in use. This category of communication goes from 
one percent to two percent of all communications in good visibility 
to 30 percent when the Ground Controller cannot see (i. e. , ap- 
proaching or in Category n condition). 

5. The estimated channel capacity for Local Control is dependent 
upon visibility conditions. In good visibility conditions the Local 
channels are well below saturation. The estimated capacity is 
195 operations /hour. In "bad visibility" conditions (i. e. , the 
controller cannot see the runways) a controller who delivers his 
messages in short terse commands will not saturate the channel. 
However, in two cases of the analysis, message rates were ob- 
served which would have led to channel saturation had the opera- 
tions rate been as high as 115 operations/hour. This would have 
handled just the two 14s as single independent mixed operations. 
For any operations rates in excess of that, short terse commands 
would be a requirement. 



7-14 



6. The major causes for increased Local Control channel loading in 
"bad visibility" are weather reports (RVR and visibility) and posi- 
tion reports (e. g. , lights in sight by the pilot). In the case of 
single runway mixed operations, position reports of arrivals com- 
mitted to turn off are important and have a substantial impact on 
channel loading. 

7. 3. 1. 5 Delay Summary and Airport Loading with Good Cab Visibility 

1. The delay /turnaround (i. e. , arrival and departure) is summarized 
in Table 7-2 as drawn from the preceding paragraph. It indicates 
that the vast majority of delay at O'Hare is due to runway limita- 
tions (75 per cent). Of the remaining surface delays only 15 per- 
cent (4 percent of all delay) is due to taxiway congestion. The re- 
mainder is either runway or ramp/gate related. 

2. To illustrate the total airport load at any time, Table 7-3 has been 
prepared. Each entry represents the average hourly occupancy of 
the cited areas based upon the flow values (operations /hour) and 
service times previously determined. The value of 4. 6 for the 
ramp areas, for example, is based upon 120 operations/hour and 

a mean service time of 137 seconds and is for the total ramp area, 
i. e. , sum of the eight ramp areas. The values shown for the Local 
Control area represent the airspace near the runway and include an 
allowance of 15 seconds after takeoff and 120 seconds prior to touch- 
down since aircraft are under surveillance and control as part of 
the runway control process. 

The last entry in this table provides an estimate of the total surface 
load and represents an addition of the individual load values. Inter- 
pretation of a total value of 21, for example, would lead to the con- 
clusion that, at any one instant of time, on the average 20 active 
aircraft, excluding those in departure queues, would be observed. 
Short term peak values of perhaps 26-29 would be expected for 
this case. The peaking effect is expected to be more important in 
the ramp and Ground Control areas where random entries take 
place; in the Local Control area, only a minimum amount of short 
term peaking is expected. 

It should be noted that two components of delay which have not been 
included in an analysis are those occurring at the gates prior to de- 
parture as well as the arrival delays instituted by Approach Con- 
trol or the Center due to airport congestion. 



7-15 



Table 7-2. Average Delay Summary in Good 
Visibility Conditions 





Average Delay 


Turnaround* 


Percent 


Area and Cause of Delay 


(seconds) 


Total 


Ramp Area Due to 


15 


3 


Ramp Congestion 






Penalty Box Due to 


36 


7 


Gate Unavailability 






Taxiways Due to 


20 


4 


Ramp Congestion 






Taxiways Due to 


20 


4 


Competing Traffic 






Runway Crossing 


40 


7 


Runway Departure Queue 


396 


75 


TOTAL 


528 


100 



♦Arrival and a Departure 



7-16 



Table 7-3. Summary of Aircraft Load (Density) 



Airport Operations Mode 





Arrivals 




Arrivals 




from East 




from West 


Ramp Areas 






4.6 




Ground Control Area 


6.6- 


■10.6 




7.6-15.4 




(7.1- 


■11. 7) 1 




(8. 2-16. 6) 1 


Local Control Area (130 Ops/Hr) 










Arrivals Q a = 36QQ 






2.2 2 




65 x 120 
Departures Q d = ^ 






2.2 3 




Total (Estimated Range) 


16 


- 21 




17 - 26 



NOTES 

1. Includes aircraft taxiing between ramp and cargo/hangar areas which 
comprise approximately 15 percent of the traffic handled by the Inbound 
Ground Position. 

2. Arrival Service Time of 120 seconds composed of 50 seconds R/W 
Occupancy plus 10 seconds turnoff plus approach time of 60 seconds. 

3. Departure Service Time of 120 seconds composed of 25 seconds while 
aircraft is at top of departure queue, 30 seconds taxi time, 50 seconds 
R/W Occupancy time, and 15 seconds for handoff. 



7-17 



7.3.2 System Effectiveness Assessment 

7. 3. 2. 1 Current System 

1. The mean delay for the good visibility periods examined was 4. 5 
minutes /operation. This is representative of an airport near or 
at capacity. The 4. 5 minutes represented about 40 percent of the 
total time the aircraft was on the airport surface being serviced 
by the ASTC system. 

2. While on the surface of the airport, the aircraft tend to expend 
fuel at the average rate of 8. 6 gallons /minute. On a yearly basis 
that amounts to about 60 million gallons or enough gasoline to sup- 
port all the cars, buses and trucks in nearby Peoria (population 
126, 000). The gasoline consumed by the 40 percent delays alone 
could satisfy nearly 10 percent of the needs of the District of Co- 
lumbia or the State of Vermont. 

3. While on the surface of the airport, the aircraft (and associated 
crew) tend to cost the airlines (and indirectly the riding public) 
$11. 23/minute. On a yearly basis that amounts to about 78 million 
dollars. The operating costs due to the delays alone amount to 
nearly 30 million dollars. 

4. On the average, one minute of aircraft delay amounts to almost 
one man hour of passenger delay. On a yearly basis, this amounts 
to 220 man years of passenger time spent holding on the surface of 
the airport. 

5. Out of an estimated 1500 total operations observed via analysis of 
time lapse ASDE film, 11 potentially hazardous situations occurred 
(nearly one percent). These situations are due to the pressure of 
demand at or in some instances in excess of capacity (e.g. , forced 
to single runway mixed operations by weather). 

7. 3. 2. 2 Future Airport Configuration 

1. The new runways (9L/27R and 4L/22R) can streamline the taxi- 
way operation and give longer potential rollout safety to aircraft 
but if operated in lieu of the current runways will not increase air- 
port capacity. 

2. The new international terminal will increase the gate capacity and 
probably reduce gate delays (assuming no increase in operations). 



7-1! 



The benefits would be at the expense of increased taxi times, 
runway crossing holds and controller workload to perform run- 
way crossings. The extent of these increases was not estimated. 

3. The new general aviation facility will have costs and benefits simi- 
lar to those of the new international terminal. 

4. The new proposed use of the current outer as a new inner and the 
current 27L/9R, 14R/32L parallel taxiways as part of a new outer 
should nearly eliminate the need to use the current inner taxiway. 
This would facilitate dealing with ramp congestion, gate limita- 
tions, one-way flow between fingers and pushbacks from the finger 
ends. However, these benefits may be at the expense of safety. 
Conflicts between arrivals and traffic on the parallels and con- 
flicts caused by aircraft taxiing on a parallel accidentally missing 
the turn at the parallel to an active runway and blundering out onto 
the runway will both be emphasized by the proposed change. Con- 
sideration should be given to this, especially at night and/or in 
bad weather. 



7-19 



7.3.3 General Observations 

1. The Inbound Ground position is the busiest position in the tower 
and yet he has the least information with which to work regarding 
the number or nature of the aircraft he will be required to handle 
over the next few minutes. In addition, this position is likely to 
experience communications workload (and channel) saturation well 
before the Outbound Ground and Local Control positions. 

2. The most serious potentially hazardous incidents observed are re- 
lated to the close sequencing of the departure and arrival operation 
on the same runway and the close sequencing of arrivals on cross- 
ing runways by Local Control. As traffic increases, the require- 
ment for higher usage rates to meet the demand is likely to in- 
crease the potential for such events. 

3. The movements of aircraft within the ramp areas, particularly 
the area between the j and linear concourses, have a definite 
impact on the operations of the Outbound Ground and Inbound 
Ground. Delays to aircraft movements because of pushbacks and 
competition for taxi between outbound and incoming aircraft cause 
additional workload for these positions in having to monitor these 
movements and adjust the traffic flow. As traffic increases the 
significance of this problem will also increase. 

4. Peaking of flight operations around specific hours of the day is 
characteristic of O'Hare's operation; that is, it is predominantly 
a through airport with the airlines planning based on maximum 
interconnection of flights. This is the primary cause in gate de- 
lays for arriving aircraft during good operating conditions and 
impacts most heavily on the operations of the Inbound Ground 
position. Increases in traffic volumes and operations under poor 
weather conditions in which flight schedules are generally dis- 
rupted will only aggravate the problem. 

5. Under low visibility conditions there is a potential for traffic flow- 
ing on the combination of the 9R/27L and 14R/32L parallel to miss 
the transition between the parallels and wander out to the active 
runways even in the current operating environment. Discussions 
with airport management and ATCT personnel indicated that such 
events have occurred in the past. If the traffic flowing along these 
parallels increased in the future by their use as part of a new 
Outer, the potential for such occurrences would increase. 



7-20 



6. The analysis indicates a general tendency for a proportionately 
higher number of holds: (a) in the area of the intersections of 
the New Scenic and Old Scenic with the Outer and the Old Scenic 
and Inner in the West Arrivals mode; (b) at the intersection of 
the Outer and T-3 in both operating modes; (c) on the Inner and 
Outer opposite the ramp areas between the F and G concourses 
and the G and H concourses; (d) at the intersection of the stub 
and North-South taxiways with the Outer. Instances (a) and (b) 
above appear to be related to the merging of traffic flows in these 
areas while instances (c) and (d) appear to be related to ramp 
congestion/gate delays. 



7-21 



7. 3. 4 Summary 

O'Hare is currently operating at or near capacity in the area of gates, 
runways, Local Control, Ground Control and Clearance Delivery. Delays in the 
taxiways which do not result from ramp or runway related problems are relatively 
minor. Planned airport layout changes can streamline the taxi flows reducing the 
impact of ramp delays and departure queues and can furnish added gate capacity. 
However, overall capacity due to runway/Local Control limitations will not in- 
crease. If anything, due to North side/South side traffic imbalance and the in- 
crease of heavy aircraft traffic, overall capacity will drop. Only new ATC equip- 
ments and/or procedures can increase the overall capacity of the airport. 

While operating at or near capacity, very large costs are being ex- 
pended — costs in fuel, money (airlines and riding public), lost time to the passen- 
gers, and risk of accident. Increased capacity will provide the option of increas- 
ing the traffic volume to satisfy projected demand with those same costs or serving 
the same traffic volume with potential cost savings. If new ATC equipments and/ 
or procedures can increase the capacity, it appears that there is a substantial 
potential in cost saving to aim at. 



7-22 



7.4 R EC OMME NDA TIONS 

The significant recommendations that can be made on the basis of the 
study findings are primarily related to the objectives and features that should be 
provided in an improved future ASTC system for O'Hare. These include: 

1. Automated intersection control equipments could be very usefully 
applied to the taxiway intersections in the areas northwest of the 
terminal (opposite the ramp area between Butler and the Interna- 
tional concourse) and at the Outer/T-3 intersection. 

2. Any future ASTC system should emphasize relief of the Clearance 
Delivery and Inbound Ground positions through more automated 
transmission of flight plan and taxi clearances and by providing 
more information regarding imminent arrivals to Inbound Ground. 
More automated transmission of taxi clearance would also signifi- 
cantly relieve the workload of the Outbound Ground position. 

3. Any future ASTC should provide for improved coordination of air- 
line gate operations and the operations of the Ground Control posi- 
tions to reduce ramp area delays as well as controller workload 
resulting from ramp congestion. 

4. Future ASTC systems should attempt to provide improved informa- 
tion to Local Control positions for use in sequencing runway opera- 
tions as well as reducing the number of potentially hazardous inci- 
dents related to sequencing of arrivals and departures on the same 
runways and arrivals on crossing runways. 

With respect to near term improvements in the current ASTC system 
a few recommendations may be made: 

1. As traffic volume increases, relief of the Clearance Delivery work- 
load and frequency saturation can be accomplished by a dual- 
position operation in peak traffic periods; that is, one controller 
(pre-tax!) would be responsible exclusively for delivery of flight 
plan clearances to air carrier traffic and the second controller 
(taxi) would be responsible for aircraft that are ready to taxi, 
including IFR and VFR flight plan clearances to general aviation 
traffic. 



7-23 



2. Consideration should be given to the feasibility of the ARTS com- 
puter generating minimal flight strips for (or at the minimum a 
sequenced list of) aircraft estimated to be landing on the active 
arrival runways in the next 5-minute period to increase the in- 
formation available to Inbound Ground for control of these air- 
craft. 

3. Red (center-line light type) stop bars or warning signs should be 
installed at the intersections of the 9R/27L and 14R/32L parallels 
to prevent aircraft from erroneously taxiing out onto the active 
runways during low visibility conditions. Installation on the 9R/ 
27L parallel should be east of the intersection and on the 14R/32L 
parallel south of the intersection. While this installation would 
be desirable for the current environment it would be mandatory 
in the future if these parallels became part of a new Outer Circu- 
lar. 

4. The airlines should attempt to develop some procedure that would 
keep the gate controller advised of whether aircraft departures 
from the gates will be significantly delayed. This information 
would be used in advising pilots of arriving flights of the situation 
in order that they may be able to communicate this information to 
Inbound Ground. This improvement would be most important dur- 
ing the peak traffic schedule periods. 



7-24 



SECTION 8 - REFERENCES 



1. Chicago O'Hare Airport Air Traffic Control Tower Training Manual. 

2. Chicago - O'Hare International Airport, Airport Operations Manual Volume I - 
Operations Manual, November 1972. 

3. Chicago - O'Hare International Airport, Airport Operations Manual Volume II - 
Emergency Plan, November 1972. 

4. Federal Aviation Administration, National Aviation Facilities Experimental 
Center, Catalog of ATC Communications and Controller Activity Data, 
September 1971. 

5. Federal Aviation Administration, Systems Research and Development Service, 
Climatological Summaries, Visibilities Below 1/2 Mile and Ceilings Below 
200 Feet. Volume 8, Chicago, Illinois O'Hare International Airport, SRDS 
Report No. RD-69-22 Vol. 8, June 1969. 

6. Northern Research and Engineering Corporation, The Potential Impact of 
Emissions Upon Air Quality, Report No. 1167-1, December 1971. 

7. Aviation Daily, Airline Statistical Annual, 1973. 

8. Federal Aviation Administration, Systems Research and Development Service, 
Airport Surface Traffic Control Systems Deployment Analysis, Report No. 
FAA-RD-74-6, January 1974. 



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GAYLORD