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Full text of "Vortex advisory system simulation of Chicago O'Hare International Airport"

depart Hi. FAA-RD-78-76 







VORTEX ADVISORY SYSTEM SIMULATION OF 
CHICAGO O'HARE INTERNATIONAL AIRPORT 



Barry E. Keeffe 



TRAN 

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514 vvi3 

V)57 




S **TK O* h 



TRANSPORTATION LIBRARY 

NOV 9 197R 
NORTHWESTERN UNIVERSITY 



JULY 1978 
FINAL REPORT 



Document is available to the U.S. public through 

the National Technical Information Service, 

Springfield, Virginia 22161. 



Prepared for 
U.S. DEPARTMENT OF TRANSPORTATION 

FEDERAL AVIATION ADMINISTRATION 

Systems Research & Development Service 

Washington, D.C. 20590 



Tl_ 574.W3 V957 



3 5556 021 008 958 



NOTICE 



The United States Government does not endorse products 
or manufacturers. Trade or manufacturer's names appear 
herein solely because they are considered essential to 
the object of this report. 



Technical Report Documentation Pag 



1. Report No. 

-FAA-RD-78-76 



2. Government Accession No. 



4. Title and Subtitle 

L VORTEX ADVISORY SYSTEM SIMULATION OF 
CHICAGO O'HARE INTERNATIONAL AIRPORT 



7. Author's) 



Barry E. Keeffe 



3. Recipient's Cotolog No. 



5. Report Date 

July 1978 



6. Performing Organization Code 



8. Performing Organization Report No. 



FAA-NA-78-12 



9. Performing Organization Name and Address 

.^Federal Aviation Administration 

-National Aviation Facilities Experimental Center 
Atlantic City, New Jersey 08405 



10. Work Unit No. (TRAIS) 



11. Contract or Grant No. 

084-451-500 



12. Sponsoring Agency Name and Address 

U.S. Department of Transportation 
Federal Aviation Administration 
Systems Research and Development Service 
Washington, D.C. 20590 



13. Type of Report and Period Covered 

Final 
March 1977 to June 1977 



14. Sponsoring Agency Code 



15. Supplementary Notes 



16. Abstract 

This report evaluates, in simulation, the procedural implications of the Vortex 
Advisory System (VAS) on the Chicago O'Hare terminal air traffic control environ- 
ment. It also attempts to demonstrate any cost benefits/capacity gains which may 
accrue using reduced VAS aircraft separation criteria on the final approach course 
based upon meteorological assurance of vortex dissipation. Utilizing the National 
Aviation Facilities Experimental Center (NAFEC) Digital Simulation Facility (DSF) , 
a real-time simulation of the Chicago O'Hare International Airport airside opera- 
tions was conducted between March 28 and June 24, 1977. There were 105 data runs 
of 1 hour and 20 minutes duration completed during this period. Two favored runway 
configurations were identified (based on O'Hare usage data during 1977) and exer- 
cised in the VAS green, standard red, and transition conditions; that is, the 
green condition reducing separation between all aircraft classes to 3 nmi, the red 
condition maintaining 3-, 4-, 5-, and 6-nmi standard heavy- jet separation; and the 
transition between the two conditions under instantaneous and 5-minute warning 
transitions were evaluated. Three vortex clear zones were exercised: middle marker 
to touchdown, outer marker to touchdown and 20-nmi fix to touchdown. Test results 
indicate that (1) no procedural implications emerged which would deter the implemen- 
tation of VAS at Chicago O'Hare Airport, and (2) arrival rate increases are suffi- 
cient to support previous cost/benefit analysis studies conducted by Landrum and 
Brown Aviation Consultants and Mitre Corporation. 



17. Key Words 

Vortex Advisory System 
Airport Safety 
Flight Safety 
Wind Dissipation 



19. Security Classif. (of this report) 

Unclassified 



18. Distribution Statement 

Document is available to the public 
through the National Technical 
Information Service, Springfield, 
Virginia 22151 



20. Security Classif. (of this page) 

Unclassified 



21. No. of Poges 

24 



22. Price 



Fo«n DOT F 1700.7 (8-72) 



Reproduction of completed page authorized 



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TABLE OF CONTENTS 

Page 

INTRODUCTION 1 

Purpose 1 

Background 1 

System Feasibility 2 

System Description 2 

SYSTEM EVALUATION 5 

Details of Approach 5 

Test Measures 6 

RESULTS 7 

Series I 7 

Series II 8 

Series III 10 

Series IV 11 

SUMMARY OF RESULTS 13 

CONCLUSIONS 15 

REFERENCES 16 

APPENDICES 

A - Comparison Table of Arrival Aircraft Classes and Pairing Mix 

B - Speed Profiles (knots) at Threshold and Outer Marker for 
Small, Heavy, and Large Weight Classes 

C - Predicted Gains (in Arrivals per Hour) 



xxi 



LIST OF TABLES 

Table Page 

1 Average Arrival Operations per Hour in Red Condition 8 

2 Baseline (Red Condition) Percentage of Aircraft Pairs and 9 

Median Separation 

3 Average Number of Arrivals per Hour in Green Condition 9 

4 Comparison of Percentage of Aircraft Pairs and Median 10 

Pair Separation for VAS Green and Baseline Red Conditions 

5 Average Number of Arrivals per Hour in Green/Red Condition 11 

6 Average Number of Arrivals per Hour for Runway Changeover 12 

Hour 

7 Controller Communications 13 

8 Controller ATC Activities 14 

9 Separation Criteria Violations for Total Aircraft Pairs 14 



IV 



INTRODUCTION 



PURPOSE . 

The purpose of this report is to summarize the results of a National Aviation 
Facilities Experimental Center (NAFEC) simulation of the Vortex Advisory 
System (VAS) . The simulation was designed to determine the procedural impli- 
cations of the VAS on the air traffic control (ATC) system within the Chicago 
O'Hare International Airport terminal environment. 

BACKGROUND . 

The introduction of wide-bodied jet aircraft, coupled with an increase in 
airport total operations, has given added significance to the aircraft wake 
vortex problem. The trailing wake vortices from a large aircraft can pose a 
serious hazard to smaller aircraft. The smaller aircraft encountering one of 
these wake vortices may be subjected to extreme rolling movements which can 
result in a loss of control, a loss of altitude, and possibly structural 
damage. At present, to reduce the possibility of this occurring, and thus 
maintain safety standards, separation between selected aircraft pairs has been 
increased from previous standards. This, of course, has resulted in a reduc- 
tion of operations below theoretical airport capacity. 

Until recently, limited knowledge concerning the characteristics and behavior 
of wake vortices mandated these larger separation standards. Studies and 
tests sponsored by the Federal Aviation Administration (FAA) have shown that 
vortex characteristics are established initially by the aircraft's gross 
weight, airspeed, flight configuration, and wingspan. Subsequently, it has 
been found that vortex characteristics are altered, and eventually dominated, 
by interactions between the vortices and the ambient atmosphere. This was 
determined from analysis of over 50,000 vortex tracks entered into the data 
base at Transportation Systems Center (TSC) , and it has led directly to the 
development of the VAS, a system designed to expedite ATC operations while 
exercising vortex avoidance. 

It has been established that the concept of wake vortex avoidance is based 
on three considerations supported by available wake turbulence data. 
These are: 

1. For a large percentage of the time, prevalent meteorological conditions 
exist which cause vortices to move quickly off the flightpath, or decay rapidly 
in the approach corridor, thus posing no hazard to aircraft following on the 
same flightpath. 

2. The duration, intensity, and movement of vortices can be reliably predicted 
if adequate knowledge of existing meteorological conditions is obtained. 

3. Vortices can be detected and tracked at selected points along the approach 
or departure paths through the use of existing sensing techniques. 



From these considerations, it became evident that airport operations are need- 
lessly limited by using larger separation standards for wake vortex avoidance 
when no real hazard exists, since vortex behavior can be predicted with 
sufficient accuracy to permit selection of appropriate smaller separation 
standards. 

From analysis of the extensive data collected on vortex behavior as a function 
of meteorological conditions, a wind criterion has been developed and tested 
to determine when aircraft separations can be uniformly reduced to 3 nautical 
miles (nmi) between all aircraft types, rather than the 3-, 4-, 5-, and 6-nmi 
separations currently required between approach aircraft pairs of various 
weight differentials. The VAS was designed to take advantage of this wind 
criterion. The VAS measures wind magnitude and direction (with respect to each 
runway heading) for comparison with the wind criterion. The comparison indi- 
cates, via a simple red/green light display in the ATC room, when aircraft 
separations can be safely reduced to 3 nmi for all traffic. 

SYSTEM FEASIBILITY . 

Chicago's O'Hare International Airport was selected for prior system feasibility 
tests based on the following criteria: adequate available real estate for the 
VAS equipment, operations near saturation during visual flight rules (VFR) and/ 
or instrument flight rules (IFR) conditions, and a significant percentage of 
large aircraft in the traffic mix. The VAS was feasibility tested at O'Hare 
by using an instrumentation system to measure vortex positions and ambient 
meteorological conditions as a function of time, and correlate these with the 
VAS separation criteria. The amount of time that the VAS indicated that reduced 
separations could be used was evaluated to determine how many additional opera- 
tions could be accommodated if reduced separations were used and the dollar 
saving which would accrue from reduced delays. This evaluation was performed 
considering all the usable combinations of approach and landing runway scenarios 
under both VFR and IFR weather conditions. Results from this previous study 
statistically validated that the system could accurately determine when 3-nmi 
separation could be used for all aircraft types, and that the criterion 
algorithm contained adequate safety margins for all meteorological and vortex 
conditions. 

SYSTEM DESCRIPTION . 

METEOROLOGICAL TOWERS . The VAS incorporates a network of instrumented meteor- 
ological towers positioned to measure the wind in each operating airport corri- 
dor. A network of towers is required since variations in atmospheric condi- 
tions preclude the use of a single, centrally located sensor for measuring 
wind in individual approach corridors. Each tower is instrumented with three 
sensors for wind magnitude and direction, one at the 50-foot level and the 
other two at the 47-foot level. The 47- foot-level sensors are mounted on 
opposite sides of the tower to provide a measurement undisturbed by tower 
shadowing. All sensor and communication electronics at each tower are housed 
in an environmental enclosure. The towers are free-standing on a concrete 
base and are marked and lighted. 



TOWER DATA COMMUNICATION SUBSYSTEM . Transmission of the data from the towers 
to the centrally located processors is accomplished with standard hardware. 
A multiplexer successively samples the sensor outputs and converts them to 
digital words which are serialized and transmitted over standard existing FAA 
control lines to a central facility. Receivers reconvert the data to a 
parallel format for input to a microprocessor. The sampling rate is 160 words 
per second, each word being 16 bits in length. 

METEOROLOGICAL DATA PREPROCESSING . Individual microprocessors are used to 
process the data from each meteorological tower. The microprocessors contain 
8k bits of read-only memory and 2k bits of random-access memory. Each micro- 
processor is packaged on a single plug-in board. The microprocessors sample 
the meteorological data output from each receiver at a sample interval rate 
of two samples per second. The sampled wind magnitude (R) and wind direction 
(9) are computed as a 64-second (128-sample) running average (R and 0). 

The wind magnitude and direction readings from the three sensors on each tower 
are compared after each sampling interval. A sensor-failure bit is generated 
if the magnitude of any sensor differs by more than 3 knots or if the direction 
of any sensor differs by more than 10°. Normally, the 50-foot-level sensor 
data are used for the VAS algorithm. If the 50-foot-level sensor fails, the 
microprocessor switches to a 47-foot- level sensor and selects the sensor which 
is not in the wind shadow of the tower. Failure of two sensors to agree 
terminates all data output from that tower. Upon detection of a failure, a 
failure word is generated identifying the sensor or tower which has been shut 
down. 

The microprocessors also calculate the recommended aircraft landing separations 
for each runway based on the windspeed and wind direction measured by the 
instrumented tower. As shown in figure 1, an elliptical VAS algorithm is used 
which includes a buffer or "transition zone." The major and minor axes are 
12.5 and 5.5 knots for the inner ellipse, and 14.5 and 7.5 knots for the outer 
ellipse. The transition zone is designed to preclude rapid oscillations between 
standard (red) and reduced separation (green) conditions, thus avoiding an 
unmanageable controller workload while still insuring the required level of 
safety from vortex effects. 

The criteria for separation and for changing separation from one condition to 
another are: 

(a) If the wind vector (R, e) is inside the inner ellipse, the condition 
is red, and standard 3-4-5-6-nmi separation applies. 

(b) If the wind vector (R, 0) is outside the outer ellipse, the green 
condition exists, and all aircraft can be separated by 3 nmi. 

(c) If the condition is red and the wind is increasing, the requirement 
exists for the wind vector to be outside the outer ellipse for 

64 seconds before the green condition is indicated. 

(d) If the condition is green and the wind vector enters the inner 
ellipse region, a change to the red condition takes place immediately. 

3 



t 



14% KNOTS 




TRANSITION ZONE 



7% KNOTS 



R = WINDSPEED 

S = WIND DIRECTION 



78-12-1 



FIGURE 1. VAS ALGORITHM WIND CRITERION 



SYSTEM EVALUATION 



DETAILS OF APPROACH . 

LABORATORY REQUIREMENTS . 

General. The Digital Simulation Facility (DSF) ATC laboratory at NAFEC 
was configured to simulate an Automated Radar Terminal System (ARTS III) 
terminal ATC system. Two-way radio communication between controllers and 
pilots as well as coordination lines between control positions were simulated 
using the Bell 300 communication system. 

Controller Positions . Two arrival, one departure, one tower/monitor, and 
two enroute feeder positions were established. The arrival positions displayed 
video for a radius of 35 nmi, the tower and departure positions displayed video 
for a 20-nmi radius, and the two enroute positions displayed a ■ 50-nmi radius. 
Keyboard functions were available at all positions. 

Simulator Pilot Positions . Eighteen simulator pilot positions were 
required. Controlled aircraft were assigned to all 18 positions. Keyboard 
functions were available at all pilot consoles. 

Geography . The area simulated was the Chicago O'Hare International 
Airport Approach Control Area, with parallel approaches to the southeast on 
runways 14L and 14R, dual approaches to the west and northwest on runways 
27R and 32L, and parallel approaches to the east on runways 9L and 9R. All 
runways had ILS capability. 

Departure configurations were to the east off runways 9L and 9R, to the 
west and northwest off runways 27L and 32R, and to the northeast off runway 
4L and 4R. 

Traffic flows were in accordance with procedures presently employed at 
Chicago O'Hare International Airport as described in the Chicago ARTCC/O'Hare 
Tower Letter of Agreement, dated July 28, 1976, and O'Hare Tower Order 7110. 6D, 
entitled "Chicago Approach Control - Radar." 

The field elevation for the airport was 700 feet mean sea level. The 
video map depicted airport runways, boundaries, fixes, navigation aids 
(NAVAID's), and descent areas. 

Sigma V Computer . The Sigma V was used in conjunction with the graphic 
digitizer to develop video maps and flight plans. It was utilized on a daily 
basis for conduct of the simulation and data reduction and analysis. 

PROCEDURES . 

Controller Procedures . Standard ATC procedures as provided for in 
FAA Handbook 7110.65 were applied. Detailed controller instructions on 
Chicago O'Hare arrival and departure procedures were defined in a handout prior 



to start of simulation. Those special controller procedures required when 
VAS was present in the system (i.e., reduced aircraft separation standards) 
were described for all controller personnel in briefings prior to simulation. 

Simulator Pilot Procedure . Prior to the start of dynamic simulation, all 
simulator pilots received a detailed briefing on the purpose and objectives of 
the simulation. They were briefed on detailed pilot procedures and their 
expected inputs. 

TRAFFIC SAMPLES . The traffic samples, representative of O'Hare traffic, were 
all controlled IFR aircraft. Traffic density was 150 aircraft per hour (9.0 
arrival, 60 departure). The arrival aircraft were a mix of large (70. percent), 
heavy (20 percent), and small (10 percent). 

TEST MEASURES . 

A complete history of each simulated flight was recorded on magnetic tape. 
During each update cycle, elements of track position, track movement, flight 
status, pilot keyboard messages, display tables, and communication line usage 
were recorded. These data were analyzed utilizing offline data reduction 
programs to provide quantitative measurements of system performance, capacity, 
separation, and workload. 

ATC SYSTEM PERFORMANCE MEASURES . Hourly operation rates were obtained for 
(1) arrivals, (2) departures, and (3) combined arrivals/departures. Average 
time in system for a completed arrival flight (in minutes) was obtained for 
each 1-hour data period. 

Total path-stretch delay (in minutes) was ascertained. This measure is the 
difference between the nominal and actual flight times of completed arrivals in 
the 1-hour data period. 

Terminal approach path separation was measured every 20 seconds between aircraft 
on the final approach for the following vortex clear zones: (1) threshold to 
middle marker (MM), (2) threshold to outer marker (OM) , and (3) threshold to 
20-nmi point on localizer. 

The number of missed approaches under green and red conditions were determined. 
The number of separation criteria violations were analyzed to determine (1) 
total number of criteria violations, (2) aircraft in violation by controller 
position, (3) time of violation, and (4) degree of separation criteria vio- 
lation. 

CONTROLLER WORKLOAD MEASURES . The following measures were taken: 

1. Number of aircraft controlled per control position during 1-hour data 
period. 

2. Average number of radar vectors issued per control position per aircraft. 

3. Average number of altitude changes issued per control position per aircraft 
controlled during the data hour. 






4. Average number of speed changes issued per control position per aircraft 
controlled during the data hour. 

5. Average number of control messages per control position per aircraft 
controlled during the data hour. 

6. Total aircraft time per control position of aircraft controlled during 
the data hour. 

7. Average duration of radio communications (controller to pilot) made per 
aircraft controlled per control position. 

VAS IMPACT MEASURES . Additional data reduction and analysis were required to 
characterize quantitatively VAS activities in terms of the following: 

a. Arrival rates 

b. Operational procedures 

c. Configuration changes 

d. Separation standards 

e. Flight deviations caused by VAS system changes and the effect on 
traffic flow. 



RESULTS 



SERIES I . 

Series I testing consisted of heavy-density (90 arrivals, 60 departures) IFR 
traffic. These tests provided the baseline data on airport operations using 
present-day (red condition) separation minima and control techniques (speed 
and spacing criteria) as employed at the Chicago O'Hare Airport during the 
final approach phase of a flight. Baseline data were obtained after 18 simu- 
lation runs. 

To insure validity, the baseline data were measured against a statistical 
analysis of 0' Hare's Performance Measurement System (PMS) Summary Sheets for 
the year 1977. The results are given in table 1. The baseline data show that 
the simulation operations compared favorably with the PMS of present-day O'Hare 
operations. 

Additionally, the baseline data were broken down by aircraft class, numbers of 
pairs (heavy-small, heavy-large, etc.), and the median separations employed. 

Aircraft were categorized into three classes based on weight criteria: 

Heavy - over 300,000 pounds gross weight at takeoff 

Large - between 12,500 pounds and 300,000 pounds gross weight at takeoff 

Small - up to 12,500 pounds gross weight at takeoff 



TABLE 1. AVERAGE ARRIVAL OPERATIONS PER HOUR IN RED CONDITION 

Arrival Runway Configuration Simulation Baseline PMS Analysis 

Runways 14L and 14R 71 70.1 

Runways 27R and 32L 69.5 (peak periods of 

Combined average, runways 14L-14R and 70.3 density, all 

32L-27R configurations) 

The mix of aircraft pairs studied was identified by separation minima required 
between various classes: 

Lead Aircraft - Trail Aircraft Separation Required 

Heavy - small 6 nmi 

Heavy - large 5 nmi 

Heavy - heavy 4 nmi 

Large - small 4 nmi 

All others* 3 nmi 

* (Large-large, small-large, small-small, small-heavy, and large-heavy) 

The median separation distances were measured both inside and outside the outer 
marker on the final approach defined as follows: 

Inside outer marker : the distance between lead aircraft and trailing aircraft 
based on lead aircraft last reported data position inside the outer marker 
prior to touchdown. 

Outside outer marker : the distance between lead aircraft and trailing aircraft 
based on lead aircraft last reported data position prior to passing outer 
marker inbound. 

The baseline data descriptive statistics are given in table 2. 

SERIES II . 

Series II testing consisted of heavy-density (90 arrivals, 60 departures) IFR 
traffic. These tests provided data on the procedural implications or impact 
of VAS reduced separation on the ATC system and comparison data on arrival 
operations gains or losses when weighed against baseline capacity data. The 
tests were conducted using the VAS in the green mode with reduced separation 
criteria employed within three distinct vortex clear zones on the final 
approach (threshold to MM, threshold to OM, and threshold to 20-nmi fix on 
localizer. The vortex clear zone is the portion of final approach corridor 
over which the VAS predicts vortex dispersion within time parameters consonant 
with a 3-nmi minimum aircraft separaton criterion. A total of 45 runs was 
accomplished. Table 3 indicates the arrival rates that were achieved. 



TABLE 2. BASELINE (RED-CONDITION) PERCENTAGE OF AIRCRAFT PAIRS AND MEDIAN 
SEPARATION 



Inside OM 

Lead a/c - Trail a/c 

Heavy-small 
Heavy- large 
Heavy-heavy 
Large- small 
All others 



Percent of Total Pairs Median Separation (nmi) 



2 

16 

4 

7 

71 



5.6 
5.0 
4.1 
4.2 
3.7 



Outside OM 

Lead a/c - Trail a/c 



Heavy-small 
Heavy-large 
Heavy-heavy 
Large- small 
All others 



2 

16 

3 

4 

75 



6.3 
5.6 

4.5 
4.8 
4.3 



TABLE 3. AVERAGE NUMBER OF ARRIVALS PER HOUR IN GREEN CONDITION 



Arrival 












Runway 


(Red) 








Threshold- 


Configuration 


Baseline 
71 


Threshold- 
72.6 


-MM 


Threshold-OM 
71.7 


20 nmi 


Runways 14L-14R 


72.7 


Runways 27R-32L 


69.5 


73.0 




74.6 


80.0 


Combined average, 


70.3 


72.8 




73.2 


76.4 


runways 14L-14R and 












27R-32L 













From table 3 it can be seen that increases in hourly operations were effected 
in every case for green verses red (baseline) conditions. This is supportive 
of MITRE and TSC predictions in this area. An analysis of types and numbers 
of pairs and the median separation employed inside and outside the OM under 
the green condition are presented in table 4. 



No procedural changes were required which would Impact the ATC system or deter 
the implementation of VAS reduced separation at Chicago O'Hare Airport during 
this test series. 



TABLE 4. COMPARISON OF PERCENTAGE OF AIRCRAFT PAIRS AND MEDIAN PAIR SEPARATION 
FOR VAS GREEN AND BASELINE RED CONDITIONS 



Lead-Trail Aircraft 



Inside OM 
Percent of Total Pairs 

Threshold to 
Base- 
line MM OM 20 nmi 



Median Separation (nmi) 

Threshold to 
Base- 
line MM OM 20 nmi 



Heavy- small 


2 


1 


2 


3 


5.6 


4.4 


3.9 


3.3 


Heavy-large 


16 


14 


15 


15 


5.0 


4.5 


4.0 


3.7 


Heavy-heavy 


4 


4 


5 


5 


4.1 


3.6 


3.7 


3.3 


Large-small 


7 


6 


8 


2 


4.2 


3.9 


3.9 


3.6 


All others 


71 


75 


70 
Out 


75 
side OM 


3.7 


3.4 


3.7 


3.6 


Heavy-small 


2 


1 


2 


2 


6.3 


5.4 


4.8 


4.0 


Heavy-large 


16 


15 


16 


14 


5.6 


5.1 


4.7 


4.3 


Heavy-heavy 


3 


6 


5 


4 


4.5 


4.4 


4.3 


4.1 


Large-small 


4 


7 


7 


7 


4.8 


4.7 


4.5 


4.3 


All others 


75 


71 


70 


73 


4.3 


4.1 


4.5 


4.3 



Results show that the percentage of total pairs remained fairly constant under 
all categories, indicating a consistency of traffic mix for comparison purposes 
(appendix A). Median separations show that sufficient separation reductions 
were obtained under green conditions to support predicted operational gains, 
and that the VAS reduced separation operation does not affect separation 
closure rates between OM and touchdown (appendix B) . 

SERIES III . 

Series III testing consisted of heavy-density (90 arrivals, 60 departures) IFR 
traffic. This series of tests was designed to investigate operational gains 
or losses and procedural implications on the ATC system when transitioning 
from one VAS condition to another under IFR conditions (table 5). (A total of 
29 runs was accomplished) . Tests were conducted with two vortex clear zones 
on the final approach path (threshold to OM and threshold to 20-nmi fix) under 
two specific operational parameters. 

1. VAS transition from green to red instantaneously. 

2. VAS transition from green to red in 5 minutes 

As can be seen from table 5 for both the instantaneous and 5-minute transitions, 
the traffic mix at O'Hare, which is predominently of the large aircraft class 
(70 percent) with a relatively small mix of heavy-small pairs, precluded any 
major difficulties in transition from a 3-nmi separation standard a 3-, 4-, 5-, 
6-nmi separation standard. 



10 



TABLE 5. AVERAGE NUMBERS OF ARRIVALS PER HOUR IN GREEN/RED CONDITION 

Arrival Rate - Threshold to OM 

Arrival Runway Configuration Zero Transition 5-Minute Transition 

Runways 14L and 14R 71.0 70.5 

Runways 27R and 32L 72.7 73.3 

Combined average, runway 71.8 71.9 
14L-14R and 32L-27R 

Arrival Rate - Threshold to 20-nmi Fix 

Runways 14L and 14R 75.5 72.0 

Runways 27R and 32L 75.5 73.6 

Combined average, runway 14L-14R 75.5 72.8 
and 32L-27R 



During the 5-minute transition phase, no difficulty was experienced in tran- 
sitioning from one mode of operation to another. The trend during this phase 
was to employ the expanded separation early in the 5-minute transition period, 
effecting a general decrease in operations rate. 

During the zero or instantaneous transition phase in most cases, no difficulties 
were experienced or special action required, due to the traffic mix at time of 
transition (i.e., large-large, large-heavy, etc.) These pairs of traffic mix 
require the same separation (3-nmi) under both red and green conditions. Where 
a traffic mix of heavy-small or heavy-large aircraft (which requires 6- or 
5-nmi separation under a red condition) existed during the transition phase, 
the determining factor for controller action was the aircraft position on final 
approach. Beyond the outer marker, separation usually could be achieved prior 
to touchdown. Where it could not, a maximum of one missed approach per transi- 
tion was required. Inside outer marker, depending upon separation being 
employed, the trailing aircraft might be required to make a missed approach, 
a condition considered operationally unsatisfactory. The simulation high- 
lighted the fact that the design of VAS should be such that when an instan- 
taneous transition occurs, aircraft within the OM should be permitted to land 
safely. 

During this series of tests, no major procedural changes were required which 
would impact the ATC system as a result of transitioning from green to red 
operation (i.e., transition from reduced separation to increased separation). 

SERIES IV . 

Series IV consisted of heavy-density (90 arrivals, 60 departures) IFR traffic. 
This series of tests was designed to evaluate VAS as a factor in the runway 
selection process. Assuming availability of a similar or higher density runway 
configuration in a green condition, it investigated benefits or impacts of 

11 



rerouting arrivals from a runway in a red condition to a runway in a green 
condition under heavy traffic densities. A total of 13 runs was accomplished, 

Results indicate that, while there is a slight decrease in overall operations 
rate (table 6) below the baseline figure (table 1) as a result of a runway 
change during the hour of changeover operations, it can be assumed an overall 
increase in operation's rate would occur over the baseline operation's rate 
during the succeeding hours that the new runway configuration would be in a 
green condition. 



TABLE 6. AVERAGE NUMBER OF ARRIVALS PER HOUR FOR RUNWAY CHANGEOVER HOUR 



Arrival 
Configurations 

Combined average, 
runways 14L-14R 
and 32L-27R 



Baseline 



70.3 



Threshold to 
OM 

67.2 



Threshold to 
20-nmi Fix 

69.6 



Runway changes from the basic configuration to a configuration of parallel 
approaches to runways 9R and 9L were implemented in this series under the same 
zones and operational parameters established in series III. 

While VAS, if adopted, is expected to be a factor in the runway selection 
process, it should be realized that many other factors would also contribute 
to the process of changeover to alternative runways, such as a noise abatement 
procedures and ground environment conditions. However, using VAS, there 
were no procedural implications found in simulation which would impact the ATC 
system to any greater degree than a runway change now impacts ATC operations. 

Due to the limitation of the DSF, this simulation dealt solely with the air 
operations of the O'Hare terminal environment, and many factors in the ground 
control operation from the runway exits to terminal aircraft gates could affect 
predicted VAS reduced separation gains, such as the scheduling interrelation- 
ship between arrivals and departures. 

While a departure position was employed and departure aircraft were incorporated 
into the simulation environment, no data were taken in relation to departure 
operations. Departures were employed only to insure that arrival aircraft 
followed prescribed inbound routing and altitude restriction similar to those 
used at- O'Hare and to provide validity of simulation results of airside opera- 
tions. 



12 



SUMMARY OF RESULTS 



Based on comparison of the baseline red condition and the VAS reduced separa- 
tion green condition data, it is clear that increased hourly operational 
arrival gains of from 2.5 (MM to threshold), 2.9 (OM to threshold), and 5.1 
(20 nmi to threshold) for combined runway configuration can be achieved util- 
izing the VAS reduced separation or no-vortex condition. (These increases are 
compatible with Landrum and Brown and Mitre Corporation capacity gain studies.) 
(references 1 and 2) (appendix C) . Similarly, the presence of VAS reduced 
separation within the terminal environment does not create any procedural 
implications or major impacts on the ATC system. 

From all test series data, any increases prevalent in the controller communi- 
cation workload (table 7) are a direct result of increased arrival rates 
gains and not as a result of any VAS operating characteristic. • Control instruc- 
tions (table 8) for all test series showed no significant incresses with VAS 
reduced separation in the areas of vectors, altitude changes, speed adjustments, 
and flightpath patterns. Separation criteria violations (table 9) showed no 
increasing trends with VAS reduced separation. 



TABLE 7. CONTROLLER COMMUNICATIONS 



Configuration 



Avg. Talk Time 
Per Push-to-talk (Sec) 



Baseline (red) 
Threshold to MM (green) 
Threshold to OM (green) 
Threshold to 20 nmi (green) 



Green-Red, 
Green-Red, 
Green-Red, 
Green-Red, 
Rwy Change, 



OM, min 
20 nmi, min 
OM, 5 min 
20 nmi, 5 min 
OM 



Rwy Change, 20 nmi 



3.3 
2.9 
2.9 
3.0 
3.0 
3.1 
2.6 
2.8 
3.0 
3.0 



Avg. Contacts 


Avg. 


Talk Time 


Per A/C 


Per 


A/C (Sec) 


6.6 


19.9 


6.3 




19.2 


4.9 




15.5 


5.9 




18.3 


5.9 




17.7 


5.7 




18.0 


5.6 




17.5 


5.5 . 




17.5 


6.4 




17.5 


6.2 




19.6 



VAS indicated a potential application in the runway selection processes 
through its ability to identify other high-capacity runway configurations in 
the green condition which might exist when an in-use configuration goes red. 

Transition from one separation condition to another on the final approach 
(green to red) did not present any problems to controller personnel and, in 
the worst case, resulted in a single aircraft missed-approach action. 

In summary, it may be stated that, although the ultimate answers to procedural 
questions can only be obtained through on-site operational test and evaluation 
due to ground operations and other factors not considered in a controlled 
simulation environment, no procedural implications emerged from the ATC 



13 



simulation of VAS reduced separation that would deter the operational Imple- 
mentation of the system at Chicago's O'Hare International Airport. 



TABLE 8. CONTROLLER ATC ACTIVITIES 



Avg . No , 



Configuration 

Baseline (red) 
Threshold to MM (green) 
Threshold to OM (green) 
Threshold to 20 nmi (gre< 
Green-Red, OM, min 
Green-Red, 20 nmi, min 
Green-Red, OM, 5 min 
Green-Red, 20 nmi, 5 min 
Rwy Change, OM 
Rwy Change, 20 nmi 



No. A/C 


Avg . No . 


Avg. 


No. 


Speed 


Avg. 


Distance 


Controlled 


Vectors 


Alt. 


Chg. 


Chg. 


Flown (nmi) 


53.6 


140.2 


45.4 




73.8 




67.8 


54.4 


146.0 


44.4 




73.8 




69.5 


54.5 


144.2 


44.9 




68.2 




66.0 


m) 54.4 


135.6 


36.9 




83.1 




66.3 


55.5 


135.2 


40.7 




83.5 




69.6 


56.3 


149.3 


36.9 


' 


83.4 




67.4 


54.5 


120.4 


48.9 




70.5 




69.3 


52.8 


127.8 


41.0 




87.5 




68.5 


52.3 


131.7 


38.1 




89.0 




66.2 


55.8 


129.8 


43.4 




62.0 




67.4 



TABLE 9. SEPARATION CRITERIA VIOLATIONS FOR TOTAL AIRCRAFT PAIRS 



Approach Zones 

Inside OM 

Total Pairs 

Median Separation (nmi) 

Percent Criteria Violations 



Test Configurations 
Baseline Green MM Green OM 



541 

4.5 
* 9 



603 
4.0 
1 



510 
3.8 
3 



Green 20 nmi 

430 
3.5 
3 



481 


444 


451 


390 


5.1 


4.7 


4.5 


4.2 


2 


3 


**7 


1 



Outside OM 

Total Pairs 

Median Separation (nmi) 

Percent Criteria Violations 

*Expanded separation (6.3- and 5.7-nmi median separation) (table 2) achieved 
by controllers for heavy-small and heavy-large pairs was not sufficient outside 
the OM to offset accordion effect at touchdown. 

**Reduced separation (4.8- and 4.7-nmi median separation) (table 4) achieved 
for heavy-small and heavy-large pairs outside OM to obtain 3-nmi separation at 
touchdown is under separation criteria of 5.0 nmi. 



14 



CONCLUSIONS 



From the results, it is concluded that: 

1. No procedural implications emerged to deter implementation of VAS reduced 
separation for aircraft arrivals. 

2. Sufficient arrival rate increases were obtained to support cost/benefit 
analysis. 

3. An orderly transition of separation conditions was obtained in 5 minutes. 

4. An instantaneous transition of separation conditions required, at worst, 
one missed approach. 

5. Arrival rates and ease of operation became more pronounced as the vortex 
clear zone increased in size, i.e., was further expanded from the runway 
threshold. 

6. VAS could have application in the runway selection process. 



15 



REFERENCES 



1. Landrum and Brown Aviation Consultants, Cost/Benefit Analysis of the 
Proposed Vortex Avoidance System and O'Hare International Airport , February 
14, 1977. 

2. Avant, A. L., Procedural Feasibility of Reduced Spacings under VAS 
Operation at O'Hare , May 1977. 



16 



APPENDIX A 
COMPARISON TABLE OF ARRIVAL AIRCRAFT CLASSES AND PAIRING MIX 

Chi-O'Hare Arrivals 

Actual IFR (Sample size - 628 aircraft) 

Class Breakdown Percent of Total 

Small 63 10 

Heavy 87 14 

Large 478 76 

Pairing Mix 566 Pairs Percent of Total 

Heavy - small 7 1.5 

Heavy - large 56 10 
Heavy - heavy 13 2.5 

Large - small 33 6 

All others 451 80. 

Actual VFR (Sample size - 852 aircraft) 

Class Breakdown Percent of Total 

Small 89 
Heavy 132 
Large 631 

Pairing Mix 758 Pairs 

Heavy - small 12 

Heavy - large 85 

Heavy - heavy 22 

Large - small 50 

All others 589 

NAFEC Simulation Arrivals 

Simulation (Sample size 90 aircraft per hour) 

Class Breakdown Percent of Total 

Small 9 10 

Heavy 18 20 

Large 63 70 

Pairing Mix 4146 Pairs Percent of Total 

Heavy - small 88 2 

Heavy - large 653 16 

Heavy - heavy 180 4 

Large - small 267 7 

All others 2958 71 

Note: 

All others = Small - small pairs 
Small - large 
Small - heavy 
Large - large 
Large - heavy 



10. 


5 




15. 


5 




74 






Percent of 


Total 


1. 


5 




11 






3 






6. 


5 




78 







A-l 



APPENDIX B 

SPEED PROFILES (KNOTS) AT THRESHOLD AND OUTER MARKER FOR SMALL, 
HEAVY, AND LARGE WEIGHT CLASSES 




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APPENDIX C 

PREDICTED GAINS (IN ARRIVALS PER HOUR) 

Threshold to MM OM 20 nmi 

Mitre Corp. Study - 1.7 3.1 4.1 

Landrum-Brown Study - 2.4 3.8 

NAFEC Simulation - 2.5 2.9 5.1 

Avg. Predicted Gain 2.2 3.2 4.6 



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