Airport Traffic Control Tower Siting Criteria: Visibility Siting

Analyses

William “Kip” Krebs and Glen HewittATO-P R&D Human Factors

william.krebs@faa.gov or glen.hewitt@faa.gov

• John Aschenbach• Rodman Bourne• Roger Bawgus• Dave Cloutier• Ronald Driggers• Bernie Garbowski

• Rob Heckart• William Kaplan• Scott Iwamoto• Steven Murrill

• Doug Norvell

Acknowledgements

The valuable contributions supporting this effort from the following people are appreciated:

• Kathy Peterson• William Vaughan• Atlantic City ATCT

Controllers• Newark ATCT Controllers• O’Hare ATCT Controllers• Tulsa ATCT Controllers• Las Vegas ATCT

Controllers

Visibility Siting Proposed Analyses:Tower Siting Order Inputs

Object Distance and Discrimination: ATCT distance from critical airport locations and ATCT height must support requirements for object visibility from the ATCT cab. An Object Discrimination Analysis shall be performed to assess observers’ probability of detection and recognition of an object on the airport surface according to the criteria below

Observation Capability

Requirements

Observation

Description

Front View Probability

Criteria1 Minimum

Detection Ability to notice the presence of an object on the airport surface without regard to the class, type, or model (e.g., an object such as an aircraft or vehicle). The observer knows something is present but cannot recognize or identify the object.

95.5%

Recognition Ability to discriminate a class of objects (e.g., a class of aircraft such as single engine general aviation aircraft).

11.5%

Visibility Siting Proposed Analyses:Tower Siting Order Inputs

Line of Sight (LOS) Angle of Incidence: ATCT distance from critical airport locations and ATCT height must support requirements for viewing distant objects on the airport movement areas, taxiways, and non-movement areas from the ATCT cab. A LOS Angle of Incidence Analysis shall be performed as described in Appendix 5, Section 2 to assess the angle at which the observers’ view of a distant object intersects with the airport surface in accordance with the criterion below:

Two-Point Lateral Discrimination: Critical points of the airport surface operations should be separated by sufficient distance to ensure that two objects at distant key locations provide the observer sufficient lateral discrimination. The observer’s viewing angle between the two points should be laterally separated by 0.13 degrees (8 minutes) or greater.

LOS Viewing Criteria LOS Viewing Angle of Incidence

Minimum Equal to or greater than 0.80 degrees

Problem Statement: What improvement in visibility (detection, recognition, identification) can be gained by increasing the height of an airport traffic control (ATC)

tower?

The Impact of ATC Tower Height on Visibility:

A First-Order Analysis

Steven Murrill and Ronald Driggers (Army Research Laboratory - Adelphi, MD)

Visibility Analysis Tool

US Army developed a target acquisition sensor model to predict soldiers’ ability to correctly detect, recognize, and identify military targets. The model is based on over 50 years of electro-optic sensor, human performance, and vision research.

Human performance predictions are based on numerous human performance field and laboratory tests.

Model AssumptionsArmy’s Target Acquisition Model can be found at http://www.hf.faa.gov/krebs/docs/ArmyTarget.pdf

Detection: Ability to notice the presence of an object on the airport surface without regard to the class, type, or model (e.g., an object such as an aircraft or vehicle). The observer knows something is present but cannot recognize or identify the object.

Recognition: Ability to discriminate a class of objects (e.g., a class of aircraft such as single engine general aviation aircraft).

Identification: Ability to discriminate objects within a class (e.g., C-172)

Model Assumptions

• Generate probability of discrimination curves using:

– Standard Target Transfer Probability Function (TTPF)1

– Modified Johnson’s discrimination criteria

– Effective number of spatial cycles on target (aircraft) calculated by scaling the human eye’s Contrast Transfer Function2 (CTFeye) by the atmospheric (optical) turbulence modulation transfer function3 (MTFturb) at each range.

– A constant contrast transfer value for all ranges.

• Assess impact of tower height on visibility from the probability of discrimination curves.

1 U.S. Army Night Vision Lab’s model2 Barton’s model3 Norm Kopeika’s turbulence model and the Tatarski height scaling model

Visibility Analysis ToolPlaced Model on Internet

Tool can be found at http://www.hf.faa.gov/visibility

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Towers

Current Towers (Level 7 or greater)Proposed Towers

Object Discrimination (Detection)

Human Factors Tower Metric

5 proposed towers (IAD, STL, CLE, ATL, IND) fall below criterion

12 current towers (IND, COU, DPA, GPT, FFZ, HVN, CLE, DET, JFK, MKL, FLL, STL) fall below criterion

Impact on Current and Proposed TowersObject Discrimination

Current Towers: provided by Tom Hilquest, Proposed Towers provided by AFTIL

(probability of detecting a front-view dodge caravan)

Problem Statement: What improvement in an observer’s perspective of the airport surface (as represented by the ATCT line of sight (LOS) angle of incidence to designated key points on the airport surface) can be gained by increasing the height of an air traffic control (ATC) tower?

Line of Sight Angle of Incidence:Visual Perception Study

William K. Krebs and Glen Hewitt(FAA ATO-P R&D Human Factors)

• 11 male and 1 female tower airport traffic controller specialists (TUL, ORD, ACY, NEW) volunteered to participate in the LOS study.

• Average age was 46.3 years with a standard deviation of 8.8. Average operational airport tower experience was 17.4 years with a standard deviation of 9.3.

• Observers participation was approximately 1 hour in the AFTIL simulation cab.

• Observers signed informed consent.

MethodsParticipants

MethodsAFTIL Tower Cab

• Observers performed common ATC visual tasks at different tower heights while positioned in a 3600 tower cab software simulation. Observers were positioned 23’ from the screen.

• Realistic airport scenes were simulated using 1 (need to verify) meter resolution images.

• Image generation was set at 64 pixels per inch on the screen which is equivalent to 20/40 visual acuity.

• Key-points were located within 10,000’ of the observer to ensure maximum number of polygons assigned to each object.

MethodsStimuli

Airport Name

Key Point Distance to Key Point

(feet)

Tower Heights (feet)

values below were not corrected for key point elevation

Number of Observations Per Question

Per Height

RIC Rwy 34 Threshold

9590 40, 94, 140, 186, 232, 277, 323, 369, 415, 461

39, 90, 100, 123, 143, 160, 170, 206, 290, 374

9

3

MEM Rwy 36R Threshold

9809 119, 158, 197, 236, 275, 315, 354, 393, 432, 471

120, 140, 150, 179, 210, 265, 280, 307, 351, 436

9

3

LGA Rwy 31 Threshold

4350 129, 130, 140, 160, 167, 205, 213, 243, 281, 319 3

FWA Rwy 05 Threshold

8960 153, 175, 216, 240, 294, 372, 450, 529, 607, 686 3

MMU Rwy 23 Threshold

4907 84, 108, 122, 151, 165, 194, 237, 280, 323, 366 3

MSP Rwy 30R Threshold

9665 58, 103, 148, 193, 238, 284, 329, 374, 419, 464 9

CPS Rwy 30R Threshold

7063 30, 64, 99, 133, 167, 202, 236, 270, 305, 339 9

OSH-2

Rwy 36 Threshold

6550 45, 75, 105, 136, 166, 196, 226, 257, 287, 317 9

MethodsProcedure

• Each observer was exposed to five towers at ten different tower heights. Observer’s task was to visually scan a designated distant “key point” on the airport surface and rate his ability to (1) distinguish boundaries of the movement areas and (2) identify position of target at the airport’s key point.

• MD-80 was located on the key-point.

• Participants vocally responded using a 6-point Likert Scale.

• Airport towers were blocked and tower height was randomized for each subject. To avoid order effects, each participant received a different order of airport towers and tower heights.

Methods6-Point Likert Scale

Question 1: How well can you distinguish boundaries of the movement areas?

0 1 2 3 4 5

Can not see runways or taxiways.

Can see target area. Can not discriminate boundaries of runways or taxiways.

Can discriminate boundaries of most of runways and taxiways; but provides no distance information.

Can discriminate boundaries of all runways and taxiways, but unable to estimate distances between movement areas.

Can discriminate boundaries of runways and taxiways, and provides some information about distances between movement areas.

Can discriminate boundaries of runways and taxiways, and can readily estimate distances between movement areas.

Question 2: How well can you identify position of target at the airport’s key point?

0 1 2 3 4 5

Unable to determine any information about target’s position

Can see target object. Unable to determine any information about the target position relative to key point or movement areas.

Able to determine the general target position relative to key point, but unable to determine if target is on or off movement area.

Able to determine that target position is in general vicinity of key point, but unable to estimate distances of target within movement area.

Able to determine that target position is near key point, and provides some information about distances of target within movement area.

Able to determine the exact target position relative to key point. Able to readily estimate distances of target within movement area.

Tower air traffic controllers response to the distant key point - “Can discriminate boundaries of most of runways and taxiways; but provides no distance information.”

Based on this response criteria, the minimum tower observation to key point line of sight angle should be 0.481.

LOS Angle of Incidence Study Question 1: How well can you distinguish boundaries of the movement areas?

6 point Likert Scale, TUL,ORD,ACY,NEW controllers (n=12), Subject rating ≥ 2

LOS Angle of Incidence Study Question 2: How well can you identify position of target at the airport’s key point?

6 point Likert Scale, ORD,ACY,NEW controllers (n=9), Subject rating ≥ 3

Tower air traffic controllers response to the distant key point - “Able to determine that target position is in general vicinity of key point, but unable to estimate distances of target within movement area.”

Based on this response criteria, the minimum tower observation to key point line of sight angle should be 0.799.

Line of Sight Angle of Incidence Method and Results

Question 1: How well can you distinguish boundaries of the movement areas?0 1 2 = (0.48 degrees) 3 4 5

Can not see runways or taxiways.

Can see target area. Can not discriminate boundaries of runways or taxiways.

Can discriminate boundaries of most of runways and taxiways; but provides no distance information.

Can discriminate boundaries of all runways and taxiways, but unable to estimate distances between movement areas.

Can discriminate boundaries of runways and taxiways, and provides some information about distances between movement areas.

Can discriminate boundaries of runways and taxiways, and can readily estimate distances between movement areas.

Question 2: How well can you identify position of target at the airport’s key point?0 1 2 3 = (0.80 degrees) 4 5

Unable to determine any information about target’s position

Can see target object. Unable to determine any information about the target position relative to key point or movement areas.

Able to determine the general target position relative to key point, but unable to determine if target is on or off movement area.

Able to determine that target position is in general vicinity of key point, but unable to estimate distances of target within movement area.

Able to determine that target position is near key point, and provides some information about distances of target within movement area.

Able to determine the exact target position relative to key point. Able to readily estimate distances of target within movement area.

Line of Sight Angle of Incidence Criterion established at 0.80 degrees

Impact on Current and Proposed Towers Line of Sight Angle of Incidence

Current Towers: provided by Tom Hilquest, Proposed Towers provided by AFTIL

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Proposed TowersCurrent Towers (Level 7 or greater)

Line of Sight Angle of Incidence

Human Factors Tower Siting Metric

(subtracted 27 feet for all towers)

0.8 degrees (48 min) LOS criterion

102 (52%) current towers below criterion

3 proposed towers below criterion

0.58 degrees (35 min) LOS criterion

58 (30%) current towers below criterion

1 proposed tower below criterion

Towers

0.80 degrees

0.58 degrees

1972 Tower Order 35' criteria2005Tower Order .8 deg criteria

Impact on Current and Proposed Towers Line of Sight Angle of Incidence

Current Towers: provided by Tom Hilquest, Proposed Towers provided by AFTIL

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Proposed TowersCurrent Towers (Level 7 or greater)

Line of Sight Angle of Incidence

Human Factors Tower Siting Metric

(subtracted 27 feet for all towers below 130 feet)

0.8 degrees (48 min) LOS criterion

50 (26%) current towers below criterion

3 proposed towers below criterion

0.58 degrees (35 min) LOS criterion

17 (9%) current towers below criterion

1 proposed tower below criterion

Towers

0.80 degrees

0.58 degrees

1972 Tower Order 35' criteria2005Tower Order .8 deg criteria

Two-Point Discrimination

Purpose: Quantify the impact of tower location on observers’ ability to discriminate two distinctly spatially separate points on the airport surface.

Criterion: 8 minutes Calculate angle

Backup Slides

Tower air traffic controllers response to the distant key point - “Can discriminate boundaries of all runways and taxiways, but unable to estimate distances between movement areas.”

Based on this response criteria, the minimum tower observation to key point line of sight angle should be 1.067.

LOS Angle of Incidence Study Question 1: How well can you distinguish boundaries of the movement areas?

6 point Likert Scale, TUL, ORD,ACY,NEW controllers (n=12), Subject rating ≥ 3

Tower air traffic controllers response to the distant key point - “Can discriminate boundaries of runways and taxiways, and provides some information about distances between movement areas.”

Based on this response criteria, the minimum tower observation to key point line of sight angle should be 1.428.

LOS Angle of Incidence Study Question 1: How well can you distinguish boundaries of the movement areas?

6 point Likert Scale, TUL,ORD,ACY,NEW controllers (n=12), Subject rating ≥ 4

Tower air traffic controllers response to the distant key point - “Can discriminate boundaries of runways and taxiways,and can readily estimate distances between movement areas.”

Based on this response criteria, the minimum tower observation to key point line of sight angle should be 2.177.

LOS Angle of Incidence Study Question 1: How well can you distinguish boundaries of the movement areas?

6 point Likert Scale, TUL,ORD,ACY,NEW controllers (n=12), Subject rating = 5

LOS Angle of Incidence Study Question 2: How well can you identify position of target at the airport’s key point?

6 point Likert Scale, ORD,ACY,NEW controllers (n=9), Subject rating ≥ 2

Tower air traffic controllers response to the distant key point - “Able to determine the general target position relative to key point, but unable to determine if target is on or off movement area.”

Based on this response criteria, the minimum tower observation to key point line of sight angle should be.

LOS Angle of Incidence Study Question 2: How well can you identify position of target at the airport’s key point?

6 point Likert Scale, ORD,ACY,NEW controllers (n=9), Subject rating ≥ 4

Tower air traffic controllers response to the distant key point - “Able to determine that target position is near key point, and provides some information about distances of target within movement area.”

Based on this response criteria, the minimum tower observation to key point line of sight angle should be 2.177.

LOS Angle of Incidence Study Question 2: How well can you identify position of target at the airport’s key point?

6 point Likert Scale, ORD,ACY,NEW controllers (n=9), Subject rating = 5

Tower air traffic controllers response to the distant key point - “Able to determine the exact target position relative to key point. Able to readily estimate distances of target within movement area.”

Based on this response criteria, the minimum tower observation to key point line of sight angle should be 2.187.