Airport Traffic Control Tower Siting Criteria: Visibility Siting Analyses

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Airport Traffic Control Tower Siting Criteria
Visibility Siting Analyses

• William Kip Krebs and Glen Hewitt
• ATO-P RD Human Factors
• william.krebs_at_faa.gov or glen.hewitt_at_faa.gov

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

• John Aschenbach
• Rodman Bourne
• Roger Bawgus
• Dave Cloutier
• Ronald Driggers
• Bernie Garbowski
• Rob Heckart
• William Kaplan
• Scott Iwamoto
• Steven Murrill
• Doug Norvell

• Kathy Peterson
• William Vaughan
• Atlantic City ATCT Controllers
• Newark ATCT Controllers
• OHare ATCT Controllers
• Tulsa ATCT Controllers
• Las Vegas ATCT Controllers

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Visibility Siting Proposed AnalysesTower 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
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Visibility Siting Proposed AnalysesTower 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 observers viewing angle
between the two points should be laterally
separated by 0.13 degrees (8 minutes) or greater.
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The Impact of ATC Tower Height on VisibilityA
First-Order AnalysisSteven Murrill and Ronald
Driggers (Army Research Laboratory - Adelphi, MD)
Problem Statement What improvement in visibility
(detection, recognition, identification) can be
gained by increasing the height of an airport
traffic control (ATC) tower?
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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.
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Model AssumptionsArmys Target Acquisition Model
can be found at http//www.hf.faa.gov/krebs/docs/A
rmyTarget.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)
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Model Assumptions

• Generate probability of discrimination curves
  using
• Standard Target Transfer Probability Function
  (TTPF)1
• Modified Johnsons discrimination criteria
• Effective number of spatial cycles on target
  (aircraft) calculated by scaling the human eyes
  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 Labs model 2 Bartons
model 3 Norm Kopeikas turbulence model and the
Tatarski height scaling model
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Visibility Analysis Tool Placed Model on Internet
Tool can be found at http//www.hf.faa.gov/visibil
ity
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Impact on Current and Proposed Towers Object
Discrimination
(probability of detecting a front-view dodge
caravan)
Current Towers provided by Tom Hilquest,
Proposed Towers provided by AFTIL
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Line of Sight Angle of IncidenceVisual
Perception StudyWilliam K. Krebs and Glen
Hewitt(FAA ATO-P RD Human Factors)
Problem Statement What improvement in an
observers 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?
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Methods Participants

• 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.

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Methods AFTIL 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.

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Methods Stimuli
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Methods Procedure

• Each observer was exposed to five towers at ten
  different tower heights. Observers 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 airports
  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.

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Methods 6-Point Likert Scale
Question 1 How well can you distinguish
boundaries of the movement areas?
Question 2 How well can you identify position of
target at the airports key point?
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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 (n12), Subject
rating 2
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.
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LOS Angle of Incidence Study Question 2 How
well can you identify position of target at the
airports key point? 6 point Likert Scale,
ORD,ACY,NEW controllers (n9), 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.
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Line of Sight Angle of Incidence Method and
Results
Question 1 How well can you distinguish
boundaries of the movement areas?
Question 2 How well can you identify position of
target at the airports key point?
Line of Sight Angle of Incidence Criterion
established at 0.80 degrees
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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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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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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
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Backup Slides
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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 (n12), Subject rating 3
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.
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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 (n12), Subject
rating 4
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.
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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 (n12), Subject
rating 5
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.
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LOS Angle of Incidence Study Question 2 How
well can you identify position of target at the
airports key point? 6 point Likert Scale,
ORD,ACY,NEW controllers (n9), 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.
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LOS Angle of Incidence Study Question 2 How
well can you identify position of target at the
airports key point? 6 point Likert Scale,
ORD,ACY,NEW controllers (n9), 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.
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LOS Angle of Incidence Study Question 2 How
well can you identify position of target at the
airports key point? 6 point Likert Scale,
ORD,ACY,NEW controllers (n9), 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.