Federal Aviation
Administration
Runway Incursion
Severity
Categorization (RISC)
Model
Presented to: International Civil Aviation Organization
By: LaGretta Bowser
Date: September 2005
Current FAA Runway Incursion
Severity Categories
Operational dimensions affecting runway incursion severity:
Available
Reaction
Time
Evasive or
Corrective
Action
Environmental
Conditions
Speed of
Aircraft and/or
Vehicle
Proximity of
Aircraft and/or
Vehicle
Increasing Severity
Category D
Little or no chance of
collision, but meets
the definition of a
runway incursion.
Category C
Category B
Category A
Separation decreases,
but there is ample
time and distance to
avoid a potential
collision.
Separation decreases
and there is a
significant potential
for collision.
Separation decreases
and participants take
extreme action to
narrowly avoid a
collision, or the event
results in a collision.
Runway Incursion Severity Categorization (RISC) Model
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Proposed Severity Categories
• “A” = A very serious incident in which a
collision was narrowly avoided.
• “B” = An incident in which separation
decreases and there is significant potential for
collision, which may result in a time-critical
corrective/evasive response to avoid a
collision.
• “C” = A minor incident characterized by ample
time and/or distance to avoid a collision.
• “D” = Insufficient information, inconclusive or
conflicting evidence precludes severity
assessment
Runway Incursion Severity Categorization (RISC) Model
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Background
• The categorization of the severity of runway
incursions is a tool to help represent risk in
the system.
• Risk = probability of an event x severity of
the outcome
• In order to be defensible, ratings need to be
valid and reliable.
– Valid = an “A” is really an “A”
– Reliable = an “A” is always an “A”
• Inter-rater: An “A” for Peter is an “A” for Paul
• Over time: An “A” today is an “A” tomorrow
Runway Incursion Severity Categorization (RISC) Model
September 2005
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Components of the Model
• A rating is assigned based on the closest
proximity (CP) and the factors that
contribute to the variability of that proximity
(probability of a collision).
– CP - both horizontal and vertical - is measured at the
end of the conflict OR the point at which all parties
are aware of the situation and have the aircraft
under control at taxi speed or less.
Runway Incursion Severity Categorization (RISC) Model
September 2005
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Components of the Model
(continued)
• Assumptions
– Some scenarios are more serious at the same CP
than others (e.g, head-on is worse than tail-chase)
– There are factors that increase the variability of the
response and resulting CP, for example:
• Actions with short response time
• Larger aircraft (more variable stopping distance)
• Contaminated runways
Runway Incursion Severity Categorization (RISC) Model
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Benefits of the Model
• Rankings are reliable – same event will
result in the same rating every time.
– Reliable ratings are necessary to have confidence in
trends of system performance.
• Counts of types of scenarios (e.g., crossing
in front of a takeoff, landovers) is automatic.
Runway Incursion Severity Categorization (RISC) Model
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How the Model Works
• Rater is asked a series of questions and
selects answers to classify the event as a
scenario
– For example, what was the aircraft doing? (taking
off, landing, taxiing, stopped)
• If taking off, did the aircraft takeoff or abort takeoff?
– What did the other aircraft or vehicle do? (For
example, crossed runway, crossed hold short line,
etc)
• Rater enters additional information about
the event into three categories: visibility,
avoidance maneuver, human error.
Runway Incursion Severity Categorization (RISC) Model
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Information Selected by the Rater
• Ceiling and Visibility, RVR, Day/Night
• Aircraft type
• Types of human error – pilot error,
controller error, communication error
• Avoidance maneuvers
(initiated/commanded)
• Characteristics of avoidance maneuver (for
example, point at which go-around was
initiated)
Runway Incursion Severity Categorization (RISC) Model
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Aircraft Type
• Aircraft Type = FAA weight categories
–
–
–
–
S = less than 12,500 lbs
S+ = 12,500 – 40, 999 lbs
L = 41,000 – 254,999
H = or greater than 255,000
Runway Incursion Severity Categorization (RISC) Model
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Avoidance Maneuver Categories
• Early rotation on takeoff (as reported by
pilot)
• Aborted takeoff (reported distance rolled)
• Swerve (reported or observed)
• Hard/maximum braking (reported or
observed)
• Go-around (point at which GAR was
initiated/commanded)
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Examples of Error Categories (Degree of Control)
• Controller unaware of (or forgot about)
aircraft or vehicle.
• Controller forgot runway was closed.
• Controller misidentified aircraft and
issued instruction to wrong aircraft.
• Pilot took off/landed on wrong runway.
• Wrong aircraft accepted a clearance.
Runway Incursion Severity Categorization (RISC) Model
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Examples of Communication
Factors
• Total communication failure (e.g., stuck mike)
• One or more party (e.g., vehicle) not on
frequency
• Completely blocked transmission
• Partially-blocked (stepped-on) transmission
• Controller unable to contact aircraft
• Pilot unable to contact controller
Runway Incursion Severity Categorization (RISC) Model
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Example
Input:
• C-150 crossed hold short lines (but did not
enter runway) with another aircraft (C-150)
taking off.
• Aircraft taking off rotated normally after
passing through the intersection (no avoidance
maneuver).
• Closest horizontal proximity = 100’ as aircraft
passed through the intersection
• Visibility: 10 miles - day
• Error: Pilot read back “hold short” instruction
correctly but then crossed the hold short lines.
Runway Incursion Severity Categorization (RISC) Model
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Example
• Output:
– Rating = 1.0 = “D”
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Example of Most Common
Scenarios
N = 906
SITUATION OF CROSSING/POTENTIAL CROSSING IN FRONT OF A LANDING :
406 (44%)
Landing a/c went around
The taxiing aircraft crossed the hold-short line, and the landing aircraft went around.
The taxiing aircraft entered the runway, and the landing aircraft went around.
The taxiing aircraft crossed the runway, and the landing aircraft went around.
282 (70%)
93
136
53
Landing a/c landed – touched down after intersection
The taxiing aircraft crossed the hold-short line, and the landing aircraft landed after the intersection.
The taxiing aircraft entered the runway, and the landing aircraft landed after the intersection.
The taxiing aircraft crossed the runway, and the landing aircraft landed after the intersection.
13
7
3
3
Landing a/c landed – touched down before intersection
The taxiing aircraft crossed the hold-short line, and the landing aircraft landed before the intersection.
The taxiing aircraft entered the runway, and the landing aircraft landed before the intersection.
The taxiing aircraft crossed the runway, and the landing aircraft landed before the intersection.
111
35
29
47
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Example of Most Common
Scenarios (continued)
N = 906
SITUATION OF CROSSING/POTENTIAL CROSSING IN FRONT OF A TAKEOFF :
242 (27%)
Aircraft took off – rotated before the intersection
The taxiing aircraft crossed the hold-short line, and the takeoff rotated before the intersection.
The taxiing aircraft entered the runway, and the takeoff rotated before the intersection.
The taxiing aircraft crossed the runway, and the takeoff rotated before the intersection.
112
37
33
42
Aircraft took off – rotated after the intersection
The taxiing aircraft crossed the hold-short line, and the takeoff rotated after the intersection.
The taxiing aircraft entered the runway, and the takeoff rotated after the intersection.
The taxiing aircraft crossed the runway, and the takeoff rotated after the intersection.
51
17
2
32
Aircraft aborted take off
The taxiing aircraft crossed the hold-short line, and the takeoff aborted.
The taxiing aircraft entered the runway, and the takeoff aborted.
The taxiing aircraft crossed the runway, and the takeoff aborted.
Runway Incursion Severity Categorization (RISC) Model
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78 (33%)
36
42
1
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