ACRP 4-09 Risk Assessment Method to

Support Modification of Airfield Separation Standards

Developed by:

Applied Research Associates, Inc. Robert E. David & Associates University of Oklahoma

Period:

Jun 2009 to Feb 2011

ADG V

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

222 224 226 228 230 232 234 236Taxiway/Taxiway Centerline to Centerline Separation (ft)

Ris

k of

Col

lisio

n pe

r Ope

ratio

n ADG V Standard = 267 ft

ADG V

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

222 224 226 228 230 232 234 236Taxiway/Taxiway Centerline to Centerline Separation (ft)

Ris

k of

Col

lisio

n pe

r Ope

ratio

n ADG V Standard = 267 ft

ADG V

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

222 224 226 228 230 232 234 236Taxiway/Taxiway Centerline to Centerline Separation (ft)

Ris

k of

Col

lisio

n pe

r Ope

ratio

n ADG V Standard = 267 ft

Project Panel Chair

Ms. Laurie Cullen – HNTB Corporation ACRP Staff Representatives

Ms. Marci A. Greenberger – Program Officer Mr. Joseph J. Brown-Snell – Program Associate

Members Mr. Gary C. Cathey - California Department of Transportation Mr. Chad A. Gunderson - TKDA Mr. Paul Herrera - Los Angeles World Airports Mr. Scott McMahon - Morristown Municipal Airport Jorge E. Panteli - MacFarland-Johnson

Liaison Representatives Mr. John Dermody - Federal Aviation Administration Mr. Chris Oswald - Airports Council International - North America Christine Gerencher – Transportation Research Board

Project Team Principal Investigator

Jim Hall – Applied Research Associates Co-Principal Investigator

Richard Speir – Applied Research Associates Project Manager

Manuel Ayres – Applied Research Associates Team Members

Hamid Shirazi – Applied Research Associates Robert E. David – RED & Associates Yih-Ru Huang – University of Oklahoma Regis Carvalho – Applied Research Associates Arun Rao – Consultant Samuel Cardoso – Applied Research Associates Edith Arambula – Applied Research Associates

Briefing Outline Background Study Objectives Project Tasks Rationale of Airfield Separations Accident and Incident Data Collected Basis of Approach Used Risk-Based Analysis Methodology Case Studies and Validation Plan to Gain Industry Support Limitations and Conclusions

Background Many airports were built before current standards were set There is a need to increase airport and aviation capacity, and

operation of larger aircraft may be required in existing airfields In many cases there are physical and environmental restrictions to

increase existing separations Available analysis alternatives are prescriptive and not based on

risk Approximately 20% of ground (commercial aviation) accidents in

the U.S. are collisions during taxiing or parking More than 50% of fatal accidents occur during landing and takeoff

operations

Modification of Standards (MOS)AC 150/5300-13 (FAA, 1989)

Modification to standards means any change to FAA design standards other than dimensional standards for runway safety areas.

Unique local conditions may require modification to airport design standards for a specific airport.

The request for MOS should show that the modification will provide an acceptable level of safety, economy, durability, and workmanship.

Study ObjectivesStudy Objectives

Develop simple and easy to use methodology to evaluate risk of collisions associated with non-standard airfield separations.

Obtain quantitative assessment for decision making when standard cannot be met.

The methodology should serve as a screening tool to evaluate the feasibility of submitting to the FAA a request for Modification of Standards.

Project Tasks

1. Literature review and rationale of airfield separations

2. Collection of veer-off accident and incident data

3. Modification of Standards (MOS) survey

4. Develop proposed risk assessment methodology

5. Perform airport survey for selected MOS cases

6. Develop risk assessment methodology

7. Develop plan to gain industry support

8. Prepare project report

Rationale for Standards - FAARationale for Standards - FAA Taxiways and Taxilanes: probability distribution of lateral

deviations plus a safety buffer of 10 ft TWY/TWY: 1.2 x WS + 10 ft (between centerlines) TWY/OBJ: 0.7 x WS + 10 ft (axis to object) TXL/TXL: 1.1 x WS + 10 ft (between centerlines) TXL/OBJ: 0.6 x WS + 10 ft (axis to object)

Runways: probability distributions of lateral and vertical deviations during final approach and initial climb, as well as probability of veer-offs during landing and takeoff

Indication that standards were developed based on best engineering judgment and experience from WW II

Rationale for Standards - ICAORationale for Standards - ICAO Taxiway/Taxiway and Taxiway/Object:

Wingtip Clearance = clearance (C) between the outer main gear wheel and the taxiway edge plus safety buffer (Z).

Runway/Taxiway Distance to accommodate potential veer-offs and provide

sterile area free of obstacles for aircraft executing a missed approach or balked landing maneuver.

Veer-off Data CollectionVeer-off Data Collection

Veer-off accidents and incidents occurring in several countries from 1980 to 2009

Taxiway/Taxilane veer-offs Identified 300 incidents in straight segments of

taxiways Only 6 relevant incidents were identified in taxilanes

Identified 679 runway veer-off accidents and incidents during landing and takeoff

Taxiway Veer-offs – Some Taxiway Veer-offs – Some ConclusionsConclusions

Taxiing airplanes are at lower speeds (normal 20 knots, max 30 knots) when compared to runway operations.

The edge of the paved area is a discontinuity and the pilot is able to stop as soon as the aircraft departs the taxiway.

The model for lateral deviation can be truncated for taxiways outside the ramp area.

The collisions occurred in curves or when other aircraft and equipment were inside the taxiway/taxilane OFA.

Taxiway Veer-offs – More ConclusionsTaxiway Veer-offs – More Conclusions

Taxiway veer-offs in straight segments occured due to poor visibility or low surface friction (e.g. Icing conditions).

Two-part models based on frequency and location were not appropriate for the methodology.

Only two fatal accidents due to taxiway veer-offs were identified; neither was relevant to this study.

Basis of Approach Used

Probability distributions of lateral and vertical deviations during operations

Boeing/FAA Taxiway Deviation Studies at ANC and JFK (Scholz, 2003 and 2005)

Airborne risk during landing derived from Collision Risk Model (CRM) runs

Ground roll risk of veer-off derived from models developed in this project (landing and takeoff)

Taxiways and Taxilanes SeparationTaxiways and Taxilanes SeparationProbability Distribution of Lateral DeviationsProbability Distribution of Lateral Deviations

X

= wingtip separation

centerline separation (CS)

WS1 WS2

= CS – (WS1 + WS2) / 2

Taxiway or Taxilane to Object SeparationTaxiway or Taxilane to Object SeparationProbability Distribution of Lateral DeviationsProbability Distribution of Lateral Deviations

0 X

obstacle

wingtip lateral deviation probability

distribution

aircraft semi wingspan

RWY/TWY Separation Risk of collision during airborne phase

Landing Final Approach Missed Approach Rejected Landing

Takeoff – Initial Climb Risk of collision during ground roll

Landing Takeoff

Deviations in Airborne PhaseDeviations in Airborne Phase

Nominal Flight Path(x = 0, y = 0)

h

y

Obstacle

x

Nominal Flight Path(x = 0, y = 0)

h

y

Obstacle

x

Nominal Flight Path

hy

Obstacle

x

Y1 = NFPh - h

X1 = XO – WS/2

Nominal Flight Path

hy

Obstacle

x

Y1 = NFPh - h

X1 = XO – WS/2

Runway Veer-off

x

Landing (or Takeoff)

12 3

Risk-Based Analysis MethodologyRisk-Based Analysis Methodology

Taxiway to Taxiway or Taxilane Taxiway to Object Taxilane to Taxilane Taxilane to Object Runway to Taxiway/Taxilane/Object

LandingAirborne phaseGround rolling phase

TakeoffGround rolling phase

Taxiway Lateral Deviation StudiesTaxiway Lateral Deviation Studies

FAA/Boeing (Scholz, 2003 and 2005) Collision risk models were developed by Boeing/FAA

based on B-747 taxiway deviation studies at ANC and JFK

The objective was to evaluate the risk of collision for B-747-800 operations

Data was collected during one year In both cases, lateral deviation data was collected in

straight segments with taxiway centerline lights

AssumptionsAssumptions

Lateral deviation for smaller aircraft are similar or smaller than those of the B-747

The taxiway or taxilane centerline is conspicuous and visible to the pilot under any operational conditions

The FAA separation standards for taxiways and taxilanes are based on similar probability of aircraft departing the lane during taxiing operations

The risk estimated with the CRM is more restrictive compared to the risk under visual conditions

ACRP 4-09 MethodologyACRP 4-09 MethodologyExample of Risk Plot for Taxiway/Taxiway Separation – ADG Example of Risk Plot for Taxiway/Taxiway Separation – ADG II

ADG I

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

62 64 66 68 70 72Taxiway/Taxiway Centerline Separation (ft)

Ris

k of

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n pe

r Ope

ratio

n

ADG I Standard = 69 ft

8.0E-7

Lateral Deviation Models for Lateral Deviation Models for TaxilanesTaxilanes

Wingtip Separation

ADG - Distances in ftI II III IV V VI

Taxiway/Object 20 26 34 44 53 62Taxilane/Object 15 18 22 27 31 36Ratio 0.75 0.69 0.65 0.61 0.58 0.58

Taxilane

TaxiwaySimilar Probability

Analysis ProcedureAnalysis Procedure Taxiways/ Taxilanes/ObjectsTaxiways/ Taxilanes/Objects

Identify the type of separation Identify the ADG or aircraft types involved Characterize the separation (between centerlines,

between centerline and object, or wingtip clearance) Identify the appropriate risk plot to use Use the centerline or wingtip clearance to estimate risk

of collision

Example - Taxiway/Taxiway Example - Taxiway/Taxiway SeparationSeparation

Taxiway/Taxiway Separation - ADG V

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

226 228 230 232 234 236Taxiway/Taxiway Centerline to Centerline Separation (ft)

Ris

k of

Col

lisio

n pe

r O

pera

tion

ADG V Standard = 267 ft

2.3E-08

Risk Analysis during LandingRisk Analysis during Landing Airborne Phase

Ground Roll Phase

Collision Risk Model (CRM) RunsCollision Risk Model (CRM) Runs

Development of Risk Curves Development of Risk Curves Airborne PhaseAirborne Phase

ADG III - CAT I

1.0E-11

1.0E-10

1.0E-09

1.0E-08

200 250 300 350 400 450 500

Runway/Taxiway Centerline Separation (ft)

Ris

k o

f C

oll

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er O

per

atio

n.

ADG III Approach Cat C Standard = 400 ft

ADG III - CAT I

1.0E-15

1.0E-12

1.0E-09

1.0E-06

0 100 200 300 400 500 600 700

Aircraft Distance from Runway Centerline (ft)

Ris

k p

er

Op

era

tio

n

-328 ft

0 ft

1500 ft

3000 ft

4500 ft

Runway Veer-off Incident Rates (U.S.)Runway Veer-off Incident Rates (U.S.)(1980-2009)(1980-2009)

Type of Incident

Number of

Incidents

Incident Rate per Operation

Incident Rate in Operations per

Incident

LDVO 512 1.195E-06 837,000TOVO 111 2.590E-07 3,861,000

Location Model – Landing Veer-offLocation Model – Landing Veer-offProb=exp((-.02568)*Y**(.803946))

R2=99 .5%

0 200 400 600 800 1000

Dis tance Y from Runway Edge (ft)

0.0

0.2

0.4

0.6

0.8

1.0

Pro

ba

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f S

top

pin

g B

eyo

nd

YP rob=exp((-.02568)*Y**(.803946))

R2=99 .5%

0 200 400 600 800 1000

Dis tance Y from Runway Edge (ft)

0.0

0.2

0.4

0.6

0.8

1.0

Pro

ba

bili

ty o

f S

top

pin

g B

eyo

nd

Y

Analysis Procedure – Runway/TaxiwayAnalysis Procedure – Runway/Taxiway

Identify the ADG Identify type of approach (Cat I or Cat II) Characterize the separation between the runway and

taxiway axes Identify plots for specific ADG (landing)

Airborne phase (lateral and vertical deviations) Ground roll phase (frequency and location)

Use axes separation to estimate risk of collision for each phase

Repeat process for takeoffs

Risk Criteria – FAA Risk MatrixRisk Criteria – FAA Risk MatrixRisk estimated is compared to risk criteria to check for acceptability

Criteria forRunway/Taxiway

Separation

Criteria forTaxiway/Taxilane/Object

Separation

Case Studies and ValidationCase Studies and ValidationAirp. ADG Type of MOS Risk

LevelExpected #

YrsRisk < 1.0E-7

Risk < 1.0E-09

Credible Severity

FAA Risk Classification

Acceptable

PHL III, IV Taxilane/Taxilane <1.0E-9 N/A Yes Yes Major Low YesANC VI Taxiway/Object <1.0E-9 N/A Yes Yes Major Low YesADS III Runway/Taxiway 1.0E-7 > 100 Yes No Catastrophic Medium YesBDR II Runway/Taxiway 1.1E-7 > 100 No No Catastrophic Medium Yes

MFV II Runway/Object 5.9E-8 > 100 Yes No Catastrophic Medium YesN07 I Taxilane/Object 1.2E-9 - Yes No Major Low YesJFK VI Taxiway/Taxiway <1.0E-9 - Yes Yes Major Low Yes

EWR V Taxiway/TaxiwayTaxilane/Object

<1.0E-9 <1.0E-9

N/AN/A

YesYes

YesYes

MajorMajor

LowLow

YesYes

MSP IV Taxiway/Taxiway <1.0E-9 N/A Yes Yes Major Low YesORD V Taxiway/Object <1.0E-9 N/A Yes Yes Major Low YesORD V Taxiway/Taxiway <1.0E-9 N/A Yes Yes Major Low YesHYA III Runway/Taxiway 8.8E-8 > 100 Yes No Catastrophic Medium Yes

LCI III Runway/Taxiway 2.0E-7 > 100 No No Catastrophic Medium YesSEA VI Runway/Taxiway 1.6E-6 N/A No No Catastrophic High* No*SEA VI Taxiway/Taxilane <1.0E-9 N/A Yes Yes Major Low YesASE III Runway/Taxiway 9.0E-8 > 100 Yes No Catastrophic Medium YesACK III Taxiway/Taxiway <1.0E-9 N/A Yes Yes Major Low YesILG IV Taxiway/Object 2.8E-8 - Yes No Major Low YesJYO II Runway/Taxiway 1.2E-7 > 100 No No Catastrophic Medium YesTAN II Runway/Taxiway 8.0E-8 > 100 Yes No Catastrophic Medium Yes

Plan to Gain Industry Support Research Product

Risk assessment methodology to evaluate airfield separations and intended to serve as a screening tool to support the submittal of MOS for FAA approval

Audience Civil aviation agencies like the FAA, ICAO, military

aviation organizations, and civil aviation stakeholders Main obstacle for implementation

Will require FAA support Implementation

Actions to present the product in airport conferences and aviation safety meetings (TRB, AAAE, ACC, ACI)

Presentation to the FAA Office of Airports

Limitations Can only be used to assess risk for straight parallel

segments of taxiways and taxilanes. Taxiway deviations for smaller aircraft were assumed to be

equal or smaller than deviations for the Boeing 747 aircraft. Application of the models for taxiway and taxilane

deviations assume the centerline is conspicuous under any weather and light conditions.

Veer-off models were developed based on incidents and accidents of aircraft with MTOW larger than 5,600 lbs.

Assumed the lateral and vertical deviation probability distributions provided by the Collision Risk Model is conservative when considering visual conditions.

Conclusions The methodology developed in this research study

provides a practical and simple guide to help airports quantify and evaluate risk associated with non-standard airfield separations.

The risk assessment obtained can be helpful to examine the feasibility of and to support MOS requests to the FAA.

The methodology is based on lateral and vertical deviation studies and models developed in this research as well as in previous studies conducted by the FAA, Boeing, and ICAO.

The methodology was validated using twenty MOS cases approved by the FAA.