ACRP 4-09 Risk Assessment Method to Support Modification of Airfield Separation Standards

1. ACRP 4-09 Risk Assessment Method to Support Modification of Airfield Separation Standards Period: • Jun 2009 to Feb 2011 Developed by: • Applied Research Associates, Inc. • Robert E. David & Associates • University of Oklahoma

2. 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

3. 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

4. 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

5. 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

6. 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.

7. Study 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.

8. Project Tasks • Literature review and rationale of airfield separations • Collection of veer-off accident and incident data • Modification of Standards (MOS) survey • Develop proposed risk assessment methodology • Perform airport survey for selected MOS cases • Develop risk assessment methodology • Develop plan to gain industry support • Prepare project report

9. Rationale 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

10. Rationale 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.

11. Veer-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

12. Taxiway Veer-offs – Some Conclusions 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.

13. Taxiway 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.

14. 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)

15. Taxiways and Taxilanes SeparationProbability Distribution of Lateral Deviations • X • WS1 • WS2 • d = wingtip separation • d = CS – (WS1 + WS2) / 2 • centerline separation (CS)

16. Taxiway or Taxilane to Object SeparationProbability Distribution of Lateral Deviations aircraft semi wingspan wingtip lateral deviation probability distribution • 0 • X obstacle

17. 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

18. Deviations in Airborne Phase

19. Runway Veer-off Landing (or Takeoff) 1 2 3 x

20. Risk-Based Analysis Methodology • Taxiway to Taxiway or Taxilane • Taxiway to Object • Taxilane to Taxilane • Taxilane to Object • Runway to Taxiway/Taxilane/Object • Landing • Airborne phase • Ground rolling phase • Takeoff • Ground rolling phase

21. Taxiway 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

22. Assumptions • 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

23. ACRP 4-09 MethodologyExample of Risk Plot for Taxiway/Taxiway Separation – ADG I

24. Lateral Deviation Models for Taxilanes Taxilane Similar Probability Taxiway

25. Analysis ProcedureTaxiways/ 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

26. Example - Taxiway/Taxiway Separation

27. Risk Analysis during Landing Airborne Phase • Ground Roll Phase

28. Collision Risk Model (CRM) Runs

29. Development of Risk Curves Airborne Phase

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

31. Location Model – Landing Veer-off

32. Analysis 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

33. Risk Criteria – FAA Risk Matrix Risk estimated is compared to risk criteria to check for acceptability Criteria for Taxiway/Taxilane/Object Separation Criteria for Runway/Taxiway Separation

34. Case Studies and Validation

35. 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

36. 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.

37. 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.