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Risk Assessment Method to Support Modification of Airfield Separation Standards (2011)

Chapter: Appendix H - Analysis of MOS Cases

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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Suggested Citation:"Appendix H - Analysis of MOS Cases." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

H-10 Approval Accidents/Incidents No accidents and incidents were identified between 1982 and 2009. Figure H-6. Cross-section of existing separation at N07. Application of Methodology Risk Plot Figure AA-28 Wingtip Sep 16.5 ft Severity Major Risk Level 1.2E-09 Conclusion Low Risk Acceptable Case Study # 7 - John F. Kennedy International Airport (JFK) MOS Issue Taxiway/ Taxiway Approval Date 3/18/2008 (submitted) Separations OFA Centerline Wingtip Standard 324 ft Existing 284–300 ft Airport Ref Code D-VI Critical Aircraft Aircraft 1 Aircraft 2 Model B747-800 B747-800 ADG VI VI Wingspan 224’ 224’ Synopsis Based on AC 150/5300-13, Chapter 2, Table 2-3, the required taxiway to taxiway centerline separation to accommodate a Boeing B747-8 (i.e., ADG VI) at JFK is 324 ft. However, the separations between some taxiways at JFK do not comply with the standards. The separation between Taxiways A and B is 284 ft, with the exception of a bridge section in which the separation is 250 ft. The separation between Taxiways P and Q, R and S, and CE and W is 300 ft. Physical space limitations at JFK make it impossible to move the existing runways and/or taxiways to obtain the standard clearances. The option of relocating runways/taxiways would have reduced the runway to taxiway separation or reduced available ramp space, which in turn would have increased ramp congestion and ultimately affected the number of available gate positions. Conditions for Restrict use of taxiway to aircraft with wingspan no greater than 42 ft.

H-11 the bridge section of Taxiways A and B (i.e., bridge crossing the Van Wyck Expressway). Aircraft traveling north should hold on the intersection NA and aircraft traveling south will hold on the intersection with Taxiway NB. Restrict simultaneous aircraft operation involving B747-800 aircraft on Taxiways CA and CB, which separation is also 250 ft. Justification Limited space availability. Maintain current level of service without increasing ramp congestion or reducing the available ramp space. Based on the analysis titled Statistical Extreme Value Analysis Concerning Risk of Wingtip of Fixed Object Collision for Taxiing Large Aircraft, the 95% confidence interval risk of wingtip collision at JFK between an Airbus A-380 and a Boeing B-747-800 on adjacent taxiways with a separation of 267 ft is as low as one in 1 billion. The existing separation between taxiways exceeds 267 ft, with the exception of a bridge section on Taxiways A and B, which separation is 250 ft. The calculated wingtip separation between an Airbus A-380 and a Boeing B747-800 traveling simultaneously on Taxiways A and B was 40 ft, which is greater than the standard taxilane wingtip requirement of 34 ft. Considering the case when the aircraft did not track the taxiway centerlines while taxiing, the wingtip separation was still greater than 10 ft. Accidents/Incidents 15 accidents and incidents were identified between 1982 and 2009. Figure H-7. Cross-section of existing separation at JFK. Application of Methodology Risk Plot AA-7 Wingtip Sep 41 ft Severity Major Risk Level < 1.0E-09 Conclusion Low Risk Acceptable Restrictions Restrict simultaneous aircraft operation involving B747-800 aircraft on

H-12 Case Study # 8 - Newark Liberty International Airport (EWR) MOS Issue Taxiway/ Taxiway Approval Date 7/28/1995 Separations OFA Taxiway/Taxiway Taxiway/Object Standard 276 ft 267 ft 138 ft Existing 260 ft 220 ft 130 ft Airport Ref Code D-V Critical Aircraft Aircraft 1 Aircraft 2 Model B747-400ER Any ADG V Parked aircraft Wingspan 213’ Any’ Synopsis The FAA standard taxilane OFA width for ADG V is 276 ft. Chapter 2, Table 2-3, of AC 150/5300-13 allows for a modified taxilane centerline to fixed or movable object of 0.6 × wingspan + 10 ft which equals 138 ft while the existing separation is as shown in Figure H-8. Restrictions Taxiway S use is restricted to B-727 aircraft. This will increase the existing separation of 220 ft to 273 ft (220 + 214/2 108/2). 273 ft of taxiway separation exceeds the standard requirements. Restrict operations on Taxiway S to B-727 Group III aircraft. Justification Based on the modified equation found in AC 150/5300-13, Chapter 2, at the bottom of Table 2-3 (0.6 × wingspan + 10 ft), taxiway OFA of 130 ft provided clearance of more than 10 ft from the airplane wingtip to the parked aircraft. Taxiway S restriction allowed for enough clearance between the two taxiways when the largest aircraft expected to travel on Taxiway JB and the largest aircraft allowed in Taxiway S traveled side-to-side. Figure H-8. Cross-section of existing separation at EWR. Application of Methodology Risk Plot AA-26 (TLN/OBJ) AA-7 (TWY/TWY) Wingtip Sep 130 ft (TLN/OBJ) 23.5 ft (TWY/TWY) Severity Major Risk Level < 1.0E-09 < 1.0E-09 Conclusion Low Risk Acceptable

H-13 Case Study # 9 - Minneapolis- St. Paul International Airport (MSP) MOS Issue Taxiway/ Taxiway Approval Date 3/6/2006 Separations OFA Centerline Wi ngtip Standard 215 ft Existing 154 ft 35 ft Airport Ref Code C-IV Critical Aircraft Aircraft 1 Aircraft 2 Model B757-300 B757-300 ADG IV IV Wi ngspan 125 ft 125 ft Synopsis In order to accommodate push-backs from Concourse B and for the aircraft to remain in the non-movement area without blocking Taxiway Q, a relocation/realignment of Taxiway Q was required. The proposed MOS was to relocate a portion of Taxiway Q between P2 and P3, moving it closer to Taxiway P. In order to maintain an acceptable level of safety on the parallel taxiways, the use of the reduced separation segment of Taxiway P was restricted to aircraft with wingspan no larger than 124.8 ft (B-757 size aircraft), and the use of the reduced separation segment of Taxiway Q was limited to aircraft with wingspans no larger than 111.9 ft (A-320 size aircraft). Restrictions Use of Taxiway P between P2 and P3 limited to aircraft with maximum wingspan of 124.8 ft. Use of Taxiway Q between P2 and P3 limited to aircraft with maximum wingspan of 111.9 ft. Operational restrictions on Taxiways P and Q to aircraft with wingspan no larger than 124.8 ft and 111.9 ft, respectively. Pavement marking changes to the 30R deicing pad renumbering circle 99 to circle 95. Adjustment to the deicing pad route to allow for a Mesaba staging area and facilitate the regional aircraft operations Concourses A and B. Reduce the painted Taxiway Q width from 75 ft to 50 ft on the affected segment of the taxiway to ensure object clearance. Change in the current Airport Layout Plan to reflect the changes to the taxiways and operational restrictions. Make regional airlines aware of jet blast issues posed by the proposed Mesaba staging area near the deicing pad. During special circumstances, when aircraft larger than 124.8 ft need to use Runway 12L/30R, parking on the east end of Taxiway P should only be granted if Taxiway Q is not in use. Justification Limited space availability to relocate Taxiway P. The taxiway OFA provides an acceptable level of safety based on the modified equations provided in AC 150/5300-13 below Table 2-3 and Table 4-1. Wi ngtip clearance of aircraft on both taxiways is acceptable when the aircraft main gear wheels remain entirely within the boundaries of the taxiway.

H-14 Figure H-9. Cross-section of the existing separation at MSP. Application of Methodology Risk Plot AA-7 Wingtip Sep 35 ft Severity Major Risk Level < 1.0E-09 Conclusion Low Risk Acceptable Case Study # 10 - Chicago O’Hare International Airport (ORD) MOS Issue Taxiway/Object Approval Date 9/30/2005 Separations OFA Centerline Wingtip Standard 160 ft Existing 131 ft Airport Ref Code D-V Critical Aircraft Aircraft 1 Aircraft 2 Model B747-400 N/A ADG V Wingspan 213’ Synopsis The existing separation between Taxiway A and the terminal core service road that is located next to Concourses C, E, F, G, and H is 131 ft, while the required taxiway object OFA is 160 ft. At the time the taxiway and terminal were built, the 131-ft OFA complied with ADG V standards. However, these standards have been revised, and AC 150/5300-13, Chapter 2, Table 2- 3, now mandates a larger OFA of 160 ft. An MOS was requested to keep the existing taxiway/object separation while subjecting the ADG V operations. Safety was maintained by placing certain operational restrictions on the use of Taxiway A. Restrictions Use of Taxiway A by ADG V aircraft should be in accordance with the conditions for MOS approval. Justification Existing taxiway to object separation was based on ADG V standards at the time of the taxiway and terminal development.

H-15 Figure H-10. Cross-section of the existing separation at ORD for Case Study # 10. Application of Methodology Risk Plot AA-12 Centerline Sep 131 ft Severity Major Risk Level 3.2E-10 Conclusion Low Risk Acceptable Conditions for Approval Taxiway A should contain green colored bi-directional centerline lights. Taxiway A centerline lights must be operational during A330, A340, B747- 400, MD11, and B777 aircraft operations. Maintain, monitor, and enforce the aircraft parking limit line among all tenants and ground personnel. Case Study # 11 - Chicago O’Hare International Airport (ORD) MOS Issue Taxiway/Taxiway Approval Date 9/30/2005 Separations OFA Centerline Wingtip Standard 267 ft Existing 251 ft Airport Ref Code D-V Critical Aircraft Aircraft 1 Aircraft 2 Model B747-400 B747-400 ADG V V Wingspan 196’ 196’ Synopsis The existing separation between Taxiways A and B is 251 ft, while the required separation is 267 ft. At the time the taxiways were built, 251 ft complied with the FAA design criteria. However, the standards have been revised and now AC 150/5300-13, Chapter 2, Table 2-3 mandates a larger separation of 267 ft. Operations on Taxiways A and B at ORD are managed by FAA Air Traffic Order ORD 7110.65C with an adequate level of safety. Therefore, after

H-16 Figure H-11. Cross-section of the existing separation at ORD for Case Study # 11. Application of Methodology Risk Plot AA-5 Centerline Sep 251 ft Severity Major Risk Level < 1.0E-09 Conclusion Low Risk Acceptable Case Study # 12 - Barnstable Municipal Airport (HYA) MOS Issue Runway/Taxiway Approval Date 8/17/1998 Separations OFA Centerline Wingtip Standard 400 ft 282 ft Existing 300 ft 219 ft evaluating other alternative solutions to the separation between Taxiways A and B, an MOS was requested to keep the existing separation while following the mentioned Air Traffic Order operation restrictions. Restrictions In accordance with FAA Air Traffic Order ORD 7110.65C, no simultaneous taxi operations on Taxiways A and B are allowed for B747-400, B777-300, and A340-600 aircraft, and no aircraft is allowed to stop on the Taxiway A or Taxiway B bridges. Justification Existing parallel taxiway centerline separation was consistent with the FAA design standards at the time of the taxiways construction. A separation of 251 ft is acceptable subject to the operation restrictions contained in FAA Air Traffic Order ORD 7110.65C. Conditions for Approval Taxiway A should contain green colored bi-directional centerline lights. Taxiway A centerline lights must be operational during A330, A340, B747- 400, MD11, and all series of B777 aircraft operations. Maintain and observe the aircraft parking limit line. No simultaneous taxi operations on Taxiways A and B are allowed for B747- 400, B777-300, and A340-600 aircraft. No aircraft is allowed to stop on the Taxiway A or Taxiway B bridges. Airport Ref Code B-III

H-17 Critical Aircraft Aircraft 1 Aircraft 2 Model ATR-42 ATR-42 ADG III III Wingspan 81’ 81’ Synopsis The northern section of Taxiway A, a 20-year old taxiway, was scheduled by HYA for rehabilitation. The existing separation between Taxiway A and Runway 15/33 is 300 ft rather than the required 400 ft by AC 150/5300-13, Chapter 2, Table 2-2. The northern section of Taxiway A is 50 ft in width while the southern section of the taxiway has a width of 60 ft. The width of the taxiway is not an issue since the entire taxiway meets or exceeds the minimum required width of 50 ft. Three options were considered and an MOS request was selected. It was determined that enough clearance space would exist between the existing runway safety area (RSA) and the runway Obstacle Free Zone, which is offset from the centerline of Runway 15/33 by 250 ft and 200 ft, respectively. The clearing between the RSA and the tip of the wing of the critical aircraft in a 50-ft-wide taxiway was calculated to be 9.7 ft. Restrictions Maintain ATR-42 characteristics as most demanding aircraft. Justification Cost feasibility. Negative impacts to the airport apron/terminal/parking capacity. Acquisition and cleaning of adjacent contaminated land needed for relocation. Airport design aircraft is less demanding than Group C representative aircraft. The RSA and runway OFA are satisfied utilizing the most demanding aircraft (ATR-42). Conditions for Approval Maintaining ATR-42 or less demanding design aircraft Figure H-12. Cross-section of the runway/taxiway existing separation at HYA. Application of Methodology Risk Plot AA-33 and AA-43 Centerline Sep Severity Catastrophic Risk Level Airborne 1.1E-09 Risk Level Ground 1.0E-07 Annual Vol. Operations 118,000 Expected # Years > 100 years Conclusion Medium Risk Mitigation Recommended

H-18 Case Study # 13 - Laconia Municipal Airport (LCI) MOS Issue Runway/Taxiway Approval Date 4/24/1974 Separations Runway OFA Taxiway OFA Centerline Standard 500 ft 166 ft 400 ft Existing 300 ft 110 ft 210 ft Airport Ref Code C-III Critical Aircraft Aircraft 1 Aircraft 2 Model B727-200 B727-200 ADG III III Wingspan 108’ 108’ Synopsis A taxiway measuring 2,700 ft long and 50 ft wide ran parallel to Runway 7/25 (currently labeled as Runway 8/26). The separation between the runway and the existing taxiway was 210 ft, rather than the required 400 ft by AC 150/5300-13, Chapter 2, Table 2-2. Due to economic constraints, the feasible solution to the separation non- compliance was to request an MOS. After a detailed analysis of several representative aircraft, it was determined that the existing separation provided adequate clearance for two critical aircraft (B727-200) traveling side by side in the taxiway and runway, respectively. Maintaining the existing separation of 210 ft as shown in Figure H-13, the clearing between the wing tips of the two aircraft was calculated to be 123 ft. Although the B-727 was listed as the critical aircraft, that aircraft was not operating at the airport at that time. MOS is predicated upon commuter service type aircraft - Piper Apache or a De Havilland Twin Otter. In 2010, LCI does not have a Part 139 certificate, and it is doubtful that in the future it would have any operations by large aircraft such as B-727. Restrictions Airport is certified by the Civil Aeronautics Board (CAB) for seasonal service, which is provided by Delta using a Piper Apache as substitute commuter. Basic transportation criteria 150/5300-6 is considered in lieu of air carrier taxiway standards. Justification Cost feasibility - taxiway already existed at time the MOS was constructed. Clearance evaluation of two of the most demanding aircraft (B-727-200) passing side-by-side in the runway and taxiway proved satisfactory. Conditions for Approval Continued commuter substitute service. Construct taxiway safety area conforming to general aviation transport criteria.

H-19 135’ 210’ Figure H-13. Cross-section of the existing runway/taxiway separation at LCI. Application of Methodology Risk Plot AA-33 and AA-43 Centerline Sep 210 ft Severity Catastrophic Risk Level Airborne 5.0E-09 Risk Level Ground 2.0E-07 Annual Vol. Operations 37,600 Expected # Years > 100 years Conclusion Medium Risk Mitigation Recommended Case Study # 14 - Seattle-Tacoma International Airport (SEA) MOS Issue Runway/Taxiway Approval Date 6/12/2009 Separations OFA Centerline Wingtip Standard 500 ft and 550 ft Existing 400 ft Airport Ref Code D-VI Critical Aircraft Aircraft 1 Aircraft 2 Model B747-800 B747-800 ADG VI VI Wingspan 224’ 224’ Synopsis Based on AC 150/5300-13, Chapter 2, Table 2-2, the required runway to taxiway separation at SEA is 400 ft for a CAT I approach, 500 ft for CAT II/III approach with a visibility no lower than ½ statute mile, and 550 ft for CAT II/III approach with a visibility less than ½ statute mile. The existing northernmost section of Taxiway B is located 400 ft east of the approach end of Runway 16L and thus complies with the requirement for CAT I approaches, but provides less than the required separation for CAT II/III approaches. With the introduction of Boeing aircraft model 747-800, the airport’s ADG changed from D-V to D-VI, and the required runway to taxiway separation increased from 400 ft to 500 ft–550 ft depending on visibility conditions. The northern 3,000 ft of Taxiway B had an existing tail height restriction of 48 ft for aircraft taxiing on it during CAT II/III approaches. This restriction would also apply to the B747-800. An MOS was requested to allow the B-747-800 to operate on the northern 3,000 ft of Taxiways A and B as had previously been approved for the B-747-400.

H-20 Restrictions Aircraft with a maximum tail height of 48 ft are allowed on the northern 3,000 ft portion of Taxiway B during CAT II and CAT III ILS operations on Runway 16L. Aircraft with tail heights exceeding 48 ft are restricted from operating on Taxiway A during CAT II and CAT III low visibility conditions. Justification Current runway to taxiway separation distance complies with prior airport ADG corresponding to D-V (Boeing B747-400). The southern portion of Taxiway B (south of Taxiway L) provides a 600-ft separation between the runway and taxiway centerlines, thus providing an adequate clearance for CAT II and CAT III operations under low visibilities. Conditions for Approval B-747-800 aircraft are not allowed to taxi on the northern-most 3,000 ft section of Taxiway B during CAT II/III approaches to Runway 16L since the aircraft’s tail height exceeds the 48 ft maximum that had previously been established for operations on that taxiway under those visibility conditions. Taxiway A must be utilized for B-747-800 taxiing when restricted use of Taxiway B is in effect. Figure H-14. Cross-section of the existing separation at SEA for Case Study # 14. Application of Methodology Risk Plot AA-40 and AA-46 Centerline Sep Severity Catastrophic Risk Level Airborne 1.5E-06 Risk Level Ground 1.2E-07 Annual Vol. Operations Expected # Years > 100 years Conclusion High Risk Case Study # 15 - Seattle-Tacoma International Airport (SEA) MOS Issue Taxiway/Taxilane Approval Date 6/2/2009 Separations OFA Centerline Wingtip Standard 324 ft 62 ft Existing 219 ft 44.3 ft Airport Ref Code D-VI

H-21 Critical Aircraft Aircraft 1 Aircraft 2 Model B747-800 B757-200 ADG VI IV Wingspan 224’ 125’ Synopsis Taxiway B parallels Taxilane W in the passenger terminal area. Taxiway B was designed to comply with ADG V requirements and provide adequate separation for aircraft up to 125 ft wingspan (B757-200). The existing separation between Taxiway B and Taxilane W is 219 ft. Since year 2009, Boeing B747-800 aircraft started operating at SEA, increasing the Airport Reference Code to D-VI and requiring 62 ft wingtip clearance (AC 150/5300-13, Chapter 4, Table 4-3). The only feasible alternative was to limit operations on Taxilane W. An MOS was filed in order to keep the existing spacing configuration and to allow B747-800 aircraft to operate on Taxiway B and aircraft with wingspans up to 125 ft to operate on Taxilane W without restrictions. Restrictions Aircraft on Taxilane W should operate at 20 mph or less. Limit operations on Taxiway B to aircraft no larger than 224.4 ft wingspan (Boeing B747-800). Limit operations on Taxilane W to aircraft no larger than 125 ft wingspan (Boeing B757-200). Restrict the use of Taxiway B during pushback of aircraft types B757, ADG IV, and ADG V. Justification Cost limitations to relocate Taxiway B to the west of the airport. Limited space and negative impact on the aircraft terminal parking to relocate Taxilane W to the east of the airport. Negative impact on airfield efficiency by restricting the use of Taxilane W to aircraft with wingspans that would provide the required 62 ft wingtip clearance. Using the modified equation on AC 150/5300-13, Chapter 4, at the bottom of Table 4-3, (0.2 × wingspan + 10 ft) the average wingtip clearance for an ADG IV taxilane and an ADG VI taxiway required a minimum wingtip separation of 42.3 ft. This distance is less than the available wingtip separation of 44.3 ft between the typical aircraft using Taxiway B (Boeing B747-800) and the typical aircraft using Taxilane W (Boeing B757-200). Statistical studies indicate that B747s are not likely to deviate from centerlines of straight taxiways such as Taxiway B. B747 operations represent less than 1% of the total operations at the airport and the number of operations for B747-800 is a very small portion of the total B747 operations. The probability of having a B747-800 on Taxiway B traveling side-to-side with a B-757 on Taxilane W is very small.

H-22 Conditions for Approval Restrict operations on Taxilane W to aircraft with a maximum wingspan of 125 ft. Aircraft on Taxilane W should operate at 20 mph or less. Maintain the existing taxiway centerline lighting and taxilane centerline reflectors to provide guidance to the pilots during taxi. Figure H-15. Cross-section of the existing separation at SEA for Case Study # 15. Application of Methodology Risk Plot AA-7 Wingtip Sep 44 ft Severity Major Risk Level < 1.0E-09 Conclusion Low Risk Acceptable Case Study # 16 - Aspen-Pitkin County Airport (ASE) MOS Issue Runway/Taxiway Approval Date 3/5/1999 Separations Runway OFA Taxiway OFA Centerline Standard 186 ft 400 ft Existing 169 ft 320 ft Airport Ref Code D-III Critical Aircraft Aircraft 1 Aircraft 2 Model Grumman Gulfstream IV Grumman Gulfstream IV ADG III III Wingspan 78’ 78’ Synopsis Based on AC 150/5300-13, Chapter 2, Table 2-2, the required runway to taxiway separation at ASE, classified as an ADG D-III airport, is 400 ft. A relocation of the existing taxiway was proposed to increase the runway/taxiway separation from 221.5 ft to 320 ft. Still, the new separation of 320 ft was less than the required 400 ft and thus an MOS was requested. Locating the taxiway at the required 400 ft was not feasible due to the space limitations that Highway 82, the airport frontage road, auto parking lots, and six other buildings posed on the area of interest. The alternative taxiway relocation only impacted the long-term and employee parking and the ARFF building.

H-23 The proposed taxiway alignment was such that the western boundary of the taxiway OFA coincided with the eastern boundary of runway OFA. The width of the OFA on the runway side is 93 ft, which is half of the standard width of taxiway OFA’s of 186 ft. However, the location of the relocated taxiway provides an OFA width of 76 ft (93 ft required by standard) between the taxiway and the apron. The apron cannot be relocated due to space constraints identified in preceding paragraph. Restrictions Location of airplanes on parking apron should be no closer than 493 ft from the runway centerline. Operations restricted to aircraft with wingspan no larger than 95 ft. Justification Lack of space to relocate the existing highway, roads, auto parking, and buildings. Full width taxiway OFA is provided on runway side of the taxiway. Limiting aircraft wing spans to 95 ft provides an adequate taxiway OFA on the apron side in accordance with AC 150/5300-13, Chapter 2, Table 2-3, using the modified formula at the bottom of the table for calculating OFZ widths for specific aircraft (0.7 × wingspan + 10 ft). Conditions for Approval Use of the airport restricted to aircraft with wingspan no larger than 95 ft. Figure H-16. Cross-section of existing separation at ASE. Application of Methodology Risk Plot AA-33, AA-34, and AA-43 Centerline Sep 320 ft Severity Catastrophic Risk Level Airborne Cat I – 8.5E-10 Cat II – 9.0E-09 Risk Level Ground 9.0E-08 Annual Vol. Operations 45,000 Expected # Years > 100 years Conclusion Medium Risk Mitigation Recommended

H-24 Case Study # 17 - Nantucket Memorial Airport (ACK) MOS Issue Taxiway/Taxiway Approval Date 5/6/1986 Separations OFA Centerline Wingtip Standard 152 ft Existing 125 ft 44 ft Airport Ref Code C-III Critical Aircraft Aircraft 1 Aircraft 2 Model ADG III Wingspan 107 ft 55 ft Synopsis An extension of Taxiway E from Taxiway C (now labeled D) to the approach end of Runway 24 would have caused the existing Taxiway F (extending from the terminal apron to the approach end of Runway 24) to be abandoned because the separation between the new Taxiway E and the existing Taxiway F did not meet standards. Abandoning Taxiway F would have caused a number of problems such as disconnection between the T-hangars and the run-up area; conflict among the north ramp, the main terminal ramp, and the southwest general aviation ramp traffic; and back taxi to achieve full length departure on Runway 15. The Taxiway E extension was located in accordance with standards so that the distance between Taxiway E’s centerline and Runway 24’s centerline was 400 ft. This resulted in the separation distance between the parallel Taxiways (E and F) being 125 ft versus the required separation of 153 ft. To avoid abandoning Taxiway F, an MOS to the standard separation between Taxiway E and F was requested. The required parallel taxiway separation for the critical ADG III per AC 150/5300-13, Chapter 2, Table 2-3 was 152 ft. While airport use by these types of aircraft was infrequent at ACK, simultaneous operation of aircraft on the parallel Taxiways E and F was still a possibility. Therefore, to maintain an acceptable level of safety, the approval of the MOS was conditioned upon several operational restrictions. Restrictions Use restricted by direction of air traffic control. Use restricted to daylight only. Use of Taxiway F restricted to small airplanes (max gross weight of 12,500 lb). Guidance signs unlighted. Existing lighting circuit discontinued. Taxiway safety area grading requirements as per AC 150/5300-12.

H-25 Justification Comply with Runway 6/24 to Taxiway E standard separation. Maintain flexibility of operations and flow by air traffic control during peak traffic conditions. Satisfactory wingtip clearance when no simultaneous operation of ADG III aircraft occurs on the parallel taxiways. Conditions for Approval Restrict operations on this portion of the taxiway to daytime. Restrict use of this portion of the taxiway to aircraft of 12,500 lb or less. Maintain this portion of the taxiway unlighted. Figure H-17. Cross-section of the existing parallel taxiway separation at ACK. Application of Methodology Risk Plot AA-7 Wingtip Sep 44 ft Severity Major Risk Level < 1.0E-09 Conclusion Low Risk Acceptable Case Study # 18 - New Castle Airport (ILG) MOS Issue Taxiway/Object Approval Date 6/29/2000 Separations OFA Centerline Wingtip Standard 259 ft 129.5 ft Existing 206 ft 103 ft Airport Ref Code D-V Critical Aircraft Aircraft 1 Aircraft 2 Model AC-130 Spectre N/A ADG IV Wingspan 132.5’

H-26 Synopsis The existing separation between Taxiway A and the movement/non- movement area near the aviation hangar located between Taxiways A3 and A4 is 103 ft. The required taxiway OFA width per AC 150/5300- 13, Chapter 4, Table 4-1 is 259 ft or 129.5 ft separation between the taxiway centerline and the object. The location between Taxiway A3 and A4 on Taxiway A is designated as a fuel truck parking area. Complying with the required OFA standard would have displaced the parking space and placed the fuel truck too close to the aviation hangar, in violation of fire code. Since there were no other available parking areas for the fuel trucks, a MOS was requested to reduce the separation between the centerline of Taxiway A and the object (i.e., fuel trucks) and thus allow enough clearance between the fuel trucks and the hangar. Reduced separation is based on C-130, the largest aircraft using the airport. Restrictions Maintain Hercules C-130 characteristics as most demanding aircraft. Justification No other parking area available for aircraft fuel trucks. The required separation would have located the parked fuel trucks too close to the aviation hangar, in violation of fire code. Using the formula (1.4 × wingspan + 20) found in AC 150/5300-13, Chapter 4, at the bottom of Table 4-1, the required separation between the taxiway centerline and the object resulted in 103 ft. Calculated clearance of 35.5 ft beyond the critical aircraft (i.e., C130) wingtip and 17.3 ft beyond the safety area edge. Conditions for Approval Movement/non-movement line painted at 103 ft from centerline of Taxiway A to delineate the parking limit for the fuel trucks. Figure H-18. Cross-section of the existing separation at ILG. Application of Methodology Risk Plot AA-11 Centerline Sep 103 ft Severity Major Risk Level 2.8E-08 Conclusion Low Risk Acceptable

H-27 Case Study # 19 - Leesburg Municipal Airport (JYO) MOS Issue Runway/Object Approval Date 3/26/1997 Separations OFA Centerline Wingtip Standard 800 ft 300 ft Existing 750 ft 262.5 ft Airport Ref Code C-II Critical Aircraft Aircraft 1 Object Model Grumman Gulfstream III ADG II Wingspan 79’ Synopsis Based on AC 150/5300-13, Chapter 2, Table 2-2, the required runway to taxiway separation at JYO was 300 ft for a C-II aircraft. Locating the parallel taxiway at the required distance would have required one T-hangar unit and two hexagon hangar units to be relocated or reconstructed. In addition to the relocation/reconstruction of the hangars, other existing infrastructure elements such as the taxiway lighting system, the drainage system, a storm water detention facility, and 60,000 square ft of apron would have been impacted. Due to the economic and airport space limitations that redesigning, relocating, and/or reconstructing the existing infrastructure elements would entail, an MOS was requested. Based on AC 150/5300-13, paragraph 209 and Appendix 11, the minimum calculated runway to taxiway separation for ADG II was 239.5 ft and thus the proposed taxiway relocation at 262.5 ft exceeded the minimum requirement. With respect to the runway OFA, AC 150/5300-13, Chapter 3, Table 3-3 requires a width of 800 ft versus the 750 ft existing separation available. However, the hangar structures were outside of the taxiway OFA, the runway safety area (RSA), and the runway object free zone (OFZ). Besides, following the recommendations of a previous study, the hangar structures were marked with obstruction lights to prevent classifying them as hazards. JYO has only right angle taxiway exits from its runway, and there are not any plans to construct acute angle exits. The 400-ft half-width standard is based on a runway with acute angle exits. Restrictions Limit runway and taxiway use to Group II aircraft. Limit Group II aircraft to right-angled exits to assure required turning radii and fillets. Mark the T-hangar and hexagon hangar units with obstruction lights. Justification Relocation/reconstruction of one T-hangar unit, two hexagon hangars, the entire taxiway lighting system, and the existing drainage system. Loss of approximately 60,000 of usable apron. Redesign and reconstruction of a storm water detention facility.

H-28 Economic feasibility. Capacity and space limitations. Adequate runway to taxiway clearance for Group II aircraft based on AC 150/5300-13 Appendix 11 calculations. Adequate turning radii and fillets for right-angled exits. Mitigation of penetration hazards by marking the hangars with obstruction lights. Conditions for Approval Unconditional approval granted with the specified operational restrictions. Figure H-19. Cross-section of existing separation at JYO. Application of Methodology Risk Plot TWY: AA-31 and AA-42 Centerline Sep TWY: 262.5 ft OBJ: 375 ft Severity Catastrophic Risk Level Airborne TWY: 1.2E-10 OBJ: 3.3E-11 Risk Level Ground TWY: 1.2E-07 OBJ: 6.0E-08 Annual Vol. Operations 103,700 Expected # Years > 100 years Conclusion Medium Risk Mitigation Recommended Case Study # 20 - Taunton Municipal Airport (TAN) MOS Issue Runway/Taxiway Approval Date 6/26/2002 (subm.) Separations Runway OFA Taxiway OFA Centerline Standard 240 ft Existing 197 ft Airport Ref Code B-II Critical Aircraft Aircraft 1 Aircraft 2 Model Beech King Air C90 Beech King Air C90 ADG II II Wingspan 50’ 50’

H-29 Synopsis The parallel taxiway to Runway 12/30 was reconstructed in 1960 and its separation from the runway spans 197 ft. In order to comply with the 240 ft separation requirement per AC 150/5300-13, Chapter 2, Table 2-1, a relocation of the taxiway was considered as the primary option. This, however, was not feasible due to the existence of a stream parallel to a portion of the taxiway, and the negative impact on aircraft parking and existing wetlands that a relocation of the parallel taxiway would cause. Therefore, an MOS was requested to keep the existing separation given the fact that the RSA and OFZ distances provided enough clearance for the critical aircraft operating at the airport (i.e., Beach King Air C90). Restrictions Maintain Beech King Air C90 characteristics as most demanding aircraft. Justification The stream running parallel to a portion of the existing taxiway posed space constraints that made the relocation of the parallel taxiway unfeasible. Negative environmental impacts on the existing wetlands caused by relocating the stream running parallel to a portion of the existing taxiway. Negative impact on aircraft parking caused by relocating the parallel taxiway. The runway safety area and obstacle free zone are satisfied by the critical aircraft, namely a Beech King Air C90. Conditions for Approval Restudy of the proposed MOS if a significant change in aircraft size or volume operations occur at TAN. Figure H-20. Cross-section of the existing separation at TAN. Application of Methodology Risk Plot AA-31 and AA-47 Centerline Sep 197 ft Severity Catastrophic Risk Level Airborne 3.0E-10 Risk Level Ground 8.0E-08 Annual Vol. Operations 31,400 Expected # Years > 100 years Conclusion Medium Risk Mitigation Recommended

Abbreviations and acronyms used without definitions in TRB publications: AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA Air Transport Association ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation

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Risk Assessment Method to Support Modification of Airfield Separation Standards Get This Book
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TRB’s Airport Cooperative Research Program (ACRP) Report 51: Risk Assessment Method to Support Modification of Airfield Separation Standards is intended to be used to support requests for modification of standards in those circumstances where the design criteria for separations between taxiways/taxilanes and other taxiways/taxilanes and fixed or movable objects as well as separations between taxiways and runways cannot be met.

The following appendices, included in the pdf and print version of the report, will be helpful in understanding the methodology.

  • Appendix A: Risk Assessment Methodology presents a methodology for five different types of circumstances: taxiway/taxilane to taxiway, taxiway to object, taxilane to taxilane, taxilane to an object, and runway to taxiway/taxilane or object;
  • Appendix F: Aircraft Database Summary presents a summary of aircraft characteristics by model; and
  • Appendix H: Analysis of MOS Cases summarizes information collected in the modification of standards survey and presents results of application of the methodology described in Appendix A to each modification of standards case.

Other report appendices, which are available online only, provide detail and information on the development of the methodology.

In addition, the project developed a

PowerPoint presentation

that may be useful for introducing and explaining the methodology to stakeholders.

In July 2021, an errata was posted for this publication: In Table 7 on page 25, the LDVO coefficient was changed from -3.088 to -13.088. The online version of the report has been corrected.

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