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H-1 APPENDIX H Analysis of MOS Cases

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H-2 This section summarizes the information collected in the MOS survey and presents results for application of the methodology described in Appendix A to each MOS case. Table H-1 shows the airports included in the MOS survey. Table H-1. Airports included in MOS survey. Case # Airport ID NPIAS MOS Type FAA Region 1 Philadelphia, PA PHL LH TWY/TWY AEA 2 Anchorage, AK ANC MH TWY /OBJ AAL 3 Addison, TX ADS RL RWY/TWY ASW 4 Bridgeport, CT BDR GA RWY/TWY ANE 5 Accomack, VA MFV GA RWY/OBJ AEA 6 Lincoln Park, NJ N07 RL TLN /OBJ AEA 7 New York JFK, NY JFK LH TWY/TWY AEA 8 Newark, NJ EWR LH TWY/TWY* AEA 9 Minneapolis, MN MSP LH TWY/TWY AGL 10 Chicago, IL ORD LH TWY/TWY AGL 11 Chicago, IL ORD LH TWY /OBJ AGL 12 Barnstable, MA HYA NH RWY/TWY ANE 13 Laconia, NH LCI GA RWY/TWY ANE 14 Seattle-Tacoma, WA SEA LH RWY/TWY ANM 15 Seattle-Tacoma, WA SEA LH TWY/TWY ANM 16 Aspen, CO ASE NH RWY/OBJ ANM 17 Nantucket, MA ACK NH TWY/TWY ANE 18 New Castle, DE ILG GA TWY/TWY AEA 19 Leesburg, VA JYO RL RWY/OBJ AEA 20 Taunton, MA TAN GA RWY/TWY ANE Table H-2 summarizes the cases by type of MOS; the majority of the cases were MOS for runway/taxiway separation and taxiway/taxiway separation. Table H-2. Number of cases for each MOS type. MOS Type Airport Number of Cases Runway/Taxiway ADS, ASE, BDR, HYA, LCI, SEA, TAN 7 Taxiway/Taxiway ACK, EWR, JFK, MSP, ORD, PHL 6 Runway/Object JYO, MFV 2 Taxiway/Taxilane SEA 1 Taxiway/Object ANC, ILG, N07, ORD 4 Total 20

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H-3 Table H-3 summarizes the cases by type of justification used to approve the MOS by the FAA, and Table H-4 presents a summary of the restrictions imposed due to the MOS. Table H-3. Justifications used to obtain MOS approval. Runway/ Taxiway/ Runway/ Taxiway/ Taxiway/ MOS Justification Total Taxiway Taxiway Object Taxilane Object Advisory Circular acceptable level of 2 3 1 1 2 9 safety Airport facilities' 2 2 1 1 2 8 capacity Communications 1 1 Delays/Congestion 2 2 Economic constraints 2 1 1 1 5 Environmental 2 1 1 4 constraints Operations capacity 3 1 1 5 Prior ADG standards 2 1 3 compliance Physical constraints 5 4 1 1 2 13 Runway/Taxiway 1 1 separation Security 1 1 Each MOS may have more than one justification Table H-4. Number of cases for each MOS restriction by MOS type. Runway/ Taxiway/ Runway/ Taxiway/ Taxiway/ MOS Restriction Total Taxiway Taxiway Object Taxilane Object Aircraft exit angle 1 1 Aircraft speed 1 1 Aircraft type/ 6 4 2 1 2 15 weight/wingspan Construction 1 1 requirements Dedicated facility use 1 3 4 Exemption/order terms 1 2 3 Markings and lighting 1 1 1 1 1 5 Operations time of day 1 1 Simultaneous facility 1 1 operations Vehicle type/ 1 1 dimensions Each MOS may have more than one restriction

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H-4 The methodology was applied to each of the 20 MOS cases, and the following sections provide a summary of the issues involved, as well as characterization of the airfield separations. For each case, the methodology developed in this study was applied, and a summary of results is presented. Case Study #1 - Philadelphia International Airport (PHL) MOS Issue Taxilane/Taxilane Approval Date 6/7/1999 Separations OFA Centerline Wingtip Standard 423 ft 198 ft 27' Existing 330 ft 153.5 ft 23' Airport Ref Code C-III and C-IV Critical Aircraft Aircraft 1 Aircraft 2 Model Dash 8-300 Boeing 767 ADG III IV Wingspan 90' 171' Synopsis One of the parallel taxilanes would be designed to serve only Terminal F (Group III aircraft) while the other taxilane would be designed to serve both Terminals E and F (Group III and IV aircraft). Proposed OFA separation distance is 330 ft. Restrictions Use of southernmost taxilane is permitted to Group IV (Boeing B-767) or Group III (Dash 8-300) aircraft. Use of northernmost taxilane is limited to Group III aircraft (Dash 8-300). Justification Handle the high traffic volume, minimize delays. Adequate clearance when the northernmost taxilane is limited to commuter aircraft no larger than 90 ft wingspan. Restrict the use of the taxilane to aircraft with wingspans up to 90 ft. Accidents/Incidents 13 accidents and incidents were identified between 1982 and 2009. Figure H-1. Cross-section of existing separation at PHL. Application of Methodology Risk Plot Figure AA-21 Wingtip Sep 23' Severity Major Risk Level < 1.0E-09 Conclusion Low Risk Acceptable

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H-5 Case Study # 2 - Ted Stevens Anchorage International Airport (ANC) MOS Issue Taxiway/Object Approval Date 6/14/2004 Separations OFA Centerline Wingtip Standard 193 ft 193 ft 62 ft Existing 174 ft 174 ft 43 ft Airport Ref Code D-VI Critical Aircraft Aircraft 1 Aircraft 2 Model A-380-800 N/A ADG VI Wingspan 262' Synopsis With the introduction of ADG VI (i.e., Airbus 380-800) to the airport operations, ANC proposed to reconstruct Taxiway R and widen it to 100 ft to meet the new ADG requirements. The projected taxiway width left an available taxiway OFA of 174 ft between the centerline of Taxiway R and the tug road vs. the required 193 ft OFA centerline separation based on AC 150/5300-13, Chapter 4, Table 4-1. Restrictions Maintain Airbus A388 characteristics as most demanding aircraft. Handle the tug road as an operational item with Antonov 124 aircraft operations. Justification Limited space availability; Cost efficiency; Security of airport operations area; Limited communication ability with tug operators; Maintain current level of cargo aircraft parking capacity. Airport already accommodates ADG VI on the existing runways and taxiways. Conditions for Tugs and vehicles operating on tug road between Taxiways Q and T are Approval limited to maximum height of 14 ft. Commuter simulation indicates jet blast from A388 on tug road should not be a problem. If drivers report jet blast related problems, airport authority must submit a proposed mitigation plan. Accidents/Incidents Nine accidents and incidents were identified between 1982 and 2009. Figure H-2. Cross-section of the existing separation at ANC.

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H-6 Application of Methodology Risk Plot AA-13 Centerline Sep 174 ft Severity Major Risk Level < 1.0E-09 Conclusion Low Risk Acceptable Case Study # 3 - Addison Airport (ADS) MOS Issue Runway/Taxiway Approval Date 11/18/2008 Separations OFA Centerline Wingtip Standard 400 ft 282 ft Existing 300 ft 182 ft Airport Ref Code C-III Critical Aircraft Aircraft 1 Aircraft 2 Model B-737 B-737 ADG III III Wingspan 118' 118' Synopsis The existing separation between Runway 15/33 and parallel Taxiway A is 300 ft, less than the required 400 ft as established in AC 150/5300-13, Chapter 2, Table 2-2 for the airport's ADG III using approach categories C and D. Relocating the parallel taxiway or the runway were not feasible options due to the limited area available to the airport for further development. Restrictions Maintain B-737 characteristics as most demanding aircraft. Justification Limited area available for relocating either Runway 15/33 or the parallel taxiway due to existing road and industrial developments. Airport safety will not be impeded by the proposed modification to the runway/taxiway separation. Conditions for None specified Approval Accidents/Incidents Two accidents and incidents were identified between 1982 and 2009. Figure H-3. Cross-section of the existing separation at ADS.

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H-7 Application of Methodology Risk Plot AA-33 and AA-43 Centerline Sep 300 ft Severity Catastrophic Risk Level Airborne 1.1E-9 Risk Level Ground 1.0E-7 Annual Vol. Operations 133,600 Expected # Years > 140 years Conclusion Medium Risk Mitigation Recommended Case Study # 4 - Igor I. Sikorsky Memorial Airport (BDR) MOS Issue Runway/Taxiway Approval Date 8/04/2003 Separations OFA Centerline Wingtip Standard 300 ft 221 Existing 268300 ft (variable) 189221 ft Airport Ref Code C-II Critical Aircraft Aircraft 1 Aircraft 2 Model ADG II II Wingspan Max 79 ft Max 79 ft Synopsis The required separation between runway and taxiway at BDR is specified as 300 ft based on AC 150/5300-13, Chapter 2, Table 2-2. Locating the centerline of 35-ft-wide Taxiway D at the required distance through its length would position the end of the taxiway (i.e., toward the approach end of Runway 11) in a tidal ditch. To avoid the ditch incursion, the taxiway centerline needed to gradually decrease from the required 300 ft to 268 ft. Based on the wingspan dimension of the critical aircraft, it was determined that adequate clearance would remain between the end of Taxiway D and the runway Obstacle Free Zone (OFZ). In addition, no part of the critical aircraft would go beyond the 200 ft half-width OFZ limit for Runway 11/29, which is a modified width permitted for ADG II within category C per AC 150/5300-13, Chapter 3, Table 3-3 notes. Restrictions Runway Safety Area for aircraft Approach Category C reduced to 200 ft half-width due to ADG II as per Table 3-3 in AC 150/5300-13. Justification Space limitation imposed by a deep tidal ditch. Satisfactory clearance of Runway Safety Area by ADG aircraft. Conditions for Location of taxiway holding position at 250 ft from runway centerline. Approval Accidents/Incidents Two accidents and incidents were identified between 1982 and 2009.

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H-8 Figure H-4. Cross-section of existing separation at BDR. Application of Methodology Risk Plot Plots AA-31 and Centerline Sep 268 ft AA-42 Severity Catastrophic Risk Level Airborne 1.1E-10 Risk Level Ground 1.1E-7 Annual Vol. Operations 64,000 Expected # Years > 100 years Conclusion Medium Risk Mitigation Recommended Case Study # 5 - Accomack County Airport (MFV) MOS Issue Runway/Object Approval Date 12/15/1992 Separations OFA Centerline Wingtip Standard 400 ft Existing 360 ft Airport Ref Code C-II Critical Aircraft Aircraft 1 Aircraft 2 Model ADG II Parked aircraft Wingspan Max 79 ft Max 79 ft Synopsis The aircraft parking area and agricultural storage shed located near the existing terminal building had a separation distance to the runway of 360 and 400 ft, respectively. Based on AC 150/5300-13, Chapter 2, Table 2- 2, the standard required runway OFA for a C-II design aircraft is 400 ft, larger than the existing separation of 360 ft between the runway and the parking area. Restrictions Maintain type C-II as most demanding aircraft. Justification Maintaining aircraft parking and keeping agricultural storage shed facilities operational. Adequate clearance when compared to the available distance between the runway and the terminal building of 360 ft. Conditions for None specified Approval Accidents/Incidents No accidents and incidents were identified between 1982 and 2009.

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H-9 Figure H-5. Cross-section of existing separation at MFV. Application of Methodology Risk Plot Plots AA-31 and Centerline Sep 360 ft AA-42 Severity Catastrophic Risk Level Airborne <1.0E-09 Risk Level Ground 5.9E-08 Annual Vol. Operations 13,870 Expected # Years > 100 years Conclusion Medium Risk Mitigation Recommended Case Study # 6 - Lincoln Park Airport (N07) MOS Issue Taxilane/Object Approval Date 4/26/2007 Separations OFA Centerline Wingtip Standard 79 ft Existing 75 ft Airport Ref Code D-VI Critical Aircraft Aircraft 1 Aircraft 2 Model Cessna 414 Chancellor N/A ADG B-I Wingspan 41 ft Synopsis The construction of four T-hangar units near the approach end of Runway 19 reduced the taxilane OFA to 75 ft versus the required distance of 79 ft. The location of the T-hangars was constrained by the Riparian Corridor of Middle Ditch, wetlands, and Part 77 surfaces. The proposed location of the hangars was the only place that met those constraints. Restrictions Taxiway and hangars should only be used by aircraft with a maximum wingspan of 42 ft. Justification Hangars location within the Passaic River Basin and constrained by the Riparian Corridor of Middle Ditch, wetlands, and Part 77 surfaces. Satisfactory OFA clearance when aircraft with wingspan up to 42 ft long travels on the taxilane based on the modified equation found in AC 150/5300-13, Chapter 4, at the bottom of Table 4-1 (1.2 wingspan + 20 ft).

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H-10 Conditions for Restrict use of taxiway to aircraft with wingspan no greater than 42 ft. 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 284300 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.

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H-11 Restrictions Restrict simultaneous aircraft operation involving B747-800 aircraft on 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

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H-19 210' 135' 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 statute mile, and 550 ft for CAT II/III approach with a visibility less than 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 ft550 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.

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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 B-747-800 aircraft are not allowed to taxi on the northern-most 3,000 ft Approval 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

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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.

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H-22 Conditions for Restrict operations on Taxilane W to aircraft with a maximum wingspan of Approval 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.

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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 Use of the airport restricted to aircraft with wingspan no larger than Approval 95 ft. Figure H-16. Cross-section of existing separation at ASE. Application of Methodology Risk Plot AA-33, AA-34, and Centerline Sep 320 ft AA-43 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

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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.

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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 Restrict operations on this portion of the taxiway to daytime. Approval 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'

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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 Movement/non-movement line painted at 103 ft from centerline of Approval 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

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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.

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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 Unconditional approval granted with the specified operational Approval restrictions. Figure H-19. Cross-section of existing separation at JYO. Application of Methodology Risk Plot TWY: AA-31 and Centerline Sep TWY: 262.5 ft AA-42 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. 103,700 Expected # Years > 100 years Operations 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'

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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 Restudy of the proposed MOS if a significant change in aircraft size or Approval 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