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28 CHAPTER 5 Validating the Methodology MOS Case Studies Comparison of estimated and historical incident/accident rates, when available; and One of the goals of this study was to evaluate the types of jus- Major conclusions on risk level and acceptance. tification used by airports when submitting MOS requests to the FAA, specifically when the non-compliance issue was related to Additional details for each analysis are presented in airfield separation. A second objective was to test and validate Appendix H. The following describes the information con- the methodology applied to those cases to evaluate how the new tained in each column of Table 12: methodology might help support such requests. To achieve these objectives, a survey was conducted of airports with MOS Airp.--FAA code of the airport. for airfield separations that have been approved by the FAA. ADG--Aircraft Design Group that defines the separation. Type of MOS--Type of procedure used in the analysis. MOS Survey Risk Level--Probability for risk severity considered. Cata- strophic consequences were considered for every analysis The Airports Division of the FAA regional offices were involving runway separation, and major consequences were contacted to obtain a list of airports that have received MOS considered for the remaining cases. The definitions for approvals related to airfield separations. Fifty-nine cases severity and likelihood classifications are based on the FAA were identified for which some information was available. risk matrix (FAA, 2010) Out of those cases approved by the FAA, 20 were selected to Expected # Yrs--Number of years that an accident is cover various regions and the spectrum of National Plan of expected to occur. Integrated Airport Systems (NPIAS) categories. The airports Risk < 1.0E-7--Yes, if risk is lower than 1 in 10 million were characterized according to geographic region, aircraft operations. operations, fleet mix, airport reference code, and NPIAS Risk < 1.0E-9--Yes, if risk is lower than 1 in 1 billion classification. The list of MOS cases selected for this study is operations. shown in Table 11. More details about each case are pre- Expected Severity--Worst credible consequence expected sented in Appendix H. for the accident, based on categories defined in the FAA risk matrix (FAA, 2010). FAA Risk Classification--Level of risk according to clas- Methodology Applied to MOS Cases sification based on FAA risk matrix (FAA, 2010). To validate the methodology and the models developed in Acceptable--Yes, if level of risk is medium or low; how- this study, the analysis procedures presented in Appendix A ever, for medium risk, measures to mitigate and control were applied to each of the 20 selected MOS cases. A summary may be necessary. of results is presented in Table 12. For each case, the following information is provided: Figures 23 and 24 present a summary of the most frequent justifications and restrictions, respectively, when submitting The non-standard situation and the compliance standards; MOS requests related to airfield separations. The analysis of the separation using the risk analysis As observed in Table 12, the methodology would help methodology; support the analysis of MOS. With the exception of one case,

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29 Table 11. Airports included in the MOS survey. Case # Airport ID NPIAS1 MOS Type2 FAA Region3 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 1 National Plan of Integrated Airport Systems (NPIAS) Classification LH: Primary, Large Hub MH: Primary, Medium Hub SH: Primary, Small Hub NH: Primary, Non-Hub RL: Reliever GA: General Aviation 2 MOS Type RWY/TWY: runway to taxiway separation TWY/TWY: taxiway to taxiway separation TWY/TLN: taxiway to taxilane separation TWY/OBJ: taxiway to object separation TLN/TLN: taxilane to taxilane separation TLN/OBJ: taxilane to object separation RWY/OBJ: runway to object separation 3 FAA Regions with Relevant MOS Cases AEA: Eastern AAL: Alaska ASW: Southwest ANE: New England AGL: Great Lakes ANM: Northwest Mountain the analysis results provided an insight into the quantitative credible consequence for taxiway/taxilane collisions risk associated with each case. Moreover, the results helped (FAA, 2010). identify the level of risk and consequently the need to include The same criterion is suggested to evaluate runway separa- additional measures to control risk. tions because it was the basis for defining design standards The cases with low levels of risk are satisfactory without ad- using the FAA/ICAO CRM. It should be noted that the most ditional measures, except to keep the conspicuity of taxiway credible consequence for aircraft veering off a runway is cat- and taxilane centerlines under any weather conditions. astrophic. As such, the acceptable risk level is one accident Based on these results, some important conclusions can be in 1 billion operations, and according to the FAA, the risk is drawn: classified as medium. The FAA also added criteria specific for airports, and the The suggested level of risk criterion for taxiway/taxilane/ maximum risk for accidents of major consequences is one object separations is one accident in 10 million move- in every 2.5 million departures or 4 10-7; however, based on ments. This criterion was met for each of the case the results of the analysis using the risk methodology, a more studies that does not involve runway separations. This conservative level may be used, and a level of one accident in is also the maximum risk for the range defined in the 10 million operations for cases involving taxiway/taxilane/ FAA risk matrix for accidents of major severity, the worst object is recommended.

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30 Table 12. Summary of results for MOS case studies. Airp. ADG Type of MOS Risk Expected Risk < Risk < Expected FAA Risk Acceptable Level # Yrs 1.0E-7 1.0E-09 Severity Classification PHL III & IV Taxilane/Taxilane <1.0E-9 N/A Yes Yes Major Low Yes ANC VI Taxiway/Object <1.0E-9 N/A Yes Yes Major Low Yes ADS III Runway/Taxiway 1.0E-7 > 100 Yes No Catastrophic Medium Yes BDR II Runway/Taxiway 1.1E-7 > 100 No No Catastrophic Medium Yes MFV II Runway/Object 5.9E-8 > 100 Yes No Catastrophic Medium Yes N07 I Taxilane/Object 1.2E-9 N/A Yes No Major Low Yes JFK VI Taxiway/Taxiway <1.0E-9 N/A Yes Yes Major Low Yes EWR V Taxiway/Taxiway <1.0E-9 N/A Yes Yes Major Low Yes Taxilane/Object <1.0E-9 N/A Yes Yes Major Low Yes MSP IV Taxiway/Taxiway <1.0E-9 N/A Yes Yes Major Low Yes ORD V Taxiway/Object <1.0E-9 N/A Yes Yes Major Low Yes ORD V Taxiway/Taxiway <1.0E-9 N/A Yes Yes Major Low Yes HYA III Runway/Taxiway 8.8E-8 > 100 Yes No Catastrophic Medium Yes LCI III Runway/Taxiway 2.0E-7 > 100 No No Catastrophic Medium Yes SEA VI Runway/Taxiway 1.6E-6 N/A No No Catastrophic High1 No1 SEA VI Taxiway/Taxilane <1.0E-9 N/A Yes Yes Major Low Yes ASE III Runway/Taxiway 9.0E-8 > 100 Yes No Catastrophic Medium Yes ACK III Taxiway/Taxiway <1.0E-9 N/A Yes Yes Major Low Yes ILG IV Taxiway/Object 2.8E-8 N/A Yes No Major Low Yes JYO II Runway/Taxiway 1.2E-7 > 100 No No Catastrophic Medium Yes TAN II Runway/Taxiway 8.0E-8 > 100 Yes No Catastrophic Medium Yes 1 MOS approval conditions by the FAA restrict the use of the taxiway under specific conditions to avoid the situation of high risk. 5 6 Physical Aircraft type/weight/wingspan Advisory Circular 5 Markings and lighting 4 Facilities capacity Dedicated facility use Economic Exemption/order terms Operations capacity 4 # of Cases # of Cases 3 Environmental Prior ADG standards 3 2 2 1 1 0 0 RWY/TWY TWY/TWY RWY/OBJ TWY/TLN TWY/OBJ RWY/TWY TWY/TWY RWY/OBJ TWY/TLN TWY/OBJ Type of Separation Type of Separation Figure 24. Most common restrictions for MOS Figure 23. Most common justifications for MOS of airfield separations. of airfield separations.