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

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Section 1—Taxiway to Taxiway or Taxiway to Taxilane Procedure to Estimate Risk of Collision 1. Identify the taxiways and the centerline separation to be evaluated. 2. Identify the ADG for analysis or the aircraft with the largest wingspan that will be using each taxiway. It is possible that each taxiway is assigned to a different ADG or specific aircraft. 3. If the assessment is for a specific ADG, the simplified col- lision risk plots can be used based only on the taxiway cen- terline separation (Figures AA-1 to AA-6 in the attachment to this appendix). 4. If the risk assessment involves specific aircraft or two dif- ferent types of aircraft, the wingtip separation chart in Fig- ure AA-7 should be used, and in this case, the following steps will be required: a. Place both aircraft at the centerlines of the parallel taxi- ways (see Figure A-2). b. Calculate the wingtip clearance for this situation using Equation 1: where WD is the distance between wingtips of the two aircraft when both are positioned at the centerline of the taxiways, CS is the centerline separation between the parallel taxiways, WD CS WS WS= − +( )1 2 2 1( ) WS1 is the wingspan for the first aircraft, and WS2 is the wingspan for the second aircraft. c. Using Figure AA-7, enter the wingtip separation and estimate the risk. 5. Using the risk level estimated, compare to 1 × 10−7, the upper probability for risk of major consequences accord- ing to the risk matrix recommended by the FAA. Example 1—Taxiway/Taxiway Separation An airport is planning to build a new taxiway to accommo- date larger capacity. The airport handles aircraft up to ADG V; however, the space available is enough for a taxiway/taxiway centerline separation of only 233 ft, as shown in Figure A-3. The standard separation for ADG V is 267 ft, and an MOS was deemed necessary to demonstrate that the available separa- tion is safe. For taxiway/taxiway separation involving ADG V, Figure AA-5 is used. Entering the separation of 233 ft, the risk of colli- sion when two ADG V aircraft are taxiing is approximately 2.3 E-08(seeFigureA-4),oronecollisionin 43,500,000 movements. The risk is lower than 1.0E-07 and therefore it is acceptable. Section 2—Taxiway to Object Procedure to Estimate Risk of Collision 1. Identify the taxiway and the object separation to be evaluated. A-5 Figure A-2. Example of taxiway/taxiway separation analysis for specific aircraft. Figure A-3. Example of analysis for taxiway/taxiway separation.

A-6 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 226 228 230 232 234 236 Taxiway/Taxiway Centerline to Centerline Separation (ft) R is k of C ol lis io n pe r O pe ra tio n ADG V Standard = 267 ft 2.3E-08 Figure A-4. Example of analysis of taxiway/taxiway separation (ADG V). Figure A-5. Example of taxiway/object separation analysis for specific aircraft. 2. Identify the ADG for analysis or the aircraft with the largest wingspan that will be using the taxiway. 3. If the assessment is for a specific ADG, the simplified colli- sion risk plots can be used based only on the centerline to object separation (Figures AA-8 to AA-13). 4. If the risk assessment involves a specific aircraft, the wingtip separation plot in Figure AA-14 should be used, and, in this case, the following steps will be required: a. Placetheaircraftatthetaxiwaycenterline(seeFigure A-5). b. Calculate the wingtip clearance for this situation: where WD is the distance between the wingtip and the object when the aircraft is positioned at the centerline of the taxiway, CS is the separation between the taxiway centerline and the object, and WS is the aircraft wingspan. c. Using Figure AA-14, enter the wingtip separation and calculate the collision risk. WD CS WS= − 2 2( ) 5. Compare the risk level estimated to 1 × 10−7, the highest acceptable probability for risk of major consequences according to the risk matrix recommended by the FAA. Example 2—Taxiway/Object Separation An airport is planning to use an existing taxiway for ADG III aircraft; however, it currently is used by ADG II aircraft, and the separation between the taxiway and an exist- ing service road is only 72 ft. The scenario is presented in Figure A-6. The airport does not have space to move the service road because it is limited by the airport peri- meter fence. The standard separation for ADG III is 81 ft, and an MOS is necessary to evaluate whether the separation is safe. For taxiway/object separation involving ADG III, Figure AA-10 is used. Entering the separation of 72 ft, the risk of col- lision when an ADG III aircraft is taxiing is approximately 1.0E-06 (see Figure A-7), or one collision in 1,000,000 move- ments. The risk is not acceptable based on the criterion of 1.0E-07; however, it may be possible to evaluate mitigation