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where TWY-OFA is taxiway object free area width and STO is taxiway centerline to object separation. ⢠Taxilane centerline to object (see Figure 3): Separation is calculated based on 0.6 times the wingspan of the most demanding airplane plus 10 ft (wingtip clearance). Reduced clearances are acceptable because taxi speed is very slow outside the movement area, taxiing is precise, and special operator guidance techniques and devices normally are present. ⢠Taxilane OFA (see Figure 4): Width is equal to twice the taxilane centerline to object separation for a single lane width and 2.3 times the wingspan of the most demanding airplane plus 30 ft for a dual lane. S WS 10TXL-OBJ = +0 6. TWY-OFA STO= 2 Appendix 9 of AC 150/5300-13 does not indicate how the safety factors or the wingtip clearances were determined (FAA, 1989). Interviews indicated that these factors were based on engineering judgment. As far back as the 1970s, and probably even before then, there were differences in airport design standards and the cri- teria used to establish instrument approaches. These differ- ences primarily affected the standards associated with runway approaches and separations. Several attempts were made over the years to resolve these differences. This issue became crit- ical in the early 2000s, when an analysis performed using the CRM indicated that aircraft located on a parallel taxiway 400 ft from the runway centerline posed a safety risk to aircraft on an instrument approach to that runway when those aircraft executed a missed approach. TXL-OFA S single lane TXL-OFA TXL-OBJ= ( ) = 2 2 3 . WS 30 ft dual lane+ ( ) 7 Figure 2. Wingtip clearance from taxiway. Figure 3. Wingtip clearance for taxilanes.
