Summary
We propose to supersede Airworthiness Directive (AD) 98-12-01, which applies to certain Pilatus Aircraft Ltd (Pilatus) Models PC-6, PC-6/A, PC-6/B, and PC-6/C series airplanes equipped with turbo-prop engines. AD 98-12-01 currently requires you to modify the fuel system to improve the venting between the collector tank, the main wing tanks, and the engine. Since we issued AD 98-12-01, the FAA determined the action should also apply to all the models of the PC-6 airplanes listed in the type certification data sheet of Type Certificate (TC) No. 7A15 that are produced in the United States through a licensing agreement between Pilatus and Fairchild Republic Company (also identified as Fairchild Industries, Fairchild Heli Porter, or Fairchild-Hiller Corporation). In addition, the intent of the applicability of AD 98-12- 01 was to apply to affected serial numbers of the airplane models listed in TC No. 7A15. Consequently, this proposed AD would retain all the actions of AD 98-12-01,would add those Fairchild Republic Company airplanes to the applicability of this proposed AD, and would list out the individual specific airplane models. We are proposing this AD to prevent engine fuel starvation during maximum climb and descent caused by poor fuel tank venting with low fuel levels, which could result in a loss of engine power during critical phases of flight.