Airworthiness Directives; Pilatus Aircraft Ltd. Models PC-12 and PC-12/45 Airplanes

This amendment adopts a new airworthiness directive (AD) that supersedes Airworthiness Directive (AD) 99-19-32, which applies to certain Pilatus Aircraft Ltd. (Pilatus) Models PC-12 and PC-12/45 airplanes. AD 99-19-32 currently requires you to inspect the flap actuator internal gear system for correct end-play and backlash measurements and accomplish any corrective adjustments, as necessary. Pilatus has identified modifications for the flap system and designed and manufactured a new flap control and warning unit (FCWU) that permits the flap power drive-unit circuit breaker to close during flight. This AD requires you to modify the flap control wiring and install a flap power drive-unit field control panel. The actions specified by this AD are intended to allow the flap power drive-unit circuit breaker to close during flight and prevent current surges in the flap control system. If the pilot cannot close the circuit breaker during flight, the flight control and warning unit (FCWU) would not sense a worn actuator. Current surges in the flap control system could decrease the electrical life of the flap power drive-unit motor contactor. Both conditions have the potential for flap system failure with consequent reduced or loss of control of the airplane.