Summary
This document proposes to supersede 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. The proposed AD would require you to repetitively inspect all flap actuator internal gear systems to ensure correct end-play and backlash measurements with any necessary corrective adjustments, incorporate certain modifications to the flap system, and install a new design FCWU. The proposed AD would also require you to modify the flap control wiring and install a flap power drive-unit field control panel. The actions specified by the proposed 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. Both conditions have the potential for flap system failure with consequent reduced or loss of control of the airplane.