Summary
The FAA proposes to supersede an existing airworthiness directive (AD) for Pratt & Whitney Canada (PWC) PW206A and PW206E turboshaft engines. That AD currently requires initial and repetitive borescope inspections of compressor turbine and power turbine blades for blade axial shift, and replacement of blade retaining rivets and certain rotor air seals as terminating action for the repetitive borescope inspections.
This proposed AD would require the same actions but needs to clarify the extent of engine disassembly that triggers the required part replacements. This proposed AD is prompted by reports of engine shutdowns and emergency landings due to severe vibration, resulting in exhaust gases escaping from the engine-to-exhaust nozzle interface, thereby triggering in-flight engine fire warnings. We are proposing this AD to prevent turbine blade axial shift, which could cause high levels of vibration, loss of engine torque, in-flight engine shutdown, and loss of the airframe exhaust duct.