Piper PA46-500TP N31062 accident near Manteo, North Carolina

Probable cause

The improperly secured pneumatic compressor discharge air (P3) line coupling nut on the engine, which ultimately allowed the nut to back off resulting in a partial loss of engine power.

NTSB analysis

After takeoff, the pilot retracted the landing gear and the turbopropeller-powered single-engine airplane’s engine lost partial power. The pilot attempted to regain engine power using a manual override but was unsuccessful. A forced landing was made at the departure airport, during which the airplane touched down at intersecting runways and traveled through the grass before coming to a stop, resulting in substantial damage to the fuselage. with the nose gear sheared off. Examination of the airplane after the accident revealed substantial damage to the fuselage.

Examination of the engine revealed that the front of the compressor discharge air (P3) pneumatic line was secured to the gas generator case. The P3 line’s rear coupling nut was lockwired to the adjacent bolt. The lockwire was removed and the coupling nut was loosely fitted (no torque) with the adjacent nipple. The exterior surface of the nut exhibited fretting wear from contact with the twists of the lockwire. The fretting wear was observed on the conical surface of the nipple from contact with the mating surface of the tube. Examination at higher magnification of the oval-shaped fretting wear along the outer surface of the “B”-nut mating with the nipple showed the fretting damage occurred due to the nut being in contact with the lockwire while the nut was attempting to move in the counterclockwise direction (in the direction loosening the nut). Since the nut would not move significantly once the lockwire was in place, it suggested that the torque at installation was low, which would have allowed the nut to loosen, thus compromising the seal of the connection. Subsequently, when the pneumatic line seal became loose, it likely resulted in the loss of P3 air pressure and the subsequent partial loss of engine power like what the pilot described. A review of the maintenance records could not determine when the P3 pneumatic line was most recently secured.

Text from the NTSB. Open the NTSB docket for ERA21LA287 for the full record.