Flight and Event
On July 6, 2021, about 1507 eastern daylight time, a Piper PA-46-500TP, registration N31062, was substantially damaged during an accident near Manteo, North Carolina. The airline transport pilot and passenger were not injured. The flight was operated as a personal flight under Title 14 Code of Federal Regulations Part 91.
The pilot reported that the fuel tanks had been topped off with Jet-A fuel before departure. He departed runway 23 at Dare County Regional Airport (MQI). Shortly after retracting the landing gear, he noted a loss of thrust from the engine. He verified that the throttle had not moved, unlocked the Manual Override (MOR), and moved it forward just under halfway to full in an attempt to increase engine power. Engine power did not increase, and the pilot began preparing for a forced landing. Subsequently, the engine surged, and the pilot initiated a climb. After a brief interruption of engine power, the airplane continued climbing, and the pilot turned back toward the airport.
As the pilot maneuvered the airplane back, the engine again lost power. He landed about midfield at the intersection of runway 35 and runway 23, aligned about 35° off the runway heading for runway 35. The airplane continued off the paved surface into grass, where the nose landing gear collapsed, resulting in substantial damage to the fuselage.
Examination Findings
Examination of the propeller revealed all blades bent aft, opposite rotation, and twisted toward low pitch with chordwise and rotational scoring in the tip region. No visible discrepancies were noted that would prevent or degrade normal propeller operation prior to impact. All visible damage was consistent with high impact forces while rotating at low power. The electric fuel pumps on the airframe operated within limits.
The engine examination showed the reduction gearbox and exhaust duct were unremarkable. All six inlet case struts were fractured. The accessory gearbox was unremarkable. The propeller shaft rotated manually, and the power section rotated freely. The gas generator case could not be rotated manually. Compressor blades and the centrifugal impeller exhibited rotational scoring.
The flow divider, fuel-to-oil heat exchanger, fuel pump, and torque limiter were functionally tested with no anomalies. The fuel control unit, overspeed governor, and propeller governor were tested, and deviations within field adjustments were noted.
The front of the compressor discharge air (P3) pneumatic line was secured to the gas generator case. The rear coupling “B” nut was lockwired to an adjacent bolt. After removing the lockwire, the coupling nut was found 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. Examination at higher magnification of oval-shaped dents along the outer surface of the “B” nut indicated material loss from a wear mechanism, with directionality suggesting relative movement between the nut and lockwire. Blackish residues consistent with fretting wear were observed. The wear residues accumulated predominantly towards one extremity of the grooves, indicating the fretting damage occurred while the nut contacted the wire and attempted to move counterclockwise (in the loosening direction).
The fittings on the rear section of the line between the filter housing and the fuel control were lockwired and secured or torqued to their respective nipple or elbow. Both fittings were tight in the filter housing.
Maintenance Records and Flight Manual
A review of the maintenance records could not determine when the P3 pneumatic line was most recently secured.
According to the airplane flight manual, the manual override lever (MOR) is an emergency device that may allow the crew to regain power and continue safe flight and landing following fuel control unit (FCU) malfunction or power lever control loss. The MOR controls fuel flow to the engine in the event of a pneumatic malfunction in the engine fuel control unit. A malfunction of the pneumatic signal (Py) input to the FCU results in fuel flow decreasing to minimum idle. Additional effects include loss of torque and Ng limiting functions, and Nf governor operation. To operate the MOR, the pilot lifts up on the lever and slowly moves it forward to take up the dead-band until the engine responds, allowing the engine to stabilize before advancing further.