What happened
On August 10, 2015, a Piper PA-28-161 Cadet, registration HB-PQI, departed from Birrfeld Airport (LSZF) for a training flight. During the takeoff roll, the student pilot reached rotation speed at approximately half the runway length. After the flaps were retracted, the aircraft reached an indicated airspeed of 79 knots.
As the aircraft entered the crosswind leg, the engine performance began to decline, accompanied by engine sputtering. The flight instructor took control of the aircraft to maintain a glide slope. Despite attempting to switch to the redundant FADEC B system, there was no change in engine power, and the engine eventually failed completely. The instructor performed an off-field landing in a nearby field at approximately 13:48 local time. The aircraft remained undamaged, and both occupants, including one lightly injured, exited the aircraft without further assistance.
The investigation
Investigators focused on the mechanical integrity of the fuel pump, a gear-driven component designed to supply Jet A-1 to the high-pressure pump. The investigation involved the disassembly and metallurgical examination of the pump's internal components, specifically the drive gear and the drive nut.
Findings
Technical analysis revealed that the drive gear, constructed from sintered steel, suffered from multiple cracks and a significant total fracture. These cracks were identified as fatigue fractures originating at the power transmission points of the polygon shaft. The investigation determined that the insufficient homogeneity of the sintered steel was a primary cause of these defects.
Additionally, the drive nut exhibited secondary fractures and wear patterns related to the sintering errors. The investigation concluded that the fuel pump components were metallurgically unsuitable for continuous long-term operation, as they became mechanically unstable over time. The failure of the drive gear led to the engine failure during the flight.