What happened
On March 10, 2021, a Diamond Aircraft DA42, registration HB-LUP, was conducting a training flight under Instrument Flight Rules (IFR) from Zurich to Bern-Belp. The crew, consisting of a flight instructor and a student pilot, was practicing emergency procedures involving a simulated right engine failure during the cruise phase.
Shortly before commencing the instrument approach to Bern-Belp, the aircraft experienced an actual failure of the left engine. This was accompanied by cockpit warnings indicating failures in both Engine Control Unit channels. The crew promptly executed emergency procedures, declared an emergency, and transitioned to Visual Flight Rules (VFR). They diverted to the nearby Grenchen airport, landing safely on runway 06 at 09:49 UTC.
The investigation
The investigation focused on the left engine's performance data, which revealed that the fuel pressure in the common-rail system plummeted from a normal cruise level of approximately 1300 bar to just 10 bar within seconds, triggering the shutdown.
Upon disassembly of the fuel high-pressure pump, investigators found that the suction valve in one of the three pump cells had been destroyed by the pump piston. The investigation revealed significant mechanical damage, including a shattered ceramic valve plate and a destroyed valve cage. Metallurgical analysis showed evidence of abrasive wear and corrosion on the valve plate and valve cage seats. Furthermore, the investigation noted that the valve plate and valve cage had not been replaced during previous overhauls, as such replacements were not mandatory under existing maintenance protocols.
Findings
- The left engine failure was directly caused by the failure of the fuel high-pressure pump.
- The pump failed because the suction valve in one of the three cells was destroyed by the movement of the pump piston.
- Lateral movement of the valve cage occurred due to material loss caused by erosion in the valve cage seat area.
- Abrasive wear (sliding wear) was present on the valve cage seat surfaces, suggesting prolonged relative movement.
- Evidence of corrosion and potential the presence of rust particles in the fuel system may have contributed to erosive wear.
- The engine manufacturer reported that three similar incidents involving suction valve failures in this engine type had occurred previously across millions of flight hours.