What happened
On 29 June 2004, a DA40D Diamond Star, registration G-HASO, was conducting a solo navigation training flight near Old Stratford, Northamptonshire. While at an altitude of approximately 2,000 ft, the pilot observed the engine caution light illuminate, followed by a drop in oil pressure. Shortly after, the engine suffered a sudden loss of power, dropping from 89% to 65% power setting before the engine stopped completely.
The pilot declared an urgency call to Cranfield Approach, set the transponder to emergency code 7700, and attempted an engine restart. Although the engine briefly restarted for 20 seconds, the oil pressure dropped again, leading the pilot to commit to a forced landing. The aircraft landed in a field, rolling for about 20 metres through crops before the nose gear collapsed and the aircraft slewed 45 degrees to the left. There were no injuries to the pilot.
The investigation
The AAIB investigation focused on the engine's oil system and the turbocharger. Examination of the engine revealed severe overheating and damage caused by a lack of lubrication. The oil scavenge pump had seized because a piece of metal debris—a fragment of the turbocharger's radial and axial bearing thrust collar—had entered the pump.
Further analysis of the turbocharger showed that the compressor wheel had sustained damage to several blades. Investigators identified traces of nickel within the compressor, a material not used in the compressor's own components. This suggested that a foreign object containing nickel had been ingested into the engine. Additionally, it was noted that an incorrect type of air intake hose (a SCAT-10 instead of the approved SCEET-10) had been installed during a recent engine change.
Findings
- The engine failure was directly caused by the seizure of the oil scavenge pump.
- The seizure occurred because a fragment of the failed turbocharger bearing was sucked into the pump.
- The turbocharger failure was likely initiated by the ingestion of a foreign object containing nickel, potentially introduced during maintenance.
- This ingestion caused an imbalance in the compressor, leading to a fatigue failure of the bearing's thrust collar.
- The resulting loss of oil through the breather vent line caused the engine to overheat and eventually seize.