What happened
On 19 December 1999, a solo navigation exercise began at Coonagh Airfield in a Rallye Club MS 880, registration EI-AYA. The pilot intended to fly a route via Portumna and Killaloe before returning to the airfield. During the return leg, while cruising at approximately 1600 ft AMSL, the engine and propeller ceased operation abruptly.
Following the sudden loss of power, the pilot identified a suitable field for an emergency landing. During the approach, the aircraft's tail struck a hedge, and upon touchdown, the nose undercarriage collapsed. The pilot, who was uninjured, exited the aircraft safely. The incident resulted in no injuries to the pilot, though the aircraft sustained damage to the engine cowling, nose gear, and tail structure.
The investigation
The AAIU investigation focused on the engine's recent history and the condition of its internal components. The engine had recently undergone a rebuild, which included replacing the camshaft, piston rings, and seals. Investigators examined the engine oil and found it was significantly discoloured and contained high levels of metallic debris.
Laboratory analysis of the oil revealed alarming concentrations of iron, aluminium, and silicon. Specifically, the iron content was measured at 806 ppm, which is eight times higher than the expected normal range. The presence of silicon was particularly noted as a highly abrasive contaminant.
Findings
- The engine failure was caused by excessive frictional heat resulting from the expansion of the No. 2 cylinder piston.
- This overheating was driven by high levels of friction within the cylinders, caused by the presence of abrasive silicon contamination.
- The silicon likely originated from the silicon carbide grit on the tips of the flex hone tool used during the cylinder de-glazing process.
- The engine rebuild was conducted in a general hangar area that lacked the necessary cleanliness standards and controlled environment required for such detailed work.
- The high levels of iron and aluminium in the oil were consistent with the scoring of the cylinder walls and piston pins.