What happened
On 2 September 2003, a Star-Lite SL-1, registration G-FARO, was conducting a private VFR flight from Dorset toward Northamptonshire. While approaching Salisbury, the pilot requested a low-level route via the railway line. During the subsequent climb to 2,500 ft, the pilot observed a reduction in engine RPM, followed by a significant and unusual drop. Despite attempts to stabilize the engine by adjusting the throttle, the engine failed completely.
The pilot declared a 'MAYDAY' and initiated a glide approach toward Old Sarum Airfield. While performing s-turns to manage the descent, the aircraft performed a 'pancake' landing on Runway 24. The impact caused the nose landing gear to collapse and fold under the airframe, resulting in damage to the engine, propeller, and both the nose and main landing gear. There were no injuries to the pilot.
The investigation
An investigation involving metallurgical and laboratory examinations focused on the Rotax 447 engine. Investigators examined the engine's internal components, including the crankshaft bearings and connecting rods. Laboratory analysis was also performed on fuel and oil samples recovered from the aircraft and the refueling container.
Engine disassembly revealed that the crankshaft bearing housing of the front piston's connecting rod had suffered a catastrophic failure. The examination showed that the internal moving parts had overheated due to a breakdown in lubrication. This overheating led to the seizure of the front piston during a downstroke, which applied enough tension to the connecting rod to break the weakened bearing housing. Following this, the rear cylinder also experienced partial or complete seizure.
Findings
- The primary cause of the engine failure was a breakdown in lubrication.
- The lack of lubrication caused significant overheating of the engine's internal components, specifically the front piston and its associated bearings.
- The seizure of the front piston created a tension load that fractured the crankshaft bearing housing.
- Analysis of the fuel-oil mixture showed a ratio between 29:1 and 35:1, which was richer than the manufacturer's minimum recommendation of 50:1.
- There was no evidence of long-term overheating, as no oil tar was present in the engine, suggesting the lubrication failure occurred during the flight.