What happened
On 22 November 2015, an ARV1 Super 2, registration G-BPMX, was conducting a private flight when the engine ceased operation shortly after takeoff. While attempting to level off at an altitude of roughly 1,000 feet, the pilot reduced power, at which point the engine stopped abruptly. Following the loss of power, the engine could not be restarted, necessitating a forced landing in a field at Lodge Farm, Gainsborough. During the landing sequence, the aircraft struck a tree stump, resulting in significant damage to the fuselage and wings, and causing the engine to seize. The pilot sustained no injuries.
The investigation
Following the accident, the AAIB, in consultation with the Light Aircraft Association (LAA), oversaw the disassembly of the aircraft's Hewland AE75 piston engine. This inspection revealed physical evidence of contact between a piston and the cylinder wall. The nature of this damage was identified as being consistent with a cold seizure.
Findings
- The engine failure was caused by a cold seizure.
- Two-stroke engines are particularly vulnerable to this type of failure if operated at high power settings before reaching optimal operating temperature, as pistons expand more rapidly than the cylinders.
- A cold seizure can also be triggered by a rapid reduction in throttle following a period of high-power operation, such as the transition from takeoff climb to level flight.
- This phenomenon is a known risk for this engine type, with similar incidents documented in previous AAIB and NTSB reports.