The pilot reported that the engine stopped suddenly after takeoff when he reduced power to level off at a height of approximately 1,000 feet. The engine could not be restarted and the pilot made a forced landing in a field. The aircraft struck a tree stump and was badly damaged but the pilot was uninjured.
With the agreement of the AAIB and in consultation with the Light Aircraft Association (LAA), the pilot dismantled the engine, revealing evidence of contact between a piston and cylinder; the damage was characteristic of a cold seizure.
Two stroke engines are susceptible to cold seizures if run at high power before fully warm because the pistons expand faster than the cylinders; cold seizure can also occur if the throttle is rapidly reduced following a period of operation at high power such as after takeoff. Previous occurrences have been reported by the AAIB and NTSB following incidents on G-BTGT (AAIB Bulletin 11/96), N12911 (NTSB Identification CEN11FA433) and N55368 (NTSB Identification LAX04LA228).
The LAA will highlight this occurrence and the susceptibility of two stroke engines in an article in their ‘Light Aviation’ publication.