Flight History
During a night-time flight in marginal VFR conditions, the pilot radioed approach control that the aircraft's engine had begun running rough and losing power, and that he was having difficulty maintaining altitude. Approach control vectored the pilot 14 miles back to the airport where he had previously completed an instrument approach. The pilot reported the runway in sight, but the aircraft crashed on final approach approximately 2 miles from the runway.
A witness reported hearing the aircraft's engine as it approached, followed by 5 seconds of silence, and then the sound of impact.
Inspection and Maintenance
An annual inspection had been completed on the aircraft about 2 weeks before the accident, and this was believed to be the owner's first flight after the inspection. During the inspection, the Nos. 1, 3, and 4 cylinders were removed from the engine and repaired.
Postaccident Examination
Postaccident examination of the engine revealed that one of the two valve keepers had not been reinstalled on the No. 3 cylinder exhaust valve, resulting in asymmetric loading of the remaining keeper. When that keeper fractured, the exhaust valve was released and entered the combustion chamber of the No. 3 cylinder, where it contacted the piston. The consequential damage fractured the Nos. 3 and 4 pistons, the Nos. 3 and 4 connecting rods, and the crankcase.