Accident Narrative
According to the surviving passenger, during the flight the pilot experienced a partial loss of engine power. The pilot attempted to land in a field, but the field was too short, and the aircraft struck trees before crashing.
Engine Examination
During an examination of the engine, a metal fragment was found in the #3 cylinder. Evidence of foreign object damage (peening) was found in the #2 and #3 combustion chambers and on the faces of their respective pistons. The spark plugs for those cylinders were damaged to the point that their ground electrodes had become displaced and shorted to the center electrodes. A metallurgical examination of the fragment revealed it came from a broken exhaust valve; however, except for peening, the valves were intact.
Historical Information
Further investigation revealed that the engine had experienced an exhaust valve failure in 1980 and had flown 98 hours since then. Pieces of that valve were not found and were assumed to have been expelled through the exhaust system. During an annual inspection on January 12, 1989, an exhaust valve fragment was found in the engine muffler. The owner was notified; the exhaust pipes were removed and inspected, and no other fragments were found.
Additional Details
The aircraft was not equipped with shoulder harnesses.