What happened
While operating in cruise flight, the aircraft's engine began to run roughly. In response to the engine instability, the pilot performed emergency procedures in an attempt to restore adequate power. However, the power could not be restored, and the aircraft became unable to maintain level flight.
The pilot subsequently executed a forced landing into a field. During the course of the landing roll, the aircraft struck a ditch, traveled approximately 20 yards, and ultimately nosed over. The occupants were not injured.
The investigation
An examination of the engine was conducted to determine the cause of the power loss. Investigators discovered that a piston ring in the number 3 cylinder had broken, which resulted in blow-by within the cylinder.
While the pilot initially reported experiencing vapor lock, investigators found no evidence to support that vapor lock had occurred. During the investigation, the pilot informed an FAA safety inspector that automobile gasoline had been used for the flight, noting that the fuel had been transported in old cans obtained from his father's house.