The Flight
The pilot was conducting a test flight to confirm the operation of newly installed avionics. On the return leg to the airport, the engine began to backfire and subsequently lost all power. The pilot executed the emergency checklist but could not restart the engine. A forced landing was made in a dirt field with the landing gear retracted.
Post-Accident Examination
Both fuel tanks were found to be approximately half full. Examination of the airframe revealed a short circuit of both magneto grounding leads in the electrical wiring between the magneto switch and the magneto. The wiring harnesses were original to the airplane, which was manufactured in 1964. The overall condition of the p-lead electrical wiring was noted as poor.
Engine Run-Up Tests
Investigators successfully started the engine and performed a run-up under two separate conditions. The first start occurred after disconnecting both p-leads at their respective magneto terminals. The second start occurred after new electrical wire was connected from the magneto switch to both magnetos.
Maintenance History
A review of the engine logbook revealed that the engine had been returned to service following a 100-hour inspection approximately one month before the accident. The logbook entry indicated that maintenance personnel checked wires, cables, and hoses for condition and security.