What happened
A flight instructor and a student pilot departed on a local training flight. Approximately ten minutes after departure, the aircraft was observed entering a descending spiral while the engine remained running. The aircraft was flying over an area specifically used for practicing forced landings.
One witness reported seeing the airplane level off as it passed behind a hilltop, immediately followed by the sound of the aircraft impacting the ground. A second witness reported hearing the engine backfiring just before the sound of the impact.
The investigation
Post-accident investigations revealed that the student pilot, who was also the owner of the aircraft, had been performing his own maintenance prior to the flight. This maintenance work included the replacement of engine pistons and rings.
During the inspection of the engine, investigators found numerous fuel stains across several engine components. Additionally, the carburetor mixture screw had been set to the maximum lean condition. The investigation also noted that duct tape and electrical tape had been used extensively to perform repairs on the air induction system.