Accident Overview
A student pilot reported that while flying toward the airport, the engine power output suddenly dropped and varied between 900 and 1,400 RPM. The power was insufficient to maintain flight, and the student realized he could not reach the airport. He sighted a level dirt road at a construction site and executed a forced landing. During the landing roll, the aircraft contacted ground obstacles and nosed over.
Investigation Findings
A teardown inspection of the engine revealed that all valves and valve seats were warped, with evidence of exhaust gases entering the intake ports. The engine was reportedly at its time between overhaul (TBO) interval.