What happened
During a local flight, approximately 30 minutes into the mission, the pilot heard an unusual popping noise accompanied by a loss of engine RPMs. In an attempt to restore power, the pilot performed several corrective actions, including adjusting the mixture control, switching fuel tanks, and applying carburetor heat.
When these measures failed to regain engine power, the pilot executed a forced landing on a gravel bar located within a river. The aircraft sustained substantial damage during the rollout of the landing. At the time the aircraft came to a stop, the engine was still producing 1000 RPM.
The investigation
FAA inspectors examined the aircraft and identified that it had not undergone an annual inspection for several years. While investigators discovered multiple mechanical discrepancies throughout the aircraft, they determined that none of these specific issues would have prevented the engine from operating normally.