What happened
While flying in cruise at approximately 700 to 800 feet MSL, the pilot reported that the engine began experiencing a gradual loss of power. The pilot attempted to correct the power loss but was unsuccessful. During the descent for a forced landing, the airplane struck a tree and then the ground, resulting in a nose-over.
The investigation
An FAA airworthiness inspector examined the aircraft following the accident and found the mixture control at the fuel metering valve positioned halfway between midrange and idle cutoff. The inspection revealed that the mixture control cable had separated from the rod end, although the rod end remained attached to the mixture bellcrank at the airbox assembly. Approximately 11 threads at the end of the mixture cable showed damage.
Regarding maintenance, the aircraft's maintenance records were reportedly destroyed in the fire. The Inspection Authorization (IA) holder who performed the most recent annual inspection informed the FAA inspector that the aircraft owner had adjusted the mixture control cable rod-end to achieve the proper cushion; the IA noted they checked the adjustment but failed to verify the security of the jam nut at the rod end. The owner stated that they did not perform any adjustments to the engine controls within the engine compartment and believed the IA had performed those adjustments. The pilot did not hold a mechanic certificate.