Incident Overview
During a normal cruise flight, the engine RPM decreased from 2,400 to 1,900. The pilot attempted to correct the power loss but was unsuccessful. Unable to maintain altitude, the pilot executed a forced landing in a field. During the landing roll, the left wing was severed after impacting a tree. The aircraft subsequently rolled inverted and came to rest.
Engine Examination
Post-incident examination of the engine revealed that the No. 3 cylinder exhaust valve had failed. Due to damage to the fracture surface, the cause of the valve failure could not be determined.
Maintenance History
Review of the engine logbooks indicated that in October 1979, the engine had been overhauled, which included replacement of the exhaust valves. Since that overhaul, the engine had accumulated approximately 1,400 hours of operation.