Incident Overview
On the third flight of the day, the engine started normally and no anomalies were observed. The pilot taxied onto the runway, advanced the throttle, and executed a normal takeoff. The airplane climbed to a cruise altitude of approximately 2,000 feet mean sea level.
Engine Malfunction
After reaching 2,000 feet, the engine began running rough, and the airplane started to descend. The pilot attempted a forced landing to a road. During the approach, while maneuvering to avoid a construction vehicle, the airplane struck wires.
Maintenance History
The engine was remanufactured to zero time on October 10, 1979, and installed on January 10, 1981. At the time of the accident, the engine had accumulated approximately 1,325 hours of operation and 20 years since its last overhaul. The engine manufacturer's service instruction recommends overhaul every 2,000 hours or 12 years, whichever comes first.
Investigation Findings
Examination of the engine revealed that the number 3 cylinder exhaust valve stem was fractured into two pieces. Evidence of a fatigue crack was identified on the fracture surface.