What happened
Approximately 20 minutes before the accident, the pilot transmitted a mayday call reporting single engine problems. Radar track data indicated that at the time of the reported failure, the aircraft entered a descending left turn, losing 1,000 feet and changing course to a south heading within 24 seconds. The pilot eventually regained control of the aircraft, and air traffic control provided guidance to the nearest destination airport.
While establishing an approach, the pilot stated intentions to circle the airport to the left and hand-pump the landing gear down. During this phase of flight, the aircraft impacted terrain approximately one-quarter mile south of the runway in a yard adjacent to a residence near the airport property. The aircraft came to rest on its nose and wings, with the empennage oriented vertically at an angle of approximately 65 degrees relative to the ground. There were no injuries reported. The impact occurred near a line of trees, though no evidence of a tree strike was found.
The investigation
Investigators examined the left engine and discovered that the No. 4 cylinder head had separated between the second and third cooling fin. A metallurgical examination determined that the fracture was consistent with fatigue cracking.
Further inspection of the left propeller and propeller governor showed no anomalies that would have prevented the feathering mechanism from operating normally. Observations during the teardown of the left propeller indicated it was not in the feathered position at the time of the accident. Maintenance records showed that both engines had accumulated approximately 345 hours since their last overhaul.
According to manufacturer documentation, the aircraft's hydraulic system is powered by a single engine-driven pump mounted on the left engine. This system provides hydraulic pressure for controlling the flaps and retractable landing gear. If the left engine loses power, the hydraulic pump ceases operation, necessitating the use of an emergency gear extension.