What happened
While in cruise flight, the pilot reported to air traffic control that the engine had ceased operating and declared an emergency. The pilot subsequently reported that oil was covering the windshield and stated an attempt was being made to perform a forced landing. During the maneuver, the aircraft collided with trees in a densely wooded area. No witnesses to the accident were identified.
The investigation
Upon examination of the wreckage, investigators found oil on the tail surfaces, the inboard bottom skins of both the left and right wings, and the bottom of the fuselage. The #2 cylinder was found separated from the engine. An inspection of the engine revealed that all eight fasteners—comprising six studs and two through bolts—that secure the #2 cylinder to the crankcase had separated.
Fretting was observed on the mating surfaces of the tail surfaces, the crankcase halves, and the cylinder base flange and crankcase deck area around the cylinder bore. Metallurgical examination of the eight fasteners determined that all had separated due to fatigue cracking, likely resulting from insufficient clamping force. Such a loss of force can occur through improper torque application during installation or if clamped surfaces move closer together over time.
Maintenance records indicated the engine had accumulated approximately 839 hours since a major overhaul performed about 13 years prior to the accident. There were no entries in the maintenance logs indicating that the #2 cylinder had been removed since that major overhaul.