Engine Failure and Emergency Descent
Less than two hours into the flight, the engine lost power during cruise. The pilot initiated an emergency descent, during which the airplane struck power lines and a tree before colliding with the ground.
Examination of the Engine
Post-accident examination of the engine accessory case revealed that the idler gear was fractured. The two attachment holes in the crank case for the idler gear shaft assembly were elongated. Investigators recovered three fractured teeth from the idler gear and two separated bolt heads. The fracture surface of each gear tooth displayed crack arrest marks and a rough surface consistent with high-stress, low-cycle fatigue. The shanks below each separated bolt head were worn to about one-third of their original diameter.
Engine Overhaul History
The engine received a zero-time equivalent overhaul on May 9, 1985, and had operated 1371 hours since that overhaul. Textron Lycoming Service Instruction No. 1009AQ specifies that the recommended time between overhaul periods for the engine is 2000 hours. The Lycoming parts catalog for the engine indicates that a bolt is required to attach the idler gear shaft assembly at one attachment hole, and a slotted nut and stud are required at the other attachment hole.