What happened
During the initial descent to land, the pilot of the unspecified aircraft reported that the engine began running rough and losing power. While the roughness briefly improved, it was followed by severe engine vibration and a total loss of engine power. In response to the failure, the pilot selected a forced landing area characterized by tree-covered terrain and snow.
The impact resulted in substantial damage to the aircraft's wings, fuselage, and landing gear. The occupants were not injured.
The investigation
Postaccident investigation of the engine revealed that the crankshaft had suffered a complete fracture at the #2 cheek. Further examination determined that on certain crankshafts, a crack originating from a shallow tool mark within the nitride layer could lead to the fatigue failure of the crankshaft cheek.
Following these findings, the FAA issued an emergency airworthiness directive on April 22, 1999. This directive required inspections for all TCM 470, 520, and 550 engine crankshafts manufactured in 1998 with fewer than 300 hours of service, to be performed in accordance with the TCM critical service bulletin within 10 hours of operation.