Overview
A certificated commercial pilot reported a loss of engine power during the initial descent to land, resulting in a forced landing on snow and tree-covered terrain. The airplane suffered substantial damage to the landing gear, fuselage, and wings.
Accident Sequence
The pilot noted that the engine began to run rough and lose power. The roughness briefly improved, but was followed by severe engine vibration and a complete loss of power. The pilot selected a forced landing area on snow and tree-covered terrain.
Investigation Findings
Postaccident investigation discovered that the engine crankshaft had sustained a complete fracture of the #2 cheek. Further investigation revealed that on some crankshafts, a crack in the nitride layer originating from a shallow tool mark could, in some cases, ultimately lead to fatigue failure of the crankshaft cheek.
Regulatory Action
On April 22, 1999, the Federal Aviation Administration (FAA) issued an emergency airworthiness directive (AD) requiring inspection of all TCM 470, 520, and 550 engine crankshafts manufactured in 1998 with less than 300 hours in service, in accordance with the TCM critical service bulletin (CSB) within 10 hours of operation.