What happened
On the evening of the incident, an Airspur cargo flight, operating as Flight 500, departed from Kalispell, Montana, under instrument flight rules (IFR). The aircraft was en route to Great Falls, Montana, when the pilot contacted Salt Lake ARTCC at 19:22 MDT to report that the engine was running poorly, necessitating a return to the departure airport.
Shortly after this communication, the pilot reported a total loss of engine power. While flying in IFR conditions, the pilot performed an emergency forced landing on a mountain ridge situated at an elevation of roughly 5,500 feet. The site of the accident was located approximately 18 nautical miles east of Kalispell. The pilot survived the impact with minor injuries.
Findings
Post-accident investigation involving the disassembly of the engine identified the mechanical cause of the failure. The investigation concluded that the #4 connecting rod failed catastrophically, which led to the subsequent loss of engine power.