What happened
The incident occurred during a night mail flight operating from Chicago to Seattle. The route included intermediate stops at Minneapolis and Missoula. At the time of the accident, the aircraft was carrying two pilots and approximately 500 lbs of mail cargo.
While traversing west Idaho in poor weather conditions, the twin-engine airplane struck the slope of a mountain in the region of Kellogg. The impact forces destroyed the airframe, and both crew members were killed in the crash.
Findings
The official investigation analyzed various potential factors, including weather, mechanical integrity, radio aids, communications, and company compliance with regulations. The board concluded that none of these elements directly caused the accident. Although there was a theoretical possibility that the magnetic compass malfunctioned, evidence suggested this was improbable.
The Accident Board determined that the primary issue was faulty navigation. Specifically, the crew failed to follow the radio range course after departing Missoula and did not ascend to a safe altitude while flying over the route from Elk River.