What happened
According to witness accounts, the aircraft was observed flying along the route of the Trans-Alaska Pipeline at an estimated altitude of 200 feet above ground level. As the plane entered a pass where the pipeline crossed rising terrain, a witness heard the engine power increase. Shortly after, the aircraft disappeared from view amidst falling snow. The witness initially assumed the plane had successfully cleared the pass because he could no longer hear the engine.
Later, a helicopter pilot operating for the pipeline company located the wreckage at the 4700-foot level of the pass. The pipeline pilot reported that visibility was one-half mile in snow with a ceiling of 100 feet obscured at the highest point in the pass. Witnesses at the base of the pass estimated the ceiling to be between 100 and 200 feet, with visibility ranging from one-half to one mile as light to moderate snow continued to fall. The crash site was situated just beyond the point where the pipeline transitioned from an above-ground installation to a below-ground one.
Findings
Investigation of the site revealed no evidence of a preimpact malfunction or failure of the aircraft systems prior to the collision with terrain. The circumstances suggest the pilot encountered deteriorating weather conditions while navigating difficult terrain, leading to the loss of control and subsequent crash.