Witness Observations
According to witnesses, the aircraft was seen flying along the Trans Alaska Pipeline at an estimated altitude of 200 feet above ground level. As the aircraft entered a pass where the pipeline crossed rising terrain, a witness heard the engine power increase. The aircraft then disappeared from view in falling snow. Shortly after, the witness could no longer hear the engine and assumed the aircraft had made it through the pass.
Accident Site and Weather Conditions
The aircraft was later found by a pipeline helicopter pilot where it had crashed at the 4700-foot level of the pass. The pipeline pilot reported that visibility was half a mile in snow and the ceiling was 100 feet obscured at the highest point in the pass. Witnesses at the base of the pass estimated the ceiling to be 100 to 200 feet, visibility half a mile to one mile, and light to moderate snow falling. The crash site was located just beyond the point where the pipeline transitioned from an above-ground installation to a below-ground installation.
Subsequent Investigation
No evidence of a preimpact malfunction was found during the investigation.