What happened
On the evening of the accident, West Coast Airlines flight 956 was operating a multi-leg service originating from San Francisco (SFO) with scheduled stops in Eugene (EUG), Portland (PDX), and Seattle (SEA). The aircraft, a recently delivered DC-9, arrived at the Eugene airport at 19:34. After an 18-minute turnaround, the flight continued toward its next destination.
At approximately 20:04, air traffic controllers authorized the crew to descend from a cruising altitude of FL140 down to 9000 feet. During the execution of a turn toward heading 300°, the aircraft descended into terrain below the permitted altitude. The plane struck the eastern slope of Salmon Mountain at an elevation of 3830 feet. At the moment of impact, the aircraft was in a 30° right bank with a slight climbing flight path of 3-4° on a heading of 265°. The force of the collision caused the aircraft to disintegrate, and there were 18 fatalities among the occupants.
Findings
Investigations concluded that the primary factor in the accident was the descent of the aircraft below its cleared altitude and into terrain that obstructed the flight path. While it was confirmed that the plane flew below the minimum safe altitude for the surrounding area, investigators could not establish the specific reason why the crew allowed the aircraft to descend below the authorized limit.