Incident Overview
An Air Force C-141 aircraft was conducting a flight from Clark Air Force Base (AFB) in the Philippines to McChord AFB, with intermediate stops at Kadena AFB, Okinawa, and Yokota AFB, Tokyo. The aircraft carried 16 people, including six Marines.
Sequence of Events
While en route to McChord during night cruising, the crew established contact with air traffic control (ATC). The ATC initially cleared the aircraft to descend from Flight Level 370 (FL370) to FL150, then to FL100. Shortly thereafter, the air traffic controller mistook the C-141 for another Navy aircraft and cleared the crew to descend to 5,000 feet (FL050). This altitude was too low for the area.
As the four-engine airplane descended through approximately 7,000 feet in limited visibility, it struck the slope of Mount Constance, which is 7,756 feet high. The mountain is located in Olympic National Park, about 52 miles northwest of McChord AFB. The impact occurred about 150 feet below the summit and triggered an avalanche.
Aftermath
Debris from the wreckage was scattered over a wide area. None of the 16 occupants survived the crash.
Probable Cause
The air traffic controller with whom the captain conversed mistook the C-141 with another Navy aircraft. As a result, he cleared him to descend to FL050 when the minimum prescribed altitude was FL100. Due to limited visibility caused by night, lack of ground visual references and clouds, the crew was unable to distinguish the mountain. This resulted in a controlled flight into terrain.