The C-54 was under contract to transport diesel oil from Narsarsuaq to various DEW Lines sites (Distant Early Warning radar line). The aircraft was prepared for a flight back to Narsarsuaq and departed Site 39 at 00:40 on an instrument flight plan. En route altitude was 11000 feet and after reaching this altitude, the co-pilot changed seats with the reserve captain to complete some paperwork. When the flight passed Frederikshaabs Glacier the co-pilot changed seats again with the reserve captain. While changing seats and starting a check of the cockpit, the aircraft struck the icecap at an altitude of 5900 feet. The aircraft slid for about 4500 feet before coming to rest. The co-pilot was the only survivor. He made a shelter from aircraft debris against the rudder section and had to wait about 12 hours for a rescue team to find him.