A Learjet 35A, N14TX, was destroyed when it impacted terrain at the Stephenville Airport, Canada. Both crew members were killed. The accident occurred in the hours of darkness with wind 040 degrees at 17 knots, a visibility of 12 miles in light snow and drifting snow. The crew conducted a tailwind ILS approach to runway 28 because runway 10 lacked an ILS. The airplane tracked the ILS until over the threshold. When the aircraft approached the runway threshold, its landing lights would have illuminated the drifting snow and the snow covering much of the runway surface, probably making it difficult to distinguish the runway’s white centre line and, perhaps, the runway edge lights. The illuminated snow drifting across the runway at a 45ø angle from behind the aircraft would give a pilot the illusion of lateral aircraft motion. The aircraft drifted to the left and touched down off the left side of the runway. Heading left off the runway, in the dark and with a lack of ground lights in that direction, the pilot had a limited horizon comprised of the snow surface illuminated by the aircraft’s landing lights, which would have made recognition of the aircraft’s attitude extremely difficult. A go around was initiated with being retracted. The aircraft then attained various bank angles of wings level, 10ø left, 45ø left, and 10ø left with the left hand wingtip contacting the ground, until the ailerons jammed. The aircraft rolled to the right after striking the ground, then went through a small stand of alders at 4,400 feet. The aircraft continued to roll to the right and crashed in an inverted, wings-level attitude 5,080 feet from the runway threshold near the centre of the airport, just east of the intersection of runways 28 and 20. CAUSES AND CONTRIBUTING FACTORS: “Shortly after crossing the runway threshold, the aircraft began moving to the left of the runway. The motion probably was undetected by the pilot until the aircraft touched down off the left side of the runway surface. The pilot did not maintain the proper aircraft attitude during an attempted missed approach, and the aircraft struck the terrain.”