Accident Sequence
The pilot reported maneuvering for a left-hand downwind leg for landing from east to west. He set up the downwind leg at 8,400 feet mean sea level, which he estimated as 1,000 feet above the airport elevation of 7,411 feet. The pilot stated that it was very dark; he could see the airport but could not see the surrounding terrain. Suddenly, he saw the ground, and the airplane impacted the terrain and came to rest. The pilot reported that the airplane experienced no malfunctions prior to the accident.
Investigation
The accident site was on the snow-covered edge of a mountain ridge at an elevation of 8,489 feet. An examination of the airplane's systems revealed no anomalies. Published terminal procedures for the runway indicated high terrain of 8,739 feet south-southeast of the airport. The published airport diagram for the airport directs right traffic for the pattern to runway 27.
Probable Cause
The pilot's improper in-flight planning and his failure to maintain safe clearance from the high terrain. Factors contributing to the accident were the high terrain and the dark night.