What happened
On May 13, 1972, a private flight departed from Lausanne-La Blécherette carrying a pilot and his passenger. The flight was intended to include a landing on the Trient Glacier. Based on favorable weather reports and advice from another pilot regarding recent snow conditions, the pilot executed a landing on the upper part of the glacier at approximately 10:25 h.
Upon landing, the aircraft left a 150-meter track in the snow. Due to a fresh layer of snow measuring between 30 and 40 cm, the aircraft could not be fully aligned with the takeoff axis. After performing engine checks and leaving the fuel mixture setting as it was during the approach, the pilot attempted a northward takeoff. During this initial attempt, the pilot extended the flaps to the maximum position, but the Piper PA-18-180 failed to lift off. After traveling 300 to 400 meters, the pilot aborted the attempt and inspected the runway on foot, noting that the snow depth had decreased to approximately 5 to 7 cm in the lower section.
Seeking to gain more distance on the nearly horizontal glacier, the pilot repositioned the aircraft 150 meters back. During the second takeoff attempt, with only 500 meters of available runway, the aircraft encountered a crevasse. The rear ski struck a serac, causing the aircraft to tumble into a crevasse, where it came to rest 30 meters below the surface. The impact resulted in two serious injuries.
The investigation
The investigation confirmed that the aircraft, registration HB-OPV, was airworthy and within weight and center-of-gravity limits at the time of the accident. The pilot held a valid private pilot license with mountain landing extensions and possessed significant experience in glacier landings. Meteorological data indicated visibility was good, though the terrain presented specific challenges due to the fresh snow layer and wind conditions.
Findings
- The pilot'ed an overly optimistic assessment of the takeoff conditions.
- The takeoff attempt was compromised by the combined effects of the snow depth, wind, and the decreasing slope of the glacier.
- The pilot failed to achieve sufficient airspeed for a safe departure.
- The use of flaps during the takeoff sequence was inappropriate for the circumstances.
- A reduction in aircraft weight might have allowed for a better evaluation of the actual surface conditions.