Summary
On 21 February 1991, a Piper PA-18-150, registration HB-PEK, was involved in an accident on the Trient glacier in Switzerland. The aircraft overturned during takeoff, resulting in its destruction. The pilot sustained minor head injuries, and the passenger was uninjured. The accident occurred at an altitude of 3225 m above sea level.
Accident Details
The flight originated from Sion airport at 1235 hours local time for a private flight with glacier landings. The pilot, accompanied by a colleague, first performed two touch-and-go landings on the Rosablanche glacier. The flight continued toward Petit Combin, where after two landings, the passenger disembarked to take photographs while the pilot completed three solo circuits. The passenger then reboarded for the flight to the Trient glacier. Three reconnaissance turns with decreasing altitude were made to assess wind and snow conditions. On the fourth approach, the aircraft landed at the foot of the Aiguilles Dorées. The snow quality was not optimal, so the pilot moved westward on the Plateau du Trient, performing two landings before stopping.
After a break, the crew reboarded with the intention of flying to the Tsanfleuron glacier. Engine start, warm-up, and takeoff acceleration were normal. When the aircraft was a few meters above the ground, the left wing suddenly lifted, and the pilot could not prevent the right wing from contacting the snow. The aircraft became unbalanced, pitched over onto its back, and slid about fifteen meters before stopping. The occupants exited the wreckage unassisted; the pilot sustained a minor scalp injury and was treated at Martigny hospital. A witness near the Trient hut alerted authorities.
Aircraft and Flight
The Piper PA-18-150 (HB-PEK) was privately operated by the Groupement de vol à moteur, Section vaudoise. The pilot held a valid private pilot license with glacier landing endorsement. Total flight experience was 343:53 hours, with 38:46 hours on type. The aircraft was regularly maintained, had valid documents, and the rear dual controls were removed. Fuel was sufficient, and weight and balance were within limits. No technical defects were found during a visual inspection of the wreckage.
Weather
The meteorological situation featured an anticyclone over eastern Europe affecting the Alps, with a southwesterly flow at 10 knots strengthening during the afternoon. At the accident time, local conditions on the Trient glacier were: wind from southwest to west at 10-15 knots, visibility greater than 20 km, few cirrus clouds, temperature about -8°C, and dew point about -12°C.
Cause
The report states that the accident was due to an overturn following a loss of control during takeoff, likely caused by a lateral wind gust. A contributing factor was the altitude-related reduction in engine power (from 112 kW at sea level to 81 kW at 3225 m).