1963 Piper PA-18 Super-Cub Accident on the Kanderfirn Glacier (HB-ORK)

Overview and Investigation Context On 7 August 1963, a Piper PA-18 Super-Cub with registration HB-ORK was involved in an accident on the Kanderfirn glacier in the canton of Bern, Switzerland. The Swiss Federal Accident Investigation Commission issued its final report on 11 March 1964. The aircraft was owned by the pilot and operated by Alpar Flug- und Flugplatzgesellschaft A.G. of Bern under a commercial operating permit. ## Aircraft and Pilot The aircraft was a two-seat, single-engine high-wing Piper Super Cub PA-18 built by Piper Aircraft Co. in Lock Haven, Pennsylvania, United States. It was powered by a 150 hp Lycoming O-320 engine with a fixed two-blade metal propeller. At the time of the accident, it was equipped with both wheels and skis. The maximum takeoff weight was 794 kg, and the accident weight was about 660 kg, including an additional snow load of 50–100 kg at the start of the takeoff roll. The center of gravity was within prescribed limits. The investigation found no technical defects. The pilot, born in 1923, held a private pilot license and a restricted commercial pilot license, both valid at the time, as well as a special permit as a glacier flight instructor. He had more than 2,100 flight hours and 10,000 landings, including more than 6,200 glacier landings, most of them in the accident aircraft. No health problems were identified. ## Flight and Accident Sequence The flight was part of commercial operations for youth camps organized by the Swiss Alpine Club. On 7 August 1963, the pilot departed Bern at 1430 MEZ to carry a passenger to Mutthornhütte. Because of bad weather, he landed at Blümlisalp at 1453 and was fog-bound for three hours. After 1800, the fog changed to light rain, and he took off at 1814, reaching Mutthornhütte a few minutes later. He chose to land on a ridge between Mutthorn and Petersgrat rather than the prepared landing site, landing at 1818. Wet snow mixed with rain fell afterward. At about 1915, the pilot returned to the aircraft and attempted to remove wet snow that had accumulated on the wings in a layer two to three centimeters thick. He cleared about one-third of the wing chord from the front and one-third from the rear, but a strip about 50 cm wide along the entire wing span remained inaccessible. The work took about 10 minutes. The air temperature was 0°C, and no wind was detected. The pilot began the takeoff roll at about 1945 MEZ, heading northwest downhill, with the carburetor preheat off. The engine reached 2,400 rpm. The takeoff roll became longer than expected. To gain more slope, the pilot turned west. Falling snow covered the windshield, so he tried to see through the right side window. Despite using the landing flaps, the aircraft did not lift off. It made several longer jumps but could not stay airborne. On increasingly uneven glacier terrain, the impacts on the landing gear became harder until the right strut broke and the right ski and wheel were lost. The pilot then focused on avoiding a rollover. After a glide of more than two kilometers and 250 meters below the start point, the aircraft came to rest heavily damaged in the rain on the glacier after a slight right turn. The pilot reached Mutthornhütte on foot via the Tschingelpass at about 2100. ## Damage and Probable Cause The pilot was uninjured. The aircraft sustained heavy damage to the landing gear, right wing, and fuselage, estimated at about Fr. 24,000, or about 50 percent of its value. The commission concluded unanimously that the accident was caused by landing-gear failure due to terrain-induced overloading during a takeoff attempt from a mountain landing site under unfavorable weather and terrain conditions. The failure to lift off in time was attributed mainly to heavy wet snow on the ground, which slowed the takeoff roll and caused additional braking on uneven terrain, and to a heavy wet snow layer on the wings that could not be fully removed and adversely affected weight and aerodynamic performance. Poor visibility in the snowfall also made the takeoff more difficult, though it was not considered a cause in itself.