1963 Piper Super Cub Accident at Claridenpass (HB-ORP)

Investigation Overview and Aircraft Details The Swiss Federal Aircraft Accident Investigation Commission opened a preliminary investigation on 12 May 1963 into the accident involving Piper Super Cub PA-18 HB-ORP. The aircraft was a privately owned Piper PA-18 Super Cub with a 150 hp engine and a weight of 794 kg. It was equipped with Federal skis that could be raised and lowered in flight. The airworthiness certificate was valid from 30 March 1963 to 8 March 1964. ## Occupants and Flight Purpose The pilot, born in 1935, held a valid private pilot license issued on 23 December 1957 and a valid BB license issued on 1 September 1959. He had approximately 700 flight hours, including about 4,200 landings and 3,500 glacier landings, and held a special permit as a glacier flight instructor. One passenger, a mechanic, was aboard. The flight was intended to recover radio equipment and instruments from a Champion aircraft, HB-UAM, that had crashed the previous day on the Hüfifirn. ## Flight Sequence and Accident The pilot departed Mollis at 1630 MEZ on 10 May 1963. He landed from the west on the sloped firn plateau of the Hüfifirn, about 0.5 km north of the Planurahütte, at 1700. After turning back to position the aircraft closer to the HB-UAM wreckage, he made a second landing and attempted to glide over the Claridenpass and take off toward the northeast. Despite a tailwind of about 15 knots, the aircraft failed to reach takeoff speed. After traveling about 0.5 km and losing approximately 100 m in altitude, the pilot encountered a steepening firn slope with an isolated crevasse. He attempted to jump it with maximum flap extension, but the right ski caught the lower lip of the crevasse, tearing off the right landing gear. The aircraft then pivoted sharply to the right around the resting right wingtip, rolled down-slope onto the left wingtip, and came to rest across the slope. ## Damage and Weather Both occupants were uninjured. The fuselage structure was severely bent and dented near the wing attachments, and the right landing gear was torn off. The wings and struts appeared externally intact, and the engine and propeller appeared undamaged. The damage was estimated at about 40%. No third-party damage occurred. At the time of the accident, the weather was clearing between two cold fronts, with heavy cloud cover or overcast conditions. Mountain peaks were in clouds, with stratus at 3,000–3,200 m. Visibility was about 20–40 km, and the wind was from the southwest at about 15 knots. ## Discussion and Conclusion The investigation found that during the attempted takeoff, the aircraft encountered soft, heavy snow on the back slope, preventing it from reaching takeoff speed despite the significant gradient. The aircraft then encountered an isolated crevasse that it could not fully clear. The skis had left very deep tracks, indicating the snow was very soft and rotten. The 15-knot tailwind, which also acted as a downdraft, likely had an additional unfavorable effect. The accident was attributed to the aircraft failing to reach the necessary takeoff speed on a steep firn slope due to deep, soft snow and a tailwind of about 15 knots, causing it to sink slightly while attempting to jump an unexpectedly appearing crevasse about 5 m wide, with the right ski catching the lower crevasse lip.