Introduction
On 22 May 1966, a Piper PA-18A Super Cub, registration HB-OPE, was involved in an accident near the Riffelberg station on the Zermatt-Gornergrat line in Valais, Switzerland. The aircraft was operated by the AéCS Section du Valais based at Sion aerodrome.
Sequence of Events
The pilot, born in 1908, held a valid professional pilot license with mountain landing endorsement and had accumulated approximately 379 hours of powered flight. On the morning of the accident, he departed Sion at 0605 to deliver supplies to the Monte Rosa hut. After landing at the hut at 0643, he picked up a caretaker and flew to Riffelberg, landing at 0650 in a snow-covered depression between the hotel and a chapel. The pilot intended to perform a solo training takeoff before loading cargo. During the takeoff, the aircraft veered to the right, struck a rocky, snow-free embankment with the right ski and wing, ground-looped, and came to rest on the snowfield. Both occupants sustained superficial injuries: the pilot a minor forehead wound, the passenger a cut lip and leg contusion. They walked to the nearby Riffelberg station and later reached Zermatt by train.
Aircraft and Pilot Information
The aircraft, a Piper PA-18A Super Cub with a Lycoming O-320 engine (150 hp) and fixed-pitch metal propeller, was equipped with skis for glacier operations. It had a total time of 2,120 hours, with 152:59 hours since its last major overhaul after a previous accident in 1964. The weight and center of gravity were within limits. No technical deficiencies were found in the engine or airframe. The pilot had 13:46 hours and 83 landings on the accident type, including 59 mountain landings on five different glaciers. This was his first landing at Riffelberg.
Environmental Conditions
The landing site at Riffelberg was a slight depression open to the northeast, with a 5-10% gradient and lateral slope of 2-5%. The usable takeoff distance was about 300 meters. At the time of the accident, the snow was hard and no tracks were left. Weather observations indicated local winds of 10-20 knots from the south to west, with crosswind conditions. The pilot reported a left crosswind after the accident.
Investigation and Findings
The investigation determined that after landing, the pilot intended to stop at the top of the depression but experienced a skid during a left turn. He then applied full power for an immediate takeoff without retracting the flaps to the normal takeoff setting (15°). The takeoff was hasty, and the aircraft drifted right due to the lateral slope and crosswind. The pilot could not maintain directional control, resulting in the collision with the embankment.
Conclusion
The accident was caused by a hasty takeoff during which the pilot could not keep the aircraft on the intended path due to the lateral slope of the runway and a crosswind that he had not detected.