Aircraft and Crew
The aircraft involved was a Piper PA-18 Super Cub, a single-engine, high-wing monoplane with two seats in tandem and fixed tailwheel landing gear, equipped with Federal skis. The aircraft was privately owned and operated by the Club d'Aviation des Placettes, Bex. At the time of the accident, the airframe had 2,073 hours total time and the engine 1,358 hours.
The flight instructor, born 1923, held a private pilot license with endorsements for glacier flying, towing, aerobatics, and instruction. He had 1,373 total flying hours, with 573 hours on the accident type and 3,740 glacier landings. The student, born 1935, held a private pilot license and a military pilot brevet, with 1,730 motor flight hours and 7 hours on the accident type. During the flight, the instructor occupied the front seat and the student the rear seat.
Accident Sequence
On 1 June 1968 at 0958, the aircraft departed Bex airfield for glacier training. The original destination was Wildhorn, but it was obscured by fog. The instructor proceeded to Petersgrat, where the north slope and ridge were also foggy, but the south slope was clear. After a reconnaissance pass parallel to the ridge, the instructor initiated an approach diagonally, almost parallel to the slope, with the sun behind. During the flare, a gust suddenly lifted the right wing. Despite immediate opposite aileron input, the left ski and left wing contacted the snow, causing the aircraft to yaw left. The aircraft sustained severe structural damage. The accident occurred at approximately 1040 at an elevation of 3,090 meters.
Investigation Findings
The investigation determined that the instructor's decision to land on the south slope was reasonable given his experience. However, the combination of fog on the north slope and clear conditions on the south slope indicated a föhn effect, which can produce gusty downslope winds. The instructor did not account for the possibility of sudden gusts from the ridge. The diagonal approach, chosen to avoid fog, exposed the aircraft to a side gust.
Probable Cause
The accident was caused by an inappropriate approach by the flight instructor, combined with a sudden gust from the ridge.