What happened
On May 10, 1963, a Piper Super Cub PA-18, registration HB-ORP, departed from Mollis to retrieve instruments from a previously crashed aircraft located on the Hüfifirn glacier. The pilot, accompanied by a mechanic, initially landed on a sloping firn plateau near the Planura Hut. After an initial landing, the pilot attempted a second takeoff maneuver, intending to glide over the Clariden Pass and execute a 70-degree turn toward the northeast.
During this second takeoff attempt, the aircraft failed to reach its required liftoff speed. As the plane traveled approximately 500 meters and lost about 100 meters in altitude, it encountered a steepening slope and a small, isolated crevasse. Despite applying maximum flap settings to clear the obstacle, the aircraft's right ski caught the lower lip of the crevasse. The impact tore away the right landing gear, causing the aircraft to pivot around the right wingtip before tilting onto its left wing and coming to rest sideways on the slope.
The investigation
Investigators examined the terrain at the Claridenfirn, approximately 100 meters below the Clariden Pass, and analyzed the environmental conditions at the time of the accident. The investigation focused on the aircraft's performance during the takeoff roll on the glacier surface and the impact with the crevasse edge. The inquiry also reviewed the aircraft's equipment, specifically its metal Federal-Ski attachment used for glacier operations.
Findings
- The aircraft was operating in heavy, soft snow that left deep tracks, which prevented the plane from gaining necessary momentum.
- A 15-knot tailwind acted as a downdraft, further hindering the aircraft's ability to achieve liftoff speed.
- The pilot encountered an unexpected 5-meter-wide crevasse that was not visible during the initial approach.
- The inability to reach takeoff speed due to the combination of soft snow and tailwind caused the aircraft to sink into the crevasse edge, leading to the structural failure of the landing gear.
Safety action
No specific safety recommendations were recorded in the final report.