What happened
On August 7, 1963, a Piper PA-18 Super-Cub, registration HB-ORK, was engaged in a commercial flight operation for the Swiss Alpine Club. The pilot was tasked with transporting passengers and goods to the Mutthornhütte. After an initial landing at a different location due to poor visibility, the pilot landed the aircraft on a flat ridge of the Kanderfirn glacier.
During the stay, heavy, wet snow fell, accumulating a layer of approximately two to three centimeters on the aircraft's wings. While the pilot managed to clear much of the snow, a 50 cm wide strip remained untouched in the center of the wing. At approximately 19:45, the pilot attempted a downhill takeoff toward the northwest. However, the aircraft struggled to gain sufficient lift, and the takeoff roll became increasingly long. As the aircraft bounced across the uneven glacier surface, the landing gear was subjected to intense stress. Eventually, the right strut failed, causing the right ski and wheel to detach. The aircraft slid for over two kilometers, ending its journey 250 meters below the starting elevation, resulting in heavy damage to the fuselage, wing, and landing gear.
The investigation
The investigation examined the aircraft's mechanical condition, the pilot's experience, and the environmental factors present at the time of the accident. The Piper PA-18 Super-Cub was found to be in good technical condition with no mechanical defects identified. The pilot, an experienced glacier pilot with over 6,200 glacier landings, showed no signs of health issues that could have contributed to the event. The investigation also focused on the terrain, noting that the takeoff area was characterized by irregular meltwater channels up to 60 cm deep and heavy, wet snow.
Findings
- The primary cause of the accident was the failure of the landing gear due to excessive stress caused by the uneven terrain.
- The takeoff roll was significantly lengthened by the presence of heavy, wet snow on the ground, which acted as a brake.
- Residual snow on the wings that could not be removed by the pilot likely negatively impacted the aircraft's aerodynamic performance and added unnecessary weight.
- While visibility was reduced by falling snow, this was not considered a direct cause of the accident.
- The decision to attempt the takeoff was driven by the need to avoid leaving the aircraft stranded on the glacier for several days.