What happened
On June 2, 2017, a Piper Super Cub PA1s-150, registration HB-PQP, was conducting a mountain flight training mission. The flight originated from Annemasse, with the crew—consisting of an instructor and a student pilot—first visiting Saint-Roch Mayères to perform landings as part of a mountain qualification training program.
After completing two landings at the first location, the crew departed for the Col du Palet altisurface. Upon approaching the site, the instructor performed a low-level reconnaissance pass to assess the runway conditions. During this observation, the instructor noted snow covering the final third of the grass runway. Due to the observed conditions, the instructor took control of the aircraft from the student to perform the landing.
Following three low-altitude passes to evaluate the snow depth, the instructor determined that a landing was possible. The aircraft touched down at the beginning of the runway. However, as the aircraft continued its landing roll, the wheels entered the snow-covered section of the strip. The large Alaskan Bushwheels sank into the thick, soft snow, and the progressive accumulation of snow in front of the tires caused the wheels to lock. This resistance caused the aircraft to pitch forward, resulting in a nose-over and the aircraft landing on its back. The aircraft sustained heavy damage.
The investigation
The investigation relied primarily on testimonies provided by the instructor and the student pilot. Investigators examined the runway conditions at the Col du Palet altisurface, which is located at an altitude of 8,005 feet. The investigation also reviewed the flight profile and the specific equipment used on the aircraft, noting the use of 31-inch Alaskan Bushwheels designed for soft or uneven terrain.
Findings
- The primary cause of the accident was the accumulation of snow in front of the tires during the landing roll.
- The aircraft's wheels sank into deep, soft snow on the final third of the runway.
- The buildup of snow created enough resistance to lock the wheels, triggering the nose-over sequence.