What happened
On March 9, 1961, a Pilatus Porter PC-6 (registration HB-FAR) was engaged in a commercial flight transporting six skiers from Montreux-Rennaz to the Breitholen Plateau at 3,800 meters. Although the original plan was to land on the Théodule Glacier, the pilot agreed to attempt a landing on the Breithorn Plateau following requests from the passengers.
After landing on the plateau, the pilot prepared for a southbound takeoff along a 200-meter stretch of terrain. This section of the glacier was characterized by a slight slope and several small snow drifts. During the takeoff roll, the aircraft encountered a tailwind. After initially lifting off, the aircraft lost altitude and struck a snow drift with the right ski, which caused the right landing gear leg to break.
Following the impact, the pilot managed to fly the aircraft to Sion Airport for an emergency landing. During this subsequent landing on a grass runway, the aircraft sustained further damage to the right wing, propeller, and fuselage. The pilot remained uninjured.
The investigation
SUST examined the flight conditions, the aircraft's mechanical state, and the pilot's experience. The investigation noted that while the pilot was a qualified professional with significant glacier landing experience, he had never previously landed on the Breithorn Plateau. The investigation also reviewed the meteorological conditions, noting a tailwind of approximately 10 knots and the presence of uneven snow surfaces. The aircraft's weight and center of gravity were found to be within prescribed limits at the time of the accident, though a previous flight had involved a slight overload.
Findings
- The primary cause of the accident was that the chosen takeoff distance was insufficient to reach the necessary liftoff speed due to the combined effects of the tailwind and the uneven snow surface.
- The pilot overestimated the benefits of the slight downward slope and did not sufficiently account for the impact of the wind and surface conditions.
- The takeoff attempt occurred outside the area of the runway that the pilot had initially deemed suitable.
- The pilot's decision to land on the Breithorn Plateau, while technically defensible for a trained pilot, lacked adequate preparation, such as consulting a more experienced glacier pilot for that specific location.