What happened
On March 18, 1978, a Bell 206 B helicopter, registration HB-XFH, was conducting commercial passenger flights for skiers near Gstaad, Switzerland. During an approach to the Gstellihorn landing site at an altitude of 2,680 meters, the pilot encountered challenging environmental conditions. The area was covered in a fresh layer of snow, and the lighting was highly diffuse.
While attempting the landing, the pilot encountered snow swirls kicked up by the rotor blades. During the initial approach, the pilot noticed snow drifts to the right of the intended touchdown point, which were difficult to gauge due to the flat lighting. The pilot attempted a go-around after the rotor wash obscured visibility. However, during a second attempt, the aircraft again entered a zone of swirling snow. Believing there was sufficient visibility to continue, the pilot descended. As the collective pitch was reduced, the pilot perceived a leftward tilt and attempted to correct with right cyclic input. This maneuver caused the HB-XFH to tilt sharply to the right and overturn.
The investigation
The investigation examined the aircraft's mechanical state, the pilot's experience, and the meteorological conditions at the time of the accident. The Bell 206 B was found to be in good mechanical condition, with no relevant technical defects identified. The aircraft's weight was approximately 1,200 kg, well within its maximum takeoff weight of 1,451 kg, and the center of gravity was within limits. The pilot held a valid commercial license and possessed significant experience in mountain flying.
Investigators analyzed the landing site, noting that an orange flag had been placed there as a visual reference, though only a small portion of it remained visible above the snow drifts. The investigation also looked at the physical impact, noting that the main rotor struck a snow drift, causing the rotor head to break below the rotor hub.
Findings
- The primary cause of the accident was loss of orientation resulting from diffuse lighting and snow swirls within the landing area.
- The pilot's second approach attempt was conducted too low; the investigation concluded that the approach should have been completed outside of ground effect at approximately 4 to 5 meters to allow the rotor wash to clear the snow before touchdown.
- The aircraft's tilt to the right was likely caused by either the main rotor striking a snow drift as the helicopter descended into the snow, or the aircraft sliding laterally into a drift due to a loss of visual reference.
Safety action
No specific safety recommendations were recorded in the final report.