What happened
On March 1, 1964, a Bell 4/7 G-2 helicopter, registration HB-XAW, operated by Heliswiss, departed Samedan for a supply mission to the Fuorcla Surlej mountain pass. During the landing phase at approximately 09:05, the pilot encountered low-contrast, diffuse lighting conditions due to snow and overcast skies.
As the aircraft touched down, it experienced an unexpected lateral tilt. Fearing the aircraft might slide on the snow, the pilot initiated an immediate go-around. During this maneuver, the aircraft's skids struck the ground a second time. This impact caused a rotor blade to strike the terrain and break away, leading to a severe imbalance that resulted in the 90% destruction of the helicopter. The pilot escaped the wreckage without injury.
The investigation
An investigation conducted by the Swiss Transportation Safety Investigation Board examined the terrain, weather, and operational procedures. The inquiry focused on the state of the landing site, which had been altered by recent snow removal and fresh snowfall. Investigators also reviewed the pilot's experience and the mechanical condition of the Bell 47 G-2, finding no technical defects in the aircraft's systems. The investigation also noted that the mountain hut warden, who typically prepared the landing site, was not present at the time of the landing to assist or provide updates on the surface conditions.
Findings
- The primary cause of the accident was the pilot being surprised by a terrain-induced lateral tilt during touchdown, which led to a pessimistic assessment of the situation.
- The decision to execute a go-around was driven by the sudden tilt and a loss of visibility caused by swirling snow.
- Insufficient power reserves prevented a safe departure; the combination of the heavy load, uneven terrain reducing ground effect, and the lack of available power during horizontal acceleration made the maneuver impossible.
- The pilot was unaware that the landing surface had changed due to recent snow management, as he had not confirmed the current state of the site with the hut warden prior to arrival.