What happened
On August 18, 1979, an SA 341 G Gazelle, registration HB-XFW, operated by Air Grischa AG, was engaged in an aerial work mission near San Bernardino, Switzerland. The mission involved transporting a heavy external load, consisting of furniture and wooden boards wrapped in a transport net, from a depot at the south portal of the San Bernardino Tunnel to a hunting lodge approximately 4.5 km away.
After lifting the load, the pilot confirmed that the torque measurements were within permissible limits while hovering out of ground effect. The pilot then transitioned into forward flight, climbing slightly and heading downslope. However, after traveling roughly 100 to 150 meters, the aircraft suddenly lost altitude and began a leftward turn toward the N 13 highway.
As the aircraft approached the busy roadway, the pilot chose not to release the external load to avoid endangering motorists on the highway. Instead, the pilot attempted to clear the road by applying full cyclic input. This maneuver caused the engine to struggle, leading to a further drop in power and an increased rate of descent. The helicopter struck the ground near an access road with the load still attached, resulting in the destruction of the aircraft and two serious injuries to the pilot and the passenger.
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 SA 341 G Gazelle was found to be airworthy, with its engine and airframe having approximately 2,000 flight hours and being properly maintained. The pilot held a valid commercial license with mountain flying endorsements and had sufficient training for the task.
Investigators analyzed the weather conditions, noting a low-pressure system over the Gulf of Genoa. At the time of the accident, the weather was rainy with a northwest wind of approximately 8 knots. The investigation also reviewed the aircraft's weight and balance, finding the takeoff weight to be approximately 1,670 kg, which was within the permissible limits.
Findings
- The pilot was operating in the lee of the terrain, experiencing a tailwind component from the right-rear that became noticeable only after leaving the flat depot area.
- The primary cause of the accident was the misjudgment of the wind's influence on the aircraft's performance.
- During the attempt to clear the highway, the sudden demand on the turbine caused the engine power to fluctuate and eventually drop, exacerbating the descent.
- The pilot's decision to maintain the external load to protect highway traffic prevented the possibility of a controlled release of the weight to regain altitude.