What happened
On August 13, 2003, an Eurocopter EC 120 B, registration HB-ZER, was involved in an accident at the Hotel Steingletscher mountain landing site in the Canton of Bern. After performing several practice approaches and landings from the west, the pilot and two passengers took a break. Upon returning to the aircraft approximately one hour later, the pilot attempted a takeoff.
During the initial takeoff phase, the pilot noted a light tailwind. After a brief hover to check engine performance and controls, the pilot attempted to turn the aircraft to the right to fly down-valley. However, witnesses observed the helicopter beginning to rotate rapidly to the left at an altitude of only about one meter. The pilot attempted to correct the rotation by applying full right pedal, but the leftward rotation continued to increase. To avoid further complications, the pilot decided to descend and land immediately. During the landing, the aircraft tilted onto its right side near a steep embankment, resulting in the destruction of the helicopter. The pilot sustained minor injuries, while the two passengers were uninjured.
The investigation
The investigation conducted by the Swiss Transportation Safety Investigation Board (SUST) focused on the mechanical and operational circumstances of the rotation. Technical examinations of HB-ZER revealed no mechanical failures or deficiencies in the engine or flight controls. The tail rotor, specifically the Fenestron system, was found to have been fully functional up until the moment of impact.
Investigators examined the meteorological conditions, noting that while the prevailing wind was from the west-northwest, local mountain winds were fluctuating. The investigation also reviewed manufacturer documentation regarding the specific handling characteristics of the Fenestron tail rotor system during low-speed flight and tailwind conditions.