What happened
On the morning of March 26, 2005, a Bell 206B Jet Ranger III helicopter, registration HB-XQO, was conducting a commercial passenger transport mission to support a heli-skiing operation. The flight was transporting three ski tourists from Nessental to a mountain landing site near Sustenlimi on the Steingletscher glacier.
While operating in the vicinity of the glacier, the aircraft collided at high speed with the snow-covered terrain on the glacier plateau, specifically below the Gwächtenhorn. The impact was severe, causing the wreckage to scatter across a ridge of snow near crevasses. The pilot and the three passengers sustained four fatal injuries in the accident.
The investigation
The Aircraft Accident Investigation Bureau (AAIB) launched an inquiry following the notification by emergency services. Due to deteriorating weather conditions, including fog and snow, the recovery of the wreckage was delayed until several days after the event.
The investigation examined the aircraft's technical condition, the meteorological environment, and the operational performance calculations. Investigators reviewed the engine components, finding that the engine was still providing power at the moment of impact. They also analyzed the aircraft's weight and balance, noting that the takeoff mass from the initial departure point in Erstfeld was approximately 150 lb above the maximum permitted mass. Furthermore, the investigation compared the pilot's performance calculations against the actual aircraft configuration, which included specific equipment like snow deflectors and high skids.
Findings
- The primary cause of the accident was the helicopter colliding with the snow-covered terrain while flying at high speed in diffuse visibility.
- The pilot failed to recognize the hazards posed by highly variable wind and visibility conditions, which significantly affected the helicopter's control characteristics.
- There was an incorrect evaluation of the required performance conditions, as the aircraft's actual mass exceeded the theoretical maximum allowable mass for landing outside of ground effect under the prevailing conditions.
- Meteorological conditions at the site involved a south-easterly wind gusting up to 20 knots, creating unpredictable airflow due to the local topography.
- The aircraft's takeoff mass was significantly higher than the permitted limit for the specific flight configuration.