What happened
On November 3, 2002, an SA 316B Alouette III, registration HB-XDA, was engaged in a VFR rescue operation following an avalanche near the Jungfraujoch region. After transporting a doctor and a flight attendant to the site of the avalanche, the pilot attempted to return to the base in Lauterbrunnen. During the return flight, the aircraft encountered deteriorating weather, including a closing cloud ceiling and shifting visibility.
Unable to maintain visual contact with the terrain or descend below the clouds, the pilot attempted an out-of-landing on the Eiger Glacier at an altitude of 3,415 meters. During the approach, the pilot experienced a loss of visual reference due to diffuse lighting on the snow. As the pilot attempted to transition into a hover and rotate the aircraft, the tail rotor struck the glacier. The impact caused significant damage to the airframe, including the deformation of the main rotor blades and the destruction of the tail rotor. The pilot, who was wearing a helmet, escaped with no injuries.
The investigation
SUST examined the wreckage and the flight logs of the mission. The investigation confirmed that the aircraft's weight and center of gravity were within limits and that the fuel met all specifications. There was no evidence of mechanical failure or technical malfunction contributing to the crash. The investigation also reviewed the meteorological conditions, which included heavy winds of up to 35 knots and rapidly changing visibility between 30 km and less than 100 meters.
Findings
- The primary cause of the terrain collision was the loss of visual reference to the snowy glacier due to diffuse lighting conditions.
- A contributing factor was a lack of critical assessment regarding the deteriorating weather and the failure to have alternative landing or flight plans prepared.
- The investigation noted that the pilot had previously observed the weather during the initial leg of the mission but proceeded with the return flight despite the worsening conditions.
Safety action
Following the investigation, SUST issued a safety recommendation regarding the necessity of survival equipment. It was noted that while the pilot was wearing a helmet, the aircraft lacked sufficient emergency gear to ensure survival in the event of an unplanned overnight stay in the mountains. The recommendation directs the Federal Office of Civil Aviation (FOCA) to ensure that appropriate emergency equipment is carried during helicopter operations in mountainous terrain.