What happened
On June 15, 1975, a search mission was initiated to locate a missing mountaineer in the Chelenlücke region of the Swiss Alps. The mission was triggered after the individual failed to return to the Tierberglihütte, where companions were waiting. Around 17:30, a pilot operating an SA 315 B Lama, registration HB-XEN, departed from the Hotel Steingletscher landing site with two mountain guides on board to conduct the search.
During the flight, the aircraft moved toward the Chelenlube area. A witness observed the helicopter flying back and forth along the Gwächtenhorn flank before disappearing into the mist. At approximately 17:50, the helicopter struck a steep rock face at an altitude of 3,180 meters, roughly 400 meters southwest of the Chelenlücke. The impact caused the three occupants to perish and resulted in the total destruction of the aircraft.
The investigation
The investigation examined the aircraft's condition, weather patterns, and physical evidence at the crash site. Investigators found that the engine was fully functional up until the moment of impact and that the aircraft's weight and center of gravity were within approved limits. The wreckage showed that the main rotor blades had struck the rock wall, leaving horizontal marks on the cliff.
Special attention was given to the damage on the rotor blades. Investigators identified deformations on the blades and found traces of blood and a fragment of a bird feather. While a definitive bird strike could not be confirmed due to the lack of species-specific protein, the physical evidence suggested a possible collision with a bird. Additionally, the investigation noted that the missing mountaineer had several opportunities to contact his companions via telephone but failed to do so, an act described as an indirect cause of the accident.
Findings
- The exact cause of the accident could not be determined, but two primary hypotheses were considered: a collision with terrain while flying in clouds, or a loss of control following a bird strike.
- Weather conditions at the time included heavy cloud cover and significant turbulence caused by thermal activity and wind channeling.
- The pilot was properly licensed for mountain operations and was found to be in good health.
- The behavior of the missing mountaineer, who failed to report his status, was identified as a contributing factor to the necessity of the dangerous search flight.