What happened
On April 16, 1996, at approximately 07:45 local time, a SA 315B Lama helicopter with registration HB-XTC, operated by Heliswiss from Bern-Belpmoos, was conducting a commercial passenger transport flight in the canton of Bern. The pilot departed Innertkirchen to pick up four passengers from Kraftwerk AG at Handegg. These individuals were routine workers who traveled to the Mattenalp landing site near the foot of the Gauli Glacier roughly every one to two weeks.
The weather conditions were clear with no clouds and light winds, but the designated landing area was covered in hard-packed snow and lay entirely within a shadow cast by the surrounding terrain. The pilot observed these diffuse lighting conditions during the final approach and decided to hover approximately 1.5 to 2 meters above the ground to ensure safety. Following standard procedure for such visibility issues, the pilot instructed the mountain guide seated on the front left to open the door and throw his backpack onto the snow to provide a visual reference for height.
However, the mountain guide was adjusting his backpack on his lap, intending to exit next. The passenger seated on the rear left, who had been assisting with previous flights, misinterpreted this action as the start of the disembarkation process. Lacking a pre-flight briefing or direct communication with the pilot due to the absence of headsets for all occupants, the rear passenger incorrectly estimated the helicopter's height above the snow as only 10 to 15 centimeters. He opened his door and stepped onto the skid, unexpectedly dropping approximately 1.5 meters onto the hard snow surface.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined the flight data, witness statements, and environmental conditions. The pilot held a valid commercial license with mountain landing qualifications and had logged over 1,000 flight hours, including roughly 600 in the accident model. The aircraft was airworthy and within weight and balance limits; no mechanical failure contributed to the incident.
The investigation highlighted that the pilot’s decision to hover and use a visual reference object was correct given the deceptive lighting. However, the lack of a formal briefing for such a short, routine hop meant critical safety protocols were bypassed. The mountain guide had intended to act as the ground helper, but without headsets connecting him to the rear passenger or clear verbal confirmation from the pilot regarding who was exiting first, a dangerous communication gap existed.
Findings
The accident was caused by two primary factors:
- Misjudgment of Height: The injured passenger severely underestimated the helicopter's altitude due to diffuse lighting conditions and the lack of contrast between the shadowed snow and the aircraft skids.
- Insufficient Communication: There was a failure in crew resource management. The passengers did not discuss the exit procedure beforehand, assuming it was routine. Furthermore, the rear passenger could not hear the pilot's instructions to the front passenger due to the lack of headsets, leading him to act on incorrect assumptions.
The passenger sustained significant back injuries from the fall. No other individuals were injured, and there was no damage to third-party property.
Safety action
This incident underscores the risks associated with short-haul mountain operations where routine complacency may lead to skipped safety briefings. It highlights the necessity of explicit communication protocols, particularly regarding exit sequences, even when passengers are familiar with the route. The use of headsets for all occupants during such operations is critical to prevent misinterpretation of pilot commands.