What happened
On May 13, 2017, an AS 350 B2 helicopter, registration HB-ZTM, was conducting a private flight from Bern-Belp to the Petersgrat mountain landing site. The flight, which included the pilot and five passengers, was intended to be a scenic trip featuring an aperitif at the high-altitude landing site.
As the aircraft approached the landing area, the pilot encountered challenging visual conditions. While horizontal visibility remained good, a heavy cloud cover and recent snowfall had created a highly diffuse, low-contrast environment. The snow-covered terrain lacked distinct visual references, making it difficult to judge altitude above the white surface.
During the final phase of the approach, the pilot attempted to land on a snow-covered slope. As the aircraft descended, it began to oscillate violently across all axes. The landing gear made contact with the snow, causing the helicopter to tilt sharply to the left. This movement caused the rotor blades to strike the cabin roof, tearing away a significant portion of the forward structure. The impact resulted in one fatality (the pilot) and left the remaining passengers with minor injuries.
The investigation
Investigators from the Swiss Transportation Safety Investigation Board (SUST) analyzed onboard flight data, radar information, and video footage captured by a passenger. The investigation also reviewed the pilot's training records, which showed he had recently completed mountain flying training and a type rating for the AS 350 B2.
The inquiry examined the environmental conditions at the time of the accident, noting the lack of visual references due to the overcast sky and the uniform snow cover. Investigators also looked into the emergency response, noting that a nearby pilot on a separate flight discovered the wreckage and provided immediate assistance, which was critical since the accident site had no mobile phone coverage.
Findings
- The primary cause of the accident was the pilot's decision to attempt a landing under highly demanding and challenging visual conditions rather than executing an alternative plan.
- The lack of visual contrast on the snow-covered terrain made it nearly impossible to maintain precise control during the descent.
- The aircraft's Emergency Locator Transmitter (ELT) was switched to the 'OFF' position, preventing it from transmitting an automated distress signal.
- The occupants lacked appropriate mountain survival equipment, as the survival backpacks provided by the operator were not carried on this flight.
Safety action
Following the investigation, SUST issued a safety notice emphasizing the importance of ensuring immediate alerting and rescue capabilities. The board highlighted that all participants in civil aviation should take precautions to ensure survivors can be located quickly, particularly in remote areas where mobile networks are unavailable. The notice also recommended that those frequently flying in mountainous regions undergo specialized mountain and survival training.