What happened
On September 21, 2015, an SA 315 B helicopter, registration HB-ZGP, was performing an aerial work mission near the Bannalpbahn mountain station in the municipality of Wolfenschiessen. The crew, consisting of a pilot and two flight assistants, was tasked with transporting a container from the mountain station to a different location.
During the approach to the mountain station, the pilot consulted a digital moving map in the cockpit. The display showed two cables originating from the station. The pilot incorrectly identified one of these displayed cables as a nearby ski lift cable, leading to a misunderstanding of the actual obstacle layout.
As the pilot began a vertical descent to land near a container, the aircraft''s tail rotor struck a cable belonging to a transport cableway. The impact was severe enough to nearly shear off all three tail rotor blades. The pilot managed to control the aircraft and perform a forward landing to avoid further complications. There were no injuries to the crew, though the helicopter sustained significant damage.
The investigation
SUST examined the flight path, the cockpit instrumentation, and the environmental conditions at the time of the accident. The investigation confirmed that the transport cableway was officially recorded in the aeronautical obstacle database. However, the investigation found that the pilot's interpretation of the digital map was flawed. Specifically, the pilot believed the displayed obstacles accounted for the cables present in the area, failing to realize that the actual cableway rope was a separate, uncounted hazard.
Environmental factors were also reviewed. While the weather was clear, the accident site was in the shadow of the terrain, which made the visual identification of the cable difficult. The investigation also noted that a nearby ski lift was not listed in the official obstacle database because it did not meet the minimum height threshold for mandatory reporting.
Findings
- The primary cause of the accident was the collision with a cable due to the incorrect interpretation of the obstacle information displayed on the cockpit's digital map.
- The visual identification of the cable was made difficult by the fact that the landing area was in the shade.
- Inappropriate work organization contributed to the accident circumstances.
- The pilot's reliance on the digital map led to a false sense of security regarding the known obstacles in the vicinity.
Safety action
Following the investigation, SUST issued a safety notice to helicopter pilots. The notice emphasizes that pilots operating near terrain must recognize that obstacle maps may be incomplete or inaccurate. It stresses the importance of correctly identifying and verifying the path of real-world obstacles and remaining vigilant for hazards that may not be officially recorded due to height thresholds or reporting failures.