What happened
On April 25, 1990, a SIA SA-315B Lama helicopter, HB-XGE, operated by Air Zermatt AG, was conducting commercial sling-load operations in the vicinity of Zermatt. The pilot, who was a local resident familiar with the area, performed two flights transporting hay from a gallery near the Brig-Visp-Zermatt railway to a barn on the Alp Bodmen pasture.
During the second rotation, after delivering the load, the pilot attempted to return to the base. While maneuvering away from the drop site, the helicopter struck a telephone line. The impact severed both 3 mm thick wires of the cable and caused immediate loss of control. The aircraft crashed onto a slope and came to rest in a protective wire fence, which absorbed much of the impact energy. The pilot sustained minor injuries, while the helicopter was destroyed. Damage also occurred to the telephone line and the protective fence.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined the flight sequence, radio communications, and environmental conditions. The investigation revealed that the pilot had been warned by a ground assistant about obstacles near the drop site. However, a misunderstanding occurred regarding which specific cables were being referenced. The ground assistant described a transport cable running to the Edelweiss restaurant, but the pilot incorrectly assumed this referred to a lower-lying telephone line he could see nearby.
Crucially, the pilot was unaware of a high-voltage telephone line that ran parallel to his intended flight path. This specific obstacle had been reported to authorities in 1983 and appeared on the 1:100,000 scale aeronautical obstacle chart, but it was not marked visually on the approach charts or clearly identified during the pilot's initial orientation at the base.
Findings
The accident was caused by the pilot's misjudgment of the cable situation at the accident site. Contributing factors included:
- A misunderstanding in radio communication between the pilot and the ground assistant regarding the location and nature of the obstacles.
- The pilot's lack of knowledge about a significant aerial obstacle (the high telephone line) located directly within the operational area.
- Inadequate flight technique for departing with an external load, specifically failing to leave the drop site via the same route used for approach.
Further contributing elements involved:
- The failure of responsible parties to report other nearby obstacles (such as power lines and the transport cable) to aviation authorities.
- Incomplete entry of obstacles in the 1:100,000 scale aeronautical obstacle chart, which lacked non-reported hazards.
Safety action
The investigation highlighted systemic issues regarding obstacle reporting. It was noted that several cables in the area had not been reported to the Federal Office of Civil Aviation (BAZL) or the military, leading to gaps in official charts. The report emphasized the need for accurate and complete obstacle data in aeronautical publications to prevent similar incidents in complex terrain operations.