What happened
On July 23, 1993, at approximately 09:30 local time, a SA-315B Lama helicopter with registration HB-XHD was conducting commercial external load operations at Weissfluhjoch in the canton of Graubünden. The aircraft, operated by Heliswiss, was tasked with transporting revised roller batteries for a cableway system from the lower station to pylons located approximately 500 meters north.
During the second rotation, a railway employee who lacked formal flight attendant training attached the load to the helicopter's external hook. The pilot lifted the cargo slowly and began a right turn while simultaneously accelerating forward. To avoid colliding with a large runway marking post situated in the direct departure path, the pilot corrected further to the right. This maneuver brought the main rotor into contact with the traction cable of the adjacent pendulum cableway. The impact caused immediate severe vibration, forcing both cabin doors open. The pilot managed to fly underneath the cables and land safely. The pilot was uninjured, but the helicopter sustained significant damage, and the cableway's traction cable was nearly severed.
The investigation
The Eidgenössische Flugunfall-Untersuchungskommission (EFUK) examined the flight dynamics, aircraft technical status, and ground operations. The pilot held a valid license with over 17,400 flight hours and was in good health. The helicopter was airworthy with no technical defects found prior to the incident. The weather conditions were favorable, with visibility exceeding 20 km and light winds.
The investigation focused on the spatial relationship between the aircraft, the load, and the obstacles. The material pickup site was located dangerously close to the cableway infrastructure, specifically between a marked safety cable and the actual traction cables. The ground crew member at the pickup site was not a trained flight attendant and lacked proper communication equipment with noise-canceling headsets. Furthermore, no professional flight assistant was present at the loading zone to assist with obstacle awareness.
Findings
The primary cause of the accident was the pilot's misjudgment of the safety distance between the main rotor and the cableway obstacles. The pilot became distracted by an avoidance maneuver intended to clear a runway marking post, leading to a collision with the traction cable. Contributing factors included the inadequate location of the material pickup site, which was too close to air navigation hazards, and the absence of a qualified and equipped flight assistant at the loading area to mitigate these risks.
Safety action
The investigation highlighted critical safety deficiencies in external load operations near infrastructure. The use of untrained ground personnel and inappropriate loading sites near active cableways poses severe risks. Proper training for ground guides and careful site selection are essential to prevent rotor strikes on fixed obstacles during heavy lift operations.