Incident Overview
On 19 July 1965, a Bell 47-J3 helicopter, registration HB-XBX, operated by Hélicoptère Suisse SA, was involved in an accident near Saas-Almagell in the canton of Valais, Switzerland. The helicopter was being used to lay a 4000-meter nylon rope over eight pylons of a 220 kV power line under construction by Kummler & Matter SA for Elektrizitätsgesellschaft Laufenburg (EGL). The flight departed at 1040 hours local time.
Flight and Preparation
The pilot, born in 1919, held a professional helicopter pilot license since 7 November 1961, with a Bell 47 type rating, and had accumulated approximately 1000 hours and 9250 flights on helicopters. He was accompanied by a flight mechanic (born 1943). Before the operation, the pilot conducted a reconnaissance with the site foreman (born 1939) and inspected the rope laid in a serpentine pattern on the ground. The rope was held down by stones at each loop. The pilot noted that the rope was of a braided type prone to twisting and looping, but the foreman stated it had been used successfully twice before. The pilot did not insist as flight safety was not compromised. One end of the rope was attached to the helicopter, and the pilot asked all personnel to clear the area.
Accident Sequence
Without the pilot's knowledge, the lead fitter (born 1929, German national) had instructed two workers to stand left and right of the rope to monitor its deployment and untangle any twists. Just before takeoff, a slight tailwind caused rapid uncoiling of the rope. The two workers, surprised by the speed, released the rope and fled. One worker (born 1938) became caught by a loop around his leg, lost his balance, and was dragged across the ground and through the bed of the Vispa river. About 40 meters away on the opposite bank, a low wall stopped his body, breaking the rope. The worker was carried by the current approximately 80 meters downstream before being rescued by a colleague. The helicopter crew, about 150 meters from the start at the time, did not notice the incident; the flight mechanic, lying prone in the cabin to observe the pendulum and release mechanism, only observed the rope break and informed the pilot, who immediately returned to the starting point.
Injuries and Damage
The worker sustained serious injuries. He was hospitalized for six weeks and unable to work for 14 weeks. The helicopter and ground equipment suffered no damage.
Findings
The investigation concluded that the accident was due to a lack of foresight on the part of the ground crew. Specifically, the lead fitter's decision to station workers in the deployment zone without the pilot's knowledge and without considering possible variations in helicopter speed increased risks. The rope type was not ideal but did not compromise flight safety, and the accident was not foreseeable by the pilot.