Aircraft and Pilot
The helicopter involved was an SA 315 B Lama, registration HB-XEY, owned by Eliticino SA, Gordola. The pilot, born 1938, held a valid professional helicopter pilot license and had accrued 5,872 hours total flight time, with 1,521 hours on the accident type. In the preceding 90 days, he had flown 190 hours total and 160 hours on type.
Flight History
On 30 June 1976, the pilot flew from Locarno to Lavertezzo, landing around 1430 hours. The mission was to transport building materials to the hamlet of Agro (elevation 1190 m). The loading area was 750 m northeast of Lavertezzo at 650 m elevation. After preparing five loads, the pilot departed at 1515 for the first flight, carrying timber of an estimated 600–650 kg. The flight was uneventful.
The second load consisted of plastic sacks containing cement, plaster, and sand, bundled in a net. During pickup, the pilot radioed that the onboard scale indicated approximately 800 kg. He requested the mechanic reduce subsequent loads by 50 kg.
Accident Sequence
Because of the higher weight, the pilot extended the outbound flight toward Agro to utilize thermals from a sunlit slope to gain altitude for the final approach. About 1 km before Agro, he began a slightly descending final approach near the middle of the valley. Suddenly, the helicopter pitched down and crashed. Witnesses at the landing site reported hearing "machine-gun-like sounds" and observed the main rotor blades bending upward. One witness noted that during this approach the helicopter flew lower and more westward than during the first flight.
The accident occurred at 1516. The impact site was at coordinates 708.675/127.380, elevation approximately 1100 m. An unmarked transport cable, crossing the valley from Arai to a rock outcrop about 450 m northwest of Agro, hung above the accident site with a ground clearance of about 110 m. The pilot was seriously injured; the helicopter was destroyed.
Wreckage and Examination
Debris was scattered along the valley axis. The right skid and shock absorber were found near the lower attachment point of the transport cable. Fragments of the tail rotor shaft lay up to 100 m downstream. The cabin, tail boom, engine, main gearbox, mast, and main rotor were found in the stream bed, partially submerged. The net with cargo lay about 12 m ahead of the cabin, with the attachment rope intact and released. The plastic sacks bore red and yellow paint traces from the tail rotor.
The pilot's red jacket, which had been stowed under the rear seat, was found torn near the cabin, with traces on the main rotor blades and tail boom. The tail rotor with its bevel gear was located about 5 m behind the tail boom.
No obvious collision marks were visible on the cable from the ground, and visual inspection showed no damage. However, forensic examination of the mirror support underside revealed distinct scraping marks, most likely caused by cable contact. Experiments with a piece of the cable produced similar marks.
Weather and Technical Findings
Weather was characterized by a flat pressure distribution and thunderstorm activity. At the time of the accident, a thunderstorm was approaching Agro. The crash occurred immediately after a heavy thunderclap. An expert concluded there was no evidence of lightning strike or static discharge.
The engine was disassembled and revealed that all three turbine stages had overheated, and microcracks were present on the blade trailing edges—a typical result of overheating. No pre-existing technical defects were found; weight and center of gravity were within limits.
Probable Cause
The investigation determined that the accident was caused by too late recognition of a transport cable.