What happened
On January 22, 2004, an SA315B Lama, registration HB-XRA, was performing external load operations near Mergoscia-Busada, Switzerland. The pilot was engaged in a series of material transport rotations, moving 350-liter containers of sand to a nearby construction site. During the final rotation of the sequence, the helicopter's cargo hook made contact with a transport cable used for mountain pastures.
The impact of the cable snagging the hook caused an immediate and violent deceleration of the aircraft. This sudden force caused the main rotor blades to deflect downward, striking the tail boom and severing part of the tail structure. The resulting loss of control caused the helicopter to spin and crash into the terrain near two local buildings. The impact was severe enough to deform the cabin and dislodge the pilot's seat and restraints. The pilot sustained serious injuries.
The investigation
Investigators examined the wreckage and the flight path, noting that the area is characterized by numerous transport cables. They identified two specific cables crossing the valley; while one was highly visible, the second cable—the one involved in the accident—was a rusty brown color. Due to the sun's position and the shadows cast by the mountains, this cable was nearly impossible to discern against the background of the forest.
Technical analysis of the SA315B Lama revealed no pre-existing mechanical defects. The investigation focused on the cargo hook system, finding that the intense force of the cable snagging caused the hook's attachment frame to break, which subsequently forced the hook to open. The investigation also noted that the pilot was not wearing a helmet during the operation.
Findings
- The primary cause of the accident was the loss of control following a collision with a difficult-to-see transport cable.
- The rusty brown color of the cable, combined with heavy shadows from the terrain, rendered it nearly invisible to the pilot.
- A lack of flight path reconnaissance meant that no specific waypoints or safety altitudes were established to avoid known obstacles.
- There was an absence of any marking on the cable to make it more visible during flight.
- A decrease in pilot concentration during the final rotation of the series likely contributed to the incident.
- The pilot's ground assistant was also unable to see the cable from their position, preventing any warning via radio.
Safety action
- The Federal Office of Civil Aviation (FOCA) should evaluate the introduction of modern cable collision warning systems for helicopters, similar to FLARM technology.
- Authorities should consider reviewing the management of decommissioned cables, such as requiring annual reports or fees to ensure unused cables are removed from the landscape.