What happened
On August 2, 2004, an Eurocopter AS350B3, registration HB-ZCB, was performing a commercial VFR cargo transport mission near Col de Jaman, Switzerland. The mission involved transporting materials for construction work on a ski lift. After completing several rotations to move concrete buckets and a generator, the pilot attempted to land on a forest path to pick up a flight assistant and a site manager.
As the aircraft descended to approximately 1.5 meters above the ground, the flight assistant, positioned on the ground, radioed the pilot to warn of a large rock positioned directly under the left skid. To avoid the obstacle, the pilot initiated a maneuver to the right. During this lateral movement, the tail rotor struck a wooden fence post located along the right side of the path. The pilot managed to bring the aircraft to the ground immediately following the impact. There were no fatalities or injuries, though the aircraft sustained damage to the tail boom, the tail rotor, and the tail rotor drive.
The investigation
SUST examined the aircraft and the operational circumstances of the landing. The investigation confirmed that the aircraft was airworthy, with all necessary certifications in order, and no mechanical failures contributed to the accident. Environmental conditions, including temperature, altitude, and weight/balance, were within safe operating limits, and wind conditions were calm.
Investigators also reviewed the roles of the crew and the selection of the landing site. It was noted that the pilot had not performed a prior ground reconnaissance of the landing area. Furthermore, the investigation looked into the training of the flight assistant, noting that while the assistant provided critical information regarding the rock, they did not warn the pilot about the fence on the right side, assuming the pilot had already accounted for it due to his seating position.
Findings
- The primary cause of the accident was a lateral shift of the helicopter to the right during the final phase of landing, which placed the tail rotor in contact with a nearby fence.
- The selection of an unsuitable landing site, characterized by narrow constraints and obstacles on both sides, contributed to the event.
- Inadequate assistance from the flight assistant, who failed to communicate the presence of the right-side obstacle, was a contributing factor.
- The pilot's limited visibility of the area directly in front of the left skid necessitated reliance on a mirror, complicating the avoidance maneuver.