What happened
On May 30, 2008, an AS350 B3 helicopter, registration HB-ZDE, was performing commercial logging operations near Monbiel-Bündelti, Switzerland. The aircraft, operated by Air Grischa Helikopter AG, was engaged in transporting logs from a dense forest area to a central landing site using a 50-meter longline. Due to the thick canopy, the pilot relied on radio instructions from a ground crew member to position the aircraft over the pickup point.
During the 29th rotation of the day, the ground crew member attached the load to the longline and moved away. A forest worker observing the operation from a safe distance noted that the load initially failed to lift because a branch had become snagged. As the ground crew member moved to clear the obstruction, a branch detached from the treetop and struck the crew member on the head. The impact caused the individual to fall forward, striking their head against a log, resulting in a loss of consciousness.
The investigation
The investigation examined the operational procedures, the equipment used, and the environmental conditions at the time of the accident. Investigators confirmed that the aircraft was properly maintained and that the weight and balance were within legal limits. The ground crew members were found to be wearing appropriate protective clothing and helmets equipped with integrated communication systems. The investigation also reviewed the meteorological data, which indicated light rain and low winds, concluding that the weather did not directly contribute to the event.
Findings
- The primary cause of the accident was a falling branch that struck the ground crew member.
- The branch was most likely dislodged from the treetop by the rotor downwash produced by the helicopter during its hover.
- All safety protocols regarding load attachment and personal protective equipment were being followed at the time of the incident.