What happened
On September 18, 2012, an Eurocopter AS 350 B3, registration HB-ZJO, was performing a commercial external load operation in the Lodano Valley, near Maggia. The pilot was engaged in the 22nd mission of the day, transporting a heavy walkway weighing 1,071 kg. The load was suspended from the aircraft's cargo hook using a 40-meter sling.
During the delivery of the load to a clearing, the pilot was guided by a ground assistant via radio because overhead branches obstructed a direct vertical view from the cockpit. After the load was placed, the pilot descended to allow ground personnel to detach the attachment straps. During this maneuver, the helicopter struck nearby trees. The impact caused the aircraft to lose control and spin around its yaw axis. The helicopter slid down a steep slope, narrowly missing the walkway, before coming to rest in a riverbed, where a fire brokedt out. The pilot was killed in the accident.
The investigation
SESA examined the wreckage, the engine, and the technical components of the aircraft. Technical inspections of the Eurocopter AS 350 B3 and its engine revealed no mechanical failures or defects; the engine was delivering power at the time of the accident. Investigators also reviewed the flight logs, which showed the pilot had completed 112 rotations that day, totaling 5 hours and 35 minutes of flight time.
Environmental factors were analyzed, including the terrain and the presence of obstacles. The investigation confirmed that the aircraft's weight and center of gravity were within prescribed limits, though the total mass with the external load was near the maximum allowable limit for the specific performance conditions at that location. The investigation also reviewed the communications between the pilot and the ground crew.
Findings
- The primary cause of the accident was a loss of control following a collision with trees.
- The collision was made possible because the use of an insufficiently long sling prevented the aircraft from maintaining a safe distance from the surrounding vegetation.
- The pilot was operating in a high-demand environment with significant natural obstacles, including branches overhanging the drop zone.
- The heavy external load was near the maximum takeoff power limits for the specific altitude and conditions.
- The ground crew was positioned in a dangerous area during the detachment process, though they managed to evacuate safely.