What happened
On May 16, 2019, an Eurocopter AS 350B3 was performing external load operations at the Audi Arena Oberstdorf ski jumping complex. The mission involved transporting approximately 800 kg windbreak masts. While attempting to lift the second mast, the load was stabilized by three guy wires.
A ground worker, acting without direct communication or visual contact with the flight assistants, cut one of the guy wires, believing it was no longer under tension. This caused the heavy mast to tilt and fall into the slack external load sling gear. The impact caused a sudden, violent upward jerk of the aircraft. The pilot, who was only wearing a lap belt and not the shoulder harnesses, was likely jolted from his seat, causing a massive and sudden increase in engine power. This surge in power, without corresponding anti-torque compensation, triggered an uncontrollable rapid rotation around the vertical axis, leading the helicopter to crash near the ski jump facilities.
The investigation
The BFU investigation examined the aircraft's wreckage, the external load equipment, and the sequence of events recorded by a local webcam. Technical analysis of the engine's VEMD data confirmed a sudden, massive increase in engine power that exceeded limits, which was the primary trigger for the loss of control. The investigation also reviewed the training and coordination between the flight assistants, the helicopter operator, and the ground personnel from the construction and ski jump organizations. The investigation found no evidence of mechanical failure in the flight controls or the tail rotor drive system prior to the impact.
Findings
- The primary cause was the sudden tensioning of the external load sling gear caused by the falling mast.
- A lack of coordination and briefing between the flight assistants and the ground workers led to the premature cutting of a guy wire.
- The ground worker acted independently without maintaining visual contact with the flight assistants.
- The pilot's lack of use of shoulder harnesses contributed to him being physically displaced from the seat during the impact, leading to the uncontrolled power surge.
- The complex environment of the ski jumping arena required high levels of concentration and strictly coordinated communication, which were absent during this operation.