What happened
On April 6, 2020, an Airbus Helicopters AS350 B3, registration LN-OFQ, was engaged in a sling load operation near Skjelbreitjørna in Sandnes municipality. The mission involved moving a container weighing nearly 1,100 kg as part of a power line construction project. After initially landing at the wrong pylon due to a misunderstanding, the pilot attempted to relocate the container to a more accessible area.
As the pilot began the lift, the helicopter was subjected to a sudden wind gust at a critical moment when the longline was being pulled taut. This caused the aircraft to enter a dynamic rollover situation. The helicopter began a rapid rotation, pitching up and rolling left before the main rotor struck the ground. The aircraft ended up on its right side, and the impact destroyed the helicopter. The pilot, who was the sole occupant, sustained only minor injuries, aided significantly by the use of a flight helmet.
The investigation
The Norwegian Safety Investigation Authority (NSIA) examined the flight recordings from the aircraft's onboard video and technical logger. The investigation established that the pilot had been briefed on the tasks but had encountered unexpected wind conditions. Investigators reviewed weather forecasts from Stavanger Airport Sola, which indicated predicted gusts of 33–38 knots, exceeding the operator's 30-knot limit for sling load operations. The investigation also looked into the sequence of the aircraft's movements, noting that the loss of control occurred in less than seven seconds.
Findings
- The primary cause of the accident was a wind gust occurring at the worst possible moment, specifically when the longline was tensioning, which initiated the dynamic rollover.
- The pilot may have performed an overly optimistic assessment of the prevailing wind conditions and the difficulty of the maneuver.
- The decision to proceed with the operation was made despite weather forecasts indicating wind speeds that exceeded the company's established safety limits.
- The pilot had access to real-time wind information from a previous flight that day, which could have informed a more cautious risk assessment.
- The pilot's use of a helmet was a critical factor in preventing more serious head injuries during the impact.