What happened
On December 7, 2015, an Airbus Helicopters AS 350 B3, registration LN-OXG, was engaged in utility operations near Brydalsfossen in Masfjorden municipality. Operated by Airlift AS, the aircraft was performing longline work to transport poles and other materials along a power line route. Prior to the mission, the pilot and the client had conducted safety job analyses (SJA) in accordance with established protocols.
During the operation, the helicopter was hovering approximately 20 meters above a steep slope. While positioned over the site, the pilot observed a tree to the left of the aircraft begin to fall. The falling tree, which was approximately 15 meters long, first struck the empty 18-meter longline before hitting a person on the ground. The impact resulted in one person sustaining two broken ribs and a punctured lung.
The investigation
The Norwegian Safety Investigation Authority (NSIA) examined the circumstances surrounding the incident, noting that the aircraft had completed 16 previous longline lifts that day without incident. The investigation focused on the mechanism that caused the tree to uproot. The pilot reported that the tree had been torn from its roots and suggested that the rotor downwash from the helicopter likely triggered the collapse.
Findings
While the event primarily resembled a ground-based industrial accident, the NSIA classified it as an aviation accident because the helicopter's downwash was the catalyst for the tree's fall. The investigation noted that while downwash from a helicopter of this size typically does not uproot healthy trees, the specific tree involved had a compromised root system. The investigation also identified a secondary risk: the falling tree could have potentially become entangled in the longline, endangering the aircraft.
Safety action
Airlift AS noted that identifying trees with unstable root systems is a significant challenge for both pilots and ground personnel. Following the incident, the operator updated its 2016 safety training course to include details of this event and to emphasize the specific hazards associated with rotor downwash.