Serious Helicopter Incident During Power Line Stringing in Norway (LN-OGN)

Incident Overview and Aircraft Details On 25 October 2022, an Airbus Helicopters AS 350B3, registration LN-OGN, operated by Helitrans AS, was involved in a serious aviation incident in Rogaland, Norway. The aircraft, manufactured in 2020 and powered by a Safran Arriel 2D engine, was conducting commercial specialized operations for stringing a 132 kV power line. The incident occurred at approximately 1400 local time, about 5 km south of Bryne, in non-controlled airspace class G. ## Operational Context and Sequence of Events The helicopter was tasked with installing pilot lines for a 9 km power line project contracted by the energy company Eviny. The operation involved using a 600 kg tool suspended from the helicopter's cargo hook to guide a 10 mm pilot line through pulleys on power line masts. The work began at mast number 20 and progressed toward one end of the line. During the operation at the third mast, the pilot was in the process of hanging the tool on the crossbeam when the helicopter began to move uncontrollably. The pilot released the cargo line one second before the right skid struck the top of a pole. Despite the impact, the pilot regained control and landed the helicopter in a controlled manner 62 seconds after the initial loss of control. ## Recorder Data and Damage Assessment Data from an Appareo Vision 1000 recorder indicated that the helicopter was in a hover with a First Limit Indicator (FLI) between 7.8 and 8.0 when the incident began. The FLI fluctuated significantly, dropping to 4.0, and a hydraulic pressure low warning light illuminated for 4 seconds. The impact caused the right skid to bend outward between the landing gear x-tubes, and minor damage occurred to the top of a power line mast. The tool and associated lines fell into soft soil without damage. ## Contributing Factors and Pilot Statement The pilot, a 55-year-old male with approximately 5,800 total flight hours, stated that he believed he experienced pilot-induced oscillations (PIO). He noted that the collective friction was set low, which he considered a potential contributing factor, while the pilot line drum friction was set high to prevent sagging. The pilot was well-rested and believed weather conditions were not a factor. The operation was conducted during the pilot's off-duty time. ## Safety Investigation Scope The Norwegian Safety Investigation Authority (NSIA) conducted a limited-scope investigation using a simplified reporting format. The investigation focused on clarifying the sequence of events and causal factors to improve flight safety, without apportioning blame or liability. The report notes that the specific tool used in the incident was not covered by the operator's standard stringing procedures, which are designated as high-risk operations requiring highly experienced pilots.