SHT Report SL 2015/13: AS 350 B3 LN-OGL Underhung Load Contact with High-Voltage Line

Incident Overview and Aircraft Details On 21 September 2015 at 12:30 local time, an Airbus Helicopters AS 350 B3 with registration LN-OGL was involved in a serious aviation incident near Lagovaggi, Narvik municipality, Nordland, Norway. The aircraft, manufactured in 2003 and powered by a Turbomeca Arriel 2D engine, was operated by HeliScan AS. The flight was a commercial aerial work operation for the Geological Survey of Norway (NGU), involving an underhung sonde suspended approximately 30 meters below the helicopter. The aircraft carried two people: the pilot-in-command and the equipment operator. No injuries were reported, and the helicopter sustained no damage, though the underhung equipment was slightly damaged. ## Operational Context and Sequence of Events The operation required the helicopter to fly at a constant height of approximately 60 meters above the terrain along predefined survey lines. The pilot-in-command used a GPS-based indicator to follow the lines, while the equipment operator used a paper map. The flight was conducted in visual meteorological conditions (VMC) with good visibility, an east wind of 2 knots, and a broken cloud ceiling at 1,550 meters. After approximately 30 minutes of flying along line 950, the helicopter approached the Skjomtinden mountain area. The pilot-in-command was focused on navigating under the cloud base at the highest terrain point. After passing this point, the equipment operator informed the pilot that a high-voltage line lay ahead along the survey line. As the helicopter descended toward the valley containing the power line at approximately 40 km/h, the pilot saw the line in his right peripheral vision earlier than expected. The helicopter was already too close to avoid a collision. The pilot attempted to maneuver away, but the sonde caught on the power line. The pilot released the sonde using both the electrical release button and the mechanical release on the collective. The power line at the point of contact was 58 meters above the ground, while the helicopter was at approximately 97 meters (320 feet on the radio altimeter). After releasing the sonde, the pilot flew away from the line, landed, and stopped. A check of the Vehicle and Engine Monitoring Display (VEMD) revealed that the engine had produced 112% torque for one second. ## Investigation Findings and Safety Considerations The Norwegian Transportation Safety Authority (SHT) noted that the operation imposed a high workload on the pilot-in-command due to the requirement to fly a specific pattern at a given height over terrain with significant elevation variations. The pilot-in-command had 880 total helicopter hours, which was below the 1,000-hour minimum specified in HeliScan AS's Operations Manual Part E (OM-E) Appendix E, though a dispensation had been granted by the chief pilot. The cloud base was lower than the company's minimum requirement of 800 feet above ground level (AGL), which may have further increased the pilot's workload. The pilot-in-command and the equipment operator used different navigation aids (a GPS indicator and a paper map, respectively), which could have led to differing perceptions of the helicopter's position. This is indicated by the pilot's experience that the power line was closer than expected when the sonde made contact. Following the incident, HeliScan AS and NGU equipped the operator with an iPad running AirNav Pro software, eliminating the need for a paper map. Additionally, NGU planned to modify the operator's GPS-driven system to define warning zones around obstacles, which would display red lines on the indicator when the helicopter approached within a defined distance. The SHT recommended that HeliScan AS and NGU conduct a risk assessment focusing on the distribution of tasks between the pilot-in-command and the operator, given that the changes would assign safety-relevant tasks to the operator.