What happened
On March 16, 2022, an Airbus Helicopters H125, registration HB-ZTV, was performing an external load aerial work mission in the Carcale Valley near Gordola, Switzerland. The flight involved transporting construction timber from a loading point to a drop-off site.
During the approach to the unloading zone, the helicopter was flying at a speed perceived by ground personnel to be higher than usual. As the aircraft moved through the valley, its main rotor struck an active high-voltage power line, severing the conductor. The impact caused the main rotor, the transmission, and the tail rotor to be instantly torn from the airframe. The remaining fuselage plummeted to the ground and caught fire. The pilot sustained fatal injuries, while no other injuries were reported among the ground crew or passengers.
The investigation
The Swiss Transportation Safety Investigation Board (SISI/SUST) examined the flight sequence, the aircraft's technical condition, and the operational environment. The investigation reviewed the pilot's experience, the mission planning, and the coordination between the flight crew and the task specialist operators (TSOP) on the ground. Investigators also analyzed the presence of high-voltage infrastructure in the flight path and the communication attempts made by ground personnel via radio prior to the impact.
Findings
- The primary cause of the accident was the collision of the main rotor with a live high-voltage conductor, as the pilot failed to perceive the approaching obstacle above the aircraft in time.
- Difficulty in accurately estimating the vertical clearance between the rotor and the power lines contributed to the event.
- Ineffective risk mitigation measures were not implemented at the construction site.
- Stress caused by inadequate planning of the pilot's personal schedule influenced the operational context.
- There was a lack of integration between aerial transport operators and construction site risk management processes.
- The investigation noted that electromagnetic interference risks from high-voltage lines were not adequately addressed in existing risk analyses.
Safety action
The investigation led to several safety recommendations and notices. It is recommended that the Swiss Federal Office of Civil Aviation (FOCA) and relevant authorities develop specific safety prescriptions for aerial operations near high-voltage lines. Additionally, safety notices were issued to construction and engineering firms to ensure that safety instructions from power line operators reach aerial transport companies and that risk management processes specifically include electrical hazards when working near energized infrastructure.