What happened
On July 13, 2022, an Airbus Helicopters AS 350 B3e, registration HB-ZVY, was performing aerial logging operations near Matenc, Faido. The mission involved extracting logs using an external load. Prior to the flight, the pilot and ground crew had been briefed on the presence of live high-voltage power lines in the area. To maintain a safe distance from the conductors, the pilot utilized a 38-meter longline.
During the approach to attach the first load, a task specialist operator (TSOP) used a grounding tool to touch the helicopter's secondary hook. As the operator made contact with the hook, an electrical discharge occurred. The shock caused the operator's hand to contract around the metal component, preventing them from releasing it. The pilot observed the discharge via radio static and intervened by lifting the hook and the operator approximately one meter off the ground until the operator was able to release the grip.
Following the incident, the operator experienced dizziness and heart palpitations. Although the mission continued briefly, the operator later sought medical attention due to persistent pain and was hospitalized for two days under observation.
The investigation
The investigation focused on the electrical interaction between the aircraft's external load equipment and the energized power lines. Investigators examined the construction of the longline, which contained copper conductors for remote hook release, and the grounding equipment used by the ground crew. The inquiry also reviewed the safety briefings and the proximity of the aircraft to the energized conductors during the maneuver.
Findings
- The incident was caused by the discharge of capacitive current through the body of the task specialist operator when they grasped the secondary hook.
- The high-voltage power lines were not deactivated during the logging operations.
- The aircraft operated at an insufficient distance from the energized power lines.
- There was a lack of sufficient technical knowledge regarding the electrical effects of operating helicopters in close proximity to live power lines.