What happened
On December 3, 2018, an Airbus Helicopters AS 350 B3, registration HB-ZCM, was performing a commercial cargo flight near Arbedo-Castione, Switzerland. After completing a series of transport rotations, the crew prepared for the final flight of the day, departing from a pickup point near Claro.
During the initial climb, the pilot executed a 270-degree turn to the left before accelerating southeast. During this maneuver, the aircraft struck the earth wire of a high-voltage power line. The impact caused the wire to snap and resulted in several short circuits, leading to a widespread power outage across parts of the Canton of Ticino. The helicopter experienced a significant loss of control and entered a descent, eventually performing an emergency landing on a nearby meadow approximately 22 seconds after the collision. The aircraft sustained heavy damage to the rotor head, control rods, and cabin roof.
The investigation
SUST examined the flight path using GPS data from a portable tablet and analyzed the aircraft's condition following the impact. The investigation focused on the crew's actions, the aircraft's equipment, and the accuracy of aeronautical databases. Investigators noted that the crew was not using the onboard intercom system, communicating instead via a handheld radio. The investigation also reviewed the accuracy of the Federal Office of Civil Aviation (FOCA) obstacle database regarding the position of the power lines.
Findings
Several factors contributed to the collision. The crew's situational awareness was reduced due to the relatively low-intensity nature of the return flight. Additionally, the crew did not perform a mental review of obstacles in the departure path, and the lack of an active collision warning system meant there was no acoustic alert to warn the pilot of the approaching wire.
Crucially, the investigation identified systemic errors in the FOCA aeronautical obstacle database, which recorded the high-voltage line with a lateral inaccuracy of more than 26 meters. This discrepancy between the official database and the actual physical location of the obstacle increased the risk of collision.
Safety action
Following the accident, the operator began purchasing new helicopters equipped with a Wire Strike Protection System (WSPS). The SUST also issued a safety notice recommending that helicopters be equipped with collision warning systems to alert crews to nearby obstacles.