What happened
On December 18, 2013, at approximately 13:50 UTC, a Eurocopter EC120B Colibri, registration CS-HEX, departed from the Monchique heliport for a power line inspection mission near Marmelete, Portugal. The flight was operated by Heliportugal, carrying a pilot and two passengers who served as the technical inspection crew.
During a repositioning maneuver intended to move the aircraft toward a new substation for continued inspection, the helicopter struck an overhead power line. The impact resulted in the death of one occupant and left the remaining two crew members with serious injuries. The aircraft was destroyed in the collision.
The investigation
The GPIAAF investigation examined the aircraft's maintenance, performance, and the circumstances of the flight. The investigation established that the aircraft's mass and balance were within normal operating limits and that the engine was delivering significant power to both the main and tail rotors at the moment of impact. While the pilot possessed adequate general experience, his specific experience flying the EC120B was not extensive.
Investigators also reviewed the operational environment, noting that the power line in question did not require specific signaling according to previous reports. The investigation looked into the visibility of the obstacle, noting that the line was projected against a leafy, wooded background, making it difficult to detect.
Findings
- The primary cause of the accident was the late visualization of the power line crossing by the pilot.
- The observer failed to identify or late-visualized the obstacle.
- There was a temporary decrease in situational awareness regarding the location of obstacles.
- The absence of obstacle information in the single-line scheme meant the hazard was not known to the crew prior to the flight.
- The lack of power line signaling and the fact that the line was obscured by a leafy background contributed to the collision.
- The accident occurred specifically during a repositioning maneuver.