What happened
On July 11, 2020, at 10:57 local time, a Bell 412 helicopter, registration EC-MPL, operated by Rotorsun, was performing a base training flight at the Marroxo fire base in Lugo, Spain. The flight was intended to familiarize the commander with the base and to test the watertightness of a recently repaired Bambi Bucket, which was deployed for the duration of the flight.
Following a vertical takeoff, the crew began a departure procedure that deviated significantly from established company protocols. While the initial climb followed the prescribed westward heading, the pilot soon initiated a descent and a sharp right turn to follow the terrain profile. During this maneuver, the bottom of the Bambi Bucket made contact with an electrical power line located to the west of the base.
The impact occurred approximately 21 seconds after takeoff. At the moment of contact, the helicopter was flying at 51 kt ground speed and 3 36 ft above the ground, leaving the bucket at an altitude of 23 ft, which coincided with the height of the power line. The contact caused the bucket to rebound upward, striking the underside of the aircraft's left horizontal stabilizer. The impact also caused the power line to detach from its concrete pole, though the line did not break.
The investigation
Since the aircraft was not required to carry flight recorders, the CIAIAC reconstructed the flight path using GPS data and video footage of the takeoff. The investigation examined the aircraft's structural damage, the damage to the electrical infrastructure, and the crew's flight management.
The investigation established that the takeoff maneuver violated several operational constraints, including prescribed flight zones, trajectory, altitude, and speed. The crew noted a slight "sway" during the maneuver but did not immediately recognize the contact with the power line. The aircraft continued the flight for an additional 23 minutes before returning to the base, where the crew eventually realized the line had been struck.
Findings
- The primary cause of the accident was the failure to adhere to established procedures, specifically regarding the takeoff trajectory, altitude, and operational zones.
- The pilot executed a non-standard maneuver involving a descent and a sharp turn into a restricted area (the northern part of the base) where obstacles were present.
- A contributing factor was the lack of information regarding the specific location of the electrical line in the crew's operational documentation; the line was not listed as an obstacle in the base's documentation at the time.
- The aircraft sustained damage to the left stabilizer due to the impact of the bucket.
- The electrical line was displaced from its mounting due to the impact.