What happened
On 20 July 2022, a Eurocopter AS-350-B3, registration EC-LBU, was engaged in a firefighting mission in the Sierra Norte de Guadalajara Natural Park, Spain. The aircraft, operated by Pegasus Aviación, was part of a formation tasked with transporting firefighters and water buckets to combat a forest fire.
After the first aircraft in the formation landed to offload personnel, the pilot of EC-LBU selected a nearby forest road as an alternative landing site. The pilot performed a high hover to clear dust from the road before landing safely. After disembarking the firefighting crew and preparing the helibucket, the pilot attempted to ascend to a hover to continue the mission.
During the takeoff maneuver, the aircraft's tail cone moved sideways, causing the tail rotor to strike the aerial wire of an electrified cattle fence. The impact wrapped the wire around the tail rotor, which subsequently dragged a metal ground support rod out of the earth. The displaced rod struck the aircraft's horizontal stabilizer and then the main rotor blades. The pilot, experiencing intense vibrations, performed a controlled emergency landing back on the same road. The pilot was unharmed.
The investigation
The CIAIAC examined the aircraft wreckage, meteorological data, and flight tracking records. The investigation confirmed that the aircraft was well-maintained and compliant with all airworthiness requirements. Analysis of the flight tracking data showed the aircraft's trajectory involved several yaw movements during the final phase of flight.
The investigation also reviewed the physical evidence at the site, noting that the electrified fence consisted of a thin braided nylon and steel wire attached to rusty iron rods. The investigators found that the rods were difficult to see because they blended into the terrain. The damage to the tail rotor, horizontal stabilizer, and main rotor blades was found to be entirely consistent with the impact of the wire and the metal support rod.
Findings
- The landing site was laterally confined by an uphill slope and an electrified fence.
- The tail rotor impact with the electrified fence wire was the primary event that triggered the sequence of damage.
- The tension from the wire pulled a metal support rod from the ground, which then struck the fuselage and the main rotor.
- Local turbulence caused by the mountainous terrain and the heat from the nearby forest fire likely contributed to the need for sudden pedal corrections, leading to the tail rotor's contact with the wire.
- The rusty condition of the fence rods made them nearly invisible, which may have contributed to an error in judgment regarding the aircraft's clearance from the obstacle.