What happened
On April 3, 2005, a Eurocopter AS-350-B3 helicopter, registration EC-HXS, was conducting aerial firefighting operations for the Government of the Principality of Asturias. While operating near Bustiello, the pilot was performing a sequence of maneuvers to deposit a "Bambi Bucket" on the ground and prepare for the pickup of a five-person firefighting crew.
The maneuver was performed entirely in a rearward flight (reverse) direction. During the descent phase, the tail rotor made contact with nearby bushes. This impact caused high-frequency vibrations throughout the aircraft and triggered the tail gear box chip detector, indicating the presence of metallic particles in the transmission.
Following the impact, the pilot executed an emergency landing in a safer area in the valley floor, approximately 7/50 meters from the initial site. The pilot remained uninjured, and the aircraft sustained minor damage to the tail rotor.
The investigation
The CIAIAC examined the flight sequence, the environmental conditions, and the coordination between the flight crew and the ground personnel. The investigation focused on the visibility limitations inherent in the backward flight maneuver and the communication protocols between the pilot and the firefighters on the ground.
Investigators noted that the terrain in Asturias often necessitates operations in unprepared landing zones, which increases the risk of obstacle strikes. The investigation also reviewed the company's operational manual regarding the interaction between pilots and firefighting crews, as well as the technical capabilities of the radio equipment used by the ground crew.
Findings
- The primary cause of the incident was the tail rotor striking bushes during a descent maneuver.
- The backward flight required for the maneuver significantly reduced the pilot's visibility of potential obstacles.
- While the firefighters were positioned in a safe area and observed the impact, they did not provide any warning to the pilot.
- There was a lack of established coordination procedures between the pilot and the ground crews regarding hazard identification.
- The radio equipment used by the ground crew leader was not equipped with noise-canceling microphones, making effective communication difficult due to high ambient rotor noise and wind.
- The company's training for ground crews did not sufficiently emphasize the importance of communicating visual hazards to the pilot.