What happened
On February 24, 2014, a Eurocopter AS 355 N, registration EC-FTX, operated by CoyotAir, was conducting a training and competency verification flight at the Casarrubios del Monte aerodrome in Toledo. The flight involved two highly qualified pilots: a verifying pilot and a pilot being verified. The objective included performing maneuvers such as approaches, landings, and ground rolls with a simulated tail rotor control failure, while also filming the session for instructional purposes.
During the training, the pilot being verified attempted two ground roll maneuvers with the left pedal held forward to simulate a tail rotor failure. In both instances, the pilot was unable to complete the maneuver, leading him to request that the verifying pilot attempt the maneuver. During this third attempt, the verifying pilot initiated the maneuver with a shallow approach. However, the aircraft was sliding to the right, contrary to the flight manual's recommendation for a leftward slide.
As the aircraft progressed, the right skid made contact with the ground and began to slide. Due to recent rainfall, the natural terrain was soft and unstable. The right skid began to sink into the earth, eventually becoming embedded. This sudden resistance, combined with the aircraft's inertia and aerodynamic forces, triggered a dynamic rollover. During the impact, the main rotor blades struck the ground, causing them to break, and the tail cone partially detached. The aircraft finally came to rest on its left side. Both crew members were able to exit the aircraft uninjured.
The investigation
The CIAIAC investigation examined the flight sequence, the aircraft's mechanical condition, and the environmental factors. Investigators reviewed footage from cameras mounted on the tail and on the ground, which captured the moment the right skid sank into the soft soil. The investigation also analyzed the flight manual's specific procedures for tail rotor failure simulations, which suggest that a leftward slide is preferable and that wind from the right facilitates the maneuver.
Findings
- The primary cause of the accident was the incorrect execution of a training maneuver.
- The ground roll was performed with excessive speed and in the opposite direction (sliding right instead of left) to what is specified in the flight manual.
- The maneuver was conducted on soft, irregular terrain that had been weakened by recent rains, causing the right skid to sink and snag.
- The crew dedicated only approximately ten minutes to flight preparation, which was significantly less than the three hours and fifteen minutes prescribed by the operator's training program.
- The presence of filming equipment and the desire to capture the maneuver for instructional use may have pressured the crew to attempt the maneuver despite suboptimal conditions.