What happened
On July 13, 2005, a Bell 412 helicopter, registration EC-JCE, was engaged in firefighting operations near Simat de la Valldigna, Valencia. The aircraft, operated by Helicópteros del Sureste, had been transporting firefighting crews between a local football field and an active forest fire for approximately 85 minutes.
While stationary on the football field, the pilot was preparing to perform water drops using a helibucket. During the process of attaching the bucket and closing the cabin door, the aircraft began experiencing significant vibrations. The pilot, believing the aircraft was experiencing ground resonance, attempted to ascend to correct the issue. However, the vibrations increased, forcing the pilot to perform an emergency landing. During the maneuver, the helicopter struck trees, resulting in substantial damage to the airframe, main rotor, and tail rotor. Both the pilot and the ground technician escaped the crash uninjured.
The investigation
The CIAIAC examined the flight sequence, the aircraft's mechanical state, and the cockpit configuration. Investigators reviewed the pilot's actions, noting that the aircraft's controls were not configured according to the flight manual. Specifically, the collective lever was fully down and loose, and the force trim system was disconnected.
Investigators also analyzed the physical evidence at the crash site and the damage to the components. While the tail rotor experienced a separation of the 90-degree gearbox and blade fragments, laboratory analysis of the recovered blade fragments ruled out pre-existing cracks or corrosion as the cause of the initial vibrations. The investigation focused on the pilot's physical movements and the lack of cockpit warnings during the period when the rotor was at 100% RPM.
Findings
- The primary cause of the accident was the inadvertent movement of the cyclic and collective controls.
- The aircraft was in an improper configuration; because the force trim was disconnected, the cyclic could move freely without providing resistance or triggering the cyclic position warning system, which is inactive when rotor RPM is at 100%.
- To communicate with the ground technician, the pilot had to use hand signals and lean toward the right side of the cockpit. This movement, combined with releasing the controls to signal, likely caused the cyclic to shift forward and to the right.
- The takeoff was not vertical, but rather a forward and rightward movement consistent with an off-center cyclic position.
- Ground resonance was ruled out as the cause, as the vibrations did not disappear upon leaving the ground.
- The damage to the tail rotor was determined to be a consequence of the impact with trees rather than a pre-existing mechanical failure.