What happened
On March 19, 2011, a Bell 407 helicopter, registration EC-KTA, operated by INAER, departed from Alcorisa, Teruel, to transport a forest fire brigade to an active wildfire near Villel and Cascante. During the flight, the aircraft was performing an emergency maneuver following a hydraulic system failure. The pilot had disconnected the hydraulic system to manage the emergency according to the flight manual, maintaining a controlled descent and a steady westward course.
As the aircraft approached the terrain, the pilot attempted a gentle right turn to adapt to the landscape. During this maneuver, the aircraft experienced a sudden lateral displacement. The helicopter impacted the ground in the municipality of Villastar with a strong leftward lateral component. Of the seven people on board, 6 fatalities occurred, and one passenger sustained serious injuries.
The investigation
The CIAIAC investigation focused on the mechanical state of the hydraulic system and the flight trajectory. Investigators examined the wreckage and determined that the left lateral servoactuator was stuck in an extended position. The analysis of the flight path confirmed that while the pilot was successfully executing emergency procedures for a hydraulic failure, the sudden movement of the cyclic controls during the final turn triggered a critical failure in the servoactuator's stability.
Technical inspections revealed that the adjustment mechanism of the left servoactuator was not properly secured. The investigation also reviewed the maintenance history and the implementation of airworthiness directives, specifically looking into why a previously issued service bulletin had not been applied to this specific component.
Findings
- The primary cause of the accident was the loss of aircraft control due to the left lateral hydraulic servoactuator piston becoming immobilized in the extended position.
- This failure was driven by a progressive misalignment of the servoactuator control mechanism.
- The misalignment resulted from the failure to comply with the instructions in Alert Service Bulletin 407-05-70, which required specific inspections and adjustments to the servoactuator system.
- The specific servoactuator involved (S/N HR2036) had been supplied by the manufacturer with a valid Certificate of Airworthiness, but without the necessary actions from the 2005 service bulletin being completed.
- The pilot was appropriately trained, licensed, and was following established emergency procedures for a hydraulic system failure prior to the final loss of control.