What happened
On March 29, 2001, an Eurocopter AS 355 F1 helicopter, registration EC-DZX, was performing a commercial aerial work mission in the Sierra del Xurés, specifically in the Curral de Abelleira area near Lobios, Ourense. The aircraft had just landed to drop off personnel from the Xunta de Galicia's Department of Environment.
As the pilot prepared for takeoff toward Salgueiros Muiños, with the engines at 100% power, a sudden, strong gust of wind struck the aircraft. This lateral wind gust displaced the helicopter to the right, causing the tail rotor to impact a rock. The impact resulted in a loss of control, and the aircraft subsequently overturned onto its right side. The pilot, who was the sole occupant, managed to shut down the engines, fuel pumps, and electrical systems before exiting the aircraft through the co-pilot door, as his own door was pinned against the ground. The pilot sustained only minor bruises and scratches, and no fire occurred.
The investigation
Investigators examined the wreckage and the impact site to reconstruct the sequence of events. They identified a circular mark on the ground, covering approximately 90 degrees, which was attributed to the tail skid making contact with the terrain during a yawing motion.
The investigation established that the tail rotor and the 90-degree transmission box were located at the base of a rock that showed evidence of being struck by the rotor blades. Furthermore, the main rotor blades were found broken at the root near the rotor head, with distinct impact marks visible on the ground. The evidence indicated that the initial impact was the tail rotor striking the rock, which led to its detachment. This was followed by a leftward yawing motion where the tail skid hit the ground, and finally, one of the skids became snagged on an obstacle, causing the helicopter to capsize.
Findings
- The primary cause of the accident was a strong lateral wind gust.
- The wind gust caused a loss of tail rotor effectiveness, preventing the pilot from maintaining directional control.
- The impact of the tail rotor against a rock led to the detachment of the tail rotor assembly.
- The aircraft sustained significant damage to both rotors, the engines, the tail cone, and the fuselage.