What happened
On May 31, 2014, at approximately 21:20 local time, a Robinson 44 II helicopter, registration EC-JTC, was performing a private flight from Sanxenxo to Caldas de $\text{Reis}$ in the province of Pontevedra, Spain. The aircraft was carrying one pilot and two passengers.
While flying over a forested area near Monte Lobeira, the aircraft was traveling at approximately 140 km/h at a low altitude. As the pilot attempted to level off a descent, a loud breaking sound was heard from the rear of the aircraft. Immediately following this noise, the helicopter experienced a sharp yaw to the right, indicating a sudden loss of tail rotor thrust.
The pilot attempted to maneuver the aircraft away from nearby high-voltage power lines, resulting in a steep turn. The aircraft eventually impacted the ground in a small, wooded area, causing the helicopter to overturn on its left side. The pilot sustained one serious injury, while the two passengers were uninjured. All occupants were able to exit the aircraft on their own.
The investigation
The CIAIAC investigation focused on the structural failure of the tail rotor assembly and the flight dynamics during the emergency. Investigators recovered the tail rotor blades, the 90-degree gearbox, and the vertical and horizontal stabilizers approximately 500 meters from the main wreckage.
Analysis of the wreckage revealed that the vertical stabilizer had sustained a heavy impact, with wood fragments embedded in the damage. The investigation also found that the tail rotor blades had struck tree branches, which subsequently caused the connection between the stabilizer and the tail cone to fail due to the intense torque and aerodynamic forces. GPS data confirmed that the aircraft was flying at a low altitude, which prevented the pilot from executing the recommended autorotation procedure prescribed in the flight manual for tail rotor thrust loss.
Findings
- The primary cause of the accident was the impact of the tail rotor blades and the lower vertical stabilizer against tree branches.
- The low altitude of the flight prevented the pilot from entering autorotation to manage the emergency.
- The loss of the vertical stabilizer and tail rotor thrust resulted in a total loss of directional control.
- The high inertia during the descent maneuver caused the tail rotor assembly to strike the vegetation despite the pilot's efforts to maneuver the aircraft.