What happened
On May 22, 2008, an EUROCOPTER AS350B, registration EC-KLJ, was performing external load operations in the municipality of Queralbs, Girona. The aircraft, operated by Helitrans Pyrinees, S. L., had been transporting concrete loads for several hours to support the construction of power line towers. During the mission, the pilot decided to extend the existing sling to ensure a fiberglass tank would remain clear of the main rotor's downwash. After retrieving a 12-meter sling and refueling, the pilot began a transit of approximately 8/00 meters toward the worksite.
While cruising at 65 knots, the pilot observed via the mirror that the sling had drifted backward and was approaching the tail rotor. In an attempt to reduce speed, the pilot lowered the collective. This action was followed by loud noises, heavy vibrations, and sudden jolts. The helicopter experienced two sharp left yawing motions, with the second being particularly violent, leading to an immediate loss of tail rotor effectiveness and the onset of autorotation. The pilot managed to execute a flare at low altitude, stabilizing the aircraft just 1.5 meters above the ground before a hard impact. The aircraft overturned on its right side, resulting in substantial damage to the airframe, including a fire in the tail cone and the detachment of the vertical stabilizer.
The investigation
The investigation focused on the movement of the sling and the pilot's recovery maneuvers. Investigators examined the company's Operations Manual and found that while procedures for installing electric towers and concrete bases were documented, there was no specific procedure for the task being performed at the time of the accident. Specifically, the manual lacked guidance regarding the risks of transporting unweighted slings or the general practice of carrying equipment inside the cabin whenever possible.
Furthermore, the investigation analyzed the pilot's reaction to the encroaching sling. It was determined that the decision to lower the collective increased the risk of the sling moving toward the tail. The investigation established that a more effective maneuver would have involved a turn centered on the tail—achieved by increasing collective and applying aft cyclic—to raise the nose and decrease airspeed without lowering the tail into the path of the sling.
Findings
- The primary cause of the accident was the transport of an unweighted sling, which allowed it to drift backward and become entangled in the tail rotor.
- The entanglement caused the loss of the tail rotor and subsequent loss of directional control.
- The pilot's attempt to slow the aircraft by lowering the collective contributed to the sling's proximity to the tail rotor.
- The operator's Operations Manual did not adequately address the risks of transporting unweighted external loads or the necessity of using counterweights.
Safety action
- REC 03/10: It is recommended that Helitrans Pyrinees update its Operations Manual to mandate that all necessary materials and equipment be transported inside the helicopter whenever possible. Additionally, the manual should strictly prohibit the transport of any external hanging items that are not properly weighted.