What happened
On Wednesday, October 13, 1999, at 17:20, an Eurocopter AS 350 B3 operating as F-GMEN was performing a sling load operation near Sallanches, France. The aircraft was transporting a 750 kg load contained within a canvas bag from a mountain refuge on the Tret-la-Tête glacier down toward the valley.
During the descent, the canvas bag failed under the weight of the cargo, causing the load to fall. In response to the sudden change, the pilot released the sling. Following this event, the pilot found that the tail rotor controls had become ineffective. To maintain the flight path toward the Sallanches aerodrome, the pilot increased airspeed. As the aircraft approached the runway and the pilot reduced speed, the helicopter entered a left yawing motion, eventually striking a tree and crashing on its right skid.
The investigation
The investigation focused on the mechanical failure of the tail rotor control effectiveness and the subsequent loss of directional control. Examination of the wreckage revealed that the sling used for the cargo had become entangled around the tail rotor assembly.
Findings
- The primary cause of the loss of control was the rupture of the canvas bag containing the cargo.
- The failure of the bag caused the cargo to drop, which subsequently led to the sling becoming wrapped around the tail rotor, resulting in the loss of anti-torque control.