What happened
On May 27, 2009, an AS 350 B3 helicopter, registration F-GVCE, was performing external load operations in the Montferrier region of France. The mission involved removing components of a decommissioned mining cableway from a forested mountainside.
While performing a stationary hover to pick up a load estimated between 700 and 1,000 kg, the pilot was in radio contact with a ground operator. As the sling tensioned, the hook became momentarily caught in the cable surrounding the load before suddenly releasing. This sudden movement caused the helicopter to surge and enter a rapid leftward rotation. The pilot attempted to correct the yaw using the right pedal and reduced collective pitch, but the aircraft continued to rotate. The helicopter subsequently struck trees and crashed on its back near the load.
The investigation
The investigation focused on the mechanics of the load attachment and the aircraft's stability during the tensioning process. Investigators examined the wreckage and found no evidence of mechanical failure in the engine, the transmission, or the flight controls. The VEMD recorded only a torque excursion consistent with the rotor striking vegetation.
Analysis of the site showed that the helicopter rotated around a fixed point—the load on the ground. Because the aircraft was not perfectly vertical over the load when the hook was attached, the tensioning of the sling induced significant pitch, roll, and yaw moments. The investigation also noted that the lack of clear horizontal references due to the mountainous terrain made it difficult for the pilot to maintain the necessary cyclic inputs to stabilize the aircraft.
Findings
- The primary cause of the accident was the loss of control of the helicopter during the tensioning of a sling load.
- The hook became snagged and then abruptly released, triggering the uncontrolled movement.
- The mountainous terrain provided poor horizontal visual references, hindering the pilot's ability to correct the sudden rotation.
- The pilot did not jettison the load during the onset of the rotation.
- The pilot was not wearing a protective helmet, which contributed to the severity of the head and facial injuries sustained during the impact.