What happened
On 4 August 2010, an AS 350 B2 helicopter, registered F-OIEL, was performing aerial work to transport external loads in French Guiana. The mission involved moving flexible fuel tanks between a landing zone at Croisée d’Apatou and a gold prospecting site at Saint Pierre.
During the fourth rotation of the day, a ground operator attached a flexible container filled with approximately 1,100 liters of petrol to the helicopter's load release hook using a sling and net assembly. After the pilot lifted the load and began the flight, the helicopter was approximately one minute into its journey when two of the four rope buckles securing the net to the hook detached. This caused the heavy fuel tank to fall from the aircraft. The sudden loss of the load startled the pilot, who attempted to release the net while the aircraft was traveling at a speed exceeding the recommended limit for such maneuvers. The falling net subsequently struck the tail rotor, resulting in a loss of control and a fatal crash into the equatorial forest.
The investigation
The BEA investigation focused on the mechanical integrity of the lifting equipment and the procedures used for load preparation. Investigators examined the wreckage, the sling assembly, and the flexible container. Technical analysis included a study of the stress concentrations on a sample hook using photo-elasticimetry and an examination of the load release hook's condition.
Testing revealed that the sling assembly was a custom-made, shortened version of a standard sling, designed by the operator to prevent the load from hitting the tail rotor. The investigation also scrutinized the compliance of the lifting accessories with the European Machine Directive and the training levels of the ground personnel involved in the operation.
Findings
- The primary cause of the accident was the inadequate attachment of the external load due to a non-compliant lifting accessory.
- The sling assembly was old, lacked manufacturer markings, and was not designed for the specific constraints of aerial work.
- The hook used was significantly worn, with a residual opening of 7 to 8mm, far exceeding the manufacturer's maximum limit of 3mm.
- The connecting shackles were intended for metal slings rather than textile slings, and the upper shackle exhibited significant play.
- The ground operator lacked specific aeronautical training for preparing inert external loads, which prevented the detection of the incorrectly secured load.
- No maintenance had been performed on the sling, and wear on its components had gone undetected.
Safety action
- The BEA issued a safety recommendation to EASA and the DGAC to ensure that sling equipment for transporting inert external loads is designed and used in accordance with the safety standards defined by the European Machine Directive.
- A recommendation was also made to EASA and the DGAC to establish specific training courses for the aerial work sector regarding the preparation and transportation of inert external loads.