What happened
On February 26, 2018, an Airbus Helicopters AS350B3e, registration F-HILF, was performing an aerial work mission in Val Cenis, France. The pilot was transporting five oxygen cylinders via an external sling load from a high-altitude Gazex site, located at 3,000 meters, to a lower delivery zone in the valley.
The cylinders were attached in a line using a rappelling rope, with each cylinder spaced five meters apart. As the pilot maintained a hover over the delivery site, a ground assistant moved into position to receive the load. During this maneuver, the rope snapped at the level of the highest cylinder, causing all five cylinders to fall onto the snow. While the ground assistant attempted to move away, one of the cylinders struck their leg, resulting in one injury (a sprained ankle and leg contusions).
The investigation
The BEA investigation focused on the integrity of the sling load and the safety management procedures of the operation. Investigators found that the oxygen cylinders were secured using a climbing rope knotted around the cylinder heads. This method lacked any protective buffering between the rope and the metal edges of the cylinders.
At the time of the incident, the temperature was -18 °C, and the rope was stiff due to the presence of ice and snow within the storage chest. The investigation established that the task specialist, responsible for verifying the load, was unable to inspect the cargo at the loading site due to the steep terrain. Furthermore, the client had not provided documentation describing the specific configuration of the load, making it impossible for the operator's specialist to verify compliance with safety standards.
Findings
- The primary cause of the accident was the abrasion of the rope against the metal head of the first cylinder.
- During the flight, the cylinders rotated randomly under the sling, causing progressive wear on the rope at various contact points with metal surfaces.
- The load configuration did not meet the required safety criteria for external sling operations.
- The decision was made to proceed with the transport despite the task specialist being unable to verify the load and the lack of descriptive documentation for the cargo.
- The ground assistant's continuous visual monitoring of the load allowed them to react quickly, which mitigated the severity of the injury.
Safety action
Following the accident, the client modified the packaging method for the oxygen cylinders to ensure they meet the safety requirements and risk management standards established by the helicopter operator.