What happened
On January 6, 2002, during the dismantling of infrastructure following international ski competitions in Adelboden, a commercial helicopter operation resulted in the loss of an external load. An SA 315 B helicopter, registration HB-XPP, was performing a lifting task to remove a 9-meter-long steel beam used for a video tower.
As the pilot began to lift the approximately 650 kg load, the beam was suspended by two textile sling sets attached to a single swivel hook. As the helicopter moved laterally, one of the slings slipped from the hook. This caused the beam to tilt, slip out of the remaining sling, and fall vertically to the ground. The falling beam struck a television production employee who had entered the danger zone, resulting in one person sustaining serious injuries to the head, shoulder, back, and leg.
The investigation
Investigators examined the lifting equipment, including the textile slings, the steel beam, and the helicopter's swivel hook. The investigation found that the slings and the method of rigging the load were otherwise structurally sound. However, the swivel hook's spring-loaded safety latch had been forcibly pulled outward and was no longer functional.
Technical measurements of the sling geometry revealed a wide spread angle of approximately 102 degrees. The investigation also noted that while the flight assistant had instructed that only essential personnel should be in the loading area, the injured individual had entered the zone unnoticed by both the pilot and the flight assistant.
Findings
- The primary cause of the accident was the inadequate attachment of the load to the swivel hook.
- The wide spread angle of the slings caused one sling to press directly against the spring-loaded safety latch of the hook. The force of the load was enough to overcome the latch, allowing the sling to escape.
- The use of a wide-angle sling configuration without an intermediate link, such as an additional sling or shackle, was improper for this type of hook.
- The presence of a person in the danger zone contributed to the severity of the incident.