What happened
During a sling load operation, a load unexpectedly detached from a helicopter's hook, causing one end of the load to fall and pivot. The loadmasters were positioned near the load as it was being moved. As the load dropped, it moved toward the rising ground, striking one of the loadmasters. The incident resulted in one serious injury.
The investigation
The ATSB examined several potential mechanisms that could have caused the inadvertent release. Investigators looked into the possibility of a pilot release system error, a failure in the manual release, or electromagnetic radiation (EMF) affecting the solenoid. However, the loadmaster did not hear the audible 'clack' of the solenoid, and the electrical system showed no faults. The investigation also considered a failure of the hook mechanism or a dynamic rollout; however, the 'D' shackle was confirmed to be the correct size and was securely positioned behind the keeper during departure. While the remote hook release mechanism had been checked and functioned during previous lifts that day, investigators could not entirely rule out a transient fault.
Findings
- The specific mechanism that caused the load to release could not be determined from the available evidence.
- The loadmasters were not maintaining a safe distance from the load during the operation.
- The positioning of the crew, combined with the load's movement upon contacting the ground, led to the injury.
- Although the crew had discussed load specifics and used tag lines, the specific risks of the load's movement in this instance were not addressed in the briefing.
- Being in the vicinity of the load while it was above head height presented an unnecessary risk.