What happened
During an initial winch evolution, a rescue crewman was transferred to a vessel's deck using a hi-line. After reaching the deck, the crewman disconnected from the winch hook and began paying out the line from a hi-line bag. As the helicopter moved slowly away from the vessel toward a rest position, the winch operator began retrieving the winch hook while monitoring the crewman.
During this process, the line became restricted inside the hi-line bag. The relative motion between the helicopter, the winch cable, and the vessel caused the weak-link to undergo sudden, increased tension. This tension was enough to cause the weak-link to fracture. Once the link broke, the sudden release of downward tension propelled the winch hook on a path toward the helicopter's main rotor disc.
The investigation
The ATSB examined the equipment and the operator's safety processes. The investigation found that the operator, which was in the training and development phase for a new search and rescue contract based in Broome, had implemented a management of change process for their new capability. However, this process failed to include risk assessments specifically for the search and rescue role equipment.
Investigators discovered that a 300 ft line had been placed into a hi-line bag that was designed to be used either as a standalone item or with only a 75 ft line. Because the bag was sausage-shaped with a narrow throat relative to the volume of line inserted, the equipment was not fit-for-purpose and created an increased risk of line restrictions during operations.
Findings
- The weak-link fracture was caused by increased tension resulting from the line becoming restricted within the hi-line bag.
- The operator's management of change process did not adequately capture risk assessments for the procurement and use of search and rescue role equipment.
- The use of a 300 ft line in a narrow-throated hi-line bag created a high risk of line restriction during hi-line evolutions.