GovWire

The Search and Rescue helicopter was on its third approach, in poor visibility, to collect a casualty from a site adjacent to high ground. The Pilot Flying (PF) selected a mode of the Automatic Flight Control System (AFCS) which would bring the helicopter to a hover. As he did so, the helicopter unexpectedly yawed towards the high ground. When a further selection was made on the AFCS to effect a go-around, the helicopter accelerated towards the terrain while maintaining height. The Helicopter Terrain Awareness Warning System (HTAWS) triggered a visual and aural caution terrain alert. The crew immediately made a climbing turn onto their planned escape heading during which a warning terrain alert triggered. The helicopter recovered to a safe height and returned to its home base.

The unexpected yaw was caused by a mismatch between the previously selected AFCS heading reference and the heading flown by the PF. While the helicopter and the flight control system were found to be serviceable and performed as designed, the crew did not have a complete understanding of the functionality of all the AFCS modes. Other factors included:

• Overriding the engaged modes by manually flying the helicopter.
• A lack of clarity between the role of PF and Pilot Monitoring (PM).
• Ineffective communication and co-ordination between the pilots.
• Imprecise application of Standard Operating Procedures (SOPs).

The operator took a number of safety actions to raise awareness of the event, improve knowledge of the autopilot modes and include the event as part of their initial and recurrent training.

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