AO-2017-001 Eurocopter AS350 BA, ZK-HKW, Collision with terrain, Port Hills, Christchurch, 14 February 2017

On the afternoon of 13 February 2017, wildfires broke out on the Port Hills between Lyttelton Harbour and the south-eastern suburbs of Christchurch. A major effort began early the following day to control the fires, using large ground parties assisted by up to 12 helicopters and two aeroplanes. In the early afternoon one of the helicopters, a Eurocopter AS350 BA ‘Squirrel’ registered ZK-HKW, crashed while returning to the dipping pond to refill an underslung monsoon bucket. The pilot was fatally injured and the helicopter was destroyed.

The suspension line for the monsoon bucket had contacted the tail rotor. The damage to the tail rotor caused the vertical stabiliser to tear off the tail boom, and the helicopter became uncontrollable and crashed.

A video recording taken from a camera mounted underneath the helicopter showed the monsoon bucket rising towards the tail rotor. The video recording also showed that an object fell from the helicopter shortly beforehand. It is virtually certain that this was the window that had dislodged from the left rear sliding door. The pilot had experienced a similar loss of the left rear window while flying the same helicopter on a firefighting mission in 2015.

The Transport Accident Investigation Commission (Commission) found that the door configuration was prohibited in the flight manual, and therefore the helicopter was being flown outside the manufacturer’s approved limits. It was very likely that the monsoon bucket flew up towards the tail rotor due to a combination of forward air speed and turbulence. At the same instant, the pilot’s slowing of the helicopter in response to losing the window resulted in the tail rotor dipping and making contact with the rising suspension line for the monsoon bucket.

The hazard of an underslung load striking a tail rotor is a known risk to helicopter operations.

Although not directly contributing to the accident, the Commission found three deficiencies that indicated the helicopter operator’s quality assurance system should be reviewed.

The Commission found that it was very unlikely that the pilot was impaired by his recent use of cannabis, but reiterates its view that the use of performance-impairing substances by pilots is a serious risk to aviation safety.

Two safety issues were identified in the inquiry:
- there may not be a good awareness within the helicopter industry of the additional risks involved with underslung load operations, particularly with the use of monsoon buckets during firefighting operations
- the operator did not have adequate systems available for the pilot to determine the actual all-up weight and balance of the helicopter for the firefighting operation, or to ensure that incidents such as the previous loss of a window were recorded, notified to the CAA and investigated.

The Commission has previously made recommendations to address the issue of substance impairment and to address industry awareness of the risks involved with underslung load operations. It made a new recommendation to address the operator’s procedural safety issues.

The Commission identified the following key lessons as a result of its inquiry into this accident:
- flight in turbulent conditions requires care in order for the pilot to avoid exceeding an aircraft or equipment speed limitation
- it is important that operators and pilots understand the reasons for and observe the specific limitations applicable to each aircraft that they operate, as variations often exist between different variants of the same aircraft type
- all operational incidents should be recorded and investigated by the operator so that the causes can be identified and corrective or preventive actions taken
- performance-impairing substances such as recreational drugs pose a serious risk to aviation safety. Their short- and long-term effects may be unpredictable and result in pilots being impaired when flying their aircraft.