An interim report outlining the cause of the Port Hills helicopter crash has been released, showing cables from the monsoon bucket caused the accident.
Former SAS solider and experienced pilot Steve Askin was flying one of 12 helicopters fighting the wildfires that broke out on the Port Hills in February.
The report, released by the Transport Accident Investigation Commission (TAIC), reveals the monsoon suspension cables struck the tail rotor, causing the helicopter to lose its vertical stabilising ability.
The helicopter then rolled to the right and descended until it struck the ground, causing Mr Askin's death and destroying the helicopter.
The crash happened while Mr Askin was flying in rotation collecting water and releasing it on certain dump sites.
The monsoon bucket used by Mr Askin could hold up to 1000 litres of water and was returning to the dipping pond when the crash happened.
Carrying a monsoon is also known as an 'underslung load' which means something is being carried under the aircraft.
TAIC says underslung loads flying back into the tail is a known risk to helicopter operations and note advice and training is available for pilots and operators to combat that happening.
A recommendation has been made to the Director of Civil Aviation reminding the aviation industry of the lessons learned from accidents involving underslung loads, in particular with monsoon buckets during firefighting operations like that on the Port Hills.
TAIC say the helicopter had flown more than 9100 hours and was in a fit condition to fly at the time.