A helicopter crash that killed a pilot fighting the Port Hills fire may have been caused by monsoon bucket cables, an investigation has found.
Steve Askin died in February, two days into the Christchurch fire, when the helicopter he was flying crashed near the broadcast tower Sugarloaf.
Two separate fires several kilometres apart started on 14 February. Two days later they combined into one large fire. The fire wasn't completely put out until April, by which time 2000ha of forestry and 11 homes were destroyed.
Up to a dozen helicopters fought the fire at a time.
The Transport Accident Investigation Commission's interim report into the crash that killed Mr Askin found the monsoon bucket's cables may have struck the helicopter's tail rotor blades, as it flew back to a pond for refilling.
It says the helicopter's vertical stabiliser detached, causing the aircraft to roll and crash.
The report recommends the Civil Aviation Authority educate pilots about the dangers of using monsoon buckets.