The final report into the helicopter crash that killed decorated former SAS soldier and pilot Steve Askin has been released by the Transport Accident Investigation Commission (TAIC).
Mr Askin, 38, was killed while fighting the Port Hills fires on Valentine's Day last year - a day after they broke out. He was the only casualty from the event.
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The investigation found Mr Askin was on his way to refill the Squirrel chopper's monsoon bucket, when he hit turbulence and wind shear - dislodging a side window.
The doors on the pilots side had been removed to make it easier for Mr Askin to see the monsoon bucket. However the doors on the left side were closed.
That door configuration he used was one prohibited in the flight manual for the model of Squirrel he was flying, the TAIC says.
Mr Askin reduced the speed of the helicopter, causing the tail rotor to dip and the monsoon bucket to swing into it - resulting in the helicopter losing control.
A video recording taken from a camera mounted underneath the helicopter showed the monsoon bucket rising towards the tail rotor.
The recording also showed that an object fell from the helicopter shortly beforehand.
It is "virtually certain" the object was the window that had dislodged from the left rear sliding door, the TAIC says.
Mr Askin had experienced a similar loss of the left rear window while flying the same helicopter on a firefighting mission in 2015.
The report found that while Mr Askin had recently used cannabis, it was very unlikely he was impaired by this.
The use of performance-impairing substances by pilots is a serious risk to aviation safety, however, the TAIC says.
"Steve loved life and lived it to the full. He is sorely missed by and all who knew him. He was an awesome man," a statement from Mr Askin’s family says.
The fatal day
Mr Askin took off in a Squirrel helicopter at 5:40am on February 14, 2017 to re-join the Christchurch firefighting operation on the Port Hills.
He spent the morning above the flames in his helicopter with a monsoon bucket swinging below.
After lunch he led three helicopters dropping water near the Sign of the Kiwi at the top of the Port Hills.
Every three to four minutes they did a circuit, hovering over a pond filling their monsoon buckets with water and then flying to the drop zone, dumping their load, and then heading back to the pond to refill.
The crash
At 2:05pm, after dropping a bucket full of water on the flames, Mr Askin headed back to the pond.
The interim report published by the TAIC found that on his approach to the land, the cable attached to the helicopter and the empty monsoon bucket had flown up and struck the tail rotor with catastrophic consequences.
The helicopter banked and rolled to the right until it hit the ground on impact.
The main rotor and engine separated from the fuselage, while the tail rotor had separated from the tail boom.
The Port Hills fires
The fires broke out in Early Valley and Marley's Hill on Christchurch's outskirts on February 13, 2017, before merging into one fire that was blazing for 66 days until it was fully extinguished, on April 22.
Tragically, the fire claimed one life - helicopter pilot and decorated soldier Steve Askin. There were no other serious physical injuries to firefighters or residents.
Originally two fires started in Early Valley Rd and Marley's Hill, the blazes merged to become one. It ravaged 1661 hectares of land - the equivalent of 1600 rugby fields.
At its peak, the fire burned 100,000 kilowatts of energy, the equivalent of up to four atom bombs. More than 300 firefighters from across the South Island, including two crews from Dunedin, responded.
Between February 13 and February 17, more than 900 calls came in to 111 - most of which were Port Hills-related.
Fourteen helicopters and more than 100 appliances and water tankers were deployed. Nine homes were lost and five others suffered damage.
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