Dodgy door latch blamed in 2018 fatal helicopter crash near Wānaka, Transport Accident Investigation Commission investigation finds

Complacency around doors opening mid-flight has featured heavily in a new report into a fatal helicopter crash that killed three people near Wānaka in 2018.

The Transport Accident Investigation Commission's report into the crash has taken nearly six years to put together - and says there are lessons to be learnt.

A mark left by a zipper on a rear rotor blade has helped the Commission prove a pair of overalls a catastrophic sequence of events led to the deaths of three men on October 18th, 2018.

DOC rangers Paul Hondelink, and Scott Theobold lost their lives when the MD500D Helicopter disintegrated midair.

Pilot Nick Wallis, son of legendary Helicopter pioneer Tim Wallis, was also killed. His brother Matt had died in a helicopter crash just months earlier. 

The report from the Transport Accident Investigation Commission, released on Thursday, has outlined for the first time how the helicopter with the three men on board went down.

It all started about a minute after take-off.

The helicopter’s left-rear door likely opened in flight and a pair of overalls flew out of the rear cabin and became entangled in the tail rotor, which broke off and collided with the main blades.

Then the whole tail broke away and the wreck burst into flames when it hit the ground.

The whole thing only took 14 seconds.

It's always difficult to read these sorts of reports, Richard Milner from the Helicopter Association told Newshub.

He's been a pilot for more than 20 years, and says there are clear take aways from the report.

"The need for pilots for to always secure their loads in all flying conditions, and to record all occurrences when they go wrong."

The report reveals the latch of the back door was worn.

Two weeks before it opened unexpectedly during another flight.

The investigators also found cargo items were not weighed before they were loaded into the helicopter, or strapped down.  

It also found a culture of normalising errors in the helicopter sector, means incidents involving doors opening mid-flight often aren't reported. 

The family owned Alpine Group, who was operating the flight, and told Newshub on Thursday the helicopter was being leased for a short period until two newly purchased helicopters arrived.

They've called it an unspeakable tragedy.

Milner is calling for the commission to speed up its report releases. This one took six years to complete.

"The amount of time the families have had to live through this tragedy waiting for the commission's report, and also for aviation in that there may have been key elements in this report which could have affected safety. We're fortunate, this hasn't happened again."

In statement to Newshub, the Department of Conservation says it has strengthened its operating model to ensure accountability systems are embedded, and staff are actively encouraged to escalate issues if they are concerned safety is being compromised.

It's a tragedy the industry hopes is providing lessons to prevent fatalities like this from happening again.