A report has found a dodgy door latch was likely responsible for a fatal helicopter crash near Wānaka in 2018, that killed three men.

Pilot Nick Wallis and DOC rangers Paul Hondelink, and Scott Theobold died when a door opened shortly after takeoff and a piece of loose clothing was sucked into the tail rotor - leading to the crash.

The chopper was heading to a tahr culling operation in the Haast area.

In its final report the Transport Accident Investigation Commission said all air crew needed to be aware it was abnormal and dangerous for doors to open in-flight, and such incidents should be reported.

The inquiry found too many pilots and operators did not report doors opening during flight to the Civil Aviation Authority.

Deputy chief commissioner Stephen Davies Howard said it was not clear exactly why the door opened, but it was likely because the latch was worn.

"Investigators found that the risk associated with doors opening in flight had become normalised.

"This normalisation has led to door opening in flight being seen as not especially hazardous and therefore not worth reporting to the Civil Aviation Authority. If an unusual or hazardous event occurs in the air and it's not reported, maintenance engineers and operators won't be aware there's a problem to rectify."

The TAIC asked the director of Civil Aviation to revise the rules to say that a door opening in flight was a safety issue and to take steps to address door-opening-in-flight occurrences that were not being promptly reported to the Civil Aviation Authority.

The commission found the opening might have been prevented if the maintenance manual had clearer instructions and they had been followed during routine maintenance.

Howard said the risk of a door opening in flight was greater if there was unsecured cargo in the cabin.

"Loose items can fly out and hit control surfaces, causing loss of control of the aircraft. Restraining the cargo in this instance could have prevented the subsequent chain of events and the loss of life."

It said the operator, The Alpine Group, now requires pilots to secure items in external cargo pods or under seats in purpose-made bags.

Howard said the lessons from the accident were that pilots must promptly report any unusual events when airborne, that operators need to enforce stringent cargo securing practices; aircraft manufacturers should provide clear instructions for maintenance, and regulators should ensure regulations are clear to all concerned.

A tragic loss of life

In a statement, The Alpine Group said it was devastated by the loss of "these three wonderful men".

"It was an unspeakable tragedy, and our thoughts remain with the men and their many loved ones."

The group, a family owned business, had been in operation since 1954 and had a proud safety record.

It welcomed the TAIC report's findings and accepted the actual initiating sequence and cause of the accident will likely never be known.

Despite this, the group had worked hard to try to identify several potential causal factors and have collaborated with the wider industry to continually improve aviation safety and ensure that similar incidents could be avoided in the future.

Lessons learned

In November 2019, the Civil Aviation Authority laid two charges against The Alpine Group Ltd in relation to the accident, under the Health and Safety at Work Act. The Alpine Group pleaded guilty to those charges and was fined $315,000 and ordered to pay $64,000 in legal costs in the Queenstown District Court .

A spokesperson said it had worked alongside TAIC to progressively address issues raised in the final report and was confident the steps already taken, and those underway would reduce the risk of this type of accident occurring again.

Department of Conservation director of health and safety Harry Maher said after the accident, its senior leadership vowed to do everything necessary to ensure all staff and contractors returned home safe after work.

"We wanted to ensure the events leading up to the crash were investigated and changes made to ensure the safety of all staff and contractors."

The Director General at the time of the incident commissioned an independent review from PwC which made a number of recommendations aimed at significantly strengthening DOC's health and safety systems including culture.

It had since strengthened its accountability systems, with staff actively encouraged to escalate issues if they were concerned safety was being compromised.

A subsequent independent review from health and safety consultancy CosmanParkes provided assurance that the necessary changes had been implemented from previous reports.

"DOC continues to monitor helicopter safety, incident management and reporting, and our overall health and safety culture.

"Health and safety are top priorities, and we will keep a focus on continuous assessment and improvement of our systems and processes and will act whenever our people have any safety concerns," Maher said.

Main Image: The three men who died in the helicopter crash near Wanaka Airport (from left) Nick Wallis, Paul Hondelink and Scott Theobold. Photo: Supplied