Mast bumping was a factor in one fatal helicopter crash near Wanaka earlier this year, and clothing flying out an open door was a factor in a second.
Pilot Matthew Wallis died in an Alpine Helicopters Robinson R44 crash into Lake Wanaka on July 21, 2018, and his brother Nick Wallis, along with passengers Paul Hondelink and Scott Theobold, died in the second crash near Wanaka Airport on October 18.
The Transport Accident Investigation Commission (TAIC) has released interim reports into the two crashes, although it will not have a finding until investigations are completed.
The interim report was presented by Jane Meares at a press conference in Wellington this afternoon.
She said there were signs on the Robinson Helicopter of the rotor having hit the cabin.
"The wreckage under examination includes evidence in the main rotor mechanism symptomatic of the helicopter having experienced mast bumping at some point in the accident sequence."
Mast bump is contact between an inner part of a main rotor mechanism and the main rotor drive shaft. It usually results in the helicopter breaking up in flight.
"There is also evidence that a main rotor blade has struck and entered the cabin in flight," Ms Meares said.
"There are score marks on the blade that match screws on the canopy bow; there is scoured paint on the screws. The same rotor blade has marks matching damage to the flight instruments panel."
"There is evidence that there have been three incidents the month prior to the accident in which doors on this helicopter opened in flight.
"Effective safety management depends on such incidents being reported and addressed, but none of these occurrences was recorded in the operator's incident reporting system.
"Another safety issue noted in the interim report is the risk posed by loose items in the cabins of helicopters.
"Evidence shows that a pair of over-trousers from within the cabin was drawn out in some way and became entangled in the tail rotor.
"Paint marks on the over-trousers matched the colour and profile of the tail rotor blades, and marks on a tail rotor blade match a zip and dome connector on the over-trousers.
"These markings strongly indicate that the over-trousers had come out of the helicopter and become entangled with the tail rotor at some point."
In a statement, David Hiatt, of the Alpine Group, said the company and the Wallis family had reviewed the interim reports from the Transport Accident Investigation Commission (TAIC) and found some of their content "disturbing".
"We respect the release of these reports at such an early stage of the investigations and unreservedly support the safety message pertaining to the stowage of loose items, as well as the recommendation to aviation participants to be reminded of occurrence notification in accordance with Part 12 of the Civil Aviation Authority (CAA) Rules."
"Neither report presents analysis or findings however, the apparent characteristics of an in-flight breakup of the Robinson R44II on 21 July 2018 are disturbing and the unexplained door separation in-flight of the Hughes 369D on 18 October 2018 is equally of concern.
"Since that accident in October we have been made aware of numerous incidents of doors opening in-flight on the same aircraft make and model."
The company had fully cooperated with the TAIC and CAA investigations and would continue to do so.
"We will not make any further public comment while the investigations are ongoing, so as not to compromise the investigations in any way."
