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The Civil Aviation Authority (CAA) is warning "loose items" on helicopters can be deadly as investigators probe whether a pair of overalls contributed to the helicopter triple fatality in Wanaka last month.
The CAA issued the safety message today after the New Zealand Herald quoted sources saying loose clothing was being investigated as a possible cause of the October 18 crash in Wanaka.
Pilot Nick Wallis and Department of Conservation rangers Paul Hondelink and Scott Theobald were killed in the crash.
It is believed the occupants of a trailing helicopter belonging to another local firm who were leaving from Wanaka Airport on the same tahr cull operation, saw clothing being sucked out of the machine and wrapping around the tail rotor.
"In some cases this has resulted in a complete loss of control of the helicopter."
It said pilots and crews needed to ensure all items in the cabin were securely stowed before take-off, even if operating with all doors fitted.
"Passengers must be briefed on the dangers of loose items in and around the vicinity of helicopters."
It was not immediately clear if the safety message was linked to the Transport Accident Investigation Commission (TAIC) investigation into the Wanaka crash.
Investigators refused to comment when approached by the Herald, saying only that its inquiry ''continues in the evidence-gathering phase''.
Multiple sources told the Herald that clothing - either overalls or possibly a jacket - was seen flying out of a door and that it was being investigated as a possible contributing factor to its catastrophic failure.
A source close to the Wallis family also said they were aware of the potential scenario.
Eldest brother Jonathan Wallis said he had heard ''a number of potential sequences that may have happened''.
But his family, including patriarch Sir Tim Wallis, who founded the Warbirds Over Wanaka airshow, were comfortable to let TAIC's ''meticulous and thorough'' probe run its course.
''TAIC's role is to disprove rather than prove theories and as a family we are confident that they will find out what happened,'' Jonathan Wallis said.
''Even though we were leasing the helicopter and it was my brother in the accident, we just have to accept that process, and we respect it.
''There are a number of different theories but I'm certain that given what they've got in front of them that they will find out what happened and they should find it at an early stage rather than a later stage.''
AIC lead investigator Barry Stephenson earlier described the inquiry as ''a big jigsaw puzzle,'' which typically would take 18-24 months to complete.
However, an interim report or urgent safety recommendations might be issued at any time if warranted.