Twenty-three seconds of silence may have contributed to a mid-air helicopter collision that killed four people and injured nine others near Sea World on the Gold Coast.
The Australian Transport Safety Bureau has found no recordings of radio calls between pilots Ashley Jenkinson and Michael James in the moments before their choppers collided about 40m off the ground and crashed on January 2.
Mr James had been coming in to land with six passengers and Mr Jenkinson was taking off with seven people on board.
Being too low for air traffic control to guide them, the pair relied on radio calls and vision.
Mr James, who survived the crash, remembers seeing passengers boarding his late colleague's helicopter (XKQ) and thinking it would pass behind his aircraft.
"They (Mr James) did not recall the pilot of XKQ making a standard "taxiing" call announcing their intention to depart," the bureau's preliminary report said.
Two other helicopter pilots from the nearby Marina Mirage were also interviewed about radio communications.
One remembered hearing Mr James' inbound call but not Mr Jenkinson's outbound call, while the second Marina Mirage pilot didn't recall hearing either.
Bureau commissioner Angus Mitchell stressed that did not mean Mr Jenkinson did not make an outbound call.
"We do know that calls made down in low altitude are not routinely picked up by that recording, which is why we would not say that that call wasn't made," he told reporters.
"We just don't have any evidence at this stage."
Mr James also told investigators he did not see Mr Jenkinson's helicopter take off.
"While video footage taken by passengers in both helicopters on mobile phones contained images of the other helicopter, this does not mean the other helicopter was visible to either pilot," Mr Mitchell said.
Sea World Helicopters had fitted both aircraft with traffic collision avoidance systems.
However the systems hadn't been integrated and were only able to issue audio alerts. Mr James said he didn't hear any alert that afternoon.
Mr James' aircraft also wasn't transmitting secondary surveillance radar responses about its position and altitude at the time, with Sea World Helicopters aware of the problem.
"The aircraft was not able to be used in controlled airspace until it was rectified. Efforts to diagnose and address the transponder problem were ongoing," the bureau's report said.
"A review of all avionics and pilot assistance systems, and radar and surveillance information, is ongoing."
The ATSB will also probe the procedures and practices for the high volume of scenic flights scheduled that day.
Sea World Helicopters director John Orr-Campbell said the company is reviewing the findings of the report.
"The release of the ATSB interim report is another reminder of the tragic loss of life suffered that day,'' he said.
Mr Jenkinson, 40, and his passengers - British couple Ron and Diane Hughes, 65 and 57, and Sydney mother Vanessa Tadros, 36 - died when the helicopter crashed.
Ms Tadros' son Nicholas, 10, has been undergoing procedures in hospital since the accident and last week had his leg amputated from the knee.
Victorian mother Winnie de Silva, 33, and her nine-year-old son Leon are recovering from injuries.
Mr James landed his aircraft safely but he and two of his passengers were injured by flying glass from a shattered windscreen.
The injured were New Zealand women Elmarie Steenberg and Marle Swart, who had been on holiday with their husbands Riaan Steenberg and Edward Swart.
"All at Sea World Helicopters pay their deepest respect to Vanessa Tadros, Diane and Ron Hughes, our friend and late chief Sea World Helicopters pilot Ash Jenkinson, their families, and those who suffered physically and mentally in the accident,'' Mr Orr-Campbell said.
"Our special thoughts go to Winnie De Silva and her son Leon as well Nicholas Tadros ... and his father Simon who has been by his side all along."
A final report into the crash is not expected before September 2024.
