Four military aircrew were on board the MRH-90 Taipan helicopter when it plunged into the sea close to the Whitsunday Islands during a multinational military drill on the night of July 28, 2023.

The chopper had been taking part in the Talisman Sabre exercise, which brings together 30,000 military personnel from Australia, the United States and several other nations.

Australia’s defence flight safety bureau report found the helicopter was waiting to land, flying in a holding pattern with “degraded” viability.

During this time, the pilots “almost certainly lost visual sight” of the other aircraft.

The helicopter began an “inadvertent and unrecognised climb” to 110m before it crashed into the ocean.

The main reason for the crash was “a loss of spatial orientation”, also known as spatial disorientation, the report found.

“This refers to a situation where a pilot is unaware of their actual orientation in relation to the earth’s surface and the surrounding environment,” the Australian Defence Force said in a statement.

“This aviation safety investigation was one of the most complex conducted by defence in recent history.”

The investigation did not seek to place “blame or liability” on any individuals or organisations, it added.

The report made 46 recommendations to the defence force, all of which have been accepted.

The Taipans, which have had a troubled history, were already due to leave service at the end of this year, with the Australian military switching to Black Hawks.