It was among a group of four choppers set to fly to Lindeman Island to collect Australian Defence Force personnel who were conducting an exercise at the location.
About 10pm they took off from Proserpine airport, entering a holding pattern while waiting for confirmation the ADF personnel on the island were ready to be picked up.
"I anticipate the evidence will show that shortly after entering the holding pattern, Bushman 83 was observed to develop an increasing rate of climb, taking it to a height above the other aircraft," Col Streit said.
It was then observed suddenly pitching nose down and descending rapidly towards the water, he said.
First information from the inquiry.