Almost 20 outstanding actions had not been implemented after previous MRH-90 Taipan incidents before a fatal crash involving the same army helicopter model, an inquiry has heard.
Captain Danniel Lyon, Lieutenant Maxwell Nugent, Warrant Officer Class Tow Joseph Laycock and Corporal Alexander Naggs were killed when their MRH-90 Taipan chopper crashed off the north Queensland coast in July 2023.
They were taking part in evening military drills during the multinational Exercise Talisman Sabre.
The helicopter was seen gaining altitude before nosediving into the ocean, the inquiry was told.
The independent inquiry into the crash off Lindeman Island on Tuesday heard there were 17 "outstanding action items" that had not been implemented following previous incidents involving the MRH-90 model.
Lieutenant Colonel Tony Cameron said there are different "camps" within the army, with some preferring the Blackhawk helicopter and others the Taipan.
However, the Army School of Aviation chief instructor said people are still confident in the MRH-90 Taipan.
"It was definitely a safe platform to fly with a robust maintenance and air worthiness system," he told the inquiry's first public hearing in Brisbane on Tuesday.
"There are pros and cons to what an MRH may be able to achieve compared with another aircraft."
Lt Col Cameron said training for MRH-90 pilots took six to nine months.
The inquiry was told Lt Col Cameron had flown with Warrant Officer Class Tow Laycock many times in his career.
"He was one of the most, if not the most, competent, professional and relied-upon senior air crewmen that we had," Lt Col Cameron said.
The inquiry was told the Defence Aviation Safety Authority had released regulations in February 2023 about the use of night vision devices, illumination and weather conditions.
Lt Col Cameron said proactive measures were issued in October 2023, after the crash.
The inquiry detailed the events leading up to the fatal July 2023 incident for the first time.
Colonel Jens Streit, acting as counsel assisting, told the inquiry the Taipan helicopter had been given the call sign Bushman 83.
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.
The air mission commander called from another helicopter to Bushman 83 over the radio, telling them to "pull up".
Bushman 83 crashed into the water, with crew from another helicopter immediately starting a search for their colleagues in the water.
"Tragically, no survivors were located. The search and rescue operation continued until the early hours of the morning of 28th July 2023," Col Streit said.
The inquiry is being led by former judge Margaret McMurdo, supported by Air Vice-Marshal Joe Iervasi and Colonel Jens Streit.
Ms McMurdo acknowledged the "dreadful effect" the incident had on the victims' families, friends and colleagues, with a minute's silence held at the start of the inquiry.
"This inquiry will strive to avoid exacerbating that pain," she said.
Australia's MRH-90 Taipan helicopter fleet was pulled from service soon after the crash, more than a year before its intended withdrawal date.
The helicopters had initially been scheduled to be withdrawn from service in December 2024.
