A retired MRH90 test pilot has apologised to the families of four Australian Defence Force officers who died during a training exercise, telling them "I did the best I could and I failed them".
An inquiry into a helicopter crash off the north Queensland coast heard the ADF ignored safety concerns from Major Ian Wilson and two other test pilots about high-tech helmets before four aviators died in July 2023.
Captain Danniel Lyon, Lieutenant Maxwell Nugent, Warrant Officer Class 2 Joseph Laycock and Corporal Alexander Naggs died in the tragedy when their Taipan ditched into the ocean near Lindeman Island during a training exercise.
On Friday, Major Wilson apologised to the airmen's families.
"Having escaped losing my own life and six of my crew in similar circumstances, I had a moral obligation to your loved ones, I did the best I could and I failed them," he said.
"I'm so sorry for your loss"
Major Wilson said in testing of the upgraded technology to the helmet-mounted visor used by pilots, he had found serious inconsistencies between the pitch, roll, bank and altitude information that the TopOwl 5.10 provided, compared to the actual readings.
The inquiry heard this could create a situation where a pilot may misunderstand the actual altitude of the aircraft … which could make a perilous situation even worse, especially when conducting low-level flying.
Major Wilson said he broke ranks after his concerns were ignored because he was certain lives would be lost if pilots continued to use the equipment due to an incident he and six crew experienced during a training exercise prior to when he left in 2022.
"That is the closest I've come to crashing, I was quite alarmed by that … I don't become alarmed easy, and I was convinced someone would crash because of that," he said.
The Taipan helicopter wreckage was pulled from the water after the crash. (ABC News)
He told the inquiry that on one occasion a colleague laughed at him when he raised concerns about the system having "multiple defects" during an in-person briefing.
"I exhausted every possible line of action I could," Major Wilson said.
In more explosive evidence heard throughout the inquiry, another test pilot Major David Lamb said he found an issue with attitude and symbology ambiguity when he carried out tests of the upgraded software.
It resulted in the flight test organisation, the Army Aviation Test and Evaluation Section (AATES) terminating testing of the technology, deeming it "unacceptable".
The inquiry heard this was "the lowest possible outcome in terms of testing," and "AATES cannot reach a more negative assessment than unacceptable".
The ADF previously stated the recovery operation required specialist equipment not available in the ADF. (Supplied: ADF)
Major Lamb told the inquiry, when flying in formation with the TopOwl helmet, "without a visual horizon in a low-cue environment at night, you can't take your eyes off the apparent closure to the aircraft in front of you, because if you do, you run the risk of losing sight of that aircraft, worse than that, running into it".
The inquiry, previously held in Sydney, heard from Lieutenant Colonel Brendan Reinhardt, another test pilot, who said the technology went ahead because it had "already been paid for."
"This software upgrade was required for some milestones," he said. "My understanding was it had already been paid for".
The crew on board the ill-fated Taipan were wearing the upgraded TopOwl software.
The inquiry heard several conditions were imposed for future testing of TopOwl – more than Major Lamb had seen on any test activity in his career.
The inquiry heard the upgraded software was approved for service generally but was not subject to any specific controls, like they had been in testing.
The ADF conducted a recovery operation off the Queensland coast. (Supplied: ADF)
Major Lamb said this was unusual and he "would have expected [the controls] to be carried through."
Counsel representing the interests of Corporal Alexander Naggs, Lieutenant Commander Matthew Tyson asked Major Lamb whether in testing, AATES looked at a scenario similar to conditions the ill-fated Taipan was in on the night of the crash.
"The four [aircraft] in the formation, 200ft, at night, over water, was your evidence that AATES has not certified the [software] for that scenario?" Commander Tyson asked.
"In forecasting that condition, we found that the ambiguity of version 5.10, which is a software function of the helmet, was unacceptable," Major Lamb replied.
The inquiry has been sitting in Brisbane this week for its fifth round of hearings.