D11 - a pseudonym for a senior aircrewman - was in an MRH-90 helicopter during a training exercise sortie when another Taipan chopper crashed into water off Lindeman Island near the Queensland coast in July 2023.
Captain Danniel Lyon, Lieutenant Maxwell Nugent, Warrant Officer Class Two Joseph Laycock and Corporal Alexander Naggs died in the crash.
D11 told an inquiry investigating the accident on Monday there was a culture within the regiment that members wanted to see missions succeed.
Before the crash, there were often not enough aircrew to replace members who dropped out of a flight because of fatigue, he said.
Four servicemen died in the Taipan crash tragedy in Queensland. (HANDOUT/DEPARTMENT OF DEFENCE)
That meant an entire aircraft could be dropped from the mission or the exercise could be cancelled.
"No one wants to be the cause of an aircraft having to drop from a sortie and possibly force a mission from not going ahead, particularly as a junior pilot recruitment," said a statement from D11 read by Counsel Assisting Colonel Jens Streit at the inquiry in Brisbane.
"I can't remember anyone who had removed themselves from a flight due to fatigue in 2023, that's not to say it didn't happen."
A fatigue risk management tool was rolled out by the army before the 2023 crash requiring aircrew to sign off on whether they were feeling tired before an exercise and if so, how much.
There are three levels to the tool: green to monitor fatigue levels, orange to actively manage and red caution over participating.
D11 told the inquiry he had previously identified being in the orange zone of fatigue but had not pulled out of a mission as a result, nor did he know any other crew who had not participated.
He said a colleague, known as D28, had identified themselves as being in the red zone earlier in 2024 but continued flying.
"His aircraft captain and the authorising officer, they had a chat to see what the issue was, why he was red and how he was feeling," D11 told the inquiry.
"I don't remember if there was like extra management put in place to manage him, but I know he went flying."
D11 said recognition of fatigue had improved since the crash, but pressures remained on the aircrew.
"I think there's still a culture of wanting the mission to succeed, this may cause some aircrew to not be 100 per cent honest with their fatigue levels," he said.
But he has observed if a member was tired to the point of being dangerous they would remove themselves.
The inquiry will continue its sixth tranche of hearings before Justice Margaret McMurdo in Brisbane this week.
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