Captain Danniel Lyon, Lieutenant Maxwell Nugent, Warrant Officer Class Two Joseph Laycock and Corporal Alexander Naggs were killed when their MRH-90 Taipan chopper crashed into waters off Queensland's Whitsunday Islands during Exercise Talisman Sabre on July 28, 2023.
Comcare has referred two briefs of evidence to the Commonwealth Director of Public Prosecutions relating to fatigue management and the TopOwl helmet system worn by the pilots, chief executive Colin Radford told a parliamentary inquiry on Friday.
The regulator was informed by commonwealth prosecutors in July 2025 that they would not be prosecuting defence as they did not consider there reasonable prospects of obtaining a conviction.
"Comcare considered there was evidence to support a view that defence may have committed one or more offences under the Work Health and Safety Act," Mr Radford said.
"I would like to stress ... that Comcare's investigation into this incident remains open.
"Whilst the two-year limitation period has expired, the WHS Act allows for proceedings to be brought outside that period in specific circumstances."
He said it was the regulator's view that inquiries being conducted by the Inspector-General of the Australian Defence Force and the Queensland coroner might extend the limitation period by a further 12 months.
Comcare might consider referring a subsequent brief of evidence to Commonwealth prosecutors, the inquiry was told.
Under questioning by senators, Mr Radford said it remained the regulator's position that prosecution should be commenced.
Appearing earlier at the public hearing at Parliament House, Director of Public Prosecutions Raelene Sharp KC said she held concerns that disclosing more information would be detrimental to the prospects of further investigation and potential prosecution.
"This outcome is not in the public interest and not conducive to the administration of justice," she said.
The Defence Flight Safety Bureau's investigation found the primary cause of the fatal crash was "spatial disorientation," which occurs when a pilot misperceives the position of their aircraft in relation to the surrounding environment.
The report concluded that the pilots were likely experiencing a level of fatigue shown to "impede optimal performance" and increase susceptibility to spatial disorientation.
A parliamentary inquiry is examining the crash, with specific reference to the decision not to prosecute any matters arising from the incident.
A report is due in September.
A separate inquiry into the catastrophic crash was told safety concerns were raised about a software upgrade for the TopOwl helmet that were worn by the pilots on the night of the crash.
The crew, from the Sydney-based 6th Aviation Regiment, were flying in a helicopter given the call-sign Bushman 83, which was the third in a formation of four aircraft as part of a training exercise.
The Aviation Safety Investigation report found that after making a turn, Bushman 83 climbed more than 100 feet within 14 seconds.
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