Four defence members killed in a helicopter crash were experiencing "hazardous" fatigue, an inquiry has heard.
Captain Danniel Lyon, Lieutenant Maxwell Nugent, Warrant Officer Class 2 Joseph Laycock and Corporal Alexander Naggs died when their MRH-90, or 'Taipan' helicopter, ditched into waters off Lindeman Island in July 2023 during a defence training exercise.
Captain Danniel Lyon and his wife Caitland Lyon, who's previously spoken at the inquiry. (Supplied)
It's the fifth round of hearings as part of an inquiry into the tragic crash.
Expert in aviation medicine, Dr Adrian Smith, today told the inquiry the men were so tired it was like they would have had the equivalent of a blood alcohol level over the legal limit.
There is no suggestion the men consumed alcohol.
Dr Smith analysed the sleep patterns of the men leading up to the crash through data from their phone records.
He estimated in the two days leading up to the crash, the men were not getting enough sleep.
The inquiry has previously heard the men were sleeping next to a commercial airport, in crowded tents with no air conditioning, and some were frequently woken by noise around the campsite.
The Taipan wreckage was pulled from waters off the Queensland coast in the days following the crash. (ABC News)
Dr Smith estimated at the time of the crash, Captain Danniel Lyon had only five hours of sleep in the 24 hours prior, and over 11 in 48 hours.
His blood alcohol content level would have been equivalent to 0.08.
Lieutenant Maxwell Nugent had slightly more sleep, and would have been considered "moderately tired" with an equivalent blood alcohol content of 0.05.
Warrant Officer Class 2 Phillip Laycock and Corporal Alexander Naggs would have been considered "extremely tired", equivalent to a blood alcohol content of 0.08.
When asked whether he believed fatigue contributed to the crash, Dr Smith said it was "highly likely" it would be considered "hazardous in an aviation setting".
Dr Smith said the data used in his report was imperfect, as there is no way to monitor the exact time they slept and woke up, and their quality of sleep.
But he was confident it provided a general overview of fatigue levels within the regiment.
Dr Smith said when applied to a model that compared aviators to a population's average, it revealed the men would have likely experienced a reduction in performance, cognitive ability and reaction times, and seen more lapses in concentration.
Dr Smith will be cross-examined.
The inquiry continues.