Sea World Helicopters pilot Ashley Jenkinson, 40, and three tourists were killed when his aircraft struck another chopper near the Gold Coast theme park on January 2, 2023.
Aviation medicine expert Jeffrey Brock on Thursday told Queensland coroner Carol Lee the inquest had reinforced his initial opinion that Mr Jenkinson was likely mildly impaired.
"There was additional information that led me to believe he was under considerable emotional distress," Dr Brock said.
Witnesses at the coronial inquest testified they saw Mr Jenkinson snorting cocaine, and drinking 12 beers and whiskey at a New Year's Eve party.
Mr Jenkinson's partner said she found him sitting in a wardrobe and crying from a "breakdown" over workplace stress a few weeks earlier.
"As a professional pilot he has developed techniques to manage his use of cocaine whether it was recreational or a serious addiction problem," Dr Brock said on Thursday.
"He has been able to conceal his use, certainly in the workplace."
Counsel assisting Ian Harvey asked Dr Brock, an army pilot who has investigated hundreds of aircraft accidents, if Mr Jenkinson had been "fit to fly".Â
"I can't exclude the possibility and probably the likelihood that he was mildly impaired," Dr Brock said.
"It wouldn't be obvious when he started flying that day."
Mr Jenkinson expected to handle six or seven scenic flights on the day of the crash during peak tourist season.
Pilots in Gold Coast's busy airspace would have had to "apply themselves rigorously" to spotting and avoiding other aircraft, Dr Brock said.
Mr Jenkinson's aircraft collided 25 seconds after take-off with another Sea World chopper that was preparing to land at a waterside helipad.
Mr Jenkinson was killed along with British newlyweds Ronald and Diane Hughes - aged 65 and 67 - and Sydney mother Vanessa Tadros, 36, when the helicopter fell 40 metres onto a sandbar.
A total of nine passengers in both aircraft were injured, including Ms Tadros's son Nicholas, who lost his leg.
Mr Jenkinson might not have recognised that his stress and fatigue had created a significant hazard, Ms Lee heard.
"People who are mildly or subtly impaired may not be aware of it," Dr Brock said.
"He may have noticed he was, in my words, 'off his game'.
"But he was a professional pilot and he was able to push on."
Sea World owner Village Roadshow Theme Parks sold its joy flights operation to Sea World Helicopters in 2019
The firm dumped the Sea World name on July 1.
The inquest is due to conclude with family statements on Friday.
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