Pilot in deadly Sydney seaplane crash had toxic gas in blood, ATSB says

The pilot of a seaplane that crashed in the Hawkesbury River in 2017 was likely "adversely affected" by engine fumes in the cabin, the Australian Transport Safety Bureau (ATSB) says.

Gareth Morgan and his five passengers were killed when the Sydney Seaplanes DHC-2 Beaver crashed into the water at Jerusalem Bay on December 31.

The chief executive of catering giant Compass, Richard Cousins, his two adult sons, his fiancee and her 11-year-old daughter were onboard the plane flying to Rose Bay when it went down.

The ATSB today released an update about its investigation into the incident, saying a toxicology report had found Mr Morgan and two of the passengers had elevated levels of carbon monoxide in their blood.

In a statement, ATSB chief commissioner Greg Hood said: "From that consultation with medical experts, and research into the effects of carbon monoxide on aircraft operations, the ATSB considers the levels of carbon monoxide were likely to have adversely affected the pilot's ability to control the aircraft."

Heavy exposure to carbon monoxide replaces the oxygen in the blood and can lead to tiredness, shortness of breath and confusion.

"Having discounted other potential sources of carbon monoxide exposure, the ATSB considers it likely that the pilot and passengers were exposed to carbon monoxide inside the aircraft cabin," Mr Hood said.

Investigators also found missing bolts in the firewall, the section which isolates the plane's engine, which could have allowed the poisonous gas to enter the cabin.

Mr Hood said six lives could have been saved if there had been an electronic carbon monoxide detector on board.

"These detectors are now inexpensive and widely available," he said.

"Had there been an alert of the presence of carbon monoxide, the pilot would have been able to take measures to reduce the risk to those on board."

The aircraft did have a disposable chemical spot detector on board, but Mr Hood said those scanners were affected by direct sunlight and cleaning chemicals and relied on pilots to regularly monitor them.

Investigators found no evidence the plane had hit a bird, or that part of it fell off, or that the controls had failed.

The ATSB today published two safety notices designed to prevent and detect carbon monoxide in aircraft cabins, recommending regular inspections for holes and cracks.

The final report is expected to be released later this year.