The pilot of a seaplane that crashed near Sydney in 2017, killing all six on board, was likely “adversely affected” by poisonous engine fumes in a cabin, a report has found.

The Australian Transport Safety Bureau (ATSB) has provided an update today on its investigation into the fatal crash of a Sydney Seaplanes DH-2 Beaver into Jerusalem Bay on the Hawkesbury River on New Year’s Eve, 2017.

The crash killed experienced pilot Gareth Morgan and British passengers Richard Cousins, his sons Edward and William, Emma Bowden and her daughter Heather, 11.

ATSB chief commissioner Greg Hood said the finding followed a recommendation from medical experts that blood samples from victims were tested for carbon monoxide.

Heavy exposure to carbon monoxide can lead to a range of effects including tiredness and disorientation, shortness of breath, impaired vision and co-ordination and confusion.

“The ATSB considers the levels of carbon monoxide were likely to have adversely affected the pilot’s ability to control the aircraft,” Mr Hood said.

“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.”

The ATSB report said investigators examining the crashed aircraft found cracks in the engine exhaust collector-ring and missing bolts in the firewall that isolates the plane’s engine.

“Any breach in the firewall can allow the ingress of gases from the engine bay into the cabin,” the report said.

The bureau has published two safety notices to the industry that recommend measures to detect and prevent carbon monoxide in aircraft cabins.

Tragedy struck the Sydney Seaplanes floatplane shortly after it took off from Cottage Point in northern Sydney ahead of its planned flight to Rose Bay.

Minutes after takeoff, the plane flew dramatically offcourse, despite clear conditions and nosedived into the Hawkesbury River.

After the crash, Sydney Seaplanes managing director Aaron Shaw previously suggested pilot incapacitation was a reason for the plane’s sudden right-hand turn off the planned route.

“Something definitely happened to the pilot to incapacitate him,” Mr Shaw told The ­Australian.

Early in the investigation it was suggested someone on board may have accidentally knocked out the pilot, Gareth Morgan, who had extensive piloting experience.

Mr Shaw told The Australian today he was pleased by the findings of the ATSB.

He said the aircraft had been freshly overhauled and certified to fly months before the tragic crash.

“We are pleased that both Sydney Seaplanes’ and our experienced pilot Gareth’s reputations as among the best in the business remains intact,” Mr Shaw said.

“Gareth was an excellent and professional pilot as well as a highly respected colleague and man. We continue to miss him greatly.”

The ATSB’s investigation into the crash is ongoing and a final report is expected in months.