A pilot was confused, disoriented and affected by poisonous exhaust gas in the moments before his seaplane plunged into a Sydney bay, killing all six people on board.
Gareth Morgan, 44, died when his aircraft crashed into Jerusalem Bay on the Hawkesbury River shortly after take-off during a New Year’s Eve joy ride in 2017.
The chief executive of catering giant Compass, Richard Cousins, his two adult sons, his fiancee and her 11-year-old daughter were also killed.
The plane was operated by Sydney Seaplanes, which has been providing flights around the city’s tourist sites for 80 years.
The family was on holiday from the UK and returning to Sydney when the single-engine 1964 DHC-2 Beaver seaplane crashed.
Photographs taken by the front-seat passenger helped investigators determine the flight path of the plane.
The plane made an unexpected, sharp turn before its nose dropped and it pitched into the water, sinking 13 metres below the surface.
After a three-year investigation hampered by the plane’s lack of a recording device, the Australian Transport Safety Bureau on Friday confirmed in its final incident report that exhaust gas leaked into the cabin, poisoning the pilot and passengers with carbon monoxide.
The pilot, who had taxied for 27 minutes before collecting passengers, had elevated levels of carboxyhaemoglobin in his blood when he died, a toxicology report found.
The other passengers also had heightened levels.
This was almost certainly due to carbon monoxide leaking into the engine bay and then through three bolt holes into the cabin, the ATSB concluded.
“The pilot would have almost certainly experienced effects such as confusion, visual disturbance and disorientation,” ATSB Chief Commissioner Greg Hood said in a statement.
The 11-year-old girl’s father in October 2020 received approval from the NSW Supreme Court to continue his lawsuit against Sydney Seaplanes over the accident.
The ATSB noted the crash may have been prevented if the pilot had access to an audible carbon monoxide detector, and is pushing for the device to be mandated.
Sydney Seaplanes has since installed audible and visual CO warning systems on their planes.
However the report identified the “root cause” of the accident as inadequate maintenance.
“Apart from daily inspections, all maintenance was conducted by an external CASA-approved (Civil Aviation Safety Authority) maintenance organisation, Airag Aviation Services,” it read.
Along with the missing bolts, the investigation also identified modified or non-standard bolts, which couldn’t be tightened properly.
Investigators were told a non-standard Phillips-head screw was fitted to a cabin access panel to “fill a hole” despite the standard bolts being in stock.
Airag had intended to replace the bolt at a later stage.
It was possible the bolt holes identified as the cause of the leak were once filled with worn, modified, or non-specified bolts like the Phillips-head, the report said.
A Sydney Seaplanes spokesman told AAP the company was required by law to outsource it’s maintenance to a CASA-approved provider.
“We placed our trust in Airag Aviation Services which, until this accident, was Australia’s most respected and experienced DHC-2 Beaver maintenance company,” he said.
“This report confirms that Airag failed in its most basic and important responsibilities… we expect Airag to now acknowledge and accept responsibility for the accident.”
When contacted Airag declined to comment to AAP.
The company did respond to a draft report in September, taking aim at the validity of the testing that identified the bolt holes as the source of the leak.
The ATSB noted the concern but dismissed it.
“The purpose of the testing was to establish if CO from an exhaust leak could enter the aircraft cabin under varying conditions, rather than replicate the exact accident flight,” the report reads.
“Of note, Airag Aviation Services did not conduct independent testing to verify the above.”