The Robinson R44 helicopter involved in Thursday's fatal crash at Bulli Tops was fitted with a rigid aluminium fuel tank known to increase the risk of fire, the Australian Transport Safety Bureau has revealed.
Manufacturer Robinson Helicopter Company issued a bulletin in 2010 requiring R44 helicopters with all-aluminium fuel tanks to be retrofitted no later than April 30 this year.
Last March the ATSB also advised R44 owners to replace the rigid tanks with flexible bladder-type tanks to improve resistance to fires in an accident.
Speaking at the scene yesterday, senior transport safety investigator Greg Madden said the helicopter that crashed as it came in to land next to Panorama House just after midday had not been retrofitted with the flexible tank.
"The Robinson R44 helicopter has been involved in a number of accidents over the last couple of years," he said.
"The bureau is most aware of the risk of having a rigid fuel tank and that's why we put out that safety advisory notice recommending the rigid fuel tank be replaced."
In 2011, two people died in an R44 accident at Cessnock.
Just a year later, film producer Andrew Wight and filmmaker Mike deGruy were killed when their helicopter, also a Robinson R44, crashed and burst into flames at Jaspers Brush.
The helicopter involved in the fatal Bulli Tops crash was operated by Bankstown Helicopters, the same operator involved in the Jaspers Brush crash.
Mr Madden said investigators were likely to remain at Bulli Tops until tomorrow afternoon to thoroughly examine the scene.
"The investigation will look at a number of factors including weather, pilot training and serviceability of the helicopter," he said.
He said they would be gathering information from air-traffic-control tapes. They would also examine the helicopter, its "various systems and components" and the impact of its main rotor with nearby trees.
Investigations were still in their early stages and a great deal of information was yet to be gathered, Mr Madden said.
"That will then be analysed and we'll then carefully work through all the evidence with regards to the accident because we've also got to understand why the helicopter, as it has come in to land, has ended up in such tragic circumstances," he said.
The helicopter was on its final approach just after midday on Thursday when it crashed while the pilot was trying to land at Bulli Tops.
All four people on board were killed.
Police have not yet released their names, and the formal identification is expected to take some time.
Mr Madden urged any witnesses to the helicopter coming in to land to contact the ATSB on 1800 020 616.