A HELICOPTER that burst into flames when it crashed south of Sydney, killing four people, was fitted with older-style fuel tanks known to pose a fire hazard.
The victims of the fiery crash at Bulli Tops on Thursday are all believed to have been former CSIRO employees who were trying to land near Panorama House, a popular restaurant and wedding venue.
The Robinson R44 light helicopter clipped a tree about 12.10pm (AEDT) before crashing and igniting.
Staff ran out with fire extinguishers but were repelled by the heat of the blaze.
They were unable to save the pilot and three passengers.
A NSW Police spokeswoman said on Friday the deceased had not yet been formally identified, but AAP understands all four were former CSIRO workers.
Australian Transport Safety Bureau (ATSB) investigators arrived at the crash site late on Thursday and are expected to remain there for days.
The ATSB has confirmed the helicopter involved in the accident was still fitted with dangerous all-aluminium fuel tanks, years after helicopter operators were warned to upgrade them.
"The ATSB has highlighted how all-aluminium fuel tanks have proven susceptible to post-accident fuel leaks, increasing the risk of a potentially fatal post-impact fire when colliding with the ground," it said on its website on Friday.
The manufacturer and the ATSB have previously recommended that the fuel tanks on R44s be replaced with safer bladder-type tanks.
The ATSB said manufacturer's figures showed 4000 R44s had been built with the all-aluminium tanks but only 1700 retrofit kits had gone out so far.
A service bulletin issued by the manufacturer in 2010 told operators the retro-fitting needed to be carried out "as soon as practical, but no later than 30 April 2013".
