I used to live near Bankstown Aerodrome. Planes take off there every 30 seconds.
Derek Darlow, a former mechanical engineer at Hoxton Park Airport, which closed this Monday, said that the planes were probably coming in to land at Bankstown Airport.
"There is an inbound reporting point in Prestons, which planes have to pass over before they land at Bankstown Airport and the planes were probably passing over that when they clipped each other,'' Mr Darlow said.
"Now that they've closed Hoxton Park Airport, there are fewer places for these planes to land and this sort of thing will be happening more and more often.''
The two planes involved, according to Bankstown flight school operators, were a Liberty and a Cessna 152.