100km limit.
From the history files:
"Taildragger67
18th Jul 2008, 12:19
If one believes the SMH, Macquarie Bank is having enough trouble with its infrastructure subsidiaries at the moment that it could barely afford to re-pave the disabled car park, let alone throw down another strip. They will:
a. squeeze everything they can out of YSSY without spending... you think BAA running EGLL into the ground was bad...;
b. use their pre-emption right to halt any development of a 'major' airport within 100km of YSSY, so as to maximise revenue flowing through that asset."
Don't ask who gave that little gem to Mac Bank, may just be the reason why everyone is hedging around, because if a new Sydney was developed within 100km, it would just be an extension of the current monopoly.