Listed Macquarie Bank offshoot Macquarie Airports (MAp) is eyeing a bigger stake in Sydney Airport after the airport's holding company reported a 16 per cent surge in December quarter earnings.

MAp, which owns 55.8 per cent of the unlisted Southern Cross Airports, has a pre-emptive right over most of the 20.9 per cent stake held by Spain's Ferrovial Group, which plans to exit its investment.

MAp is entitled to 15 per cent of this stake and has already said it plans to spend AU$700 million to acquire it. But it is willing to spend AU$1 billion to buy Ferrovial's full stake if the airport's other owners - Hochtief and the Ontario Teachers Trust - pass up the chance.

"We would expect MAp will acquire 15 per cent instead of 20.9 per cent because we think the other 5.9 per cent will be taken up by other shareholders," MAp spokeswoman Karen Halbert said.

"But if not, we will consider going up to the 20.9 per cent figure."

Macquarie's stake in the airport looms as a contentious issue, given the bank's involvement in the consortium seeking to buy Qantas.

The bank argues there is no conflict of interest as MAp is run as an independent entity. Macquarie owns 16 per cent of MAp and has a further 7.8 per cent direct stake in the airport through other entities.

Sydney Airport has been a star performer in MAp's six-airport portfolio, accounting for 40 per cent of MAp's revenues.

Buoyed by a 7.2 per cent surge in December quarter passenger numbers, Southern Cross reported underlying earnings of AU$156 million. Revenues were 11% higher at AU$188 million.

Comparing December half numbers, earnings rose 12.5 per cent to AU$294 million.

Airport chief executive Russell Balding said the airport had benefited from a number of "commercial initiatives", notably the AU$20 million retail expansion at Mascot's domestic (T2) terminal.

"We look forward to a further improvement post the scheduled completion in the coming quarter," Mr Balding said.

Revenue from traditional aeronautical charges such as landing fees surged 11 per cent to AU$77.2 million, while retail activity contributed AU$43.1 million, up 7.9 per cent.

Revenue from commercial trading - including car parking - rose 9.6 per cent to AU$24 million.

Airport spokesman Michael Samaras played down the effect of car park fee rises posted last October, citing improvements such as extending undercover parking and a new valet service.

"The number of passengers at the airport is up, and there is therefore an increase in the number of people using the car parks," he said. (Australian dollar is the currency used in this report unless otherwise stated)