The federal government says the airport in the city's west will be capable of handling 10 million domestic and international passengers a year through a single terminal when it opens in 2025, but it will lack a rail connection.

Paul Bredereck, the managing director of regional airline Jetgo, told an aviation industry conference in Sydney the plans for Badgerys Creek appeared to be "small league" in terms of vision.

"For God's sake, it is a major international airport and no express rail service to the CBD?" he told the CAPA 2015 Airport Innovation Day.

"In the last few weeks I have driven from Bankstown to Sydney Airport. It is not a pleasant experience. Buses from Badgerys Creek to the CBD? Who are you kidding?"

CAPA executive director Peter Harbison said it would be a "farce" if the airport did not have a rail link when it opened. "History will say what idiots were these politicians for not doing that," he said.

Mr Bredereck, who said his airline would eventually operate at Badgerys Creek because of the lack of slots at Kingsford Smith, also said the government should consider planning for an eventual four runways at the airport rather than two.

"If the city is a world-class city and you are building a world-class airport for the future, do it properly," Mr Bredereck said. "Do it once, do it well."

Department of Infrastructure and Regional Development deputy secretary Andrew Wilson said four runways "would just not fit" on the site, but Mr Bredereck said it had been done on similar-sized sites overseas and should be looked at.

Mr Wilson said the new airport would need to cater for any plausible range of services, including domestic and international passenger and cargo flights by full-service and low-cost airlines and freight providers.

The airport will begin with a single runway, but over time it will develop into a parallel runway facility capable of handling 80 million passengers a year.

"It will be neither a shed in a paddock nor a grand monument," he said. "Think of Adelaide Airport today and you would be in the right ballpark."

The federal and NSW governments have announced a $3.5 billion roads package to improve links to Badgerys Creek. But Mr Wilson said the airport would not have a rail link at the time of its opening.

"Rail is just one means of public transport," he said. "The first public transport to and from the airport will be buses provided through an efficient road network. Rail is a longer-term requirement."

Mr Wilson said the airport will not have a curfew, in a move that could help Sydney obtain late-night services from Asian and Middle Eastern carriers, which have been lost to Melbourne and Brisbane as a result of the curfew at Kingsford Smith airport.

But it is unclear if the new airport will be treated as a "regional airport" under the government's bilateral air agreements. That would allow airlines from countries that faced caps on flying to Sydney, Melbourne, Brisbane and Perth to fly to Badgerys Creek even if the cap to the other airports had been reached.

The Department on June 30 finished nine months of detailed consultations with Kingsford Smith operator Sydney Airport, which has a first right of refusal over the development.

Mr Wilson said that process had involved 76 meetings, and his department was now using the information to compile a "notice of intention" setting out the key terms of the proposed development.

"If everything goes well it is possible the notice of intention will be with Sydney Airport by the end of this year," he said, adding environmental impact statement documents could be released for public consultation in November and December.