Prepare the cabin for landing.

After more than four decades of turbulence the federal government is about to clear the way for a second Sydney airport.

Sites to the north, west and south of the city, and stretching as far as Canberra have been floated to handle increasing air traffic limited by an 11pm to 6am curfew and hourly quotas at Kingsford Smith Airport.

A 24-hour floating airport off Botany Bay was even suggested.

Now cabinet is expected to give the all-clear to Badgerys Creek, about 50km west of Sydney's CBD.

"This issue has been debated uphill and down dale since 1973," Prime Minister Tony Abbott has said.

For some people the case for a second Sydney airport goes back even further.

As a young civil servant in March 1969 Peter Harbison remembers being asked to gather information on six potential sites.

"One of my first jobs was doing background research for a Senate sub-committee on a second Sydney airport," the now aviation consultant told AAP.

Since then it has been a case of one step forward, two steps back, including a sod-turning ceremony at Badgerys Creek in 1992 by then Labor aviation minister Bob Collins.

Back then it was hoped the airport would be operating in time for the 2000 Sydney Olympics.

It was not to be.

Nearby residents opposed the $6 billion development. Despite an environmental impact statement giving the site the thumbs-up, it stalled with the government of the day deciding it was not a priority.

"The reality is we need to start building," Harbison argues.

Once the deal is inked "you are talking realistically about another decade" before aircraft will be landing at a greenfield site.

That's because there are many issues to address including the likelihood of fog on the Cumberland Plain, fuel line and transport links to and from the airport. And there's another environmental impact statement to be done.

Harbison reckons the ideal solution would have been an additional runway at Kurnell on the site of the former oil refinery, linking to Kingsford Smith and providing adequate capacity for the next 50 years.

"But that's not going to happen."

He also thinks the military air base at Richmond on Sydney's northwest fringe should be used as an overflow airport until a new facility is up and running.

In western Sydney opinions are divided about Badgerys Creek, but support is growing for the development.

A recent Fairfax-Nielson poll found 72% backing for an airport there.

David Bolger, a western Sydney director of the Sydney Business Chamber, acknowledges not everyone in the region is convinced.

"But the tide is turning in western Sydney with most of the community realising the benefits," he told AAP.

Blacktown City Labor councillor Stephen Bali insists there is still strong opposition to the airport, but denies he's making a not-in-my backyard argument.

"This area is not the same as it was when the Badgerys Creek site was first proposed," he said, noting that by 2050 there will be four million living people in western Sydney, making it the third-largest economy in the country.

And residents would be living within 18km of the runway.

Bali says aircraft noise is only part of the problem, with air quality of equal concern.

"The only way the air can get back out is via a sea breeze and we can wait a long time for that."

Australian Airports Association boss Caroline Wilkie doesn't have any sympathy for residents neighbouring the airport site.

"If people are silly enough to move in next door, there are consequences to that," she told AAP.

"There wasn't development around the area when the site was first proposed so everyone who has come in since have known it was a possibility this airport would start up."

Wilkie says the Badgerys Creek proposal is "what makes sense" for the long term.

But in the interim there should be discussions about increasing the capacity of Kingsford Smith.

"The noise matrix have changed, the aircraft have changed – you can have aircraft coming in over (Botany) Bay earlier," she said.

"We could get a lot more access to Sydney Airport if there was an intelligent debate about curfews and caps."

The federal government already has approved Sydney Airport's 20-year master plan, which confirms capacity can be managed until at least 2033.

NSW Premier Barry O'Farrell is prepared to back the Badgerys Creek plan so long as the commonwealth coughs up sufficient funds for road and rail links.