Canberra Airport Managing Director, Stephen Byron.

Canberra Airport managing director Stephen Byron. Photo: Graham Tidy

Opposition to a second Sydney airport at Wilton will help a fresh push for a high-speed train, Canberra Airport's managing director Stephen Byron says.

Even though major airlines and the federal government want a second airport near Sydney and have ruled out Canberra, the airport and NSW Premier Barry O'Farrell believe four decades of political indecision will continue to stop the project from proceeding.

Instead, Sydney's Kingsford Smith Airport's capacity constraints are creating a more compelling case for a high-speed rail link to Canberra, says Mr Byron, who committed to a $140 million terminal at Canberra airport last week.

Wollondilly Council's deputy mayor Benn Banasik said 400 people at a rally opposed to a second airport at Wilton on Saturday included transport and infrastructure experts and people from Campbelltown and surrounding towns.

He said Wilton homes would be directly under flight paths of the proposed site while 600 homes would be within a five-kilometre radius and 20,000 people lived within a 30- kilometre radius.

Mr Banasik said studies over 25 years had ruled out Wilton, and even though federal Transport Minister Anthony Albanese favoured Wilton for political reasons, environmental studies would rule it out as an airport site.

''Wollondilly is home to five major dams that feed Sydney's drinking water supply. It is actually in a catchment zone,'' Mr Banasik said.

''It is quite amazing that they would even consider putting it in that area. I guess politics knows no bounds when you are in an election period for federal government, unfortunately.''

He said ecologist Ian Wright and transport analyst Philip Laird, from Wollongong University, who spoke on the Sydney-Canberra high-speed train case, were among those to address the rally.

Mr Byron said the Joint Study into Aviation Capacity for the Sydney Region released earlier this year questioned Wilton's viability in 2030. He said the site did not have an existing natural catchment as a base for underpinning an airport.

Richmond's Royal Australian Air Force facility would need to be developed as an interim airport with a price tag of more than $10 billion, on top of $7-11 billion for Wilton, according to the joint study.

''So if you think about it, a high-speed rail to Canberra might save up to $22 billion in government costs to build airport capacity in Sydney,'' Mr Byron said.

While a high-speed train would also lead to more air traffic, Canberra airport would not have the noise-sharing requirements of a second airport at either Wilton, Badgery's Creek or Richmond, which would need a curfew as well to comply with environmental restrictions.

''The key difference is that at Badgery's Creek and Wilton there are existing houses built under flight paths,'' Mr Byron said. ''This in turn means that airports there would most likely operate with noise sharing with more people getting affected.''

Rural corridors into and out of Canberra airport would avoid noise sharing. Canberra did not have a curfew.