The environmental approvals process has started for a new airport at Badgerys Creek.
The federal government has begun surveys of the site chosen for Sydney's second airport.
Infrastructure Minister Warren Truss says an environmental referral is being prepared, the legal process required before an environmental assessment can start.
He expects the assessment process, including public consultation, will start before the end of the year.
In August the government issued a formal notice to consult, meaning discussions could begin with Sydney Airport Group about developing and operating the airport in western Sydney.
The government hopes the Badgerys Creek airport will be finished by the mid-2020s.