Infrastructure analysts at the Commonwealth Bank warn that Sydney Airport may hit capacity 20 years earlier than it expects.

The airport's management has previously said it will have sufficient capacity to meet the city's air transport needs until 2045.

However, Commonwealth Bank infrastructure analysts Andre Fromyhr and Matt Crowe estimate that Sydney Airport is likely to near or reach its maximum capacity in 2025, based on the bank's passenger forecasts.

The bank's estimate is consistent with a finding by a joint Federal and NSW Government study that found signs of constrained capacity would emerge at Sydney Airport from around 2020.

That report found that all peak morning (6am-noon) and evening (4pm-7pm) weekday slots would be allocated by 2020, and that there would effectively be no free slots by 2027, with unmet demand for more than 100 flights per day.

While Sydney Airport is likely to hit constraints in about a decade, the CBA report finds that it could currently handle 61 per cent more passengers if it matched world's best practice utilisation of existing facilities, exemplified by Beijing's main airport.

London (Heathrow), Hong Kong, Bangkok, Atlanta and Tokyo's Haneda airport rank next for capacity utilisation, with Sydney in the middle of a group of 20 airports studied by the bank, with a similar utilisation to Charles De Gaulle Airport in Paris.

However, Sydney had the best utilisation rate of any airport in Australia, comfortably above Melbourne and well ahead of Brisbane and Perth.

To match Beijing, the analysts suggest Sydney Airport could increase the number of flights by 34 per cent and cater more for larger aircraft to increase the average number of passengers per flight by 19 per cent.

The report also noted that less restrictions on the number of flights and a reduced night time curfew would increase the Sydney Airport's capacity, but that these seemed unlikely to occur in the short-term, given intense political opposition.

'Flawed'

Sydney Airport issued a statement to say it had ample capacity to meet forecast demand to at least 2045 and that the analysis was based on "flawed assumptions".

"In particular, the report assumes no changes to the current configuration of the airport, ignoring the fact that Sydney Airport is constantly investing in additional capacity - in excess of $2 billion has been spent in the last 10 years," the statement noted.

"And we are consulting with stakeholders on the new vision concept plan, announced in December 2011, that would unlock additional capacity and drive greater efficiency for airlines and passengers."

Sydney Airport also said the report did not take into account the fact that aviation was becoming more efficient.

"Sydney Airport has achieved a 40 per cent increase in passengers since 2000 with virtually no increase in aircraft movements and is one of the busiest A380 airports in the world.

"We agree that due to outdated regulations, Sydney Airport is underutilised compared to other international airports.

"Australia and Sydney would benefit from a fresh look at policies that better reflect the growth in larger, greener and quieter aircraft to replace the existing regulatory settings that were made close to 20 years ago and haven't kept pace with these changes."

Master plan

The Federal Opposition's infrastructure and transport spokesman Warren Truss says Sydney Airport is currently developing its master plan, due to be released next year.

He says people should wait until that plan is released and can be evaluated before reaching a judgment on when Sydney will need another airport.

"Sydney Airport believe that they'll be able to meet the traffic needs of Sydney out to something like 2045, so they've got to be given the opportunity to demonstrate how they intend to do that," Mr Truss said.

"There's no doubt at all that Sydney airport can continue to meet the needs of Sydney air traffic for quite a few years. Precisely how many is a matter we'll need to assess in the context of their master plan review."

Mr Truss says it is appropriate to reserve and consider other sites so that Sydney has options about the location of a potential second airport.

"I think it is appropriate that a site is reserved - like Badgery's Creek, that's been in place for a long, long time - so that there is an option," he said.

"The [Federal] Government is also currently doing work on a possibility of an airport at Wilton. There have been talks of using Richmond a little more than has been the case in the past.

"All of those options have to be considered. That's a decision that we would want to make in government... when we have access to all of the available information."

However, the Commonwealth Bank report also finds that Sydney Airport will almost certainly need to spend more on staff and facilities to cope with the increase in passengers in the shorter term, even if it does not expand its capacity.

CommSec analyst Juliana Roadley told ABC News 24 that changes in technology mean Sydney Airport must keep investing in infrastructure to keep up with increasing demand.

"If you're seeing more passengers arriving you've got to come up with more avenues of access for those arrivals as well, and that'll mean more taxi bays, more parking, so its really a growth structure over time," she said.