A decision over where to site a new runway in the south east of England will be taken "shortly", Transport Secretary Chris Grayling has said.
The decision has been deliberated for years and was delayed most recently by the upheaval caused by the Brexit vote.
In July 2015, Heathrow looked close to being the winner, after an official commission recommended its plan.
But in December the decision was delayed for further studies.
In June, following the UK's vote to leave the European Union, it was decided to delay the final go-ahead until October.
Three plans have been in contention:
- a third runway at Heathrow
- a new runway at Gatwick
- an extension of one of Heathrow's existing runways
Mr Grayling said he has spent the summer looking at the plans.
"They're all very well crafted proposals, they're all very interesting, they've all got great potential. We need to decide which is best for Britain," Mr Grayling told the BBC.
"You will get an announcement shortly. We haven't taken the decision yet," he said.
The transport secretary also refused to rule out granting a free vote to Conservative MPs on the issue of airport expansion, saying "decisions about parliamentary handling… have not yet been taken".
The decision is politically fraught, with some senior government ministers opposing the expansion of Heathrow.
Foreign Secretary Boris Johnson has long been opposed to making Heathrow any bigger, saying it is "basically undeliverable".
Justine Greening, the education secretary, is also against its expansion, arguing it would mean extra noise pollution for her west London constituency.
In July 2015, after three years of deliberation, the Davies Commission recommended the building of a third runway at Heathrow.
The plan involves building a new 3,500m runway about two miles north of the two runways Heathrow already has, at an estimated cost of £18.6bn.
Heathrow Airport is one of the world's busiest, handling 70 million passengers in 2012. More than a third transfer to other flights, making it a major hub airport.
But it operates at 98% of its capacity - much closer to capacity than other major London airports and rival hubs in Europe.