The Cabinet is set to finally decide on whether to give the go ahead for a third runway at Heathrow.
The divisive issue is on the agenda as Prime Minister Theresa May chairs a meeting of ministers on the Cabinet's economic sub-committee.
If the committee signs off the Airports National Policy Statement (NPS), it will then go before the full Cabinet for approval later on Tuesday morning.
If the project gets the green light, Transport Secretary Chris Grayling is likely to make a statement to MPs, who are expected to be given a vote on the NPS within 21 sitting days.
Approval would be a political headache for Foreign Secretary Boris Johnson, MP for Uxbridge and South Ruislip, who has said he would "lie down in front of bulldozers" to stop the proposed runway.
Proponents of building a third runway at the major hub say it is the best option to increase capacity and boost the national economy while being cost-effective.
However, critics warn the plan is "expensive and complex" and bad for the environment - while one group hinted legal action may be taken against the Department for Transport (DfT) over its "dodgy" handling of the process.
Alternative schemes include expanding Gatwick Airport in West Sussex.
Any announcement in favour of a third runway is likely to be met with dismay by MPs from across the divide whose constituencies are already affected by Heathrow air traffic.
On Monday, Liberal Democrat leader Sir Vince Cable, whose Twickenham seat stands to be affected by expansion, branded the scheme "ill-conceived".
Meanwhile Extend the Runway, a group advocating increasing capacity by lengthening the airport's northern runway, said the DfT "lacks both expertise and attention to detail" and had not listened to its proposal.
"People should have zero confidence that the DfT have run a rigorous process on Heathrow's expensive and complex plan," the group said on Twitter.
The No Third Runway Coalition, which counts Sir Vince and Labour shadow chancellor John McDonnell among its members, said the DfT's process had been "dodgy and has favoured Heathrow Airport Ltd from the start".
"That will be proven in court, if it comes to it," they added.