The Government today signalled a likely major expansion at Heathrow by saying there was "a strong case for introducing further capacity".
Transport Secretary Ruth Kelly put out proposals for consultation which include a third runway at the west London airport, a sixth terminal, changes to runway take-off and landing patterns and changes in the routes Heathrow aircraft take.
The public will now have until February 27 to make their views known.
Ms Kelly said: "Heathrow supports 170,000 jobs, billions of pounds of British exports and is our main gateway to the global economy. But for too long it has operated at nearly full capacity, with relatively minor problems causing severe delays to passengers.
"If nothing changes, Heathrow's status as a world-class airport will be gradually eroded - jobs will be lost and the economy will suffer. London and the UK's nations and regions alike are reliant on the good international connections that the Heathrow hub provides.
"Equally, I am clear that any decision on expansion has to be compatible with meeting tough local environmental tests on noise and air quality.
"I fully understand this is an issue which raises strong feelings on all sides which is why we are making every effort to encourage people to make their views known."
The Government is now proposing that a third runway - by around 2020 - to be built at Heathrow north of the A4 will be 2,200 metres long rather than the originally-proposed 2,000 metres.
With added terminal facilities and an improved rail and road network, the new runway would enable Heathrow to handle around 700,000 take-offs and landings a year - nearly 50% more than today.
The Government is also proposing a "mixed mode" operation for Heathrow's two existing runways - where the runways are used for both take-off and landings rather than the alternation method currently in use.
This would allow for up to 540,000 flights a year ahead of the building of the new runway, with mixed mode ceasing once a third runway is ready.
The consultation document said a third runway would bring net economic benefits of around £5 billion.
On the environment, the Government said that a short, third runway could be added at Heathrow by around 2020 and would meet EU air quality limits.
The consultation also said that it agreed with Heathrow operator BAA that a new - sixth - terminal would be necessary to accompany a third runway.
The new runway would lead to the loss of around 700 properties "including the community of Sipson (village)".