What are the three options being considered to expand the UK's airport capacity?
It's more than a year since an independent commission came out in favour of building a third runway at Heathrow - but somehow, the final decision still hasn't been made.
So on the eve of the Government announcing which scheme it will back to expand the UK's airport capacity, we take a look at the three shortlisted plans.
A third runway at Heathrow
Sir Howard Davies's Airports Commission recommended in July last year that a third runway should be built at Heathrow.
The plan assessed by the commission would cost £17.6 billion, although the airport announced in September that it could expand for less money and provide economic growth faster.
The commission said an additional £5 billion of improvements to road and rail links would be necessary to enable the extra passengers to travel to and from the airport.
Heathrow bosses have previously expressed their reluctance to cover this cost.
Sir Howard's report predicted that the scheme would lead to 138 million air passengers each year by 2050, up from 75 million in 2015.
Some 783 homes would be demolished for a third runway, including the entire community of Longford and much of Harmondsworth.
The expansion would generate about 77,000 new jobs by 2030.
A second runway at Gatwick
Ministers are considering the building of a new runway at Gatwick costing £7.1 billion.
The West Sussex airport claims it is the only scheme that does not require taxpayer funding and has attempted to discredit a number of findings made by the Davies Commission.
The Airports Commission claimed surface access improvements would cost £800,000 and the expanded airport would be used by 82 million travellers each year by 2050, compared with 42 million today.
Gatwick argues that London needs "two world class airports", adding that cities such as New York, Paris and Tokyo do not rely on one "mega hub" for all air travel.
The proposal involves 167 homes being lost, which is the lowest out of the three options.
A second runway would be expected to lead to 32,000 additional jobs by 2050.
An extended runway at Heathrow
A second shortlisted option for Heathrow involves extending the west London hub's existing northern runway to form the equivalent of two runways.
This £14.4 billion proposal was put forward by Heathrow Hub, a consortium that includes former Concorde pilot Jock Lowe.
Its supporters claim aircraft would be able to simultaneously land on one of the runways and take off from the other.
They say this would provide the benefits of increased capacity while avoiding "significant new communities" being brought into the noise footprint of flights.
According to the Airports Commission the number of passengers using the airport each year would jump to 131 million by 2050.
The cost of improving surface access would be £5.5 billion and 242 homes would be lost.
The increased capacity would support 77,000 new jobs by 2030.
The scheme promoters disagree with some of the figures provided by the Airports Commission.