Expansion of Heathrow and Gatwick are the shortlisted options being considered by a government-backed commission into airport expansion. In its interim report, the commission also says a new airport will be needed in the South East by 2030.
Of the three options for expansion presented by Heathrow Airport Ltd in the summer, the Airports Commission is only progressing one of them: the plans for a new runway to the north west of the existing airport.
The other Heathrow idea being investigated by the Commission comes from a pressure group called Heathrow Hub: the extension of one of the current runways.
The proposal is to build a third runway to the north west of the existing airport. It is a different proposal to the one approved by Gordon Brown when he was Prime Minister.
The new runway is further to the west - and anyone who knows this area will work out it brings the runway of Britain's busiest airport into conflict with Britain's busiest motorway, the M25. Look at the plan and you will see the runway is built over the top of the motorway.
That is not unusual. At Paris' Charles de Gaulle airport, a motorway passes under one of the runways in a tunnel. But it does mean this option is not cheap.
Some believe today's report did not draw firm conclusions in order to avoid a politically divisive issue before the next election.
Expansion of Heathrow and Gatwick Airports are the shortlisted options being considered by a government report into airport expansion.
Heathrow is the third busiest airport in the world in terms of passenger numbers. It carried more than 69 million people in 2011.