The view from the air traffic control tower at Heathrow.
Debate rages over Heathrow's proposed third runway. Here are some of the arguments put forward by each side:
ARGUMENTS FOR THE THIRD RUNWAY
• Heathrow needs more capacity
Heathrow runs at close to 100% capacity. With demand for air travel predicted to double in a generation, Heathrow will not be able to cope without a third runway, say those in favour of the plan.
Because the airport is over-stretched, any problems which arise cause knock-on delays. Heathrow, the argument goes, needs extra capacity if it is to reach the levels of service found at competitors elsewhere in Europe, or it will be overtaken by its rivals.
Passenger numbers may be down as recession takes hold, but proponents argue we should not base transport decisions on the bad times, but look ahead to future upturn in demand.
• The third runway will boost the economy
The third runway will be worth £7bn a year to the economy, according to airport owner BAA.
Some say a third runway is the only solution to the congestion at Heathrow.
Tens of thousands of jobs will be created - in construction in the short term - and for business and in tourism over the longer term.
Lack of expansion at Heathrow would threaten London's position as trading capital of the world, throttling the very international links Britain was built on.
Business leaders argue London deserves and needs an airport of international quality.
• Pollution concerns are overplayed
Those pushing for the new runway argue that pollution caused by the airport will be closely monitored. Meeting targets is a condition of expansion.
By 2020, when the runway would be completed, new technology will mean planes are much quieter and less polluting. The Airbus A380 already demonstrates that planes are moving in this direction.
If the runway were not built, the argument runs, there would be no cut in emissions. Flights would simply move to other European airports. CO2 would not be reduced, merely transferred elsewhere to the UK's detriment.
• There is no alternative
Building a brand new airport in the Thames Estuary is not feasible according to those in favour of the third runway.
Transport Minister Geoff Hoon says lack of transport infrastructure, fears of 'bird strike', cost and lack of available finance all make the project prohibitive.
ARGUMENTS AGAINST THE THIRD RUNWAY
• We need to reduce, not increase, emissions
Heathrow generates 50% of UK aviation emissions. This makes 6% of total emissions, according to Department for Transport figures.
With a third runway and as the UK as a whole cuts emissions, Heathrow's contribution to overall UK emissions would rise significantly by 2050, some calculate to as much as 50% of total.
A third runway could mean an extra 200,000 flights a year over London.
Why should aviation capacity be increased indefinitely? At a time when most accept the need for emission cuts, say opponents, should we not stick with the capacity we have and allow market forces to price out inessential flyers?
• Health of Londoners at risk
A Greater London Authority (GLA) report suggested Heathrow would even now breach the EU regulations on levels of Nitrous Oxide due to come into force in 2010. Extra flights would only make this worse.
Even the Environment Agency admits that with a third runway, Heathrow would breach these limits.
The GLA study also found that the airport would breach noise pollution limits as a result of the extra flights.
• Economic case overstated
Many of the new passengers the extra runway would bring would be transit passengers. According to former BA boss Bob Ayling they would spend little or nothing in London, only boosting airline profits.
According to Sir David King, former chief scientific adviser to the government, the runway would over time come to be seen as a 'white elephant'.
Long before investment in it were repaid, demand for flying will have fallen away as pressure to reduce carbon increases and competition with other forms of travel grows. The downturn is already forcing people to find substitutes for air travel. This pattern will continue, he suggests.
• Impact on the local area
Transport infrastructure around Heathrow already struggles. The extra demands would create gridlock.
To make way for the runway, Sipson - a village of 700 houses - would be demolished and hundreds of acres of greenbelt land would be swallowed up.
For historical reasons, Heathrow is badly located. It is the only major airport with flight paths over a large capital city, for instance.
Some, like London Mayor Boris Johnson, believe this is a perfect opportunity to start again and propose a new airport in the Thames Estuary.
Planes would approach and leave over water, reducing the impact of noise and the airport could operate 24 hours a day.