Airport expansion: What are the three options?
The grounding of Boris Johnson's idea for an airport in the Thames estuary leaves three options for expanding UK airport capacity on the table. Which will be cleared for take off?
As demand for air travel rockets, some politicians, business leaders and aviation experts argue the UK urgently needs to expand its airport capacity.
The Airports Commission says there is a need for one additional runway in the South East of England by 2030.
It has shortlisted three options:
- A third runway at Heathrow
- Lengthening an existing runway at Heathrow
- A second runway at Gatwick
Boris Johnson had championed the idea of an island airport in the Thames estuary - dubbed Boris Island - but on 2 September the commission declared the idea would not be shortlisted, citing the huge price tag and environmental concerns.
Despite this, the London mayor has insisted the proposal is not dead and the decision is just a "temporary set back".
The commission is carrying out a detailed look at the shortlisted options before a public consultation in the autumn. Its final report is due in 2015.
What do you need to know about each option?Heathrow
The first option involves a new 3,500m runway to the north-west of Heathrow's two existing runways.
The second would mean extending the existing northern runway by at least 6,000m to the west and allowing it to operate as two separate runways.
The airport is one of the world's busiest, handling 70 million passengers in 2012. More than a third transfer to other flights, making it a major hub airport.
But Heathrow operates at 98% of its capacity within a current limit of 480,000 flights per year, much closer to capacity than other major London airports and rival hubs in Europe.
In normal conditions, a flight at Heathrow takes off or lands every 45 seconds but during bad weather aircraft fly more slowly over the ground.
This reduces the landing rate and causes delays - and because Heathrow's runways are full there are no spare slots into which to schedule the delayed flights. Lack of capacity therefore results in cancellations.
Heathrow's submission says extra capacity - through either option - would be delivered by 2025-9.
Pros: Heathrow expansion is seen as the best short-term option to keep Britain competitive with its European rivals, like Amsterdam Schiphol and Paris Charles de Gaulle. Expanding the airport would be "quicker and cheaper" than any rival hub option, says the airport. Heathrow is a big employer and supporters cite a knock-on effect on businesses in the area.
Cons: The environmental impacts. Susan Pearson, of the Airport Watch campaign, says Heathrow would become the biggest emitter of carbon dioxide (CO2) in the country and noise pollution would become even worse for the 725,000 people already living under the flight path. Added to that, there would be a loss of homes.
Another medium-term option is to switch Heathrow to 'mixed mode' operation - this would see both runways used for arrivals or departures.
But this would have major implications for noise levels and the commission itself has so far rejected this. Heathrow's owners, Heathrow Airport Holdings, also reject the idea.Gatwick
This proposal would involve a building a new runway, at least 3,000m in length, built far enough away from the existing runway to allow for fully independent operation.
Gatwick is the world's busiest single-runway airport, but relatively few passengers - about 5% - use Gatwick to transfer to other flights.
Gatwick says its case is "robust and compelling". The expansion would cost between £5bn and £9bn, and be financed privately.
Airport chiefs say the new runway could be opened by 2025 and would have less of an environmental impact than a third runway at Heathrow.
Depending on how the second runway is used, passenger numbers would be expanded from about 34.2 million passengers a year to between 67 and 87 million.
Gatwick backs a "constellation" approach in which London would be served by three main airports, each with two runways.
Pros: If Gatwick added a second runway, fewer people would be affected by noise and pollution than the number affected by a third runway at Heathrow, which is closer to central London. Gatwick already has good transport links to London.
Cons: An existing agreement means no new runway will be built at Gatwick until 2019. The north terminal was built where the second runway would have been. A high-speed link between Gatwick and Heathrow would be a long-term, expensive project.Options not on the shortlist: Thames estuary
Mayor of London Boris Johnson has long championed a new four-runway hub airport to replace Heathrow, but the commission has rejected the idea.
One version of the Isle of Grain plan, designed by the company of architect Sir Norman Foster, includes new high-speed rail links and a Thames crossing and barrier. It is estimated the cost would be £50bn.
But commission chairman Sir Howard Davies says there are "serious doubts" about its delivery and operation in the estuary.
"The economic disruption would be huge and there are environmental hurdles which it may prove impossible, or very time-consuming to surmount," Sir Howard says in the commission's report.
But Mr Johnson says Gatwick is not a long-term solution and Heathrow expansion would create "unbelievable levels of noise, blight and pollution", but a new airport to the east of London would "create the jobs and growth this country needs to remain competitive".
Pros: Likely to be privately funded and provide an airport hub large enough to compete with European rivals. Create thousands of new jobs to the east of London. Solve the noise problems affecting London residents.
Cons: Critics say it is likely to devastate the economy around Heathrow, and there is a serious risk of bird strike to aircraft using the airport. Air traffic controllers say it is in the worst spot for traffic. Environmental campaigners say it would be a threat to rare wildlife. The cost and length of time it would take to complete are also cited as problems.
The commission last year decided not to shortlist proposals for expanding Stansted or Birmingham, but said there was likely to be a case for considering them as "potential options" for any second new runway by 2050.
A plan to open up RAF Northolt - the RAF's main base in London, which is about six miles from Heathrow - for short-haul civilian flights was also rejected, with the commission saying it "did not provide a realistic option for managing capacity at Heathrow".
Transport Secretary Patrick McLoughlin has said the country needs to increase its aviation hub capacity to compete with international rivals. It is a view echoed by some other politicians, business leaders and aviation experts.
But there are others who say no credible case has been made to increase the UK's airport capacity.
Friends Of The Earth campaigner Jenny Bates says: "The overall business case for further expansion of our airports is just not convincing, as it is not compatible with meeting our climate change targets."
Airport Watch, a group opposed to airport expansion that might harm the environment, has said more effort should be made to utilise existing capacity.
And the Aviation Environment Federation has said the idea the UK is facing an airport capacity crisis is a myth.