By Chris Page BBC News

Belfast will soon be linked to 37 foreign cities by scheduled flights

The speed of the turnaround is one of the most important parts of budget airlines' operations.

The staff say teamwork is the key - engineers are lying on their backs below the wings making their final checks, ground staff are completing the paperwork, and bags are being taken on and off.

At 1000 GMT - half an hour after the plane arrived - it's airborne again, bound for Switzerland.

This sort of operation now happens about 40 times every day at Belfast International Airport.

As soon as the concrete is dry, we can start flights to Europe Micahel O'Leary, Ryanair

Northern Ireland has become one of the fiercest battlegrounds in the cut-price flight business.

At the start of 2004, there was only one daily international flight to continental Europe.

By this summer, Belfast will be linked to 37 foreign cities by scheduled flights.

The arrival of Ryanair at George Best Belfast City Airport in October 2007 raised competition to new levels.

Ryanair is now flying from the George Best City Airport

It started flights to four destinations in the UK as Aer Lingus opened its first base outside the Republic at Belfast International.

Ryanair Chief Executive Michael O'Leary says he is prepared to launch about 10 international routes - if a runway extension at the City Airport gets the go-ahead.

"As soon as the concrete is dry, we can start flights to Europe," he says. City of Derry Airport says it is also discussing international routes with Ryanair - and several could be established by the end of 2008.

It's absolutely ridiculous that there's a disused rail link running within a mile or so of the airport ? if you've got a rail link, it should be used Toby Nicol, Easyjet

The biggest airline operating out of the International - Easyjet - says it is considering more flights to destinations in Spain, France and Italy in particular.

However, Easyjet claims the International Airport urgently needs better transport links to the city.

Spokesman Toby Nicol says: "Road access to Belfast International Airport is something of an embarrassment compared with airports in the rest of Europe."

"It's absolutely ridiculous that there's a disused rail link running within a mile or so of the airport - if you've got a rail link, it should be used."

DRD Roads Service says �3bn has been set aside for investment in roads over the next 10 years and all routes to and from airports will benefit.

Translink says a rail link to the airport is something it keeps under review - but at the moment there are not enough passenger numbers to justify building a halt.

But some experts believe the growth rate in passenger aviation will not be sustained.

Simon Calder - the travel editor of the Independent - says:�"I'm not sure how much room there is for growth out of Northern Ireland.

"I think there is still some more potential - but it's for more links to the United States, or Dubai - the long-haul destinations which would seal Northern Ireland's place on the� international aviation map."

Ryanair has warned its profits may halve this year because of the global economic slowdown and rising oil prices.

Easyjet is aiming for business and tourist flyers

Easyjet reported a drop in passenger numbers in January and its share price has suffered.

But budget airlines argue a recession might actually be good news for them in the long term - because business travellers would switch to low-fares carriers.

Green campaigners say the government's targets to lower carbon emissions will not be met if budget carriers keep growing.

John Woods of Friends of the Earth believes the era of cheap flights will come to an end in the next ten years.

"Two things are driving costs�up - the price of carbon and the price of oil.

"We'd be foolish to build our future prosperity on cheap flights."

Airports and airlines have dismissed suggestions that growth in Northern Ireland has peaked.