EU emergency talks called on volcanic ash air chaos
EU transport ministers are to hold emergency talks by video conference on easing the air travel crisis caused by a volcanic ash cloud in Europe's skies.
More than 6.8 million passengers have been affected so far, as the crisis enters its fifth day.
Airports and airlines are questioning the need for curbs said to be costing airlines $200m (£130m) a day.
The International Air Transport Association (IATA) has criticised European governments' response.
"We must move away from this blanket closure and find ways to flexibly open air space, step by step," IATA head Giovanni Bisignani told a news briefing in Paris.
MAJOR EU AIRPORTS 0800 19/04
Heathrow - closed
Frankfurt - closed after reopening on a limited basis for several hours on Sunday
Paris Charles de Gaulle - closed
Schipol, Amsterdam - closed
Rome - limited service
Madrid - limited service
The enormous shroud of fine mineral dust particles now stretches from the Arctic Circle in the north to the French Mediterranean coast in the south, and from Spain into Russia.
Airspace remains closed, or partially closed, in more than 20 countries.
Sixty-three thousand flights have been cancelled in the four days since the clampdown began.
And the prospect of a return to normal air travel remains far from clear.
Speaking ahead of the EU talks, Transport Commissioner Siim Kallas said: "We cannot just wait until this ash cloud dissipates."
The Spanish Minister for Europe, Diego Lopez Garrido, had said on Sunday that up to half of the flights across Europe could operate on Monday.
He was speaking after talks with Eurocontrol, which co-ordinates air traffic control in 38 nations. It had recommended the current flight ban.
But Brian Flynn, deputy head of operations for Eurocontrol, told the BBC that while half of the European landmass could be clear of ash cloud, that did not mean half of the flights could go ahead.
The flight bans came amid fears that the ash - a mixture of glass, sand and rock particles - can seriously damage aircraft engines.
The international airports council, ACI, said a total of 313 airports had been paralysed by the restrictions and the global backlog was affecting more than 6.8 million travellers.
In another development, hundreds of thousands of Kenyans working in agriculture, the country's largest export sector, face economic uncertainty because of the flight bans.
Refrigerated stores at Nairobi airport and on farms are now completely full, and a huge amount of fresh flowers and vegetables destined for the European market is in danger of perishing, the BBC's East Africa correspondent, Will Ross, reports.
The problems have also led to the postponement of next Saturday's Japanese MotoGP.
The EU transport ministers' video conference, hosted by Spain, is set to consider a proposal that passengers from countries like Britain, who are stranded in the US or Asia, would fly into Spain and then continue their journey by train, boat or coach.
Robert Peston, BBC Business Editor
The two biggest British airlines are incurring painful losses. British Airways is losing around £25m ($38m) a day; and Easyjet up to £5m ($7.6m) a day. But they also have substantial borrowing facilities and cash, and can cope with a financial pain so long as it doesn't last too long.
Many other airlines across Europe are less fortunate, which is why ministers are telling me that a Europe-wide financial support scheme for the airline industry - funded by taxpayers - is a very live issue.
As for the impact on the wider economy, supermarkets say that supplies of imported flowers and exotic fruit and vegetables are beginning to run low. And businesses dependant on air freight are hurting. But the crisis would probably have to endure for many more days yet for the cost to be big enough to upset Europe's economic recovery.
Dutch Transport Minister Camiel Eurlings was "advocating for a different approach to the problem", the Dutch transport inspectorate said.
This would entail "drawing a distinction between areas with low concentrations and those with high concentrations" of ash when making decisions on air safety.
The UK Transport Secretary, Lord Adonis, said information from various test flights on Sunday, assessing the impact of the dust on jet engines, would be considered during the conference.
Siim Kallas said European authorities were working to find a solution that did not compromise safety.
Southern Iceland's Eyjafjallajoekull volcano began erupting for the second time in a month on Wednesday.
Iceland's Meteorological Office said tremors from the volcano had grown more intense but the column of ash rising from it had eased to around 5km (3.1 miles).
Ash still 'very worrying'
Britain has extended a ban on most flights in its airspace until at least 1900 local time on Monday (1800 GMT).
Stranded passengers give their views
Ireland, Germany and the Netherlands are keeping their airspace closed until 1200 GMT on Monday. Spain has re-opened its airspace after a brief closure. Officials there have suggested its airports could be used as an entry platform into Europe.
Our business editor, Robert Peston, understands that British Airways fears it may not be allowed to fly normal services until Thursday at the earliest.
One measure being discussed by the British government is the possibility of deploying the Royal Navy to collect some of the estimated 150,000 Britons who are stranded abroad.
While several airlines carried out test flights and reported planes showing no obvious damage after flying through the ash, a scientific test flight over Britain concluded that the situation could still be dangerous.
I've been stranded in Madrid since Thursday. We've been told we cannot get a flight until 26 April at the earliest.
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