Europe begins a new working week on Monday with officials hoping to significantly increase flights to half the normal number and the EU discussing how to tackle the 5-day-old air travel crisis caused by volcanic ash.
Pressure was building on authorities for a solution because the closure of most of Europe's airspace has cost the airline industry hundreds of millions of dollars, millions of passengers have been stranded, and importers and exporters have been hurt.
The crisis has had a knock on effect across the world and its impact on everyday life in Europe has deepened. In Britain, companies reported that staff had been unable to get back from Easter holidays abroad and hospitals said they were cancelling some operations because surgeons were stuck far away from home.
A senior EU official said the current situation was not sustainable, as airlines called for a review of no-fly decrees after conducting test flights at the weekend without any apparent problems from the ash cloud from an Icelandic volcano.
We cannot wait until the ash flows just disappear, said Transport Commissioner Siim Kallas, adding that he hoped 50 percent of European airspace would be risk-free on Monday.
Spain's European Union affairs minister Diego Lopez Garrido told reporters after a meeting at European aviation control agency Eurocontrol: The forecast is that there will be half of flights possibly operating (on Monday).
Iceland said tremors from the volcano had grown more intense but that the column of ash rising from it had eased back to 4-5 km (2.5-3 miles) from as high as 11 km when it began erupting on Wednesday from below the Eyjafjallajokull glacier.
Italy and Austria said they would reopen affected airports on Monday.
Only 5,000 flights took place in European airspace on Sunday, compared with 24,000 normally, Eurocontrol said. It said 63,000 flights had been canceled since Thursday.
EU transport ministers will discuss the crisis in a video conference on Monday that Spain has called in its capacity as the 27-nation bloc's president.
We can examine the results of the test flights and look and see whether there is any updating of the regulatory structure which might make it possible for flights to take place, British Transport Minister Andrew Adonis told BBC television.
Dutch state broadcaster NOS quoted Transport Minister Camiel Eurlings as saying Europe's response to the ash cloud had been too severe, and that the United States did not completely close its airspace in response to similar eruptions.
The Dutch airline KLM, which has flown several test flights, said most European airspace was safe despite the plume of ash, and dispatched two commercial freight flights to Asia on Sunday.
Volcanic ash is abrasive and can strip off aerodynamic surfaces and paralyze an aircraft engine. Aircraft electronics and windshields can also be damaged.
Senior Eurocontrol official Brian Flynn said the International Civil Aviation Organization published rules that needed to be adhered to worldwide, and guidelines to interpret at continental level.
One could say that the guidelines are interpreted slightly more rigorously in Europe than in the United States, when it comes to responsibilities of air traffic control agencies and pilots, he told Reuters.
The clampdown poses a growing problem for airlines, estimated to be losing $200 million a day, and for the millions of travelers stranded worldwide.
Weather experts said wind patterns meant the ash plume was not likely to move far until later in the week.
For some businesses dependent on fast air freight, the impact has been immediate.
Kenya's flower exporters said they were already losing up to $2 million a day. Kenya accounts for about a third of flower imports into the European Union.
The air travel disruption is the worst since the September 11 attacks on New York and Washington in 2001, when U.S. airspace was closed for three days.
U.S. President Barack Obama, German Chancellor Angela Merkel and others canceled trips to Poland for the funeral of President Lech Kaczynski on Sunday.
Britain said it was considering using the navy and requisitioning merchant ships to ferry home citizens stranded abroad. The response to the crisis is threatening to become an issue in the campaign for Britain's May 6 election.
The British travel agents' association Abta was quoted by the BBC as saying it had made a rough estimate that about 150,000 Britons were stranded abroad.
At no time in living memory has British airspace been shut down and affected this many people, an Abta spokeswoman told the BBC.
For travelers, businesses and financial markets, the biggest problem is the sheer unpredictability of the situation.
Economists say they stand by their predictions for European growth, hoping normal air travel can resume this week.
But if European airspace were closed for months, one economist estimated lost travel and tourism revenue alone could knock 1-2 percentage points off regional growth. European growth had been predicted at 1-1.5 percent for 2010.
That would mean a lot of European countries wouldn't get any growth this year, said Vanessa Rossi, senior economic fellow at Chatham House.
It would literally stifle the recovery. But the problem is it is incredibly hard to predict what will happen. Even the geologists can't tell us.
Disruption spread to Asia, where dozens of Europe-bound flights were canceled and hotels from Beijing to Singapore strained to accommodate stranded passengers.
Many U.S. airline flights to and from Europe have been canceled.
Russian airports remained open, routing planes to North America over the North Pole to avoid the ash cloud.
(Reporting by London, Geneva, Dublin, Paris, Amsterdam, Brussels, Reykjavik, Washington, Frankfurt and Berlin newsrooms; Editing by Ralph Gowling)