The European Union presidency says that air traffic over Europe could return to about 50 percent of its normal level on Monday, if weather forecasts confirm that skies over the continent are clearing of volcanic ash.
European transportation ministers from countries affected by the ash a volcano in Iceland began spewing into the sky last week will meet on Monday by video conference in an effort to reopen closed airspace.
The volcanic ash has brought chaos to the region - canceling most trans-Atlantic and European flights and leaving thousands of airline passengers stranded for days, as well as disrupting commerce.
European Transport Commissioner Siim Kallas says Europe has never experienced a transportation disruption like this and that officials need to take action to get things moving again. "This is clear also, that this is not sustainable. So we cannot go ahead and just wait until the ash cloud will disappear," he said.
Kallas says Monday's meeting will try to find a technological solution to the flight disruption, but he stressed that safety considerations will come first. "It is clear that safety is our first and utmost priority, so we cannot compromise with safety. But we are working based on new evidence about test flights, how to assess the situation and how to find solutions to increase air space without compromising safety," he said.
Spanish Secretary of State for E.U. Affairs Diego Lopez Garrido says the ash cloud over Europe is moving to the northeast, which could clear half of the air space over the continent. "Probably there will be half of the European Union territory influenced by this ash cloud. And from this perspective, the forecast is that there will be half of the flights possibly operating in Europe," he said.
But Britain, Germany and the Netherlands say their airspace will remain closed for much of Monday.
Meteorologists say conditions over Europe were unstable on Sunday and that shifting winds made air travel dangerous. They also note that the irregular eruptions from the Icelandic volcano, which continues to spew ash into the sky, is adding to the unpredictability of the situation.
Volcanic ash consists of rock, glass and other particles that can stall aircraft engines.
KLM Royal Dutch Airlines said it flew four planes in a normal pattern above 3,000 meters from Amsterdam to Dusseldorf on Sunday. The airline's pilots said they did not encounter residue from the ash cloud and that jetliners were not damaged.
Lufthansa flew 10 empty planes from Frankfurt to Munich on Saturday without incident, and Air France flew several successful test flights.
Some aviation officials have criticized the airline shutdowns, arguing that they were based solely on computer models. Air Berlin chief Joachim Hunold was quoted on Sunday by German media as saying that no one has yet sent weather balloons into the atmosphere to collect data on the volcanic ash.
Analysts say airlines are losing about $200 million a day because of the European and trans-Atlantic shutdowns.
Air travel in Southern Europe - including Spain, southern Italy, Greece and Turkey - remains open.
The last major disruption to European aviation followed the September 11 attacks on the United States almost a decade ago. U.S. airspace was closed for three days and European airlines canceled all trans-Atlantic flights.
The volcano in southeastern Iceland began erupting on Wednesday, for the second time in a month, after being dormant for nearly 200 years.