European officials acted Monday to end the air paralysis caused by a volcanic eruption in Iceland, agreeing to let air traffic resume in designated "caution zones" following a five-day shutdown that left millions of travelers stranded.
European Union transport ministers agreed during a crisis videoconference to partly reopen Europe's skies.
The agreement creates three zones - a "no fly" zone immediately over the ash cloud, a caution zone "with some contamination" where planes can fly subject to engine checks for damage and a third, open-skies zone.
"From tomorrow (Tuesday) morning on we should see progressively more planes start to fly," said EU Transport Commissioner Siim Kallas.
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The easing came as the aviation industry - facing losses of more than $1 billion - criticized the official handling of the crisis and urged authorities to lift restrictions that have grounded planes across the continent and sent tremors through the fragile European economy.
The deal led airlines across Europe to lift their flight bans. German airline Lufthansa said it would bring 50 planeloads of passengers home and Britain announced it would reopen some of its air space over the next 24 hours.
Britain's National Air Traffic Service said Scotland's airports and air space would reopen at 0600GMT (2 a.m. EDT) Tuesday, and London's airports - including Heathrow, Europe's busiest - might be able to reopen later Tuesday. British Airways said it hoped to start flying from London at 7 p.m. (1800GMT) Tuesday.
Airlines have been ramping up the pressure on European authorities, saying test flights suggested planes can fly safely through the ash plume. Airlines including KLM, Lufthansa and British Airways have run flights over the last few days, and none reported problems or damage.
"The analysis we have done so far, alongside that from other airlines' trial flights, provides fresh evidence that the current blanket restrictions on airspace are unnecessary," said BA chief executive Willie Walsh. "We believe airlines are best positioned to assess all available information and determine what, if any, risk exists to aircraft, crew and passengers."
But scientists and pilots urged caution.
"Mixing commercial and safety decisions risks lives," said Philip von Schoppenthau, secretary-general of the European Cockpit Association, a union representing 38,200 pilots from 36 European nations.
"Our members have many firsthand experiences of the extremely abrasive and clogging effects of such clouds," he said.
Millions of travelers have been stuck since the volcano under Iceland's Eyjafjallajokull glacier begun erupting Wednesday for the second time in a month, spewing a vast cloud of ash that has drifted over most of northern Europe and is now spreading west toward North America.
Eurocontrol, the air traffic agency in Brussels, said less than one-third of flights in Europe were taking off Monday - between 8,000 and 9,000 of the continent's 28,000 scheduled flights. Officials said more would operate Tuesday - though it wasn't immediately clear how many.
German Transport Minister Peter Ramsauer said all planes under the "control zone" plan, all planes will be thoroughly checked once they've landed.
"Much stricter tests and checks will be applied to all planes," Ramsauer said, in hopes of gaining more data about the possible risk the ash cloud represents. "Nobody knows how long the situation will continue," he said.
Airports in central Europe and Scandinavia have reopened, and most of southern Europe remained clear, with Spain volunteering to be a staging-post for overseas travelers trying to get home.
As British schools reopened after the Easter break with empty desks and missing teachers - thanks to an estimated 150,000 Britons stranded abroad - authorities resorted to extraordinary measures.
The government said it was sending three Royal Navy warships, including the aircraft carrier HMS Ark Royal, across the English Channel to bring home stranded citizens. One ship was heading to Spain to pick up soldiers trying to get back to Britain after a tour of duty in Afghanistan.
Spain volunteered to become the new hub of Europe to get stranded passengers moving again. Infrastructure minister Jose Blanco said Spain could to take in around 100,000 people under the new emergency plan, which focuses on trying to bring Britons home far-flung points in Asia, Latin America and North America.
British Prime Minister Gordon Brown said the ash cloud had created "the biggest challenge to our aviation transport network for many years," and European officials said the disruption was worse than that caused by the Sept. 11 attacks.
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With grit-locked travelers desperate to get home, tensions boiled over at Incheon International Airport in South Korea, where 30 frustrated passengers blocked a Korean Air ticketing counter and demanded officials arrange travel to anywhere in Europe after hearing about the test flights.
"We need a flight, we need a time," Thierry Loison, who has been stuck at the airport since Friday on the way back to France, told Korean Air officials. "We were like animals this morning."
Others complained of rail fares that rose suddenly and hotel rates that tripled overnight. Graham Wishart, 65, stuck in London when his flight to Toronto was canceled, said his hotel bill had gone from £68 to £189 a night ($104 and $289.)
"People are raking in dough here from people who are stuck as a result of this natural disaster," he said. "It's just not right."
As pressure mounted from airlines, European civil aviation authorities held a conference call Monday about what steps could be taken toward opening airspace. Critics said the coordinated action came too late.
"It's embarrassing, and a European mess," said Giovanni Bisignani, chief executive of the International Air Transport Association.
IATA accused European governments of offering "no risk assessment, no consultation, no coordination, and no leadership." The group urged governments to more urgently "focus on how and when we can safely reopen Europe's skies" - such as through more in-depth study of the ash cloud to identify safe corridors for planes.
Ash and grit from volcanic eruptions can sabotage a plane in many ways: the abrasive ash can sandblast a jet's windshield, block fuel nozzles, contaminate the oil system and electronics and plug the tubes that sense airspeed. But the most immediate danger is to the engines. Melted ash can then congeal on the blades and block the normal flow of air, causing engines to shut down.
Airlines said the test flights showed the danger was exaggerated. But a senior Western diplomat said Monday that several NATO F-16 fighters suffered engine damage after flying through the volcanic ash cloud.
The official declined to provide more details on the military flights, except to say that glasslike deposits were found inside the planes' engines after they patrolled over European airspace.
The crisis caused by the volcano has hit everyone from Icelandic fisherman - unable to transport their catches abroad - to Kenyan farmers whose Europe-bound produce sits rotting in warehouses.
The most immediate impact has been on airlines, already struggling because of the recession-induced travel downturn.
IATA estimated the industry was losing $200 million a day. British Airways said it was losing up to £20 million ($30 million) a day and other airlines were also racking up huge losses.
The prospect of continued losses and flight cancelations pushed down shares of many airlines.
Video still showed smoke billowing into the air from the volcano, but Britain's Meteorological office said "eruptions from the Eyjafjallajokull volcano are weakening."
Scientists in Iceland said the new volcanic ash plume is lower, which would pose less of a threat to commercial aircraft in the future. Geologists saw a red glow at the bottom of the volcano, suggesting the eruption is turning to lava flow, and said there is less ice in the crater, which would reduce the plume.