Eurocontrol, the air traffic control agency in Brussels, said 21,000 of the continent's 28,000 scheduled flights were going ahead Wednesday. Air traffic controllers lifted all restrictions over German airspace, but some restrictions remained over parts of Britain, Ireland and France.
Giovanni Bisignani, the head of the International Air Transport Association, called the economic fallout from the six-day travel shutdown "devastating" and urged European governments to examine ways to compensate airlines for lost revenues, as the U.S. government did following the Sept. 11, 2001 terror attacks.
He said it would take three years for the industry to recover from the week of lost flying time.
Spain, which has remained mostly open throughout the crisis, developed into a key emergency travel hub, arranging for hundreds of special flights to move over 40,000 people stranded by the travel disruptions.
At Bilbao in northern Spain, more than 2,000 weary Britons packed a ferry Wednesday and headed for England after days of searching for an escape from the volcanic ash travel nightmare.
The ferry normally takes 1,000 people on its twice-weekly, 30-hour trip to Portsmouth in southern England. This time, however, it was carrying around 2,200 people and had to ask strangers to share sleeper cabins.
Sam Gunn, 42, from the English city of Birmingham, endured two hungry days sleeping at JFK Airport in New York after his flight home was canceled. He ultimately settled for a flight to Madrid, then caught a long bus up to Bilbao to get on the ferry.
"Oh, I've been traveling all over the world," he said, chuckling.
German aviation agency Deutsche Flugsicherung said the decision to reopen the country's airspace Wednesday was made based on weather data, not economics. It said the concentration of volcano ash in the sky "considerably decreased and will continue to dwindle."
"Bremen, Hamburg, Hannover, Berlin, Frankfurt and Munich are open again," said Axel Raab, a spokesman for German air traffic control.
"We cannot say what it will look like in the next few days. If the volcano becomes active again, new closures might happen," Raab added. "This is a decision that was made based on meteorological data."
A test flight carried out by the German Aerospace Center found various levels of volcanic ash at different sites over Germany. The highest concentration of ash was over eastern Germany, which the report said was comparable in density to a plume of dust above the Saharan desert. The airspace above the northern city of Hamburg was entirely free from ash.
The center reported no damage to the airplane that flew the test flight.
The Finnish Air Force said volcanic ash dust was found in the engine of an F-18 Hornet jet but it caused no significant damage to the aircraft. Officials say the fighter-bomber's engine had "contaminants on its inside surfaces" that would be further analyzed.
A French weather service plane also took samples of the air Tuesday and found no volcanic ash problems either, transport minister Dominique Bussereau said.
Emirates airline, the Mideast's biggest, sent 37 flights from Dubai to Europe, including 12 flights to Britain and seven to Germany. Its first flight to land in Britain was a double-decker Airbus A380 carrying more than 500 people.
Airlines lost $400 million each day during the first three days of grounding, Bisignani told a news conference Wednesday in Berlin. At one stage, 29 percent of global aviation and 1.2 million passengers a day were affected by the airspace closure ordered by European governments, who feared the risk that volcanic ash could pose to airplanes.
"For an industry that lost $9.4 billion last year and was forecast to lose a further $2.8 billion in 2010, this crisis is devastating," Bisignani said. "Governments should help carriers recover the cost of this disruption."
He noted that the scale of the crisis eclipsed the events of Sept. 11, when U.S. airspace was closed for three days.
In Iceland, where all the trouble began with an April 14 eruption, there was no sign Wednesday that the Eyjafjallajokull volcano would stop erupting anytime soon, according to Pall Einarsson, a geophysicist at the Institute of Earth Sciences in Reykjavik.
"We cannot predict when it will end," he said. "(But) ash production is going down and is really insignificant at the moment."
However, scientists at Zurich's Federal Institute of Technology said Wednesday that an initial analysis of data from the volcano showed that closing Europe's airspace was warranted for safety reasons.
The scientists analyzed samples collected over the weekend by specially equipped weather balloons and concluded that the concentration of particles was "very high," at up to 600 micrograms per cubic meter, according to Prof. Thomas Peter.
The scientists also said the composition of the magma is changing, causing some concern that it might take on a more explosive form.
According to Peter Ulmer, a professor of petrology, the volcano has been pushing out magma with a higher silicate content since April 14. If the level of silicate reaches 56 percent or the share of magnesium falls below 4 percent, then the magma can become explosive even without the presence of huge ice caps like the current volcano.
Still, Ryanair chief executive Michael O'Leary called the shutdown imposed by European governments excessive.
"It might have made sense to ground flights for a day or two. That's understandable. But there should have been a much faster response by the governments, the transport ministers and the regulators," he told The Associated Press.
"Nobody in their right mind would want to fly through a dark plume of smoke. But by the time that that cloud has dispersed through 800 or 1,000 nautical miles of air space, a full ban should never have been imposed," O'Leary said.
But Eamonn Brennan, chief executive of Irish Aviation Authority, defended the governments' responses. He said there was "no safe, quick fix" for the problem and the closures allowed Europe to come up with a scientific-based, risk-mitigation scheme to handle an unprecedented situation.
"It's important to realize that we've never experienced in Europe something like this before. So it wasn't just a simple matter of saying: Yes, you could have operated on Saturday or Sunday or Monday," he told the AP. "We needed the four days of test flights, the empirical data, to put this together and to understand the levels of ash that engines can absorb."
British officials denied they opened the country's space after pressure from the airline industry, but airline chiefs had been openly furious with the blanket shutdown.
"I don't believe it was necessary to impose a blanket ban on all U.K. airspace last Thursday," said British Airways chief executive Willie Walsh. "My personal belief is that we could have safely continued operating for a period of time."
BA raised the stakes in its showdown with aviation authorities Tuesday by announcing it had more than 20 long-haul planes in the air and wanted to land them in London. Despite being told the air space was firmly shut, radar tracking sites showed several BA planes circling in holding patterns over England late Tuesday before the announcement that air space was to be reopened.
"We were circling for about two hours," said Carol Betton-Dunn, 37, a civil servant who was on the first flight to land at London's Heathrow, from Vancouver.
She said the passengers were initially told the flight would be going to London, then that it was heading for an unspecified European airport, then that Shannon in Ireland would be their destination.
"It's been exhausting," Betton-Dunn said.
Britain's transport secretary, Andrew Adonis, denied the government decided to reopen the skies to air travel under pressure from airlines.
"They have obviously wanted to be able to fly their planes -- of course they have -- but that has not been the issue at stake here," he told the BBC.
At Heathrow's Terminal 3 on Wednesday, no one was allowed inside the departures level without a valid ticket. The departure boards still showed about half the flights as canceled.
Despite the uncertainty, passengers were optimistic. Juanjo Dominguez, a 25-year-old web designer from London, was at the airport for his afternoon flight to New York.
"I feel good, hopeful," Dominguez said. "I am still keeping my fingers crossed."
At the terminal's arrivals level, there was just a small trickle of passengers arriving from New York and Madrid.
In Spain, the airport in Barcelona -- near the border with France and thus a gateway to the rest of Europe -- took in flights from New York, Orlando, Vancouver, Paris, Nice and Rome. Airports in Barcelona and Madrid also chartered nearly 300 buses to get people to other cities in Europe, and Palma on the Mediterranean island of Mallorca handled 50 extra flights.
Deutsche Lufthansa AG chief executive Wolfgang Mayrhuber welcomed the government's decision to reopen the skies but criticized how the flight disruptions were handled.
"From the beginning, we had the suspicion that the forecasting model could not be all right," Mayrhuber said.
Lufthansa, Germany's biggest airline, planned to operate some 500 flights on Wednesday, compared with 1,800 on a normal day. However, he said his company would not seek government compensation.
"We don't need a bailout, we don't need an umbrella," he said. Lufthansa is Europe's largest airline group by sales. It owns or holds stakes in carriers including Swiss International Airlines, Austrian Airlines and British Midland.