Airports throughout Europe were bustling Wednesday as the danger posed by ash from Iceland's volcano was downgraded, but authorities said it could take weeks to clear the backlog of passengers and cargo.
Air travel resumed across most of the Continent Tuesday. European governments banned air travel last week when Iceland's Eyjafjallajokul volcano erupted, spewing corrosive ash into the air. Eurocontrol, the European air traffic control agency, estimated that by the end of Wednesday more than 100,000 flights would have been canceled since April 15.
The agency 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.
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.
Giovanni Bisignani, director general of the International Air Transport Association, said 29 percent of global aviation and 1.2 million passengers a day were affected when officials closed their airspace out of concern the ash could pose a risk to airplanes. He estimated that airlines lost about $1.7 billion during the six-day flight ban.
"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.
He urged governments to look for ways to mitigate the impact of the lost revenues. "The scale of the crisis eclipsed 9/11 when U.S. airspace was closed for three days," Bisignani said.
European air traffic controllers estimated more than 75 percent of normally scheduled flights -- about 27,500 -- would go forward Wednesday. Most of the airspace over the Continent was open Wednesday, but some restrictions remained over parts of northern France, northern Germany and southern Scandinavia, according to a statement on the Eurocontrol website.
"The situation will be evolving minute by minute during the day," the agency said.
Many European airports partially opened on Tuesday; Wednesday was the first full day of operations at airports in Britain. About 150,000 Britons were trying to make it home after being stranded outside the U.K.
Eve Dickinson, a passenger on the first flight Tuesday into London's Heathrow Airport, was happy to be back on British soil after being stranded in the U.S.
"We are very, very lucky to have just touched down ... to be home," she said.
The problems caused by the air travel ban spilled over to manufacturing and agriculture industries. Some manufacturers, including Germany's BMW, had to stop production temporarily because the flight cancellations prevented them from getting parts that are normally shipped by air. Kenya's growers lost an estimated $12 million as flowers and fruit rotted while waiting to be transported.
Although Bisignani criticized the widespread closures, 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.
In Iceland, the Institute of Earth Sciences Nordic Volcanological Center said in a Wednesday update on its website that Eyjafjallajokull was continuing to erupt, but activity was less explosive.
"We cannot predict when it will end," said Pall Einarsson, a geophysicist at the Institute of Earth Sciences in Reykjavik. But "ash production is going down and is really insignificant at the moment."
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.
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, Paris, Nice and Rome, among others. Nearly 300 buses were chartered from Barcelona and Spain to get people to other cities in Europe.
Contributing: Deborah Tedford and The Associated Press