Berlin: Airlines lost at least $1.7 billion (Rs7,582 crore) in revenue during the volcanic ash crisis, an industry group said on Wednesday as the debate heated up over European governments’ handling of a week of airspace closures.

On Wednesday, aircraft were flying into all of Europe’s top airports—London’s Heathrow, Paris’s Charles de Gaulle and Frankfurt. Still experts predicted it could take days—even more than a week—to clear a backlog of stranded passengers after around 102,000 flights were cancelled worldwide.

Eurocontrol, the air traffic control agency in Brussels, was expecting 21,000 of the continent’s 28,000 scheduled flights to go ahead on Wednesday, as airlines patched together operations with aircraft and flight crews scattered all over the globe.

Air controllers lifted all restrictions on German airspace, but some restrictions remained over parts of Britain, Ireland and France.

In Iceland, where all the trouble began on 14 April with a volcanic eruption, there was no sign 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."

Flying again: People waiting to board flights operating from Gatwick airport near London on Wednesday. Lefteris Pitarakis/AP

He said it would take three years for the industry to recover from the week of lost flying time.

Spain, meanwhile, has developed into a key emergency travel hub, arranging for hundreds of special flights to move over 40,000 people stranded by the travel disruptions. Its airports and airspace have mostly remained open throughout the crisis.

German aviation agency Deutsche Flugsicherung said the decision to reopen the country’s airspace on Wednesday was made based on weather data, not economics. It said the concentration of volcanic ash in the sky “considerably decreased and will continue to dwindle".

A test flight carried out by the German Aerospace Center found various levels of volcanic ash at different sites over Germany. The centre reported no damage to the aircraft that flew the test flight.

A French weather service aircraft also took samples of the air on Tuesday and found no volcanic ash problems either, according to French transport minister Dominique Bussereau.

Passengers, many of whom were stranded for days, welcomed the airport reopenings.

“It’s good for us at least," Mats Tillander, a Swede at Frankfurt International Airport, who spent four days trapped in Texas, told AP Television News. But he was not sure who to believe in the dispute over whether the airspace closings were overkill. “I don’t know what’s right and wrong."

Airlines lost $400 million each day during the first three days of grounding, Bisignani told a news conference Wednesday in Berlin.

“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."

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 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 said. “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."

Deutsche Lufthansa AG, Germany’s biggest airline, planned to operate some 500 flights on Wednesday, compared with 1,800 on a normal day.

Deutsche Lufthansa chief executive Wolfgang Mayrhuber criticized how the flight disruptions were handled, saying decisions were made on what he called forecasts of questionable reliability.

“From the beginning, we had the suspicion that the forecasting model could not be all right," Mayrhuber said.

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.

Shawn Pogatchnik in Dublin, Slobodan Lekic in Brussels, Angela Charlton in Paris, Frank Jordans in Geneva, Jennifer Quinn and Sylvia Hui in London and Carlo Piovano in Reykjavik, Iceland, contributed to this story.