Airlines lost at least $1.7bn in revenue during the volcanic ash crisis, an industry group said, Wednesday, as the debate heated up over European governments' handling of a week of airspace closures.

Associated Press reported on Wednesday, that planes were flying into all of Europe's top airports - London's Heathrow, Paris' Charles de Gaulle and Frankfurt.

Experts also predicted it could take days – even more than a week – to clear a backlog of stranded passengers, after about 102,000 flights were cancelled around the world.

Eurocontrol, the air traffic control agency in Brussels, said 21,000 of the continent's 28,000 scheduled flights will go ahead on Wednesday, as airlines patched together operations with planes 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.

The head of the International Air Transport Association , Mr Giovanni Bisignani, 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 United states government did, following the September 11, 2001 terror attacks.

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

Meanwhile, Spain 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, but 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 Centre, found various levels of volcanic ash at different sites over Germany. The highest concentration of ash was over eastern Germany, but the report said its density was comparable 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.

A French weather service plane also took samples of the air 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,' he said.
Airlines lost $400m each day during the first three days of grounding, Bisignani told a news conference Wednesday in Berlin. At one stage, 29 per cent 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.