Airlines lost at least 1.7 billion dollars during the volcanic ash crisis, the industry said today.

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 US did following the September 11 attacks.

He said it would take three years for the industry to recover from the week of lost flying time that stranded millions around the globe.

Eurocontrol, the air traffic control agency in Brussels, said 21,000 of the continent's 28,000 scheduled flights will go ahead today.

Experts predicted it could take days - even more than a week - to clear a backlog of passengers from over 100,000 cancelled flights.

"The crisis is petering out," said Brian Flynn, deputy head of operations. "The potential area where there could be any possible risk of some particles of ash cloud (has) dissipated throughout most of Europe."

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 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 because of the weather conditions."

"Bremen, Hamburg, Hannover, Berlin, Frankfurt and Munich are open again," said 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.

"This is a decision that was made based on meteorological data."

Airlines lost 400 million dollars each day during the first three days of grounding, Mr Bisignani said.

At one stage, 29% of global aviation and 1.2 million passengers a day were affected by the airspace closures.

"For an industry that lost 9.4 billion dollars last year and was forecast to lose a further 2.8 billion dollars in 2010, this crisis is devastating," Mr Bisignani said. "Governments should help carriers recover the cost of this disruption."

He noted that the scale of the crisis eclipsed the events of September 11, when US airspace was closed for three days.