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The body that represents the world's airlines, IATA, has criticised Europe's governments for the way they closed air space because of volcanic ash.
The head of the airline industry body, Giovanni Bisignani, told the BBC:"This is a European embarrassment and it's a European mess".
Millions of passengers have been affected by the crisis, which is now into its fifth day.
Britain ordered three Royal Navy ships to help bring home stranded nationals.
And the French railway company SNCF has said it will offer reduced fares and 80,000 extra seats between Paris and London this week.
Mr Bisignani, of the International Air Transport Association, has said the scale of the crisis facing the airline industry is now greater than at the time of the 9/11 attacks on the US.
"The decision that Europe has made is with no risk assessment, no consultation, no co-ordination, no leadership," he said.
"Europeans are still using a system based on a theoretical model which does not work... instead of using a system and taking decisions on facts and on risk assessment."
He said airspace closures were costing airlines $200m (£130M) a day in lost revenue.
At the weekend, some European airlines staged test flights through parts of the ash trail blowing from Iceland, leading to questions about whether the current flight bans were necessary.
But Italy's civil aviation authority closed the country's northern airspace up to a height 22,000 feet until 0800 local time (0600 GMT) on Tuesday, after briefly opening it for two hours.
EU transport ministers are to hold emergency talks by video conference on the crisis.
EU Transport Commissioner Siim Kallas said: "We cannot just wait until this ash cloud dissipates."
Safety 'paramount'
The enormous shroud of fine mineral dust particles now stretches from the Arctic Circle in the north to the French Mediterranean coast in the south, and from Spain into Russia.
It comes from southern Iceland's Eyjafjallajoekull volcano, which began erupting for the second time in a month on Wednesday. Airspace remains closed, or partially closed, in more than 20 countries.
Tens of thousands of flights have been cancelled since the clampdown began, and the prospect of a return to normal air travel remains far from clear.
The flight bans came amid fears that the ash - a mixture of glass, sand and rock particles - can seriously damage aircraft engines.
Britain has extended a ban on most flights in its airspace until at least 1900 local time on Monday (1800 GMT).
British Prime Minister Gordon Brown announced the move to deploy the Royal Navy ships.
He defended the continuing flight ban, saying: "I think the first thing we have got to say is the safety of air passengers is of paramount importance."
Hundreds of thousands of Kenyans working in agriculture, the country's largest export sector, face economic uncertainty because of the flight bans.
Refrigerated stores at Nairobi airport and on farms are now completely full, and a huge amount of fresh flowers and vegetables destined for the European market is in danger of perishing, the BBC's East Africa correspondent, Will Ross, reports.
The problems have also led to the postponement of next Saturday's Japanese MotoGP.
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