Recriminations flew after Europe's aerial lockdown ended as a budget airline was forced into a U-turn on compensation for passengers Thursday and the industry demanded governments share the bill.
Iceland's Eyjafjjoell volcano, which paralysed the skies above Europe for nearly a week, continued erupting, prompting several small airports in Sweden and Norway to close to passengers.
But all the continent's major air hubs were up and running again at close to full capacity with airlines struggling to clear a huge backlog of passengers.
According to Eurocontrol, the body coordinating air traffic control across the continent, 28,500 flights should take to the skies on Thursday, saying it was the average for a normal day.
Hundreds of thousands of travellers were left stranded across the globe by the shutdown which began last Thursday, having to shell out for hotels, food and alternative travel arrangements.
The chief executive of Ireland's low-cost carrier Ryanair, Michael O'Leary, initially said he would only refund the cost of tickets bought by stranded customers but the airline later agreed to pay for food and accommodation expenses incurred by travellers after an outcry.
"Ryanair confirmed this morning that it will comply with EU261 regulations under which EU airlines are required to reimburse the reasonable receipted expenses (as set out in EU261) of disrupted passengers," the airline said.
It emphasised that the EU regulation did not entitle passengers to compensation for their ordeal, sparked by a cloud of ash from the volcano which grounded flights across Europe for almost a week.
In the statement, O'Leary said that Ryanair would continue its efforts to change "absurd" EU legislation so reimbursements were "limited to the ticket price paid in the same way they are for train, coach and ferry operators".
On Wednesday, O'Leary said the EU legislation was not designed to cover a week of expenses for passengers who had paid just 20 or 30 euros for their flights, saying: "We will not be meeting those bills" for food or hotels.
Norman Baker, transport spokesman for Britain's opposition Liberal Democrats, then accused O'Leary was rubbing "salt into the wounds for those who have been stranded overseas" while the EU Commission warned that airlines must scrupulously honour passengers' rights.
Airlines, many already in difficulties during the downturn, want governments to pick up part of the bill after haemmorhaging money during the crisis.
The International Air Transport Association (IATA) put the overall cost to the airline industry at 1.7 billion dollars (1.3 billion euros)
"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," said IATA chief Giovanni Bisignani in Berlin.
"Airspace was being closed based on theoretical models, not on facts."
But as the recriminations flew, one vulcanologist advising the United Nations said the authorities had had no choice but to close their airspace because of the lack of hard facts about aircraft behaviour in volcanic ash.
"There is at the moment no reliable data on the exact concentration of ash in the atmosphere and when an aircraft can fly, or not, through such plumes," said Henry Gaudru, president of the European Vulcanological Society.
Because of this lack of knowledge, closure to air traffic "was the only measure that could be taken," he argued.
Iceland's civil protection authority said that Eyjafjjoell volcano was still erupting on Thursday morning, but was largely stable from the day before.
"The plume remains low and the tremors haven't increased," said a spokeswoman.
Normal timetables were resuming at most airports.
Activity at the main airport in Paris was "back to normal" but London Heathrow said it would "take some time" before the complete resumption of normal services.
It was also business as usual at German airports, with only a handful of cancellations were reported at Frankfurt airport, the country's largest.
Lufthansa, Europe's biggest airline by passenger numbers, said it would operate at its full daily capacity of 1,800 flights.