Reporting from London — Airlines sent their jets back into the skies of Europe in large numbers Wednesday but faced an enormous backlog of passengers that will probably take days to clear.
About 22,500 flights were expected to travel through European airspace, more than 80% of the usual number, the most since volcanic ash from Iceland began stranding planes and passengers across the continent April 15, the aviation agency Eurocontrol said.
But previously grounded air fleets weren't the only things flying. So were the recriminations. Critics accused authorities of having bungled their response to the airborne grit by imposing an unnecessary near-total flight ban that cost the airline industry $1.7 billion.
After several days of enforced inactivity, Europe's busiest airports, including those in London, Paris and Frankfurt, Germany, were back in business. Most long-haul services were restored; short- and medium-hop flights were being phased in more gradually. Joyful reunions lighted up arrival terminals across the continent
Restrictions on airspace remained only in a few areas, including Finland and northern Scotland, Eurocontrol said. But the Brussels-based agency said it expected air traffic to return to "almost 100%" Thursday.
London's Heathrow reopened Tuesday night, the last of the big European airports to resume operations. The relief was palpable among passengers who had been wondering whether they would ever be able leave.
"We've been here five days. We didn't have enough cash for a hotel," said Kurt Lang, 23, an Australian who has been traveling the world with his fiancee. They had camped out at Heathrow to try to catch the first flight to Bangkok, Thailand.
"It was quite fun watching the first plane come in last night around 10.30 p.m.," Lang said. "There was a lot of cheering and people saying, ‘Welcome to Heathrow.'"
But thousands of travelers face more delays as airlines work through long waiting lists.
About 100,000 flights were canceled because of ash from the Eyjafjallajokull volcano, creating such a volume of stranded passengers that some carriers have had to push re-bookings well into next week. Airlines were also left scrambling to get their planes to the right airports.
Experts say a full return to normal travel patterns is likely to take days.
The shutdown of airspace over Northern Europe for nearly a week has become the subject of angry finger-pointing, especially here in Britain, where aviation authorities abruptly lifted restrictions on all the country's airports Tuesday night after heavy lobbying from airline executives. Flights had resumed on the Continent during the day, prompting critics to question why the ban was still in place here.
The government's sudden reversal came after consultations with scientists and jet manufacturers over how much ash a plane's engines and other components could tolerate. The discussions led to a raising of the danger threshold.
Officials defended their earlier decision to err on the side of caution.
"You've got to make sure people are safe and secure. We would never be forgiven if we had let planes fly and there was a real danger to people's lives," Prime Minister Gordon Brown said. "We've had discussions with manufacturers of planes, we've had discussions with the air safety authorities, and we've had to make sure that it's safe to fly in particular zones, with a low level of ash but not a complete absence of ash."
A leading British scientist told the BBC that the new safety regulations on flying through ash were "10 times" less stringent than before, but that the government was correct to have held extensive discussions before relaxing the standards.
The head of the International Air Transport Assn., the airline industry's main trade group, told reporters in Berlin that authorities throughout Europe used flawed methods to calculate risk.
"Airspace was being closed based on theoretical models, not on facts. Test flights by our members showed that the models were wrong," Giovanni Bisignani said.
He called the widespread grounding of flights "an embarrassment for Europe," one that has cost the industry more than the panic after the Sept. 11 attacks, when the United States closed its airspace for three days.
At the peak of the European ban, 29% of global commercial flights were canceled, affecting 1.2 million passengers a day, Bisignani said.
Aviation officials warned that the situation remained changeable, because the volcano continued to erupt. But scientists said the new plumes of ash were not reaching the same altitudes as before, so their effect on air travel was likely to be much less.
Janet Stobart of The Times' London Bureau contributed to this report