The International Air Transport Association says disruptions to European air travel from the volcanic ash cloud have cost the industry at least $1.7 billion.
IATA's chief executive, Giovanni Bisignani, said the scale of the disruption was worse than after the September 11, 2001 terrorist attacks in the United States.
Most of Europe's main airports were operating today after Britain late on Apri 20 reopened all of its airspace.
Airlines struggled to resume normal schedules but warned that it would be days before many passengers could be brought home.
Iceland's civil protection agency on April 21 said that the Eyjafjallajoekull volcano has lost nearly 80 percent of its intensity since its weekend peak.
Millions of travelers were stranded after European governments decided to close their airspace last week following the volcano's eruption.
Experts had warned that volcanic ash could cause planes' engines to fail.
compiled from agency reports