But delays on trans-Atlantic flights were expected because another band in mid-ocean was still blocking the air routes between Europe and North America, the European air traffic agency Eurocontrol said.
"While most of these flights are operating, many are having to make significant re-routings to avoid the area of ash cloud coverage, resulting in delays," according to a statement from the agency.
Air traffic charts showed that airliners on both the westward and eastward tracks across the Atlantic were being diverted far to the north, over Greenland, to avoid the danger zone around the Icelandic volcano whose eruptions forced a five-day suspension of air traffic in Europe last month.
The resulting travel chaos saw the cancellation of more than 100,000 flights - stranding passengers around the world and causing airlines direct losses of more than euro1 billion ($1.3 billion).
The Association of European Airlines said the losses caused by this weekend's disruptions, which affected less than 2 percent of scheduled flights, were likely to be negligible.
"In terms of airspace closures, there were bits and pieces here and there, but these were relatively short term," said David Henderson, a spokesman for the group.
"Trans-Atlantic traffic has also not been severely disrupted, but there has been lengthy re-routings which affected fuel burn, and also led to knock-on disruptions and delays," he said. "Those are the kind of losses that it will be much harder to put figures to."
Air France KLM reported a 15.9 percent slump in traffic in April because of airport closures brought about by the ash. The disruptions cost Air France KLM euro35 million ($46 million) per day in operating income for all suspended operations, the company said Monday.
Air France KLM said the affect on cargo traffic was minimal, with a drop of just 2 percent in April, since most goods were stocked until flights resumed.
Eurocontrol said all airports in Europe were operating normally Monday, including those in Spain. Up to 20 Spanish airports, including international hub Barcelona, had closed over the weekend. Lisbon airport also reopened after being forced to close Sunday.
But Eurocontrol warned that a finger of oceanic ash was still threatening parts of the Iberian peninsula.
"During the afternoon, areas of higher ash concentration are predicted to move in a northeasterly direction from Portuguese airspace towards the center of Spain with the potential of airport closures during the afternoon and evening," spokeswoman Kyla Evans said.
Eurocontrol says it expects approximately 28,500 flights to take place within Europe - slightly below the average for this time of year.
