Northern Europe was set to bear the brunt of air traffic disruption from Icelandic volcanic ash on Wednesday, but experts said the eruption was rapidly dying down.
The ash from the Grimsvotn volcano has caused far fewer problems than in 2010, when more than 10 million people were hit by a six-day European airspace shutdown after another Icelandic volcano erupted. Airlines put their revenue loss then at $1.7 billion.
The latest episode forced 500 flight cancellations on Tuesday, with Scotland especially hard hit. It also exposed disarray among the people who decide on aviation safety as they try to apply new rules to avoid another mass airspace shutdown.
Budget airline Ryanair was again vocal in its criticism and airline association IATA said that more coordination was needed.
In Iceland, volcano experts had good news for airlines as they said that the eruption was petering out.
President Olafur Grimsson told the BBC, "The volcano seems to be calming down. The eruption is gradually being diminished and the ash cloud is definitely smaller than it has been."
For Wednesday, Eurocontrol, the Brussels-based agency responsible for some of the world's busiest air corridors, said the ash cloud may affect parts of Denmark, southern Norway and southwest Sweden, with some impact on flights.
German air safety authorities said that they would have to halt landings and take-offs at Bremen airport from 0300 GMT, followed by Hamburg an hour later and possibly Berlin from about 1000 GMT. Hannover might also be affected.
Traffic in Scotland and northern England was the main ash victim on Monday, but Britain said that it thought this would ease. UK air traffic control body Nats said no ash was expected over Britain from 1am (0000 GMT) on Wednesday.
Among travellers affected were US President Barack Obama, who left Ireland for Britain late on Monday ahead of schedule.
The Barcelona soccer team flew to London early for Saturday's Champions League final against Manchester United.
New rules still imperfect
Eurocontrol said that the approximately 500 flights cancelled on Tuesday were out of around 29,000 expected that day across the continent.
New procedures put the onus on airlines to make judgments on whether it is safe to fly through ash, in coordination with the forecasting authorities and civil aviation bodies.
Showing the problems, sources told Reuters that a British research plane designed to sample ash remained grounded for a second day in a wrangle over its deployment.
The rules are also not accepted by all, with Germany backing a tougher stance for the sake of safety, aviation sources said.
"The potential for a patchwork of inconsistent state decisions on airspace management still exists," IATA director general Giovanni Bisignani said in a statement.
Ryanair said that it had safely sent two planes into what authorities had deemed high ash zones over Scotland.
"You have to ask why a combination of bureaucratic incompetence in the CAA (Civil Aviation Authority) and the Met Office
last night shut the skies over Scotland ...," Ryanair chief Michael O'Leary told BBC television.
Grimsvotn erupted on Saturday and smoke belched as high as 20 km (12 miles) into the sky. The eruption is its most powerful since 1873 and stronger than the volcano that caused trouble in 2010.