Some European flights resume
Many European flights took to the skies Tuesday for the first time in days but the travel chaos was far from over.
London's airports - among the busiest in Europe and a major worldwide hub - are likely to stay closed until today, Wednesday, and forecasters said more delays were possible if the dense ash cloud remains over much of the country.
Airspace in Germany also remained officially closed until 8 p.m. (1800 GMT) Tuesday but a limited number of flights were allowed in at low altitude.
But it was the first day since last Wednesday's eruption of Iceland's Eyjafjallajokull volcano - dormant for nearly 200 years - that travellers were given a glimmer of hope.
Cheers and applause erupted as flights took off from Paris' Charles de Gaulle Airport, Amsterdam and elsewhere.
The Eurocontrol air traffic agency in Brussels said it expected a little over half - 53 per cent - of the 27,500 flights over Europe to go ahead Tuesday, a marked improvement over the last few days.
The agency predicted close to normal takeoffs by Friday.
"The situation today is much improved," said Brian Flynn, deputy head of operations at the Brussels-based agency.
But with more than 95,000 flights cancelled in the last week alone, airlines faced the enormous task of working through the backlog to get passengers where they want to go - a challenge that could take days or even weeks.
Passengers with current tickets were being given priority - stranded passengers were being told to either pay for a new ticket, take the first available flight or to use their old ticket and wait for days, or weeks, for the first available seat.
Although seismic activity at the volcano had increased, the ash plume appeared to be shrinking.
Still, scientists were worried that the eruption could trigger an even larger eruption at the nearby Katla volcano, which sits on the massive Myrdalsjokull ice-cap and has erupted every 80 or so years. Its last major eruption was in 1918.
Magnus Tumi Gudmundsson, geophysicist at the University of Iceland, said there was circumstantial evidence that an eruption could occur within the next 18 months at the nearby Katla volcano.
"We can of course expect similar (travel) disruption with the Katla eruption," he said. "But it all depends on prevailing winds."
Of the eight eruptions in the last 40 years, only the recent eruption at Eyjafjallajokull was followed by winds blowing southeast toward northern Europe.
An international pilots group warned of continued danger because of the ash, which drifted over the North Sea and was being pushed back over Britain on Tuesday by shifty north winds.
The volcano is also grumbling - tremors, which geologists believe to be caused by magma rising through the crust, can be heard and felt as far as 25 kilometres from the crater. "It's like a shaking in the belly. People in the area are disturbed by this," said Kristin Vogfjord, geologist at the Icelandic Met Office.
A Eurocontrol volcanic ash map on Tuesday listed the airspace between Iceland and Britain and Ireland as a no-fly zone, along with much of the Baltic Sea and surrounding area. The ash cloud also spread westward from Iceland, toward Greenland and Canada's eastern coastline.
Still, planes were being allowed to fly above 20,000 feet (7,000 kilometres) in the United Kingdom.
Flights resumed in Scotland, but only for a handful of domestic flights. Switzerland also reopened its airspace. Some flights took off from Asia to southern Europe and planes ferried people to Europe from Cairo, where at least 17,000 people were stranded.
Airports in central Europe and Scandinavia have reopened, and most of southern Europe remained clear, with Spain volunteering to be an emergency hub for overseas travellers trying to get home.
Spain piled on extra buses, trains and ferries to handle an expected rush of passengers.
Many Asian airports and airlines remained cautious, and most flights to and from Europe remained cancelled.
The aviation industry - facing losses of more than US$1 billion - has sharply criticised European governments' handling of the disruption that grounded thousands of flights on the continent.
But Gideon Ewers, spokesman for a London-based pilots group, says historical evidence of the effects of volcanic ash demonstrates that it presents a very real threat to flight safety.
Ash and grit from volcanic eruptions can sabotage a plane, stalling engines, blocking fuel nozzles and plugging the tubes that sense airspeed.