Iceland's volcano began erupting Wednesday, sending ash several kilometres in the air [AFP]
European airlines and airports have called for the reassessment of restrictions imposed on air travel due a cloud of volcanic ash hanging over the continent.
Millions of passengers have been stranded by the closure of air space over northern Europe, but after a number of test flights in the ash cloud, airlines and airport officials on Sunday questioned if the measures had been an overreaction.
"While Europe's airlines and airports consider safety to be an absolute priority, they are questioning the proportionality of the flight restrictions currently imposed," ACI Europe and the Association of European Airlines (AEA) said in a statement. YOUR MEDIA Send us your stories, pictures or video here:
http://yourmedia.aljazeera.net/ "Airlines must be able to fly where it is safe to fly and make decisions accordingly. It is what our passengers demand of us." The European Union has said that it hopes up to 50 per cent of European airspace could be open to flights on Monday.
"Forecasts are that half of the flights planned [in Europe] could take place tomorrow," Diego Lopez Garrido, the Spanish secretary of state for European affairs, said.
Authorities are under pressure to allow flights to resume with the shutdown on flights costing the aviation industry an estimated $200 million a day, according to the International Air Transport Association.
Siim Kallas, the EU transport commissioner, told reporters in Brussels on Sunday that "it is clear that this is not sustainable". "We cannot just wait until this ash cloud dissipates."
Test flights
Three major European airlines said they had carried out test flights through the ash cloud without any damage to aircraft. iN depth Flight cancellation updates Video: Flying over erupting crater Volcano travel chaos spreads How ash can damage aircraft
"Verification flights undertaken by several of our airlines have revealed no irregularities at all; this confirms our requirement that other options should be deployed to determine genuine risk," Ulrich Schulte-Strathaus, the head of the Association of European Airlines, said. Dutch carrier KLM said it had returned seven airplanes to Amsterdam from Duesseldorf without passengers and would now allow three freight flights to take off for Asia. "We observed no irregularities either during the flight or during the initial inspection on the ground," Peter Hartman, the airline's chief executive who was aboard Saturday's flight, said. "We hope to receive permission as soon as possible after that to start up our operation and to transport our passengers to their destinations." Also on Saturday, Germany's Lufthansa airlines flew 10 empty long-haul planes to Frankfurt from Munich at low altitude levels between 3,000 and 8,000 metres, Wolfgang Weber, a spokesman, said. "We simply checked every single aircraft very carefully after the landing in Frankfurt to see whether there was any damage that could have been caused by volcanic ash," he said. "Not the slightest scratch was found on any of the 10 planes." Air France it had also carried out a successful test flight over France, travelling from Charles de Gaulle airport in Paris to Toulouse in southern France.
'Global experiment'
David Learmount, the operations and safety editor of Flight International magazine and a former Royal Air Force pilot, said putting planes back into the air was a "global experiment".
"What we don't know is about what Europe is suffering at the moment, which is low intensity, widely spread ash. What KLM has found out is that the damage may be relatively insignificant," he told Al Jazeera. IN VIDEO
Residents on volcano's slopes struggle to save their livelihoods "But if the efficiency of the engines is downgraded by abrasion of the fan blades, that can downgrade the efficiency of the engine, which will mean that for the rest of that engine's life it will be using more fuel than it otherwise would have done. "So to get airborne a couple of days earlier, you might pay the price of it for the rest of that aircraft's life." Eurocontrol, the regional grouping of air traffic controllers, has said the skies will not reopen again until there is absolutely no risk from the ash cloud. But Brian Flynn, the deputy head of operations, said he understands the frustration being felt by airlines. "As soon as we are able to, with confidence, and when I say we, I mean the entire community of aviation experts [and] aviation authorities, are able to declare parts of the air space and airports open that will be done." Aviation officials had warned that airplane engines could become clogged with the tiny particles of rock and glass spewed out by the Eyjafjallajokull volcano in Iceland - though almost invisible to the naked eye - if pilots attempt to fly through the dust.
Francois Fillon, France's prime minister, said that restrictions would remain over the north of the country into Monday.
"The weather conditions indicate that the situation will still be difficult for several days," he said.
Ash cloud window
However, air traffic officials said a gap in the ash cloud would allow selected flights to go ahead after Barcelona, Nice, Marseille and Bordeaux airports were reopened until at least 1300 GMT on Monday.
"We are going to profit from this situation to re-route a maximum number of flights via these airports, which will allow us to bring home the greatest possible number of our fellow citizens stuck abroad," Fillon said. Authorities in Germany also reopened a number of airports for several hours, for flights heading in an easterly or northerly direction. The Eyjafjallajokull volcano began erupting on Wednesday, sending ash several kilometres into the air, and generating a plume of particles. Powerful tremors from the volcano continued to jolt parts of southern Iceland on Sunday, blanketing surrounding farmland with ash and forcing farmers and their livestock to find refugee indoors. Iceland's Meteorological Office said the tremors had grown more intense and had increased from a day ago. But it added that the steam and ash rising from the volcano had eased to 4-5 km from as high as 11 km when the volcano began erupting last week.
Some of Europe's airlines and airports have called into question whether the mass restrictions imposed on the continent's airspace, due to volcanic ash in the area, are necessary. 

Millions of travellers have been stranded by the cancellations; however, some airlines have made test flights to see if there were any immediate effects on jets after flying through ash. Authorities fear that the ash can cause vital aircraft parts, such as the engines, to fail in-flight.

Three large airlines — KLM, Air France, and Lufthansa — have already made test flights.  Ulrich Schulte-Strathaus, the head of the Association of European Airlines (AEA), commented: "Verification flights undertaken by several of our airlines have revealed no irregularities at all; this confirms our requirement that other options should be deployed to determine genuine risk."

KLM, meanwhile, said that it will allow three freight planes to make flights to Asia, and had transferred seven passenger planes from Duesseldorf, Germany to Amsterdam, without any travellers.

"We observed no irregularities either during the flight or during the initial inspection on the ground. We hope to receive permission as soon as possible after that to start up our operation and to transport our passengers to their destinations." said KLM chief executive Peter Hartman.

ACI Europe and the AEA also commented about the issue in a statement: "While Europe's airlines and airports consider safety to be an absolute priority, they are questioning the proportionality of the flight restrictions currently imposed." "Airlines must be able to fly where it is safe to fly and make decisions accordingly. It is what our passengers demand of us."

Airport closures and cancellations are estimated to be costing airlines about US$200 million daily, the International Air Transport Association reports.

The operations control head for Eurocontrol, Brian Flynn, rebuffed notions that aviation officials were being too cautious, describing the issue as an "unknown phenomenon". "With the over-riding objective of protecting the travelling public, these exceptional measures have to be taken," he remarked. "... As soon as we are able to, with confidence, and when I say we, I mean the entire community of aviation experts and aviation authorities, are able to declare parts of the air space and airports open that will be done."