The aviation industry sharply criticized European governments on Monday for their handling of airport closures, saying there was “no coordination and no leadership” in the volcanic ash crisis that shut down European airports for a fifth straight day.

Some smaller airports reopened, and European officials had hoped that flights could return to about 50 percent of normal on Monday if the skies were clearing.

But authorities in Britain, France, Germany, and the Netherlands - home to three of Europe’s largest airports - said their air space was still closed. Britain said it was keeping flight restrictions on through until at least early Tuesday, while Italy briefly lifted restrictions in the north then quickly closed again on Monday after conditions worsened.

Austrian authorities reopened the country’s airspace, though many flights there remain cancelled, and Stockholm’s Arlanda Airport was reopening for limited air traffic. Finland opened its Tampere and Turku airports but kept its main airport in Helsinki shut, and most Norwegian airspace reopened on Sunday evening.

The International Air Transport Association says the airport lockdowns are costing the aviation industry at least $200 million a day and affecting millions of travellers since the volcano in Iceland begun erupting on Wednesday.

Meeting in Paris, the group expressed its “dissatisfaction with how governments have managed it, with no risk assessment, no consultation, no coordination, and no leadership” and called for greater urgency in reopening Europe’s skies.

Several major airlines safely tested the skies with weekend flights that did not carry passengers. The announcement of successful test flights prompted some airline officials to wonder whether authorities had overreacted to concerns that the microscopic particles of volcanic ash could cause jet engines to fail.

Meetings on the crisis sprung up like mushrooms after a rain. The British government’s emergency committee, known as COBRA, met to discuss the situation. Later Monday, transport ministers from Britain, Germany, France and Spain were meeting via videoconference, and all 27 EU transport ministers will hold a meeting late afternoon, said French Transport Minister Dominique Bussereau.

“We will try to outline corridors, if we can, based on the evolution of the cloud, to allow the reopening of as large a number of flight paths as possible, as quickly as possible and in good security conditions,” he said.

EU Transport Commissioner Siim Kallas told reporters in Brussels that “it is clear that this is not sustainable. We cannot just wait until this ash cloud dissipates.”

“Now it is necessary to adopt a European approach” instead of a patchwork of national closures and openings, said Diego Lopez Garrido, state secretary for EU affairs for Spain, which holds the rotating EU presidency.

Regulators need to take into account that airlines from Holland to Austria flew successful test flights on Sunday despite official warnings about the dangers of the plume, he said.

KLM Royal Dutch Airlines said it had flown four planes on Sunday through what it described as a gap in the layer of microscopic dust over Holland and Germany. Air France, Lufthansa and Austrian Airlines also sent up test flights, although most travelled below the altitudes where the ash has been heavily concentrated.

National air safety regulators have the right to close down a country’s air space in cases of extreme danger. But they can also grant waivers to airlines to conduct test flights or to ferry empty airliners from one airport to another at lower altitudes not affected by the main ash clouds.

Mr. Kallas called the problems spawned by the eruption unprecedented and said there were no EU-wide rules for handling such a crisis.

“There is currently no consensus as to what consists an acceptable level of ash in the atmosphere,” said Daniel Hoeltgen, a spokesman for the European Aviation Safety Agency. “This is what we are concerned about and this is what we want to bring about so that we can start operating aircraft again in Europe.”

KLM said its received permission from Dutch and European aviation authorities for planes of various types to fly the 115—mile (185—km) flight from Duesseldorf in western Germany to Amsterdam’s Schiphol Airport at an unspecified normal altitude above 10,000 feet (3,000 meters). They did not encounter the thick though invisible cloud of ash, whose main band has floated from 20,000 to 32,000 feet, the height of most commercial flight paths.

“With the weather we are encountering now - clear blue skies and obviously no dense ash cloud to be seen, in our opinion there is absolutely no reason to worry about resuming flights,” said Steven Verhagen, vice-president of the Dutch Airline Pilots Association and a Boeing 737 pilot for KLM.

Meteorologists warned, however, that the situation above Europe remained unstable and constantly changing with the varying winds - and the unpredictability was compounded by Air France said its first test flight Sunday, from Charles de Gaulle airport to Toulouse in southern France, “took place under normal conditions.”

“No anomalies were reported. Visual inspections showed no anomalies,” Air France said in a statement soon after it landed. “Deeper inspections are under way.”

It did not say how high the planes had flown.

Germany’s Lufthansa flew 10 empty long-haul planes on Saturday to Frankfurt from Munich at low altitude, between 3,000 and 8,000 meters (9800 and 26000 feet), under so-called visual flight rules, in which pilots don’t have to rely on their instruments, said spokesman Wolfgang Weber.

“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,” Mr. Weber said. “Not the slightest scratch was found on any of the 10 planes.”

German air traffic control said Air Berlin and Condor airlines had carried out similar flights.

Air Berlin, Germany’s second-biggest airline, said it had transferred two planes from Munich to Duesseldorf and another from Nuremberg to Hamburg without problems on Saturday. They flew at 9,840 feet (3,000 meters).

A technical inspection of the aircraft after landing “did not reveal any adverse effects,” the company said.

Air Berlin Chief Executive Joachim Hunold declared himself “amazed” that the results of the German airlines’ flights “did not have any influence whatsoever on the decisions taken by the aviation safety authorities.”

The Swiss Federal Office of Civil Aviation began allowing flights on Saturday above Swiss air space as long as the aircraft were at least at 36,000 feet (11,000 meters). It also allowed flights at lower altitudes under visual flight rules, aimed at small, private aircraft.

Ash and grit from volcanic eruptions can sabotage a plane in various ways: the abrasive ash can sandblast a jet’s windshield, block fuel nozzles, contaminate the oil system and electronics and plug the tubes that sense airspeed. But the most immediate danger is to the engines. Melted ash can then congeal on the blades and block the normal flow of air, causing engines to lose thrust or shut down.

Scientists say that because the volcano is situated below a glacial ice cap, magma is being cooled quickly, causing explosions and plumes of grit that can be catastrophic to plane engines, depending on prevailing winds.

“Normally, a volcano spews out ash to begin with and then it changes into lava, but here it continues to spew out ash, because of the glacier,” said Reynir Bodvarsson, director of Swedish National Seismic Network. “It is very special.”

Mr. Bodvarsson said the relative weakness of the eruption in Iceland also means the ash remains relatively close to the earth, while a stronger eruption would have catapulted the ash outside of the atmosphere.

In 1989, a KLM Boeing 747 that flew through a volcanic ash cloud above Alaska temporarily lost all four motors. The motors restarted at a lower altitude and the plane eventually landed safely.

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