Britain sent Royal Navy warships on Monday to rescue those stranded across the Channel by the volcanic ash cloud, and the aviation industry blasted European transport officials, claiming there was “no coordination and no leadership” in the crisis that shut down most European airports for a fifth day.

Eurocontrol, the air traffic agency in Brussels, said less than one-third of flights in Europe were taking off on Monday - between 8,000 and 9,000 of the continent’s 28,000 scheduled flights.

Some smaller airports reopened on Monday but authorities in Britain, France, Germany, and the Netherlands - home to four of Europe’s five largest airports - said their air space was still closed. Britain said it was keeping flight restrictions on through early Tuesday while Italy briefly lifted restrictions in the north then quickly closed down again after conditions worsened Monday.

Meanwhile, scientists in Iceland offered some hope that conditions at the erupting volcano were easing. The new ash plume is lower, which would pose less of a threat to commercial aircraft in the future.

Geologists saw a red glow at the bottom of the volcano, suggesting the eruption is turning to lava flow and that there is less ice in the crater - which would reduce the plume.

“We hadn’t seen that before,” said Kristin Vogfjord, a geologist at the Icelandic weather office.

In Britain, leaders made contingency plans to bring people home. Prime Minister Gordon Brown said the aircraft carrier HMS Ark Royal and assault ship HMS Ocean would be sent across the English Channel. A third ship is being spent to Spain to pick up soldiers trying to get back to Britain after a tour of duty in Afghanistan.

“I expect Ocean to be in the Channel today. I expect the Ark Royal to moving towards the Channel later,” Mr. Brown said after a meeting of the government’s emergency committee, known as COBRA.

He said Britain was speaking with Spanish authorities to see whether Britons stranded overseas could be flown there and then taken home by boat or bus.

Mr. Brown said the ash cloud had created “the biggest challenge to our aviation transport network for many years.”

The International Air Transport Association says the airport lockdowns are costing the aviation industry at least $200 million a day. Millions of travellers have been stuck since the volcano under Iceland’s Eyjafjallajokull glacier begun erupting on Wednesday for the second time in a month.

In Paris, the IATA 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.

Transport ministers from Britain, Germany, France and Spain were meeting on Monday via videoconference and later joined by all 27 EU transport ministers, 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,” Mr. Bussereau said.

Eurocontrol said on Monday that southern Europe, including Portugal, Spain, parts of Italy and France, the Balkans, Bulgaria, Greece and Turkey, and parts of northern Europe were currently open for flights.

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.

Tensions boiled over at Incheon International Airport in South Korea, where 30 frustrated passengers blocked a Korean Air ticketing counter and demanded officials arrange travel to anywhere in Europe after hearing about the test flights.

They held up a makeshift sign saying, “We want to come back home,” each word written on a separate piece of paper and held by an individual traveller.

“We need a flight, we need a time,” Thierry Loison, who has been stuck at the airport since Friday on the way back to France, told Korean Air officials. “We were like animals this morning.”

Passengers complained about having to sleep on the airport floor due to a lack of hotel rooms and said they were only receiving a voucher for one meal a day at McDonald’s. Some were running out of money.

“We are on the floor,” Andrew Turner, a graduate student en route to London after a holiday in Sydney, told Korean Air officials, referring to sleeping accommodations. “We have one meal a day ... at the moment a lot of people are not eating.”

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.

“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.”

Meteorologists warned, however, that the situation above Europe remained unstable and constantly changing with the varying winds - and the unpredictability was compounded by the continuing eruptions.

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.”

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