By the CNN Wire Staff
London, England (CNN) -- The UK is sending Royal Navy vessels to bring home travelers stranded by the ash cloud disruption, British Prime Minister Gordon Brown said Monday.
The HMS Ark Royal and HMS Ocean were making their way back to British waters, while the Defense Ministry worked to pinpoint locations that most need help.
Transport across Europe has been crippled since the eruptionbeneath southern Iceland's Eyjafjallajokull glacier worsened last week, prompting local evacuations and shutting European airspace.
With planes languishing at airports, stranded travelers have crammed onto boats and trains and rented cars to reach their destinations.
"I believe this is one of the most serious transport disruptions we have faced," Brown said. "It's got financial consequences as well as human consequences and we will do everything in our power to make sure all the arrangements are in place to help people, where possible, to get back home".
Brown said he spoke to Spanish Prime Minister Jose Luis Rodriguez Zapatero about using airports in Spain -- which have been less affected by the air travel chaos -- as a hub through which to bring people back to Britain. Further information would be released later Monday, Brown said.
A third Royal Navy vessel, HMS Albion, en route to pick up troops in Spain, may also be able to assist, Brown said.
UK travel has been badly hit by the ash cloud, with airspace largely shut since last Thursday morning and not expected to open until 0000 Greenwich Mean Time on Tuesday at the earliest.
Some airlines have begun to push for the restrictions to be lifted.
A British Airways test Sunday found no damage to the aircraft at a variety of altitudes, the airline said in a statement Monday. It did not say what type of plane it flew.
"The analysis we have done so far, alongside that from other airlines' trial flights, provides fresh evidence that the current blanket restrictions on airspace are unnecessary," said Willie Walsh, British Airways chief executive.
European transport commissioner Siim Kallas said Monday the situation was "unsustainable".
"It is now clear that we cannot just wait until this ash cloud dissipates".
But, he added, "there can be no compromise on safety" and any decision to reopen airspace "must be based on scientific evidence".
Meterologist Derrick Ryall of the MET Office in London said there was no "defined safe limit" for volcanic ash.
"No one has said what a safe limit for aircraft is, so therefore it's very difficult for these judgments to be made," he said.
European authorities were meeting Monday to plan further response to the ash cloud.
Some European airports reopened Sunday, including several in France and Germany, and all 16 that had been closed in Spain.
But officials in each country emphasized that decisions were being made around the clock and could change at any time.
A few dozen test flights Sunday offered hope that the skies over much of Europe may be safe for air travel, but officials made no promises that the massive disruptions due to volcanic ash are about to go away.
"The results coming from these flights is ... there's no impact in the area," European Union Secretary of State Diego Lopez Garrido said.
But an expert who has flown over Europe to check the air said he saw "dangerous" conditions.
Guy Gratton, head of the Facility for Airborne Atmospheric Measurements at Britain's Cranfield University, flew into the skies Thursday and saw "a really strange and complex set of layers of ash," with a layer of perfectly clear air suddenly giving way to a layer of ash, he told CNN.
If particles of ash enter a jet engine, when they come out they can solidify on turbine blades, he said.
A group of his colleagues took to the skies Sunday, and in some places saw "quite high concentrations of ash," he said.
"I suspect it's going to be a few days yet" before it's safe to fly, Gratton said.
Two key air travel groups issued a joint statement Sunday pushing authorities to ease flying restrictions. Airports Council International Europe, which represents airports, and the Association of European Airlines said they question "the proportionality of the flight restrictions currently imposed".
Olivier Jankovec, director general of ACI Europe, said airports have lost close to 136 million euros ($184 million) so far. More than 6.8 million passengers have been affected, he said in a statement, adding that the effect is worse than after the September 11, 2001, terror attacks on the United States.
"While safety remains a non-negotiable priority, it is not incompatible with our legitimate request to reconsider the present restrictions," he said.
"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 AEA said in their joint statement. "The eruption of the Icelandic volcano is not an unprecedented event and the procedures applied in other parts of the world for volcanic eruptions do not appear to require the kind of restrictions that are presently being imposed in Europe".
Airlines have been losing at least $200 million a day, according to the International Air Transport Association, the trade group representing airlines.
CNN
