European skies were a virtual no-fly zone for a fourth day on Sunday, with volcanic ash drifting from Iceland reaching as far as Russia, stranding tens of thousands of people as over 17,000 flights were cancelled.

About 30 countries have now closed or restricted their airspace, with the volcanic ash creating chaos over the vast swathe of the European continent, right from the Arctic Circle in the north to the French Mediterranean coast in the south and from Spain into Russia.

Over 40,000 flights have been cancelled since the volcano erupted with throwing ash and fine particles across the European skies on safety concerns.

The grounding of major airliners was costing the industry at least $200 million a day, according to International Air Transport Association (IATA).

The flight cancellations also affected attendance of world leaders at the funeral of late Polish President Kaczynski.

U.S. President Barack Obama was unable to fly to Krakow city for the funeral. Prince Charles and British foreign Secretary David Miliband also cancelled their journey to Poland to attend the last rites of Kaczynski, who died in a plane crash in Russia last week.

In Britain, flight restrictions were extended until at least 0100 BST (0530 IST) tomorrow and forecasters say the ash cloud could remain over the UK for many more days.

In a bid to ease the travel chaos, Netherlands and a few other countries have started test flights to see if jets could safely fly, either below or over the ash clouds.

Dutch airline KLM and German airline Lufthansa carried out test flights in their countries’ airspace to see if it is safe for planes to fly.

KLM said its aircraft had been able to fly its normal operating altitude of 13km over Dutch skies and no problems had been reported.

The plane’s engines were being inspected for possible damage, with a view to getting permission from the aviation authorities to start up operations again.

German carrier Lufthansa said it flew 10 planes from Frankfurt to Munich at lower altitudes.

“We have found nothing unusual, neither during the flight, nor during the first inspection on the ground,” KLM chief executive Peter Hartman, who took part in his airline’s test, said in a statement.

British Airways cancelled all flights in and out of London for the whole day today.

Germany and most Scandinavian and central European countries kept the flight ban in place, extending the biggest airspace shutdown since World War II.

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