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Pain in the Ash: A Guide to Europe's Air Turmoil

A massive plume of ash pouring out of an Iceland volcano has snarled European air traffic, closing airports and causing flight cancellations unseen since the aftermath of 9/11.

But what exactly is this phenomenon and why has it left tens of thousands of travelers stranded across the region?

"[Volcanic ash is] essentially very, very fine particles of glass, like a glass powder. It's not good for aircraft," Watson, Matthew, a natural hazard expert, told CBS Radio News.

Iceland Volcano Eruption

The plume is traveling between 20,000 feet and 36,000 feet - the normal altitude range for commercial jetliners. Aircraft flying through the ash cloud face the danger of engine failure, among other potential mishaps.

"Jet engines compress air to create thrust and volcanic ash would basically clog the engine," Brent Bown, professor of aviation technology at Purdue University, told CBS Radio News.

During the early 1980s, two Boeing 747s were severely damaged by the ash clouds spewing from Galunggung Volcano on Indonesia's Java island. One of these, a British Airways flight, lost power on all four engines. While the pilots managed to restart the engines at a lower altitude, the resulting glide still ranks as one of the longest ever performed by an aircraft not specifically designed as a glider.

Another 747 encountered similar problems while flying through the ash clouds over Mt. Redbout, near Anchorage in Alaska. And at least 10 Jumbo jets and 10 DC-10s suffered multiple engine failures in 1991 from ash from Mt. Pinatubo in the Philippines.

The very fine particles also present a hazard to the aircraft's airframe and powerplants. They easily scratch and erode paint, aluminum and glass. This damages the wings' leading edges, and has a sandblasting effect on cockpit windscreens and landing lights. Inside the engines, the particles stick to the engine's hot parts, forming a glasslike coating, and grind up turbines, bearings, and other moving parts, restricting air flow through the turbine. This may lead to the immediate loss of thrust and eventually engine failure.

The ash can block the pitot tubes and other sensors that supply vital information on speed and outside air pressure. It also can clog air filters, such as the ones through which air flows to the passenger cabin.

So why can't pilots simply fly around the plume?

One of the main dangers posed by ash is that it is not visible at night or in cloud, and that an aircraft's weather radar cannot pick it up. Radar works on the principle of detecting water droplets in clouds, but since the ash clouds are dry, they do not reflect radar signals.

Ash particles conduct electrical charges. Often, the first indication that the pilots have of volcanic ash is the appearance of St. Elmo's Fire - a harmless electrical phenomenon that creates a ball of light around the wingtips - created when the charged particles strike the aircraft.

This is the first time that a volcanic plume has covered an area of dense air traffic. About 20,000 flights take place in Europe each day, and the ash caused about 20 percent of these to be canceled. Usually, the eruptions occur in regions where there is limited airliner traffic, such as the "Ring of Fire" that extends across the Pacific rim from Indonesia to Chile.

The air traffic standstill will continue, depending on how long the volcanic eruptions continue to shoot ash into the atmosphere, and on the prevailing winds in coming days. The plume appears to be following the jet stream which normally curves across the British Isles and Scandinavia.

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