Analysis: why ash is a threat to planes

A huge cloud of volcanic ash from a violent volcano eruption in Iceland forced the closure of vast swaths of international airspace over northern Europe on Thursday, leaving hundreds of thousands of passengers stranded.

Ash spewed by an eruption under the Eyjafjallajokull glacier, Iceland's second major eruption in less than a month, blew eastwards across the Atlantic, closing major airports more than 1,000 miles (1,700 kilometers) away. Britain, Denmark, Norway and Sweden all shut down their airspace, and there were major disruptions in Belgium, France, Finland, Germany, the Netherlands and Spain.

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“Volcanic ash poses a very real threat to airplane engines,” journalist and former geologist Ted Neil told FRANCE 24. “Any plane flying from Europe towards the United States right now risks running into the cloud, it’s just not a chance worth taking”.

Neil, who is the editor of Geo Scientist, a magazine published by the UK-based Geological Society of London, described the threat posed by volcanic ash as “one of the most unpredictable and potentially lethal” to affect flying airplanes.

He said: “Volcanic ash clouds tend to settle in the atmosphere at an altitude of eleven thousand metres, which is an airplane’s normal cruising height. The reason they are so dangerous is because the dust is so thin that it is basically invisible – the only way to clearly identify this type of cloud is from a satellite in space”. As a result, pilots can fly into such clouds unknowingly, allowing the tiny invisible particles of volcanic glass and dust to get sucked into the plane’s engine, where they melt, coagulate together and eventually clog the engine.

‘A sudden and inexplicable four-engine failure’

Neil says ash clouds present pilots with one of the most confusing and frightening scenarios. “All of the engines shut down one by one for no understandable reason. The lights are still on and everything else seems normal: fuel levels are OK, because fuel is still going into the engine - it’s just not being ignited. So the plane will suddenly and inexplicably find itself with four-engine failure, effectively becoming an engineless glider,” he said.

This occurrence is very rare and was unheard of before 1982, when a British Airways flight from Kuala Lumpur narrowly avoided disaster after flying into an ash cloud over the Pacific. The incident prompted the aviation industry to rethink the way it prepared for ash clouds, resulting in the international contingency plans activated on Thursday. When a cloud is identified by a satellite, air space is closed as a precautionary measure.

According to Neil, it is difficult to predict where and how long air space will be affected by the ash cloud. “It depends on how violent the volcanic eruption is and how long it keeps spewing ash into the atmosphere, and also on how winds steer the clouds,” he said.

As a result, the thousands of passengers stranded across airports in Europe could see their travel plans disrupted for anything between 24 hours and several weeks.