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Volcanic ash damages machinery.
The effect on jet aircraft engines is particularly severe as large amounts of air are sucked in during operation, posing a great danger to aircraft flying near ash clouds. Eruptions which are charged with gas start to froth and expand as they reach the surface, causing explosive eruptions sending fine ash up into the atmosphere; if it reaches high altitudes—where aeroplanes cruise—the ash can be dispersed around the globe. Very fine volcanic ash particles (particularly glass-rich if from an eruption under ice) sucked into a jet engine melt at about 1,100 °C, fusing onto the blades and other parts of the turbine (which operates at about 1,400 °C). They can erode and destroy parts, and cause jams in rotating machinery. Ash can also ” blind” pilots by sandblasting the windscreen requiring an instrument landing, damage the fuselage, and coat the plane so much as to add significant weight and change balance. Propellor aircraft are also endangered.
The effect on the operation of a jet engine is often to cause it to cut out—failure of all a plane’s engines is not uncommon. The standard emergency procedure when jet engines begin to fail had been to increase power, which makes the problem worse. The best procedure is to throttle back the engines, and to lose height so as to drop below the ash cloud as quickly as possible. The inrush of cold, clean air is usually enough to cool, solidify, and shatter the glass, unclogging the engines.
There are many instances of damage to jet aircraft as a result of an ash encounter. After the Galunggung, Indonesia volcanic event in 1982, a British Airways Boeing 747 flew through an ash cloud; all four engines cut out. The plane descended from 36,000 feet (11,000 m) to 12,000 feet (3,700 m), where the engines could be restarted.
In April 2010 airspace across much of northern Europe was closed—which was unprecedented—due to the presence of volcanic ash in the upper atmosphere from the eruption of the Icelandic volcano Eyjafjallajökull.