According to Dr. Dougal Jerram, an earth scientist at the University of Durham, UK, "Eruptions which are charged with gas start to froth and expand as they reach the surface. This results in explosive eruptions and this fine ash being sent up into the atmosphere. If it is ejected high enough, the ash can reach the high winds and be dispersed around the globe, for example, from Iceland to Europe. These high winds are exactly where the aeroplanes cruise." Volcanic ash can harm a plane mainly in four ways:
1.Sandblasting effect. Ash can "blind" pilots by sandblasting the windscreen requiring an instrument landing, damage the fuselage, and coat the plane (KLM Flight 867 and BA Flight 9). In addition, the sandblasting effect can damage the landing lights, making their beams diffuse and unable to be projected in the forward direction (BA Flight 9). Propellor aircraft are also endangered.
2. Clogging of the plane's sensors. Accumulation of ash can also block an aircraft's pitot tubes. This can lead to failure of the aircraft's air speed indicators.
3. Electromagnetic wave insulation. Volcanic ash particles are charged and disturb communication by radio.
4. Combustion power failure. The effect on jet aircraft engines is particularly severe as large amounts of air are sucked in during combustion operation, posing a great danger to aircraft flying near ash clouds.
