This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
June 24, 1982 a Boing 747 flying from Singapore to Perth encountered a strange phenomenon in an altitude of 11.300m - a cloud of light surrounded the airplane, then suddenly all four engines lost power without apparent reason. The pilots managed to descend slowly by gliding and were preparing for the worst - an emergency landing on the sea - when the engines restarted and the aircraft regained height. The plane barely made it back to the airport of Jakarta.
Only later the cause of this bizarre incident was discovered: the increased volcanic activity of Mount Galunggung the same night sent volcanic ash more than 16 km into the sky. The volcanic ash sucked by the compressor into the engines of the plane melted in the combustion chamber, but re-solidified on the turbine blades, clogging the jet engine. When the plane descended it left behind the almost invisible ash cloud and fortunately the solidified ash flaked off from the blades - the engines restarted to work properly.
The strange light noted by pilots and passengers around the plane was also due the volcanic ash, as the friction with the hull of the plane electrified the ash grains, forming the haunting appearance of a St. Elmo's fire around the aircraft.
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The international aviation community was greatly alarmed by this previously unrecognized hazard for airplanes, as another airplane experienced also similar problems when crossing the ash plume of Mount Galunggung.
Estimated six eruption columns per year rise high enough to endanger air traffic and since the year 1982 80 modern jets were damaged by volcanic ash, 10 experienced the loss of engine power. Knowing of the possible disastrous effects of volcanic ash on modern jet engines in 2010 the airspace above Europe was closed in response to the ash plume coming from the Icelandic volcano Eyjafjallajökull - a decision harshly criticized afterwards , but as a paper published in 2011 argues, necessary.
Bibliography:
LOCKWOOD, J.P. & HAZLETT, R.W. (2010): Volcanoes - Global Perspectives. Wiley-Blackwell, Oxford: 539
SCHMINCKE, H.-U. (2004): Volcanism. Springe, Berlin-Heidelberg: 324