It was on 24 June 1982 that the world learned, in dramatic fashion, precisely what kind of damage tropopausal volcanic ash can do to an aircraft.
A British Airways Boeing 747-200 flying from Kuala Lumpur, Malaysia bound for Perth, Australia was flying over Indonesia at night with 262 people on board. Suddenly the slipstream noise was magnified and St Elmo's fire surrounded the aeroplane in a ghostly glow. Then one by one the engines began to fail until all four stopped.
The crew decided to head for Jakarta, the nearest international airport, and declared an emergency. During the glide descent they continually went through the engine relight procedure until, when they had cleared the lower limit of the ash cloud, they had success. All four engines relit, but the crew closed down No 2 because it continually surged.
The other engines' performance had been seriously impaired, and the ash had sandblasted the front windscreens so badly the crew could not see through them sufficiently to land the aircraft. The pilots had to cock their heads to the side to look out of the direct vision windows which had been less badly affected.
The aircraft landed safely at Jakarta, but the engines were irreparable.
Since then a network of volcanic ash advisory centres - nine of them worldwide - have been set up to monitor occurrences and track their progress until the clouds dissipate.