A hero airline captain, his courageous crew and their fearful passengers know just what it is like to fly into a cloud of volcanic ash.
Captain Eric Moody was commanding a London to Auckland 263-passenger British Airways Boeing 747 in June 1982 when it encountered an ash plume from the erupting Mount Galunggung in Java, Indonesia.
At first Captain Moody, co-pilot Roger Greaves and senior engineer officer Barry Townley-Freeman were unaware of exactly what had happened.
A strange St Elmo's Fire-like light had appeared on the cockpit windscreen and sulphur-smelling smoke started filling the passenger cabin.
Then, within minutes, all four engines had failed.
The plane managed to glide sufficiently out of the ash plume for three of the four engines to restart.
Despite very limited windscreen vision and facing a host of other landing problems, the crew managed to get the plane safely down at Jakarta airport.
It was later discovered that as the ash cloud was dry it did not show up on the weather radar designed to detect the moisture in clouds.
The cloud sandblasted the windscreen and clogged the engines, which restarted when enough of the molten ash broke off after solidifying.
The crew received various awards for their heroic efforts.
The incident showed, and still shows, the perils to passenger planes of volcanic ash.
Not only can volcanic ash reduce visibility for pilots, but it can cause jet engines to fail.
Sometimes aircraft many miles from the scene of an eruption can be in danger, with giant plumes of ash rising high into the sky and then travelling vast distances.
When Mount St Helens erupted in Washington state in America in 1980 the plume reached as high as 90,000ft in just 30 minutes.
In 15 hours, it had travelled 600 miles downwind and within two weeks ash had circled the earth.
One of the biggest difficulties facing flight crews is the problem of distinguishing ash clouds from ordinary clouds, both visually and on radar.
One of the lessons learnt from the 1982 BA incident was the need for pilots to be instructed to look for signs, including the odour of sulphur in the cabin and electrical friction on the edges of the aircraft.
In December 1989 a KLM Boeing 747 flight from Amsterdam to Anchorage in Alaska lost power in all four engines after entering a cloud of ash from the erupting Mount Redoubt volcano in Alaska.
The plane dropped more than two miles before the crew were able to restart the engines. The aircraft landed safely in Anchorage but needed millions of pounds of repairs, including the replacement of all four engines.
More than 20 aircraft were damaged by the ash cloud from the June 1991 eruption of Mount Pinatubo in the Philippines. The cloud travelled more than 5,000 miles to the east coast of Africa.
There have been various international conferences on the problem of volcanic ash and its effect on aviation safety.
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