Nine Volcanic Ash Advisory Centres around the world are responsible
for advising international aviation of the location and movement
of clouds of volcanic ash.
The VAACs are part of an international system set up by the International
Civil Aviation Organization (ICAO) called the International Airways
Volcano Watch (IAVW).
The IAVW was set up in the early 1980s in
response to a number of serious incidents in which
jet transport aircraft had encountered volcanic ash
in flight and lost power on one or more engines. In
June 1982, for example, a British Airways Boeing 747
lost all four engines and suffered severe damage on
encountering volcanic ash over Indonesia. The aircraft
descended to 12,000 feet before being able to restart
some engines and make an emergency landing in Jakarta.
The IAVW comprises observations of volcanic ash from volcano
observatories and other organisations, satellites and aircraft
in flight, the issue of warnings in the form of NOTAM and SIGMET
messages and, since the mid 1990s, the issue of volcanic ash advisory
messages from the VAACs identifying areas of volcanic ash and
their predicted movement.