Given the seriousness of the volcanic ash hazard, the International Airways Volcano Watch was born under the impulse and aegis of ICAO (International Civil Aviation Organization) with the co-operation of numerous states and several international organizations among which WMO (World Metorological Organization). In the current status of airborne equipment, the airborne weather radars do not detect but very rarely volcanic ash clouds. The location of these particular clouds must therefore be imperatively communicated to the pilots in-flight by using special safety messages regularly updated. These alert messages (volcanic ash SIGMET) are issued by a meteorological watch office (MWO) for its area of responsability (Flight Information Region).