In a May,2009 report The U.S. Geological Survey(USGS) warned it was “ helping to lead a major international effort to warn the aviation community about the hazards of volcanic ash clouds. Aircraft that encounter volcanic ash clouds have lost engine power. If aircraft have to lower their flying altitudes to stay beneath an ash cloud, airport approaches are affected, and some airports can be forced to shut down.” It reported:
In 1989, a wide-body passenger jet destined for Anchorage airport flew into the volcanic ash cloud generated by Mount Redoubt, Alaska and lost thrust in all 4 engines. The plane entered the ash cloud at 25,000 feet, accelerated, and then rapidly descended to 13,000 feet. The pilot was finally able to restart its engines. The Alaska Range in the area where the plane lost power has peaks from 7,000 to 11,000 feet, so this was an extremely close call. In 1992, the effects of volcanic eruptions on aviation were felt well beyond Alaska when a volcanic ash cloud from the Mount Spurr (Alaska) eruption drifted across the continental U.S. and Canada, shutting down airports in the Midwest and Northeast two days after the eruption. The Spurr cloud affected citizens who are normally not concerned about volcanoes.Volcanoes are active throughout the rim of the Pacific Ocean, as well as in other locations. Many of these volcanoes are in current flight paths.