On a recent consulting assignment, I learned that volcanic ash in the atmosphere can cause real problems for airplane engines, and the airlines must balance safety and efficiency in response to these events. The goal from a safety perspective is to avoid aircraft encounters with volcanic ash. From the perspective of efficiency, the  goal is to minimize re-routing of aircraft.

Because of this, the International Civil Aviation Organization (ICAO) coordinates the activities and operations of nine Volcanic Ash Advisory Centers (VAACs) in strategic areas around the world. These centers produce advisory information about volcanic ash and its presence in the atmosphere used by airlines in flight planning and air traffic control to warn in-flight aircraft.

Because normal aviation radar is ineffective in locating volcanic ash clouds, the VAACs detect eruptions and forecast how the ash is going to disperse in the atmosphere. Standard advisories include eruption location, the specific volcano producing the event, wind speed and direction and, most importantly, flight levels affected by the ash so that aircraft en route or scheduled to depart can be advised to fly well above or around the affected area.

These Airways Volcano Watch facilities operate much in the same way that airport fire services are maintained — in constant readiness but with the hope that they will rarely have to be used.

Checkout the 2008 eruption of gas from Kilauea in Kauai, Hawaii: