The airspace above the Aleutian Islands is one of the heaviest traveled in the world, with more than 50,000 large aircraft per year and 10,000 passengers per day traveling between Asia and North America and Europe. (Source: AVO)

    On December 15, 1989, KLM Flight 867 from Amsterdam was descending into Anchorage International Airport when it flew though a thick cloud of ash from Mt. Redoubt. All four engines stalled and the standby electrical system failed. After descending more than 14,000 feet, the crew was finally able to restart the engines and safely land the plane. In this case the ash caused more than $80 million in damage to the plane, but fortunately no lives were lost. (Source: USGS)