A perilous passage through volcanic ash.

A perilous passage through volcanic ash 

Despite a new warning system designed to prevent such encounters, several planes last week made potentially disastrous trips through ash from an erupting Alaskan volcano. The incidents leave many wondering what went wrong.

In the most serious event, a Boeing 747 operated by KLM Royal Dutch Airlines lost power in all four engines on Dec. 15 when it flew through an ash cloud at 37,000 feet about 75 miles northwest of Anchorage. The plane plunged more than 13,000 feet before pilots restarted its engines, says Ivy Moore of the Federal Aviation Administration (FAA) in Anchorage.

The incident occurred the day after FAA issued its first of several airline advisories concerning the hazards from several eruptions of the Redoubt volcano, says FAA's Richard Stafford in Washington, D.C. The advisories are part of a volcano watch system set up early this year, which uses satellite information to spot ash clouds and notifies airlines about the danger. Redoubt provided the system's first real test.

"The information was out there. The advisories and the warnings were out there. I'm just curious why the plane went into the ash cloud," says Michael Matson, who helped design the system at the National Oceanic and Atmospheric Administration (NOAA) in Washington, D.C.

The Redoubt volcano has erupted sporadically since Dec. 14, producing several ash plumes that reached 30,000 to 40,000 feet. Its last eruption series occurred between 1966 and 1968.

The NOAA team analyzing the satellite data first spotted a volcanic cloud from Redoubt on Dec. 14, one day after the U.S. Geological Survey notified them that earthquake activity under the volcano had stepped up dramatically. The NOAA experts use infrared- and visible-light images from four satellites to identify volcanic clouds. Image analyzers spotted Redoubt's initial ash cloud because it was higher, and thus colder, than normal weather clouds. But in the hours before the KLM encounter, high weather clouds nearby prevented NOAA from tracking plume movement, says NOAA's Otto Karst.

As federal authorities investigate the incident, participants in each level of the volcano watch program will review the system to see what, if anything, they can improve.

FAA's Nicholas Krull, who helped set up the program, says the system functioned according to design, notifying carriers and leaving them to decide whether or not to fly through the area. He adds that it may not be possible to avoid all such encounters.