火山灰上天了 我们还乘飞机吗?

It's MORNING EDITION, from NPR News. I'm Steve Inskeep.

In the summer of 2008, three big volcanoes erupted in Alaska. One created an ash cloud that stretched across North America. And what is noteworthy now is how noteworthy it wasn't then. Flight disruptions were quite minor.

These volcanoes barely made the news, which is quite a contrast with what Europe just experienced when a volcano erupted in Iceland. It illustrates the differences in both geography and air regulations. NPR's Richard Harris has the story.

RICHARD HARRIS: Three mountains in the Aleutian Islands blew their tops in quick succession. Kasatochi, Okmok and Cleveland all spewed giant ash plumes into the air. And Chris Nye from the state of Alaska's Volcano Observatory says all three eruptions came without warning.

Mr. CHRIS NYE (Alaska's Volcano Observatory): The most surprising thing we got was a call from the Space Station, saying, do you know that one of your volcanoes is erupting? And it was a clear blue day, and they sent us beautiful, beautiful photographs of the top of this plume. And we had to say, no, we don't know that it's erupting - really embarrassing.

(Soundbite of laughter)

HARRIS: Well, not really embarrassing, so much as a reminder that we aren't keeping a close eye on every single volcano on our turf. And those eruptions were every bit as big as the one in Iceland.

Mr. NYE: Certainly, the distance that the - particularly the Kasatochi plume traveled across North America was more than the current Icelandic eruption is doing.

HARRIS How far did it go?

Mr. NYE: All the way across North America to the East Coast. And then there are reports from the Kasatochi eruption of vibrant sunsets in Europe from that summer, so that's suggesting something very, very high in the atmosphere actually made it that far.

HARRIS: But the eruption was handled very differently in the U.S., compared with Europe's reaction to the Iceland volcano. In Europe, government authorities decide whether the skies are safe or not. In contrast, in the U.S., data about ash clouds is given to the airlines, and it's mostly up to them to decide whether it's safe to fly or not.

During the Alaskan eruptions, the government closed only small patches of airspace immediately around the volcanoes. Leonard Salinas, a flight dispatcher for United Airlines, says it wasn't so hard to cope with those eruptions.

Mr. LEONARD SALINAS (Flight dispatcher for United Airlines): With more airspace, we were able to route around or completely miss the cloud by routing completely further south and around and then going to Asia, or for the flights coming from Asia doing polar routes.

HARRIS: Salinas says the airlines follow a simple rule: zero tolerance for flying through ash. But they didn't quite live up to that standard during the Alaskan eruptions because forecasts aren't 100 percent accurate.

Mr. SALINAS: There was some inadvertent encounters. That was because where the airspace was open, closed very quickly when the upper air winds brought some ash across that was not forecast in that area. So that was a non-forecast area, but that did occur.

HARRIS: He says as far as he knows, no damage resulted from those encounters. But since the 1980s, at least 15 planes have been damaged by ash along the busy North Pacific air routes, according to the U.S. Geological Survey. And planes can easily sustain tens of millions of dollars in damage. Pilots do their best to get out of those situations as quickly as possible, even if they can't see the cloud they're in.

Mr. SALINAS: If a crew picks up any indication of a smell or something erratic with any type of instrument, then we know there must be a problem and the crew will do everything to get out of that area.

HARRIS: Nobody has ever crashed as a result of flying through ash, but at least twice, jumbo jets have lost power in all four engines for a frightening few minutes.

With these encounters as a backdrop, airlines are very motivated to avoid ash in the atmosphere. Salinas says the difference in Europe is that the airspace is very confined, so airlines have less leeway to find their own way around ash clouds. So he says the difference in approach reflects geography more than philosophy.

Richard Harris, NPR News.