Q&A: Protecting aircraft from volcanic ash

Until the Eyjafjallajokull volcano in Iceland grounded jets across Europe, few people appreciated the danger volcanic ash posed to aircraft. When the ash gets sucked into jet engines, it melts and can jam up the machinery and damage other internal parts.

An international network of nine Volcanic Ash Advisory Centers continuously monitors the skies for threatening ash. The skies above Alaska — home to 8% of the world’s active volcanoes and 80% of those in the U.S. — are watched by meteorologists in the center based in Anchorage. More than 10,000 people fly over their airspace every day en route between Asia and North America.

David Hadley is a senior meteorologist with the Alaska Aviation Weather Unit who has monitored ash for the Anchorage Volcanic Ash Advisory Center since it opened in the late 1990s. He explained how the process works.

How often do you find a plume of volcanic ash?

It’s likely less than 10% of the time, but when it’s happening, it seems like it’s forever. We’ve had as many as three volcanoes erupting at the same time up here in Alaska.

Do they affect aircraft?

We have a lot of Pacific routes affected by volcanic ash all the time, but they’re not headline news. When the plume from Redoubt volcano [on Alaska’s southern coast] was going on last year, Alaska Airlines canceled something like 26 flights between Seattle and Anchorage.

Are volcanoes spewing more ash than they used to?

No. It’s like anything — the more frequent air travel became, the more problematic volcanic ash became.

Walk us through an alert.

When we get notified that a volcano is erupting, the first thing we do is put out an initial SIGMET [Significant Meteorological Information alert] to let the world know there’s a hazard in this area. As soon as we get additional information — from pilots or satellites or even webcams — and we can estimate the size of an eruption, we’ll contact the U.S. Federal Aviation Administration. Then we’ll follow up with another SIGMET.

How do you monitor the ash via satellite?

There are geostationary satellites that stay in the same place and can get a nice continuous feed of data. They measure the radiative temperature emitted by clouds or whatever else. We can discern the ash from the clouds, the ocean and the land because ash has its own particular radiative temperature.

There are also polar orbiter satellites that are much lower in the atmosphere. They have good high-resolution cameras, plus a scanning device that just goes back and forth and senses the radiation. They can get a much more detailed look, but you only get a snapshot of it because they’re constantly moving around the Earth.

What happens if you don’t have a good satellite image?

We also use Doppler radar to measure the ash in the atmosphere. It’s mainly for meteorologists to detect drizzle and rain, which are fairly large spheres. But an ash plume has particles large enough for it to see, especially during the initial phases of an eruption when larger things are coming out.

Sometimes we have no other choice but to rely on the computer model. We put in the name of the volcano, the summit elevation and an estimated height of the initial burst. Once we have that, it will give us the [shape of the] plume.

Do ash plumes automatically force planes to be grounded?

No. In the U.S., the FAA does not close airspace. Every airline has their own policy on how they treat volcanic ash plumes. What we do is provide the warning to say, “Here’s the ash, here’s the area it encompasses, and here’s the level of concern.”

In 1989, a KLM 747 aircraft flew into an ash plume from the eruption of Mt. Redoubt about 110 miles from Anchorage, and all four of its engines failed. The plane plunged 13,000 feet with 244 passengers aboard before the engines restarted. Could that happen again?

That incident was the primary driver to get us Doppler radar in the state of Alaska, which we didn’t have at the time. We didn’t have complete access to all the information that we have now.

Can pilots see volcanic ash from the cockpit?

If you’ve got a vigorous eruption, it will shoot much higher than the weather cloud, and if it’s during daylight you might see it. But if it’s thin or if it’s night, you might not see it.

If there’s a storm system in the area with precipitation and clouds, the ash could be buried within it. If you’re already in a cloud, you wouldn’t know that a volcanic cloud lies ahead.

If they can see it, can they fly around it?

Quite often, if a volcano is sending a plume in one direction, they can fly on the other side of it without being in any danger. They can also provide us a description of what they see.

Can you prepare for these ash plumes?

When a volcano is at an elevated risk for eruption, we’ll run the model and pretend it erupted just to say, “If it erupts in the next couple of hours, here’s where the plume would go and how fast it would move.”

After the KLM incident here back in the 1980s, we know what ash can do. So we do our best, and we do it with a scientific eye. It’s a challenge, but we stand up to it pretty well.