How volcanic ash can bring down an airplane

When Indonesia’s Mount Sinabung erupted on Monday morning, the volcano spewed a roiling cloud of ash and gases more than 23,000 feet into the air. The eruption prompted a “red notice” for the aviation industry, alerting pilots to the ash cloud so they could steer clear of it. But could tiny particles of volcanic ash really bring down an airplane?

Absolutely. In fact, the mixture of crushed rocks, gases, and tiny shards of glass in a volcanic ash cloud can sandblast the plane’s exterior, melt onto the engine, and fry key navigational and communications systems. That’s why nine Volcanic Ash Advisory Centers around the world keep watch for volcanic eruptions like yesterday’s — one of Sinabung’s biggest since the volcano woke back up in 2010, volcanologist Janine Krippner says. “Ash plumes can travel thousands of kilometers away from the volcano itself,” Krippner says. “So being able to track the ash clouds in real time, to divert the planes around, is so, so important.”

Using a combination of satellite imagery, pilot reports, and data from volcano observatories, these Volcanic Ash Advisory Centers issue color-coded warnings: Green means a volcano is sitting quietly; yellow says the volcano is starting to get restless; orange that an eruption is looking likely; and red means a big eruption is on its way, or already here. The advisories don’t tell pilots what to do — that’s up to the airlines’ policies — but they do provide key information about the size and location of the ash cloud and where it’s likely to head next. By early Tuesday morning, local time, satellites showed that the ash cloud had blown apart, and the advisory was canceled.

The sandblasted and clouded windscreen of the Boeing 747 aircraft that flew through the ash cloud of Alaska’s Redoubt volcano in 1989.
The sandblasted and clouded windscreen of the Boeing 747 aircraft that flew through the ash cloud of Alaska’s Redoubt volcano in 1989.
 Photo: USGS and the University of Alaska Anchorage in Anchorage

The Volcanic Ash Advisory Centers were formed by the International Civil Aviation Organization after several planes almost crashed from flying through ash clouds. In 1982, for example, two airplanes flying through ash from Indonesia’s Mount Galunggung lost power to their engines and had to make emergency landings. One of them, a British Airways Boeing 747, plummeted more than 20,000 feet before the pilot could restart three of the four engines. Then, in 1989, a jumbo jet nearly crashed after it flew through volcanic ash from Alaska’s Mount Redoubt, and all four of its engines cut out.

Volcanic ash can damage an airplane in multiple ways. One of the most dangerous is by gumming up the engine. Volcanic ash contains tiny glass particles that can melt in a jet engine’s heat. This molten glass can stick to key components, cutting the engine’s power, or killing it completely, reports natural hazards expert Carina Fearnley in The Conversation. At such high speeds, ash pummeling the exterior of the plane can also break antennas, cloud windscreens, and generate static electricity that distorts navigation and communication signals. If ash flies into tubes that measure airspeed, it can also break the plane’s speedometer.

NASA and US Air Force employees blow ash up a C-17 aircraft’s engines to simulate flying through a volcanic ash cloud. The ash was sourced from an ancient volcano in Oregon.
NASA and US Air Force employees blow ash up a C-17 aircraft’s engines to simulate flying through a volcanic ash cloud. The ash was sourced from an ancient volcano in OregonPhoto by Tom Tschida / NASA AFRC

We don’t know exactly how much ash is safe to fly through, although scientists and engineers are getting closer to an answer. For a long time, the aviation industry avoided flying when any ash was in the air. But after millions of people were stranded and billions of dollars were lost during the eruption of Iceland’s Eyjafjallajökull volcano in 2010, scientists began trying to figure out if there’s a middle ground, Earth Magazine reports.

All told, planes have had run-ins with volcanic ash about 253 times between 1953 and 2016, according to a report from the US Geological Survey. Only nine of those experienced engine failure, and none crashed. It’s not completely clear why certain ash clouds can have such a devastating effect on certain engines, and why other planes can fly through relatively unharmed. One possibility is that the composition of ash can vary from volcano to volcano.

There’s another problem, too, Krippner says: not every volcano is monitored, so it’s still possible for planes to fly through ash clouds without warning. It’s something she thinks about a lot, especially on flights over volcanic regions of the Pacific. “If I’m in a plane and I start to smell sulfur, what am I going to do?” she says. “There are so many volcanoes that could produce an ash plume, at any time.”

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