Volcanic Ash Studied for Plane Safety

May 10, 2007 — Some volcanic ash launched into the sky by eruptions may be more deadly to jet engines than others, suggests a new study.

When it erupted in 1982, Indonesia's Galunggung volcano famously caused temporary engine failure in two Boeing 747 passenger jets flying downwind. Both planes had to make emergency landings in Jakarta.

Preliminary work on the changing microscopic textures of ash coming from Galunggung may lead to a better way to predict when a big cloud of the tiny glass shards is about to be let loose into the airways.

"The continuous observation on volcanic ash textures during an eruption...may provide an opportunity to forecast the forthcoming behavior of the eruption," said geologist Orkun Ersoy of Hacettepe University in Ankara, Turkey.

Ersoy is the lead author of a paper on the matter in the May issue of the Bulletin of the Geological Society of America.

One way the textures can signal an impending eruption is by revealing when more water is mixing with the molten rock underground — which is one way to really make a volcano very angry.

The Galunggung volcano is of particular interest for aviation safety, said Ersoy, because of its history causing jet trouble.

When the miniscule ash particles are sucked into jet engines, they melt and spray as molten glass onto the relatively cool fuel nozzles, turbines and other essential engine parts. The result is an immediate loss of power.

"There have been some very notable encounters of aircraft with ash," said geologist Marianne Guffanti, chief of the U.S. Geological Survey's Aviation Hazards Project.

In fact, there have been nearly 100 cases in all, with a few so severe that pilots lost all power and had to glide their planes until the engines could restart — perhaps after the accumulated volcanic glass coatings in the engines cooled, cracked and fell away.

Luckily, no plane has yet crashed from an ash encounter, Guffanti said.

"The only known safety strategy is to avoid it," she said. The problem with that strategy, however, is that onboard radar can't detect ash, nor can pilots readily see it. Even with satellite technology, it's hard to keep track of every volcano on Earth every day, as well as the plumes of ash they emit.

"If you fly to Japan you are going through a big hunk of the globe with a lot of volcanoes," said Guffanti. And because each ash cloud can travel hundreds of miles, there's really no such thing as a "remote" volcano to aviators, she said.

That's why work like Ersoy's is helpful, she said. It is an attempt to increase the warning time of ash eruptions, which is key to getting planes routed around the dangerous clouds.

"Nobody wants to take that risk," said Guffanti. "None of the airlines want to fly through ash."