With the volcano in Iceland, Mother Nature is giving high-flying Europe a lesson in risk, aviation technology, scientific uncertainty and economics. Experts aren't sure what amount of volcanic ash — made up of sand and tiny abrasive glasslike particles — is dangerous to jet engines and what density is safe. And for that matter, they can't say how much of the ash is floating in any one spot along the air traffic routes or where it is specifically going next. When people turn to science for answers, they get a lot equivocation. It is one of the hardest risk decisions society has faced in a while, says Paul Fischbeck, a risk analysis expert at Carnegie Mellon University and a former military pilot. When the Eyjafjallajokull volcano first spewed, the answer was simple. Authorities usually shut down airspace when there's volcanic ash. It's the precautionary principle of erring on the side of caution, Fischbeck said. “Standard safety procedure is: Don't go there if you don't know,” said Michael Fabian, a professor of mechanical engineering at Embry Riddle Aeronautical University in Prescott, Ariz. Fischbeck believes authorities should fly more test flights into the plume to see what kind of damage occurs and at what frequency to help them make a more informed decision. Engineers worry about immediate catastrophic damage when the ash dust congeals in an engine turbine, blocking air flow and shutting it down, Fabian said. In 1989, when a Boeing 747 flew through volcanic ash over Alaska, all four engines failed and the plane dropped more than two miles in five minutes, before engines restarted. Ash can also cause long-term abrasive damage to planes that could lead to later disasters if not dealt with. Fabian said the reason engineers know so little about the risks from volcanic ash is that it would take many hours and great expense to do repeated tests. And tests would be needed for the 20 different types of engines currently flown. And even if engineers knew how much ash a plane's engines could handle, atmospheric scientists can't say how much ash is in any one place or predict what will happen next. The ash becomes more diluted as it goes higher in altitude but also clumps together at times like sediments in a river, he said. Fischbeck, a former pilot, and Fabian, an airline engine expert, said they rely on the pilot's judgment. “To me if the pilot is willing to risk his own life, I'll go,” Fabian said.
