To fly through ash or not? That’s no easy question

To fly, or not? There’s no right answer about when it’s safe to fly through a cloud of volcanic ash. But it’ll be all too obvious if there’s a wrong answer, experts say.

With the volcano in Iceland, Mother Nature is giving high-flying Europe a lesson in risk, aviation technology, scientific uncertainty and economics.

And how these fields intersect is messy.

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.

But airlines know what canceled flights can do to their bottom lines. And passengers know when those canceled flights cross the line from inconvenience to pain.

So Monday night, a smattering of flights took off in northern Europe, followed by more flights on Tuesday. European Union transport ministers divided the northern skies into three areas: a “no-fly” zone immediately over the ash cloud; a caution zone “with some contamination” where planes can fly subject to engine checks for damage; and an open-skies zone.

At one point Monday, the volcano’s eruptions were said to be weakening, but by Monday night the plume seemed to intensify, and it was unclear how long newly reopened airports in northern Europe would be able to remain operational.

If airports do reopen, passengers may have to decide for themselves what risk is acceptable.

When people turn to science for answers, they get a lot equivocation.

“There are really no facts about risk. It’s just how we interpret the information we have,” said David Ropeik, an instructor in risk perception at Harvard and author of the book “How Risky Is It, Really?”

“This is a great example of how the pace of modern technological invention is making a lot more people nervous about just how sure science can be about anything,” he said.

It is one of the hardest risk decisions society has faced in a while, agrees Paul Fischbeck, a risk analysis expert at Carnegie Mellon University and a former military pilot.

“With the amount of uncertainty, this now I think is a very hard decision,” he said. “How much risk are you willing to accept to reduce economic hardship and inconvenience?”

It isn’t a small amount of money at stake. It’s billions of dollars with millions of stranded passengers, said Fischbeck. But if an airplane goes down, the company would be shut down by lawsuits, he said.

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.

But the days went on and the pain for airline companies and passengers increased and then people started questioning: How bad is it? How do you know?