[Guest post by DRJ]
Planes are flying again in most of Europe but scientists disagree on whether or when it’s safe to fly:
“Six days after volcanic ash shut down the skies over much of Europe, planes are back in the air, but science still can’t answer the question:
Is it safe to fly again?
Mother Nature has given Europe a lesson in risk, aviation technology, scientific uncertainty and economics. And how these fields intersect is messy.
Watching the same people who earlier said it was too dangerous to fly now say it’s safe “is just more proof that risk is a subjective idea,” said David Ropeik, a risk perception expert at Harvard University.
When people turn to science for answers, they get a lot equivocation.
“We really don’t have as good a handle as we should on the ash particle size, the ash concentration and most important, just exactly how high the ash got up into the atmosphere,” said Gary Hufford, a U.S. government volcano expert based in Anchorage, Alaska.
Would he get on a plane and fly into the ash cloud? “I would be cautious,” he said in a Tuesday conference call.”
Here are some of the scientific issues:
“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, said Jon Davidson, a professor of earth sciences at Durham University in England. The ash becomes more diluted as it goes higher in altitude but also clumps together at times like sediments in a river, he said.”
The rarity of this type of event together with the lack of scientific studies makes this more of a risk assessment decision than a scientific matter.