By now, everyone has undoubtedly heard the ongoing story of the Eyjafjallajokull volcano (no, I can’t pronounce it either) in Iceland, and the effect that its eruption has had on air travel, particularly in Europe. Because of the potential for damage to jet engines by the very fine volcanic ash, most air routes to and through Europe were shut down for several days. (For example, on April 17, more than 75% of normally scheduled flights were canceled.) Flight restrictions began to be eased by this past Wednesday, and by yesterday most areas were expecting to be back to normal activity. All of this has led to some questions about how the whole affair was handled.
No one seriously disputes the idea that volcanic ash can cause significant damage to jet engines. There have been a few previous incidents in which planes’ engines were disabled after flying through volcanic ash clouds. (For example, a British Airways flight in 1982 lost its engines after flying through an ash cloud over Indonesia.) Because of this, the initial reaction of the aviation authorities was, essentially, to say that no level of ash greater than zero was safe.
A blanket assumption of that sort is bound to raise some questions, especially when some of the potential questioners are losing tens of millions of dollars a day as a result. As reported in an article at New Scientist, several European airlines (including British Airways) conducted test flights, after which they examined the aircraft engines for damage. After some discussion, a new standard was established: it is now possible to fly in the presence of volcanic ash, provided the density of ash does not exceed 2 mg / m³. Apparently this level was set in consultation with the engine manufacturers, but the data on which it was based have not been disclosed.
Although it seems reasonable to assume that the safe concentration level is some number greater than zero, it is not clear that any very incisive analysis was carried out to establish the new standard. (As several comments on the New Scientist article pointed out, disassembly of a modern jet engine is not something that can be done in a couple of hours.) The current situation may represent a reasonable compromise, but I hope that some more attention is given to the underlying question before the next crisis.
There is one other related observation I should make. I have, in the past, been disparaging of “security theater” in air travel, and of precautions taken against what Bruce Schneier calls “movie plot” threats. As this incident illustrates, life can be disrupted by natural phenomena. Planning to feed, shelter, and protect people who are displaced in an emergency pays off regardless of what (volcano, earthquake, terrorist act) causes the disruption.