Precaution Does Not Fly
Besides grounded flights and airlines claiming losses above one and half billion dollars, there are tons of rotten perishable goods to dispose of; delays in international shipments of various goods and probably also missed business opportunities. And passengers still slowly making their way back home here and there.
What has truly hit me about this story is not the magnitude of economic damage, tho. It is that the competent national and European authorities issued blanket bans, binary decisions in which the forecasted presence of ash was enough to completely shut down air traffic.
Yet, when the European transportation ministers finally had a meeting - after some five days, soon afterwards the airspaces were reopened.
Is it because the ash magically disappeared, or because thei nitiale "zero tolerance" approach was flawed? I bet on the second option.
Some interesting information can be found in this document prepared byt the Italian agency ENAC: exploratory flights, with various aircrafts, were ran over Italy and no damage was observed even after flying into an airspace indicated as contaminated. The only important recommendation there is to avoind flying into visible ash clouds.
It seems that decisions of great importance for the economy of entire nations and the lives of hundreds of thousands were taken on the basis of dispersion models of dubious reliability and - more damning - without the support of empirical measurements and observations. It is not even known what ash concentration remains safe for jet engines*; a rather generic statement from the British CAA says that manufacturers of airplanes and engines have agreed on a safe threshold of 0.002 g/m3 - while concentrations above Britain always remained way lower.
Why this does not surprise me much? First, because for bureaucrats it is easier to say NO than YES - in other words, the default response when asking for an authorization is negative unless a set of conditions is met. Second, because the EU has adopted the infamous precautionary principle as a policy. In fact, it seems that even ICAO has adopted a similar principle - and more curiously, that they rely on dust dispersion models without requiring actual measurements of ash concentration.
Now you see what precautionary principle does.
* Not even considering the many different models and specifications of jet engines out there.