Aviation authorities did the prudent thing and halted air traffic over the Continent. That's something that routinely happens everywhere when huge plumes of volcanic ash threaten aviation. The difference here, though, was that the ash was drifting over an area that is home to 600 million people, with some of the busiest airspace in the world. Stopping air traffic in this area thus became very painful financially to many companies within a short time.
Safety dictates that aircraft not fly through volcanic ash at all. Ash of the kind being coughed up by Ejyafjallajökull isn't like sand or ordinary dust: it is made of microscopic, jagged, sharp pieces of glassy rock that can chew through just about anything far faster than ordinary sandblasting. Worse yet, the ash has a relatively low melting point—lower than the internal temperatures in jet engines—so first it chews away at engine parts, then it melts inside the engine and clogs it up. Sometimes the engine stops. Even if the engine doesn't stop, it may suffer millions of dollars worth of damage and fail shortly thereafter.The damage doesn't stop with engines. The ash can sandblast windows, turning them opaque within minutes, making it impossible for pilots to see outside the aircraft. It can block pitot tubes, which are essential for determining the speed of the airplane (failing pitot tubes are one possible explanation for the crash of Air France Flight 447 not so long ago).
Anyway, it would be foolish to fly through this ash, and the few aircraft that inadvertently did so suffered great damage (historically, there have been many incidents of engine failures and damage from volcanic ash in aviation). So air traffic had to be more or less grounded in Europe, given the way the wind was spreading ash all over the place, like spreading frosting on a cake with a spatula.
In theory, there's nothing to be done about this. It's nature, and it's something you just have to try to put up with. But in this case there was too much money at stake to just sit by and accept reality. Lots of greedy airlines wanted to restore their revenue streams, come hell or high water, and they put pressure on government bodies. Eventually, the authorities decided that safety wasn't that important, after all, and that money should be given priority, and so the airspace over Europe was reopened.
Fortunately for everyone, the ash cloud was beginning to diminish at about the same time. This gave airlines the mistaken impression that they were right, and that the authorities had been too cautious. In fact, we were just lucky. The planes are flying again now.
I didn't actually see any ash clouds over Paris, even though high-altitude ash plumes swept over us. I didn't see any ash falling on the ground, either, nor did I smell anything. However, since my reasoning is not crippled by greed, I know that the mere absence of visible ash doesn't mean that anything is safe. I was somewhat concerned about breathing the ash (which can cause lung damage), but fortunately the ash stayed high in the sky and didn't fall over Paris (although it certainly fell in places in the U.K.).
I worry that the fact that airlines got away with being careless this time may encourage them to compromise on safety in other ways in the future. Airlines care only about money, not safety. They remain safe only as long as it is economically expedient to do so, which means that they remain safe mainly out of a fear of being heavily fined for any lapses in safety, as well as out of a fear of scaring off passengers if they have accidents. But if those two factors weren't around to twist their arms, the airlines would cheerfully operate with zero safety. Some of them are still taking chances as it is, as they have with this ash cloud.
Anyway, it's over now, provided that Ejyafjallajökull doesn't start spewing a zillion tons of ash again and provided that the winds remain favorable. If Ejyafjallajökull wakes up its neighbor, Katla, then these recent ash problems will seem trivial in comparison to what may come.
