> The threat level for airplanes is set to orange... for anyone dumb enough to fly over an erupting volcano.
Even 180km away from the eruption, airplanes can be seriously damaged [1].
Jet engines really, really do not like to ingest anything else than air and, maybe, a tad bit of water.
Volcanic ash is particularly bad because it is so abrasive, having been freshly formed without any opportunity for erosion to smooth it down like regular dust.
That's not the only problem - volcanic ash also has a low enough melting point that it'll melt in the combustion chamber of a jet engine and leave glassy deposits on cooler components.
Prevailing winds are key. Reykjavíkings told me that during that big eruption many moons ago, all traffic to Europe was ended but traffic to North American continued merrily along.