What's the problem ???
David Learmount, on Flightglobal (q.v.) rightly says that "the" problem is twofold:
1) A volcano in Iceland is erupting vioently
2) A very stable High-pressure system is unusually far North and directing the plume south-eastwards.
#2 is unusual for this time of year.
This is an unprecedented situation, which is why none of the "risk assessment" or researchers have predicted it (for all their Ph(u)Ds from Llaregub U).
Because of the above, engine manufacturers have not spent time and money collecting samlpes of volcanic ash to throw at engines on test-beds (And probably won't in the future, for cost/benefit reasons, which is sensible).
OK, it causes chaos and hardship for passengers (and airlines), which insurance companies will no doubt still be disputing in years to come.
The situation will ease when the weather pattern changes - maybe a Low will send the stuff from this and any bigger bang northwards, over the Pole and into Nothern Canada or even Alaska - then what will Sarah Palin say ???
N.B. Tongue ever so slightly in cheek at times ...