Just had a briefing at work this morning on some of the reasons for why the cloud is staying where it is and why the airspace restrictions are in place.
1. The high pressure system thats sitting on the UK is stopping the ash dispursing properly and at some points causing the ash to circle and come back again.
2. There is an inversion at 8000ft which is stopping the ash from falling which is why there is not much on the ground.
3. The ash particles are so small that you cannot actually see them (you apparantley need a very powerful microscope).
4. Noone knows that size of particle that affects jet engines, from the aviaition authorities, the countries that have dealt with this kind of problem in the past to the engine manufacturers.
5. Because the engine manufacturers don't test for this problem they won't commit to a size/concentration that is safe.
6. NATS put the restrictions in place for controlled airspace because neither the DofT or CAA would make a descision. Once they had the other ANSP's followed their lead. (I think they would have rather the government had taken the lead but theres an election on and all
)
7. They had already done some work on what to do if a volcano had erupted in Iceland but this situation has far far exceeded the worst case predictions. I think that they expected a couple of days before it blew away, not the potential week - 10 day scenario that is shaping up.
8. They won't allow overflights FL350+ because of the potential for an emergency, which is then compounded by the ash.
9. The reason that you can't just route around it (like the yanks and aussies do) is that we don't have enough airspace to do that. (i think people forget that the UK is smaller than most US states)
Thats pretty much all i can remember.