Now, all sensible people wouldn't have any problems with flight-restictions when you're exposed to the smoke and volcanic ash. But what sort of consentration in the air is it in the lower part of the atmosphere a few thousand kilometers away?
Is it really sane to have EMS and SAR helicopters (all helicopters for that sake) grounded far far away from the eruption. As long as you can't see these particals in the air, I doubt that they are more harmful than the very visible SAND you normally see when landing in dry places. (damages to surfaces, not ingested)
And for engine damage, this should be avoided with the use of sand-filter?? I am not talking about partical-seperator, but proper sand-filter.
But this ash is really special, so normal means won't help.
But hey, there might be "other" reasons to keep a total ban I'm sure.