My post and all the responses to it have mysteriously disappeared so I'll try again.
I have read all the 116 pages of this thread (not much else to do when you are grounded) and I really want to get to the bottom of it.
So this is my take on the whole sorry saga.
1. The engine manufacturers set a zero tolerance to volcanic ash to minimise the chances of litigation, understandably.
2. The airlines didnt want to set a higher limit for the same reason, also understandable.
3. ICAO tried to accept those above to come up with a figure they could use in their ash avoidance doc 019 but were unsucessful and so they reluctantly published zero as the limit KNOWING it to be at best unrealistic and at worst absurd!
4. All the other safety bodies around the world accepted this as the law KKNOWING it to be based on an unrealistic perameter at best and bloody absurd at worst.
Rules and laws in aviation have to be followed of course. Its not hard to follow a rule, however silly, but its much harder to interpret it, that takes intelligence and common sense.
In my view and with the advantage of hindsight I would say whoever it was(maybe someone can tell us?) who first decided to close European controlled airspace so abruptly, panicked and made a rash decision. Understandable, perhaps. (No doubt it was a committee, not one person, brilliant previous comment-'you never see a statue of a committee!)
SO what should have happened?
First, as soon as the eruption occurred NOTAMS and warnings issued as to where and how far the dust was and what the danger was. Presumably we can tick that box.
Then instead of rushing to judgement and closing most of European airspace KNOWING the law was ultra conservative and KNOWING such a decision would cause utter chaos, all the relevant bodies, 1, 2,3 and 4 above plus the govts concerned should have been consulted beforehand.
Yes this would have taken time, maybe 24 hrs and maybe some answers would not have been forthcoming but a better decision could have been arrived at which could have saved over $2 billion dollars WITHOUT COMPROMISING SAFETY.
The mantra of all the bodies that govern aviation goes like this
'Our primary concern is safety'
That is a given, we all know that and comply with it but just mindlessly repeating it over and over is not a defence.
Sometimes I get the impression it should be
'Our primary concern is protecting our backsides'
'We were just following the rules'
These are among the sad famous last words before a fall.