Dani/Lomapaseo
I couldn't agree more - the whole thing hinges on the concentration/density (call it what you will) of the ash.
Saying that a report "looks scientific enough to be accepted" is either hopelessly naive or a blatant fishing mission...
I have no vested interest in all of this, but from what I've read and heard from Professor Stipp of Copenhagen University I'm quite concerned that "looking scientific enough to be accepted" was exactly the hoped for result (with new research funding to follow)... The reasons given for the importance of the research are a direct rehash of RAeS and other reports pointing out the general problems of volcanic ash (sandblasting, melting and solidifying within the engine, etc.). All of that is well known and largely irrelevant to the concentrations found in the vast majority of the closed area. Neither the Finnish F18 nor the UK Typhoon reported abrasive damage (hardly surprising) and the deposits found in the engine (because someone went looking for them) didn't lead to engine handling problems (as far as I have read)... To infer that airspace closure was justified because there was ash in the air and it has previously caused problems is the only input to the press' hype that the report has to offer (and this is unscientific speculation with no visible analysis). The question of why no one knew what safe concentrations were is conveniently sidelined by all the discussion of a report which does nothing to address this central issue.
Incidentally, the report has been produced by a team of chemists with no discernable prior knowledge of aircraft operations, atmospheric physics, meteorology,.......
What would be far more interesting would be to hear if the particle sizes which this report has undoubtedly described have any effect on the dispersion models used i.e. does the highly accurate knowledge of particle size change the predicted ash distributions/concentrations? If this was combined with well reasoned, scientific numbers for acceptable concentrations we would have a real result...