Originally Posted by
brooksjg
The trouble with 'careful reading' of anything is that it can STILL be selective!
The stated reason why the track of the NASA DC-8 blundered into the ash
[...]
All of which is valid but misses the point. The DC-8 hit ash that wasn't visible (wrapped in ice/cloud or whatever)
and wasn't forecast to be there. NO airspace closure regime, including the previous "zero tolerance" is going to help you avoid that situation, other than not flying at all, ever.
This incident is therefore completely irrelevant when discussing what forecasts / measurements / levels should be used to close airspace,
because it occurred in airspace that would have been open under any regime.
Furthermore,this "invisible but dangerous" ash is either a freak/one-off, so there is only this one incident, or it is common but we only
know of this one incident because the a/c happended to have the instruments on board. If it's a one-off then it is irrelevant for safety or commercial considerations, if it's not, then other a/c have been flying (unknowingly) through the same stuff for years, so
we already know the maintenance cost.