An empirical perspective
It's clear from the posts here and the generally available information that there's no firm and conclusive position on this issue. Of course safety first. Of course, consideration to the economic impact downstream. But, this issue may be a 'first', but there are warnings that it may not be over and could resurrect itself in the coming days weeks and months. In the unthinkable position of airspace being closed down like this going forward for a number of times of equal or greater length, then there needs to be a Plan B.
Whilst I accept the modelling of the MO and the response by NATS and Eurocontrol I'm still a little bothered by the lack of empirical evidence. The BA flight spent much of its time above FL200 so I'm not sure how valuable that 'test' was. Right now we have clear skies (forgive the pun) and for me at any rate a need to perform some flight tests up to FL200 across the whole of UK airspace and indeed the same in mainland Europe and start getting empirical evidence of what the true impact of this is on airframes and engines. Not to solve the problem today as such but to gain the much needed instrumentation to plan for if this happens again.
Apart from people stuck out of position (not to mention a/c) we need to consider medical supplies, transplants and vital product import / export via cargo flights. None of these can take priority over air safety, but I'm yet to be conviced we have conducted here in the UK or across Europe the definitive due diligence to fully understand the impact to this at an engineering level. Without that, and the feedback from a/c and aero engine manufacturers we will still be, to some extent, guessing on the impact. Air safety needs more than this. These are unusual times and we therefore need unusual solutions and I think a more diligent set of airborn tests are needed. The MO can tell us what they predict is going on up there. NATS can take the correct route of caution, BUT, if much of this is hidden behind lack of empirical facts then whilst the current issue may resolve itself through a meteorogical change later this week (and I do hope so), we currently have the window of opportunity to conduct much more stringent and in depth testing of cause and effect. And yes, this means being airborn in one way or another. I'd like to see more effort put into this to equip us with a better engineering perspective than we currently have. Right now, it appears there are differing lines of action and behaviour across Europe and we need a consensus with the fact to support it. Until we have them and the chance to debate them, any repeat of this may leave us no further forward with only a repeat of the same. We cannot afford to have that - on any level. FL200 or otherwise.