effect of silica in the engines of the Finnish F18s, NASA's DC8 in an earlier eruption, the air samples taken by Cranfield, the muck picked up by the Scottish heli crew, and the new evidence that World Airways picked up engine deposits on a short hop to Maastricht today
There WILL be plenty of evidence of ash encounters and probably also ash damage so long as the 'new' arrangements remain as they now appear to be.
We STILL have science and measurement deficits. I heard earlier today on broadcast radio some comment about UK 'changing to the US model for ash drift forecasting'. Reportedly, this model is already the one used by Eurocontrol, which (also said) explains the differences between the ash mappings from various sources. Problem is, it's still modelling. If there's concern about flying THROUGH an ash layer, let alone flying IN it and the layers are NOT homogeneous in either extent or thickness (as detailed in the report of the German research aircraft flight linked from here today a few pages back), then clearly modelling does not meet the requirement. ANY mathematical model will produce AVERAGE particle densities over relatively large areas / heights and accuracy will fall off as the time from original, real data input increases.
So where is the planning and finance for direct measurement of ash concentration at a lot of point over UK, from ground level up to (say) FL40? Does the science to do this even exist? Could ATC systems (human and automated parts) actually cope with the additional workload to transform ash-cloud data into instructions for individual aircraft? I can't see any possibility of achieving this safely, or at all.
So the reality MAY turn out to be relatively broad-brush data covering large areas of airspace. I'm thinking, for example, of an 'unsafe' area of 10 by 10 kilometres and extending from FL10 to FL15, moving at maybe 40kph in a known direction. Trying to re-route aircraft around such an area in real time seems completely impractical given current ATC and routeing methods. So what use would more detailed ash data be in practice? The outcome in any case would be closure of destinations and / or routes for hours at a time - very disruptive.
As has been pointed out, the alternative of setting a high particle density as the 'safe to fly' limit and then flying willy-nilly (no pun intended) through whatever ash clouds are there will result in very long inspection delays, followed by (probably) very costly and frequent engine overhauls. (Reports SEEM to suggest that engines ARE damaged by relatively small amounts of ash but tolerate it for some time. NASA DC8 incident report says aircraft flew 80 hours of research at Kiruna and then back to Edwards AFB with no symptoms BEFORE the real damage was actually found. Nevertheless, all 4 turbines had to be rebuilt: cost $2m+.)
At the very least, given the fact that some clouds of ash are quite thin, some on-board ash-detection instrument is vital (if feasible at all!). Then at least in some cases it would be possible to climb / descend slightly so as to avoid flying in an ash layer for long periods. But who's doing the R&D??
Not out of the woods yet, by a long way!!