errr - since one of my postings got caught in some diversions about plane-spotting, MRI, liquid Helium, etc. could I please also request a return to the original topic!
Ok - we now have some evidence that the BA 'test' /
PR flight that ended up at Cardiff having meandered around some 'ash-containing' bits of sky did not ACTUALLY have a significant 'ash encounter'. Great - Willy Walsh was in no serious danger after all!
Doesn't make any difference to a REALLY basic question: IF (probably WHEN) volcanic ash becomes a problem in N Europe again, what reliable measures exist to measure the extent of ash encounters soon after they happen? Visual external inspection is OK if there's something to see. Don't rely of flight crew reports: frequently, there will have been nothing to report, from inside or outside the aircraft.
So the answer is there are NO effective measures. Does that make you guys on the firing line happy? Well, it shouldn't. Remember particularly ash damage MUST be cumulative and that aircraft utilisation is often on reciprocal routes, repeated ad nauseam.