The so-called "test flights" should have produced clear evidence that aircraft are capable of negotiating certain prespecified atmospheric conditions. If so, what were the specified conditions and where are the data? It appears that numerous aircraft on Sunday flew in relatively low-ash or even ash-free areas of Europe. When these aircraft landed there were almost instantaneous claims from various airlines that no problems had been encountered, yet insidious damage to an aeroengine by repeated exposure to particulates would surely only be detectable by a proper engine stripdown after having conducted several test flights? Ideally, one would include some worst-case conditions in the test battery to provide a safety margin, just as in aircraft test flights. Using older aircraft with parachutes would make a lot of sense! Do we seriously think that BA would send up an expensive 747-400 into an ash cloud? Of course not! I take the event to be purely a publicity stunt until such time as they provide actual data to prove otherwise.
I have no objection to the "no ash" threshold being revised if it is done in a scientifically transparent and defensible way. It is a standard process in risk assessment that thresholds are objectively revised in light of new evidence. But, where exactly is this new evidence? Sending a few planes up for random forays on unspecified missions and then not openly disclosing the findings is not the way to go about this!