Originally Posted by Stoic
I think you will find that the ash clouds that have done the damage in the past to eg. BA009 and the NASA aeroplane were in visible ash cloud, not invisible ash cloud. Emperor and new clothes comes to mind.
Incorrect. The cloud the NASA plane flew through was entirely unnoticeable, 200 miles North of the predicted ash cloud, and only picked up because they were a atmospheric research plane that had sensitive equipment onboard. They also only flew through the ash for 5 or 10 minutes. Had this been a normal flight, nobody would have realised. Nevertheless, the engines were damaged significantly, and their remaining time was estimated to be 100 hours instead of 1000 hours.
Again, this was an encounter with an extremely thin concentration of ash for a very short period. Continued operation in these conditions would have probably resulted in more sever damage.
(Source: NASA volcanic ash incident report)