For what its worth.....speaking as a many years experienced aircraft engineer with a fair bit of boroscope experience......I have seen engines damaged by volcanic ash...some minor damage, the engine still worked, produced power etc but had suffered damage that required it to be removed for overhaul. the problem is the ash cant be seen easily unless its a dense cloud. (Like the Eric Moody experience..although at night they didn't see it) For the airlines to take the risk of damaging the engines...its a big risk. I fully agree its moving towards the 'calculated risk' scenario now. BA conducted a flight over UK/Wales etc, there was reportedly no evidence at all of any ash deposits/damage etc. Engine boroscopes were done before and after the flight with no damage....does this prove anything? depends on exactly where they flew compared to the Met/Nats reported ash areas. If the airlines repeatedly flew through these areas then the damaged may be caused. if they are willing to accept the possible damage and overhaul costs of the engines then Ok....from my own personal experience, it comes down to a financial decision. They can 'safely' fly however, the engines would have to be inspected (boroscoped) almost every day or two (depending on the type/ammount of flights) and the airlines take the risk of the overhaul cost. (I'm willing to do the overtime!!!)...potentially the risk/cost of damage will exceed the cost of operating. (Removing engines takes time, as well as the potential lack of spares in the near future...) I would be happy to take a flight in the current situation if I know the airline is tsking all the steps to monitor the engines etc properly......