"Brooksig" suggested that he had complete faith in the Met models.!!!
Why then do we dept from JFK to LHR with a fcast on limits and a suitable Alt, which on arrival has a Metar which makes the approach feasable. All I am suggesting that to canx flts on a computer ash model however accurate is daft. We need a method of actually finding the ash level at an airport on arrival, just as we find out the RVR or w/v at the airport just before making the approach.