Not a regular thing in terms of the scope of this groundstop, but it is widely accepted by the aviation community that volcanic ash can wreak absolute havoc on aircraft. It is, for all intents and purposes, microscopic jagged glass-like rock particles. At best, it can "sandblast" the paint off the fuselage of an aircraft. In more-sevvere instances, it can scratch the windshield (windscreen, if you prefer) of the jet so severely that it becomes like frosted glass, totally opaque. At absolute worst, it can be sucked into the turbines/engines, demolish them from the inside out, and cause them to all fail at once.
