Very interesting article, I suspect that the cost of flight through volcanic ash may not be truely felt for some time to come, but it will come when engines start to fail power assurance checks and have to be replaced, it is not clear that anyone really knows what the cloud consists of and the effect of those contaminants on hot turbines, particularly the Willie Walshes of this world ! Keep your eyes on those gauges!
It was explained to me that ash can bond to, corrode and errode blades and other internals. All policy I understand is immediate possible engine change if flown into known ash.