However, having been involved in several FAA AD's over the years, 8 months and it's still not released is inexcusable. AD's by definition affect flight safety. Normal flow time for a 'routine' AD is a couple months - seldom going much beyond 3 months even if there are lots of comments (emergency AD's don't go through public comment and can go out in a few days). While getting the blade inspection AD released may not have affected this accident, it's pretty clear to me that someone in the FAA dropped the ball.
Well of course hindsight is much clearer than foresight.
However both the manufacturer and the FAA have processes developed under continued airworthiness rules to assess in-service experience coupled with today's analysis. Such experience includes probable causes and population at risk, (of a blade fracture) certification basis, and any unexpected in-service additional safety concerns beyond a safe engine shutdown.
The risk analysis does consider a given that a blade fracture will occur sometime in the future, but given such a fracture other combinations of risk in the in-service experience ala crew error or parts being liberated beyond the engine itself (possibly some others that I can't remember at this time)
In the end such analysis need show that the risk of a far more serious event than currently experience in the data must be extremely low and not significantly contribute to the underlying risk of flying that product in its expected lifetime.
It does not mean that a simple blade fracture will not occur while they are dotting the "Is" and crossing the "Ts" in a proposed AD but based on data available nobody close to this would have expected the result in this flight.
OK it is obvious that an unexpected combination did occur and the AD does have to be adjusted. So let's just get after this bottom line lest we end up only blaming somebody instead.