Lyman,
Lets be clear here:
In the instance of the EASA or the FAA initiating an AD for a problem or event such as the subject of this thread, these agencies may "consult" with the manufacturing folks involved or the airline for factual information, but decide the appropriate action to be taken independently of either party. A recommendation from the NTSB is not required for an AD to be issued, but because of the Charleston event, the NTSB initiated an investigation concerning the GEnx engine problem.
In the instance of either agency proposing changes to certification requirement, aircraft, engines, pitot tubes, avionic equipment, onboard weather radar, you name it, they issue draft proposals and ask for comments and recommendations. Then they decide on each one as I previously noted. For an example, you should read this and then Google to find the detailed response that Airbus gave...
Airbus backs overhaul of pitot icing certification standards
Private Jet,
Doesnt this kind of thing almost always happen with new engine types? Thats a rhetorical question... yes it does.
You gave the right answer to your question. Unexpected issues seem to always emerge regardless of all the testing and certification steps that are taken and all the lessons learned from previous engines. For the GEnx, it would seem to be an inadequacy of a manufacturing process or processes for the component involved, not necessarily a general design problem of this component.
TD