The FAA posted an AD (Airworthiness Directive) mandating an immediate inspection (NOT an immediate grounding) of the wingroot attach points on all US B-17s. The US aircraft that were grounded (not all were, it was voluntary) were out of an abundance of caution after one airplane was found to have a left wing that was about to fall off (figuratively speaking, but it was pretty close). The owners of the Sally B followed suit out of caution. The FAA has a proposed method of inspection that while possibly expensive would allow the airplanes to continue to fly when passed. First is a visual insp. of all wing attach points for abnormal or excessive wear, cracks, etc.. If any are found then an eddy current insp. of the root/wing fittings is mandated. If there are no issues or when the airplane is repaired then the airplane is fit to fly. If the airplanes DOES NOT PASS, then you're looking at either a permanent grounding or a very, very large pile of money to make the airplane compliant. At least that's what I got from the AD Notice. This is like a lot of other ADs that have been put out, that it's relating to the B-17 makes it esp. noteworthy. Very, very few airplanes have not had at least one AD Notice on them. Some have been comparatively minor so to speak, some have been major. ALL MUST be complied with.