Originally Posted by
threemiles
FAA says when then new MCAS software is certified and out it shall be implemented by an AD Note. I am not sure this is the right sequence if FAA feels something is very critical. Because the interim AD had nothing in it but hot air it reads like the MCAS problem is minor. Now they say it deserves implementation of the fix by AD note not by Service Bulletin. Again, this smells and the FAA does not seem to act logical and independantly but rather as the long arm of Boeing and US commercial interests. A logical step would be a grounding order by FAA until the fix can be implemented.
A Service Bulletin (SB) is the means by which the manufacturer embodies the necessary instructions for implementing the modification or for continued airworthiness. It identifies all the technical and engineering data necessary for implementation.
An Airworthiness Directive (AD) is an instrument issued by a national airworthiness authority (like the FAA) which usually identifies the applicable SB to be enacted, and a time by which it must be incorporated and/or any exceptions. It is a legal document in the context of a nation's airworthiness system and typically carries a responsibility for an aircraft operator/owner to comply with. A manufacturer's SB is not.