Maybe now is the time to repost one of mine that was deleted. A Flight Critical System was not referenced in the AFM, and the system turns out to be reliant on one only AoA vane. On vane failure, PF side is affected, PNF’s is not. Upon failure, one pilot has an emergency, PNF’s “does not”. Creates confusion to say the least: “What are you doing!”
Without AoA display there is no ability to cross reference. Without knowledge of the system, aircrew is challenged by similarity to UAS.
There has been one fatal accident seemingly related to this lack of included description in the Flight Manual.
FAA has issued an ESB AD to mitigate this lack of system inclusion in the Flight manual. On its face, it appears this will solve the ongoing threat to flight safety.
Will it? There is no reason to believe it will not. Whatever reliabilitty issues there were, (sole source of data driving activity of system), the resolution seems appropriate, and sufficient. Reliability aside, The system can now be mitigated on failure due this add to the AFM.
Questions. How can a flight critical system be fitted to an aircraft such that the operator is not completely informed of its existence and functionality? Can the design be improved and the system modified? To be determined, and Probably not...