Originally Posted by PJ2
The modification I believe must be approved by the manufacturer and the country's regulator... someone?
To my knowledge, the AOM is not formally approved. The official document is the Airplane Flight Manual (AFM), which is approved as part of the type certification. The airline submits the AOM to its regulatory authority, which either tacitly accepts it or requires changes, but does not issue a formal approval. The manufacturer does not formally approve the airline's AOM.
From
FAA AC 25.1581-1 Airplane Flight Manual:
3. Definitions
a. Airplane Flight Manual (AFM). An FAA-approved document that contains information (operating limitations, operating procedures, performance information, etc.) necessary to operate the airplane at the level of safety established by the airplane's certification basis.
b. Flightcrew Operating Manual (FCOM). A document developed by a manufacturer that describes, in detail, the characteristics and operation of the airplane or its systems.
c. (etc.)