This standard defines the functionality and principle interfaces for the Common Functional Module (CFM) to ensure the interoperability of Common Functional Modules and provides design guidelines to assist in implementation of such a CFM. It is one of a set of standards that define an ASAAC (Allied Standard Avionics Architecture Council) Integrated Modular Avionics System. This definition of interfaces and functionality allows a CFM design that is interoperable with all other CFM to this standard, that is technology transparent, that is open to a multi-vendor market and that can make the best use of COTS technologies. Although the physical organisation and implementation of a CFM should remain the manufacturer’s choice, in accordance with the best use of the current technology, it is necessary to define a structure for each CFM in order to achieve a logical definition of the CFM with a defined functionality. This definition includes: - The Generic CFM, which defines the generic functionality applicable to the complete set of CFMs. The generic functionality is defined in 4.1. - The processing capability, which defines the unique functionality associated with each CFM type within the set. This functionality is defined in 4.3. - The logical and physical interfaces that enable CFMs to be interoperable and interchangeable, these are defined in Clause 6. - The functionality required by a CFM to support the operation of the System is defined in Clause 6.