Purpose: This document is the specification of a generic interface to be used between avionics computing equipment that exchange binary message-oriented data. Several avionics architectures have been considered. For example, the interface could be used between an Flight Management Computer (FMC) and a Communication Management Unit (CMU) Mark 2, between an FMC and an ACARS MU, or between any two avionics Line Replaceable Units (LRU). Throughout this document, the term FMC may apply to any type of navigational unit. The term CMU may apply to any on-board router. The layer functionality defined herein operates independently of device type.

This interface was developed so that various manufacturers can elect to partition aspects of Air Traffic Services (ATS) applications and protocols in different manners between these two physical LRUs or logical partitions. This specification was developed by defining the major functionality that should be implemented in either the FMC or the CMU in support of ATS applications and then defining the interfaces to support these functions at each layer, assuming various configurations.

This interface can be implemented in various hardware environments including integrated architectures, over an additional ARINC 429 data bus, Ethernet, or other supportive bus interface architectures. Specified herein are protocols that support this interface regardless of how the functions may be allocated in any particular hardware architecture. These protocols are not limited to the ARINC 429 data bus or ARINC 646 Ethernet bus systems; therefore, the data structures designed in this interface are also not constrained to any specific bus type.