scope:

Purpose of This Document

This document contains the physical form and fit dimensions, the electrical interface definition, and a description of the functions, operations, and interfaces of the Communications Management Unit (CMU) Mark 2.

The CMU Mark 2 is used to provide management and access to the various datalink networks and services available to the aircraft. The CMU Mark 2 may also host various applications related to datalink, including both Company and Air Traffic Services. A brief white paper on the role of the CMU Mark 2 in Communications, Navigation, and Surveillance/Air Traffic Management (CNS/ATM) is provided in Appendix A.

The CMU Mark 2 is defined in terms of capability levels. There are two classes of capabilities, Level 0-2 defines communications service capabilities and Levels A-D defines application capabilities, see Section 4.1. The CNS/ATM definition is still in progress.

The CMU level 0-A definition has been completed. Future supplements will complete the definition of the other levels. The text for levels 1-2 and levels B-D is preliminary. This document assumes that the architecture of the airborne CMU Mark 2, is as shown in the system block diagrams included as attachments. These architectures are consistent with guidelines provided by ARINC Report 660: CNS/ATM Avionics, Functional Allocation and Recommended Architectures.

COMMENTARY

Equipment manufacturers should note that this document aims to encourage them to produce high Mean Time Between Removal (MTBR), high performance equipment. They are at liberty to accomplish this by the use of design techniques they consider to be the most appropriate. Their airline customers are more interested in the end result than in the means to achieve it.