Purpose of This Document

This document sets forth a general philosophy, basic guidance and certain specific recommendations for the design and use of an onboard maintenance system (OMS).

The OMS described incorporates the traditional areas of failure monitoring and fault detection, BITE, BITE access, and an airplane condition monitoring system (ACMS), formerly known as aircraft integrated data system (AIDS). It further describes the capability to provide onboard maintenance documentation (OMD) and the requirement for total integration of these functions. It describes the requirements for all the elements of the OMS, including a central maintenance computer (or CMC function) and all the member systems which interface with it.

This document is intended to provide a better mutual understanding among the designers and users of the specified OMS including all its member systems, with a view toward achieving an optimum balance between critical factors such as BITE effectiveness, operator interface simplicity, cost, and system complexity. A description of one possible architecture for an OMS is also included in the document. This description is not intended to delineate the design for an OMS, but to provide an example for understanding the requirements for such a system.

This document discusses the role of an OMS in the airlines' maintenance concept and the fault detection and BITE characteristics desirable in all avionics equipment to support the broader goals of an OMS. Beyond the guidance applicable to BITE, this document provides specific guidance for the design of an OMS which provides for:

- A standardized, English-language-based user interface for performing all BITE tests and line maintenance functions on the airplane.

- Where appropriate, storage of BITE reported fault data within a line replaceable unit's (LRU) nonvolatile memory (NVM) for later use.

- Reporting of fault status in the air and on the ground via operator displays and/or electronic/magnetic communications links.

- Integration of the fault isolation design to provide complete coverage, from fully automatic BITE through interactive, BITE assisted fault isolation to manual troubleshooting procedures. - Ground-test capability for fault isolation and performance of LRU replacement tests, functional tests, and system tests.

- OMD in both displayed and selectively printed forms.

- Airplane condition monitoring function integrated with the BITE/line maintenance function design.

Airframe and equipment designers are encouraged to take advantage of this guidance information, beginning with the earliest design phases of new equipment.

Users may also find this information helpful in standardizing maintenance planning and procedures, and in securing appropriate recognition for such procedures from the regulatory agencies. It is particularly important that the guidelines set forth herein should be considered in terms of the overall perspective of the users' needs, rather than some more limited objective.