Page 61 - RCM - A practical Guide_V1

RCM - A Practical Guide

Function. The normal, characteristic actions of an item, sometimes defined in terms of performance
capabilities.
Functional failure. The failure of an item to do its normal actions within specified limits.
Functional Failure Mode Code A code allocated to functional failures as part of a Failure Mode and Effects Analysis (FMEA). The
(FFMC). code identifies the associated functions, functional failures and engineering failure modes.
Functionally Significant Item A system or part thereof, other than structure, which is selected for RCM analysis; or any item
(FSI) within a system, or part thereof, that is allocated a preventive maintenance task(s) as a result of
RCM analysis, because in either case any of the following criteria apply:
Its failure would be undetectable during operations, or would have significant consequences in
terms of safety (on the ground or in flight), the environment, operational capability or cost of
repair.
Its functional failure rate is high.
There are OEM maintenance recommendations or existing maintenance tasks associated with it.
Note: This definition reflects the term Maintenance Significant Item (MSI), which is contained in
ATA MSG-3, but has been expanded to emphasize that it excludes elements of structure and
that the additional criteria at (b) and (c) are directed mainly to retrospective RCM studies of
legacy maintenance programmes.
Hard time (HT) task. A task to restore a condition or replace an item before some specified maximum age limit to
prevent or reduce the probability of a functional failure.
Hidden failure consequences The risk of a multiple failure resulting from undetected earlier failure of a hidden function item.
(Safety and Non-safety).

Hidden failure A failure not evident to the crew or operator during the performance of normal duties.
Infant mortality. The relatively high conditional probability of failure during the period immediately after an item
enters service.
Lightning/HIRF Significant L/HIRF components are significant if they protect critical systems and/or structure.
Item (LHSI)
The LHSI list includes the aircraft critical system or structural L/HIRF protection components (i.e.
bonding, connectors, and structural panels with protection) provided by the OEM Design
Engineering team and any additional protection components identified by the analysis.
Mean time between failures A basic measure of reliability for repairable items.
(MTBF).
MSG-1. A working paper prepared by the 747 Maintenance Steering Group, published in July 1968 under
the title Handbook: Maintenance Evaluation and Program Development (MSG-1); the first use of
decision-diagram techniques to develop an initial scheduled maintenance program.
MSG-2. A refinement of the decision-diagram procedures in MSG-1, published in March 1970 under the
title, MSG-2: Airline/Manufacturer Maintenance Program Planning Document; the immediate
precursor of RCM methods

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