Page 28 - RCM - A practical Guide_V1

RCM - A Practical Guide

Describing the Functional Failure
For simple functions the functional failures are often simply the inverse of the function.
Car braking system:
1. To stop the car
a. Does not stop the car
For a more complex functional statement there are likely to be several functional failures which break
down the specific performance standards in question and they will be formed along the lines of…
Car braking system:

2. To stop the car within 100 metres on a dry surface and to achieve this at its gross
vehicle weight
a. Does not stop the car at all
b. Stops the car at a distance more than 100 metres
c. Stops the car within 100 metres but at a weight less than gross

3 - What causes each functional failure?
A failure mode is a physical change in an item that leads to the loss of function.
They can sometimes be referred to as ‘Failure Mode’, ‘Failure Cause’ or ‘Engineering Failure Mode’.
RCM, as previously stated, introduces maintenance to mitigate the effects of failure but that
maintenance is targeted at the failure mode. The characteristics of the failure mode will decide what
kind of maintenance is applicable and effective.
There is enough wiggle room, grey area and subjectivity in RCM to enable an analysis to tie itself in
knots and that is arguably more true for failure modes than any other area. Operating context,
functions and functional failures are facts extracted skillfully from available material but failure
modes…they are a different story.
It’s all too easy for an analyst to get lost or make things up that feel reasonable at the time but bog
down the progress of an analysis later. To help keep failure modes in the realm of the believable a
technique, borrowed from genealogy, is a quick test of whether a failure mode is viable or not.

Defining failure modes
The 4 Ps
The key to the success of any subjective discipline is good common sense. The 4 Ps gives an analyst a
defensible approach to its application to failure modes.
There are many possible sources of information for failure modes from operators data taken extracted
from a maintenance management system, manufacturers data, technical manuals etc and the
engineering experiences of those involved in the analysis. But lets ask ourselves if what we’ve put
down on paper is really…

( Plausible - Is likely to be true?
Subjective ( Possible - Is it able to exist?

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