Page 30 - RCM - A practical Guide_V1

RCM - A Practical Guide

Using the ABS example, the failure mode could be expressed as:
ABS ring cracks due to corrosion
(Equipment) (Detail) (Verb) (Additional)
Or simply:
ABS ring corrodes
(Equipment) (Detail) (Verb)
Both are acceptable, and in this case, it would be down to the analyst’s preference to
determine how detailed they would like it to appear but there is detail enough in both to
adequately inform the decision-making process.
Black-box method
Having said all of that about the benefits of explicit failure modes, there is a place in RCM for
calculated woolliness. What do I mean by that?
Sometimes, normally in the case of electronic equipment which tend to display random failure
characteristics, there is little point (and probably wholly impractical anyway) in going inside the ‘black-
box’ to identify the specific cause. In these instances, it is acceptable to list a failure mode at a higher
level and this is referred to as the black-box method.
Applying this method means, in broad terms, that an item has ‘failed for any reason’ to deliver a
desired output and in black-boxing we are accepting that the actual cause is largely immaterial based
on perceived failure characteristics and possible mitigation. That is an important point…
RCM is most effective when the analyst understands exactly how the equipment works. Black-boxing is
not an excuse for laziness or a substitute for that understanding. If an analysis does not understand
how an asset works then it should - without exception - find out. Only then can the decision to black-
box be truly defensible.
4 - What happens when each failure occurs?
RCM is zero based.
That statement is often thrown out there but, so what? For failure effects that means that the analysis
needs to assume that no mitigation or maintenance is applied and that every failure mode can run its
course.
The most effective failure effect statements tell the story of what happens starting at the asset in
question, to its parent and on to the overall platform to which it is fitted.
Defining effects
What happens at the item?
In some FMEA formats the effects are populated before the failure mode, the upshot of that is that
there may not be a logical place to record the effects of the mode on the asset, but it is worth bearing
in mind to inform the decision-making process.
What physical effect does the failure mode have on the asset?
What functional effect does that, therefore, have on the asset?

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