Page 27 - RCM - A practical Guide_V1

RCM - A Practical Guide

❑ stop is the verb
❑ the car is the object
❑ within 100 metres on a dry surface and to achieve this at its gross vehicle weight is the
performance parameter

2 - In what ways does the item fail to perform its function?
Does failure mean the absolute inability to perform a function or could it mean that the asset can still
perform the function but not at an adequate level of performance? In RCM terms, it’s both of those
things.
You could describe failure as:
Any identifiable deviation from the original condition which is unsatisfactory
for a user

or (more usefully)

The inability of the item (or equipment it is part of) to meet a specific
performance standard.
An RCM study must (where practical) consider total and partial failure of a function. This is where the
importance of the performance standard comes to the fore.
Defining failure
The effect of function statements on functional failures
Poorly, ill or lazily formed functional statements can (will) have a detrimental effect on the way that
failure can be described or understood.
As an example, let’s look at our car braking system from the Defining functions section:
1. A car braking system has the primary function to stop the car
a. This function is so scant in detail that it is a binary choice. It can do it or it can’t.
b. Functional failure = Can’t stop the car.
2. The car braking system must be capable of stopping the car within 100 metres on a dry surface
and to achieve this at its gross vehicle weight
a. This second evolution of the function gives the analyst a much better range of
understanding and does not limit the possible definitions of failure.
b. Functional failure = Can’t do it at all
c. Functional failure = Does it but not within the distance
d. Functional failure = Does it but not at the gross weight
So what does that matter? The effects and, therefore, mitigation will be different for each functional
failure. RCM, remember, is about understanding and without the fuller definition of item 2 above, we
only understand a partial picture.

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