Page 33 - RCM - A practical Guide_V1

RCM - A Practical Guide

MITIGATION STRATEGY
From this point, let’s assume that we are armed with a fully populated (and accurate) FMEA. That
means that questions 1 - 4 of the 7 basic questions of RCM have been answered. To select the correct
mitigation strategy, we now need to answer questions 5 - 7.
5. Why does each failure matter?
6. What, if anything, should be done to predict or prevent each failure?
7. What should be done if no maintenance task is selected?
Each RCM standard develops its own take on the decision diagram and each one allows for a level of
tailoring but what they all have in common are the first two actions will, together answer question 5…
❑ Will the operator know about it?
❑ Do I care about it?

5 - Why does each failure matter?

Using the detection method
Will the operator, during the course of their normal duties, eventually
become aware of the loss of function? (Or words to that effect).
Note that although this question is asked in the context of a single failure mode, it is concerned with
the loss of function and not necessarily the presence of the failure mode. What that means to us is
that every failure mode, under the same functional failure, must have the same answer to this
question…
Yes

The operator, whoever that may be in the context of the function, must be able to identify the loss of
function without going out of their way to do it.
Take, for example, an operator whose machine comprises a single oil pump. If that operator tries to
use the machine, and the fuel pump has failed for whatever reason, the machine will grind to halt, and
most importantly not perform its function. The operator will notice that.
In complex items the ability to recognise functional failures is further enhanced by the addition of
instruments and warning devices such as lights or audible warnings etc.
Instrumentation can also help the crew to determine whether the equipment is operating as well as it
should. If it is not, then this can be an indication that a potential failure condition exists.
The functional failures that will be noticed by the operator are deemed to be evident.
No

There are, though, some functions whose failure will go unnoticed (because the use of them is not
usual). Most of these failures must be detected by inspections or tests of some kind.
Take, for example, an operator whose machine includes two fuel pumps. Pump 1, as in the single
example above, is active and Pump 2 is a standby unit. If that operator tries to use the machine, and

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