Page 29 - RCM - A practical Guide_V1

RCM - A Practical Guide

( Probable - Is it likely to happen?

Objective Proven - Has it happened?

If it is proven then it is an easy decision to include that failure mode for consideration, the difficulty
here is that a huge number of failure modes will be theoretical based on the subjective knowledge or
fears of the analysis team. Those are the failure modes that will benefit from the application of the 4 P
technique as a sanity check.
The 5 whys
As previously mentioned, the effects of failure decide whether action is required or not, but it is the
failure mode that tells us what kind of action is appropriate.
It is essential that a failure mode is detailed enough to inform that decision-making process. An ill-
formed failure mode will limit the options open to an analysis.
For example:
Car braking system:

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
Why? - Brakes don’t apply as expected
Why? - ABS stops them
Why? - ABS thinks car is skidding
Why? - Inconsistent frequency from the ABS ring
Why? - ABS ring cracks
Why? - ABS ring corrodes
c. Stops the car within 100 metres but at a weight less than gross
Ok, so in that example there 6 whys but the technique isn’t about asking 5 whys every time, it’s about
asking the right number of whys to get to what feels like the right answer.
For RCM it isn’t quite root cause analysis because we can’t do anything about Dave, who makes the
ABS rings, having a rubbish time at home leading to poor manufacture etc. No, we’re looking for the
engineering failure mode against which we can act.
Describing the Failure Mode
A failure mode should consist of at least a noun and a verb but could up to four elements:

Equipment Detail Verb Additional

The parent asset that The specific asset within the The present tense version of More explanatory
contains the failure mode parent that has failed what has happened to the information if required.
detail

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