Page 21 - RCM - A practical Guide_V1

RCM - A Practical Guide

The six graphs show us that that the presence of a well-defined wear-out region is far from universal.
Only patterns A and B show clear wear-out characteristics. These two curves are associated with many
simple items and account for only 6% of all items.
When pattern C is also considered those items that might benefit from a life account for only 11% of
all.
It must follow, then, that up to 89% of items do not display definite wear-out characteristics and
would, therefore, not benefit from an age limit on operating life.
In the 6% of items showing a pronounced wear-out region the effectiveness of an age-related life limit
depends upon a high probability that the item will survive to that limit.
What also came out of these analyses is the fact that the traditional view of all complex items falling
into the bathtub curve pattern is dispelled. Only 4% of complex items fall into this category. The vast
majority of complex items align with patterns D - F, showing no concentration of failures directly
related to operating age.
Moubray commented that the percentages hailed from aviation and may not be true for industry and
that the ever advancing level of technology almost inevitably leans toward Pattern F.

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