It’s okay to require time directed tasks, if the basis is sound and the “wear-out”
characteristic is established for the component involved, but don’t forget that few
components (no more than 20% in the four studies cited) exhibit this characteristic.
Condition directed tasking makes a lot more sense than time directed tasking when
considering the finding that no less than 80% of components included in any of the
four studies previously cited exhibited a “random failure characteristic” and no
“wearout” for the majority of their conditional probability period of operation after
manufacture, overhaul or repair. The actual numbers for the four studies are 94%,
96%, 80% and 88%, respectively, displaying random failure and no wearout.