Adaptive Flexible Maintainability Demonstration - ANew Way to Learn More with Less Resources that Improves on Test Method 9
Christopher Jackson · 2018
Many approaches to maintainability demonstration tend to focus on the techniques and test plans outlined in Military Handbook (MIL-HDBK) 470A. [1] In particular (and for continuous, duration-based systems) `Test Method 9' involves using a stratified sampling technique to generate 30 maintenance actions based on underlying failure mechanism hazard rates. The hazard rates are typically expert judgments that are made when completing (for example) a Failure Mode, Effect and Criticality Analysis (FMECA). But these hazard rates are not the result of any empirical or analytical analysis - effectively invalidating any demonstration approach that is based on them. Notwithstanding, MIL-HDBK-470A's Test Method 9 is repeatedly used to demonstrate maintainability based on uncertain estimates. Further, using a stratified sampling technique with original failure mechanism failure rates means not only are test results automatically invalidated when our understanding of these hazard rates improves, but the data from pre-existing maintainability demonstration test is now incomplete. A new maintainability demonstration test needs to be undertaken, with at best only some of the observations of previous demonstration tests being usable. And finally, Test Method 9 (and similar approaches) never include low frequency-long duration tasks that have significant impact on key maintainability metrics.