Local, Next higher level, End effects

The FMECA process specified by MIL-STD-1629A provides a structured description of the Effects while the SAE JA1011 “minimum RCM” Effects are described by free text. One may question why LRCM chooses free text over the more stringent military structure

The Effects long text field is one of several aspects that set RCM apart from the MIL-STD-1629A FMECA standard. The latter uses a three part “Local”, “Next higher level” (NHL), and “End” Effects structure. The Local Effects describe what happens within the part or component that failed. The NHL Effects describe what happens at the next hierarchical level, for example in the assembly or subsystem in which the failed component resides. The End Effects describe how the end Item’s mission, for example, how mission of the armored vehicle, ship, or fighter plane is affected by the failure.

This FMECA Effects style is too constraining in a maintenance management context, and, at the same time, of insufficient detail for practical continuous reliability knowledge improvement. The FMECA standard was not conceived for use by in-service maintenance personnel. It is meant, primarily, for project design. System engineers use design oriented reliability engineering software based on FMECA. That software requires that in  the FMECA structure the NHL Effects at one level become to the Failure Mode at the next higher level. This strategy assists automated fault tree development for troubleshooting manuals.  FMECA oriented design and simulation software invokes component reliability prediction models such as those contained in MIL-HBK 217 and NPRD-95. The SAE JA-1011 approach, on the other hand, encourages a maintenance oriented knowledge elicitation and management process. Its structure is more flexible, free text based, and moderated by judgment based firmly upon current operating context. It targets in-service maintenance issues by answering (to the extent required):

1. What sequence of events (component level to organization) could be touched off by the failure mode?
2. How does the failure make itself known? What observable events lead up to the failure?
3. How is safety or the environment impacted (without using the words “safety” or “environment”)?
4. How are costs or operations (quality, mission) impacted?
5. Is there any additional damage caused? What are the currently mitigating circumstances or tasks?
6. How long will it take and what actions must be accomplished to correct the failure?
7. How does the likelihood of this failure depend on deeper causes? Has it happened before? How often? Under what circumstances? How likely or unlikely is this failure mode considered to be?

The Effects that evolve from a living RCM process are more reality grounded than  those of FMECA. Consequently, it is relatively easy to extend LRCM to the FMECA three levels if so required by design or project engineering staff. This will be possible as long as the JA1011 Effects have been recorded by answering the above questions at a level of detail commensurate with the failure consequences. However, the reverse (transforming  a FMECA to a SAE JA11011 style Effects) will usually be difficult or impossible to achieve.

© 2011 – 2014, Murray Wiseman. All rights reserved.