A client developed a novel FMECA technique that I think has much to recommend it. A key difference lies in the way “Occurrence” is handled. Generally, when we develop a FMECA, we assign a somewhat-arbitrary number (1 – 10) to the occurrence factor. In this approach, the failure rate (in FIT’s) is used for each of the components. The total of the FIT’s for the components in the subsystem considered is then used to normalize the FIT for each component. In this way, the most critical components can be determined. The total can also be rolled up to the next higher level. Another feature of this approach is that the failure mode of the component (for example: open, shorted, parameter change) can be included in the analysis since, in some cases, a particular failure mode can have a more …
FMECA or FTA?
There are two ways to approach fault analysis -- Failure Modes, Effects and Criticality Analysis (FMECA), which is currently the most common approach, and Fault Tree Analysis (FTA). Both look at the effects of component failures on a system, but come at it from different ways. FMECA starts from the lowest levels of the system and considers the effect at the top level of the system of a failure at the lower level. FTA starts with a possible failure mode of the system, and then works down to see what could cause it. The Reliability Toolkit1, gives selection criteria for when to use either of these two approaches. The primary concern is safety of public or operating and maintenance personnel A small number of clearly differentiated “top events” can be identified Completion of a functional …
