Fault Tree Analysis: FaultTree+ provides an example of a Windows-based engineering reliability software tool. In the past, engineers avoided exact reliability analysis partly due to the tedious nature of developing manual fault trees. Software like FaultTree+ simplifies analysis so that relatively large fault trees 6000 elements and up can be developed and analyzed with relative ease. Lookup tables of standard component failure rates are combined with analytical simplifying techniques. These make fault tree analysis a real option for the shop-floor engineer. The fault trees themselves focus efforts on fault areas of concern from the minimum "cut sets" of interest (and non-interest), to the overall contributions that various faults have on overall reliability. (A cut set is one way the top event can occur. The top event is typically an undesired outcome a failure.) The locomotive example here is typical; the fault tree illustrates design areas not previously considered in the overall unit reliability. Sensitivity analysis can test the numerical values used for the event probabilities, as well as the model logic itself. Often overall "top" event reliability is known, but the individual reliabilities are not. Individual reliabilities may be taken from generic tables. In any event, the Fault Tree identifies the fault paths of interest, and their logic, providing the opportunity to focus on the critical few that matter.

In the example, we build the fault tree on FaultTree+, assigning failure data as we go. We have several selections of failure models and information to select from. Once complete, we can run the...