The integration between eXpress diagnostics and the fault tree analysis (FTA) provides a unique way of examining the critical events within a FTA. The eXpress diagnostics will for all levels of the FTA define whether a fault is detected by the diagnostics designed in eXpress and uniquely isolated.

Evaluating the Impact of Non-Detected Faults Upon Safety

Events which are both undetectable and not a single point of failure for the critical event would lead to a higher likelihood of occurrence for the critical event. This higher likelihood of occurrence can be examined by inserting a failure for the undetected events and then examining how the likelihood of occurrence is increased by the presence of the undetected failure.

Evaluating the Impact of Prognosis Upon Safety

Prognostics are used with the eXpress FTA to learn the beneficial impact upon safety that will be received when the prognosis is implemented in the system. This is done by adjusting the likelihood of occurrence of the critical event for the prognosis given the confidence that the prognosis will actually occur.

For example, if a root failure with an established prognostic test leads to a critical event then the likelihood of the critical event occurring will be reduced by the confidence of the prognosis actually occurring multiplied by the failure rate within the given period of performance of the root failure.

Evaluating the Impact of Unique Fault Isolations Upon System Availability

Root failures of critical events which are isolated with non-critical events may lead to false aborts of the system when the non-critical fault occurs. Examining the unique isolation details of the root failures for the critical events in the FTA will provide a convenient method of determining how the developed diagnostics will impact system availability by determining which non-critical failures will most likely lead to false system aborts.

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