Faults may be inserted into the FTA by selecting the root failures and changing the status from “Unknown” to either “Failed” or “Not Failed”. When the event status has been changed then all of the dependent events of the selected root failure will be highlighted in red or green depending on whether “Failed” or “Not Failed” was selected. The likelihood of the dependent events will then be recalculated based upon the assumption that the given root failure is proven “Not Failed” or indicted as “Failed”.

The process of inserting faults allows for determining how faults which are either undetectable or not immediately repairable will affect the likelihood of the critical event occurring when the failure occurs. Using this process case studies can be performed to determine which failures are the most critical and most likely to need mitigation through improved detection, improved repair processes or system mitigation using redundancy.

Fault Insertion showing likelihood of occurrence of dependent events when the failure occurs