Fault Insertion and Event Status

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”.

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Three Different Views to Display the FTA

One of the unique features of the eXpress FTA is that it provides three different ways of viewing a given fault tree: “As Modeled”, “Simplified” and “Optimized”.

• As Model FTA – The as modeled FTA shows the events exactly as defined in the model without any kind of simplification or optimization.
• Simplified FTA – The simplified mode removes unnecessary events based upon the user defined setting for degree of simplification.
• Optimized FTA – The optimized mode both simplifies and reorganizes the logic of the tree to account for multiple occurrences of the same event (so that displayed failure probabilities are equivalent to those calculated from the Minimal Cut Sets).

Display FMECA Chart

In eXpress, fault trees are displayed using the same graphic interface that is used to display eXpress FMECA charts. One benefit of this tight integration is that each fault tree also serves as an index to information in the corresponding FMECA. This is particularly powerful when your FMECA has custom columns containing project-specific data. Many companies treat their FMECAs as data repositories for multiple design and analysis disciplines. With the eXpress FTA module, this information remains at your fingertips as you evaluate the system-level impact of failures using fault trees.

Display FMECA Chart using Fault Tree Events

During fault tree editing, FMECA rows that are related to the selected fault tree can be optionally displayed (instead of the fault tree diagram) on the right-hand side of the screen. When one or more entries are selected in the Explorer Tree on the left – which the fault tree events, then the chart will be further filtered to list only FMECA rows related to the selected entries.