Reliability Importance Measure Calculations

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The concept of reliability importance measures was introduced in 1969 by Professor Zygmund Birnbaum. Importance measures are calculated whenever Reliability importance measures is selected under Calculations on the General page in the FTA calculation properties. For more information, see General Page. The following topics provide calculation information for the importance measures supported by the FTA module:

• Birnbaum Importance Measure

• Criticality Importance Measure

• Fussell-Vesely Importance Measure

• Fussell-Vesely Alternative Importance Measure

When reliability importance measures are calculated, results for the four previous methods are shown on the Importance Measures page in the Properties window for the gate. Additionally, on the Cut Sets page, the Normalized Probability column shows results for what SAE ARP476 calls the ‘ith’ cut set importance measure. For more information, see Importance Measures Page (Gates Only in System Files) and Cut Sets Page (Gates Only in System Files).