Cut Sets Page (Gates Only in System Files)
The Cut Sets page is shown in the Properties window only for gates in System files because results can be calculated only for System files. Display-only results are shown on this page only if cut sets have already been calculated. For more information, see Calculating FTA Results.
• If only qualitative analysis has been performed, the Cut Sets page lists only the events in each cut set because probabilities of occurrence are not calculated.
• If quantitative analysis has been performed, the Cut Sets page lists the calculated probabilities of occurrence for each cut set followed by the events in this cut set. The results shown in the first column depend on the FTA calculation type:
◦ For a gate in a time dependent or Lambda Tau tree, the label for the first column is Probability. The values shown depend on the results that were calculated. Typically, they are unreliability values. However, if unavailability results were calculated, then they are unavailability values instead. If neither unreliability or unavailability results were calculated, this column is not shown.
◦ For a gate in an SAE tree, the label for the first column is either Average Probability Per Flight or Worst Case Probability Per Flight, indicating the type of probability selected for calculations. While average probability is the default, you can choose to calculate results based on either average probability or worst case probability.
If reliability importance measures were also calculated, Normalized Probability is the second column shown. The values shown are results for what SAE ARP476 calls the ‘ith’ cut set importance measure. Each value provides a percentage of cut set failure probability with respect to the top level event failure probability. The following formula is used to calculate this measure:
At the bottom of the Cut Sets page are buttons for saving cut set results for the gate to a Microsoft Excel spreadsheet or to print them to a printer. For more information, see Excel and Print Buttons.