MIL-1629A Criticality Analysis

This topic describes how to enable and use the MIL-1629A Criticality Analysis utility. If you prefer to use the criticality analysis methods that are performed directly in the FMRA, see Qualitative Criticality Analysis or Quantitative Criticality Analysis.

Enabling and Accessing the MIL-1629A Analysis

If you wish to be able to access the MIL-1629A Criticality Analysis window on your computer, select the Enable MIL-1629A Criticality check box on the Settings page of the Application Setup. When this option is selected, the MIL-1629A Criticality command will be visible on the Home tab of the ribbon.

This command will be available only if at least one criticality analysis field is enabled in the project. Furthermore, in order to be able to calculate results, there must be at least one failure mode defined for each item before you open the window.

Using the Utility

When you open the utility, use the Select Items window to select one or more items from the current project that you want to include in the criticality analysis and click OK.

When the MIL-1629A Criticality Analysis window opens, the worksheet will display the specific data fields from the item, function and failure mode properties that are relevant for criticality analysis.

Note the following:

  • For most of the fields that are editable in the worksheet, you will be able to view/edit the property in either the MIL-1629A Criticality Analysis window or the Item Properties/FMEA/FMRA. Any changes made in one location will be visible in the others. The only exceptions are the Mode Ratio and Prob of Loss columns. These properties can be entered and viewed only via the MIL-1629A Criticality Analysis window. The values that you enter are saved with the failure mode (and visible the next time you view this failure mode in the MIL-1629A Criticality Analysis window), but they are not visible in the Failure properties window in the FMEA or FMRA.

For the Prob of Loss, if you want to assume a total loss, accept the default setting of 1 (actual loss). If you want to enter a specific decimal value (e.g., 0.3 or 0.73), click in the field and select or create a constant model defined with the appropriate value.

  • The reliability type for each item must be set to Define at this level.
  • The sum of the values in the Mode Ratio column must be equal to 1 for each item. For example, if an item has four failure modes, the ratios could be something like: Mode A - 0.1, Mode B - 0.3, Mode C - 0.45, Mode D - 0.15 (i.e., 0.1 + 0.3 + 0.45 + 0.15 = 1).
  • The cells with a green background color will display the calculated results after you enter all required inputs and click the Calculate button.

The Display Options at the bottom of the window allow you to customize the worksheet to meet your specific needs:

  • Select Show current age, quantity and duty cycle if you are using those properties in the item reliability calculations. If the Current Age is 0, the Quantity is 1 and the Duty Cycle is 1 (i.e., there is one item that operates continuously and is subjected to the same loads and/or stresses as the rest of the system), these fields are not relevant and do not need to be displayed. (See Setting the Operation Properties for an FMRA.) These values are not considered in the original military standard methodology and should not be changed if you want to follow that standard exactly. Note that if you change these values, the values you enter will be used in calculations even if you subsequently hide the properties.
  • Select Show columns for qualitative analysis if you want to display the Mission Phase/Operational Mode and Failure Probability columns, which are applicable only if you are performing qualitative analysis.
  • Select Include causes with failures if you want to display the cause descriptions in the same column with the failure modes. If only the failure modes are displayed, you will be able to edit the descriptions directly in the MIL-1629A worksheet, if desired. If both the failure mode and cause descriptions are displayed in the same cell, you will not be able to edit the text without closing the MIL-1629A Criticality Analysis window and returning to the FMEA/FMRA.
  • Select Change 'Expected Failures' caption to 'Failure Rate' if you want to change the name of the column from Expected Failures to Failure Rate. The values displayed in the column will remain unchanged.

When the worksheet displays all of the required inputs for quantitative criticality analysis, click Calculate to perform the calculations. You can then click Send to Excel to export all of the information currently displayed in the worksheet to an Excel file, or click Reports to select from a set of predefined report forms that can be generated in either Word or Excel.

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