	Related Topics:
	FMEAs

Choosing the FMEA Structure

On the General page of the Project Properties window, you use the FMEA Structure field to choose how you want to display Effect and Cause records in the FMEA hierarchy. You have three options:

If you want to display the FMEA records in the same way as previous versions of Xfmea/RCM++, choose Effects Before Causes. This flexible structure assumes that each effect of a failure mode may or may not depend on which cause(s) occurred. When using the RPN risk assessment method, this allows you to use different effect severity ratings for different causes that are associated with the same failure mode if it is appropriate in the context of a particular analysis.

For example, if you have defined a failure mode rather generally, you might encounter a situation like the one diagrammed below where, for the same failure mode, one effect may result if Cause 1 or Cause 2 occurs but a different effect may result if Cause 3 occurs.

It should be noted that a "best practice" FMEA analysis approach typically encourages failure modes to be defined more specifically (i.e., where any of the causes of the failure mode will result in any or all of the effects) and the "Effects Before Causes" structure also supports that type of data entry. You would simply define all of the effects together in the same record (using CTRL+ENTER to force linebreaks in the text box when needed) and then choose a single severity rating that you want to use to calculate the RPN for all of the causes (e.g., the severity of the most serious individual effect, the severity of the most likely effect, or the severity of all effects occurring together). The following picture shows the analysis based on the severity of the most serious effect.

If you will always be defining the failure modes more specifically (i.e., where any of the causes of the failure mode will result in any or all of the effects) and you want the software to display causes and effects at the same level of the hierarchy under the failure mode that they are both associated with, choose Grouped Effects and Causes. This allows you to define the causes and effects associated with a particular failure mode in any order (instead of requiring effects to be entered first as in the "Effects Before Causes" structure). It also stores a separate description and severity rating for each effect. When using the RPN risk assessment method, the software will automatically choose the highest severity rating to calculate the RPN for all of the causes associated with that failure mode.

Choose Causes Before Effects if you are performing a reliability centered maintenance (RCM) analysis and/or you wish to enter information in the following order:
- Functions
- - Functional Failures (i.e., the Failure record in Xfmea)
  - - Failure Modes (i.e., the Cause record in Xfmea)
    - - Effects

This structure assumes that the functional failures will be defined rather generally and requires that there can be only one effect record per cause. To describe multiple effects in the same record, use CTRL+ENTER to force linebreaks in the text box when needed.

Switching Between FMEA Structures

While you can switch the FMEA structures for a particular project, the following limitations apply:

When switching from the "Causes Before Effects" structure to the "Effects Before Causes" structure, all records are converted without changes.
When switching from the "Effects Before Causes" structure to the "Causes Before Effects" structure, each effect record is duplicated under each cause record.
When switching from the "Grouped Effects and Causes" structure to the "Effects Before Causes" structure, all records are converted with the highest severity ratings being used for the new effects.
When switching from the "Effects Before Causes" structure to the "Grouped Effects and Causes" structure, all effect records associated with a given failure are merged into one effect record. All cause records are associated with the new grouped effect record.
You cannot directly switch between the "Causes Before Effects" structure and the "Grouped Effects and Causes" structure. You must first convert to the "Effects Before Causes" structure and then convert to the other structure.