Other FMEA Guidelines
As FMEA worksheets are completed, the following general guidelines should be kept in mind:
• Analyse different design options separately to ensure that reliability implications can be considered when deciding on which option to choose.
• If the system operates in more than one phase in which different functional relationships or operating modes exist, conduct analyses for all phases and modes of system application. For example, when performing a functional FMEA for an aircraft, a failure with the landing gear does not adversely impact the plane while it is cruising but does have a very negative impact during landing. Failure consequences that are different for the various modes of operation must be considered.
• If redundant sub-systems exist, consider the effects of redundancy by evaluating the effects of failure modes when the redundant sub-system is available and is not available.
• Determine and state the viewpoint(s) being considered in the FMEA analysis. Different viewpoints include safety, mission success, availability, repair cost, failure mode, effect detectability, etc.. Otherwise, a safety-related FMEA, for example, might give a low criticality number to an item whose reliability seriously affects availability but which is not safety critical.
• If the system under development is similar to an existing system, look at field and experience data, including warranty information, benchmarking studies, risk analysis results, customer feedback and historical quality data from the field to gain additional insights.
• As the design evolves, update the FMEA so that it can be used to influence the design and provide comprehensive documentation upon design completion. This includes using test results to update the analysis throughout the implementation and production stages.
The goal of FMEAs is to get correct results using the fastest, least expensive approach. As a result, consider for complete evaluation in a FMEA only those potential failure modes that are real or legitimate issues. For a new design, particularly when the effects of failure seriously affect safety, reliability, high warranty costs, etc., the FMEA should take into account the failure modes of all components. For an existing design, the FMEA may need to consider only functional failure modes of sub-assemblies, particularly for modular components in electronic systems where design details are not known. When failure modes present unacceptable consequences, the design must either be modified to comply with supplied requirements, or recommendations for fixing or improving the design must be fed back into the analysis.