FMEA for multiple failures

Failure mode and effects analysis (FMEA) usually only considers single failures in a system. This is because the consideration of all possible combinations of failures in a system is impractical for any but the very simplest example systems. Even if simulation is used to automate the work of producing an FMEA report, consideration of all possible combinations of failures is not possible, and even if it was possible, an engineer could not be expected to spend the time needed in order to read, understand and act on all of the results. This paper shows how to use approximate failure rates for components to select the most likely combinations of failures for simulation, and how to prune the resulting report to such an extent that it is practical for an engineer to study and act on the results. The strategy outlined in the paper has been applied to a number of automotive electrical subsystems, and the results have confirmed that the strategy described works well for realistically complex subsystems.