Failure Mode, Effects, and Criticality Analysis (FMECA)

FMECA enhances the qualitative aspects of FMEA by introducing a quantitative criticality assessment, as defined in standards like MIL-STD-1629A. Criticality is typically calculated in two ways: modal criticality and item criticality. Modal criticality is calculated for each failure mode and can be expressed as [latex]C_m = lambda_p alpha beta K_e[/latex], where \(lambda_p\) is the part failure rate, \(alpha\) is the failure mode ratio (the fraction of part failures attributable to this mode), \(beta\) is the conditional probability that the failure effect will result, and \(K_e\) is the severity factor. Item criticality is then the sum of the modal criticalities for all failure modes of a particular item.

This quantitative approach is particularly valuable in high-risk industries like aerospace, defense, and nuclear power, where a more granular and defensible method than the standard RPN is required. The output is often a criticality matrix, which plots severity categories against probability of occurrence levels. This matrix provides a clear visual representation of the highest-risk items, allowing engineers and managers to focus resources on mitigating the most critical potential failures, especially those that could lead to catastrophic system loss or loss of life.