FMEA is a bottom-up, inductive analytical method which may be performed at either the functional or piece-part level.
FMECA extends FMEA by including a criticality analysis, which is used to chart the probability of failure modes against the severity of their consequences.
The result highlights failure modes with relatively high probability and severity of consequences, allowing remedial effort to be directed where it will produce the greatest value.
[1] By the early 1960s, contractors for the U.S. National Aeronautics and Space Administration (NASA) were using variations of FMECA under a variety of names.
[4] FMECA was subsequently used on other NASA programs including Viking, Voyager, Magellan, and Galileo.
Piece-part FMECA considers the effects of individual component failures, such as resistors, transistors, microcircuits, or valves.
However, Functional FMEAs can be performed much earlier, may help to better structure the complete risk assessment and provide other type of insight in mitigation options.
The criticality analysis may be quantitative or qualitative, depending on the availability of supporting part failure data.
Functional descriptions are created for the systems and allocated to the subsystems, covering all operational modes and mission phases.
For each piece-part or each function covered by the analysis, a complete list of failure modes is developed.
Failure effects are determined and entered for each row of the FMECA matrix, considering the criteria identified in the ground rules.
Severity classification is assigned for each failure mode of each unique item and entered on the FMECA matrix, based upon system level consequences.
One of the following will be entered on each row of the FMECA matrix: Failure mode criticality assessment may be qualitative or quantitative.
For qualitative assessment, a mishap probability code or number is assigned and entered on the matrix.
is usually fed into the FMECA from a failure rate prediction based on MIL–HDBK–217, PRISM, RIAC 217Plus, or a similar model.
For functional level FMECA, engineering judgment may be required to assign failure mode ratio.
After performing FMECA, recommendations are made to design to reduce the consequences of critical failures.
This may include selecting components with higher reliability, reducing the stress level at which a critical item operates, or adding redundancy or monitoring to the system.
FMECA is the most popular tool for failure and criticality analysis of systems for performance enhancement.
The FMECA is widely used for the failure mode identification and prioritization of mechanical systems and their subsystems for predictive maintenance.
RAC CRTA–FMECA and MIL–HDBK–338 both identify Risk Priority Number (RPN) calculation as an alternate method to criticality analysis.
Weaknesses include the extensive labor required, the large number of trivial cases considered, and inability to deal with multiple-failure scenarios or unplanned cross-system effects such as sneak circuits.