FMEA: the 7 steps and action priority (AIAG–VDA)
FMEA (Failure Mode and Effects Analysis) is a preventive risk analysis: it systematically works out how a product or process can fail, with what effect, for what cause, and which actions prevent or detect the failure. Since 2019 the joint handbook of the American AIAG and the German VDA has been the reference. The main types are design FMEA (DFMEA), process FMEA (PFMEA) and FMEA for monitoring and system response (FMEA-MSR).
The 7 steps
- Planning and preparation: purpose, scope, team and timing (the 5Ts: InTent, Timing, Team, Tasks, Tools).
- Structure analysis: building up the elements of the system or process and their interfaces.
- Function analysis: assigning functions and requirements to each element.
- Failure analysis: building the failure chain (failure effect – failure mode – failure cause).
- Risk analysis: current prevention and detection controls, and rating severity (S), occurrence (O) and detection (D) from 1 to 10.
- Optimisation: actions with owners and due dates, followed by re-rating.
- Results documentation: summary and communication.
Rating S, O and D
- Severity (S): the consequence of the failure effect. 9–10: a safety or regulatory requirement is affected; 1: no discernible effect.
- Occurrence (O): how likely the failure cause is to occur with the current prevention controls.
- Detection (D): how likely the current controls are to detect the failure before it reaches the customer. 1: almost certain detection; 10: cannot be detected.
Action priority (AP) instead of RPN
The former risk priority number (RPN = S × O × D) weighted the three factors equally, so a severe but rare failure could end up with a low RPN. The AIAG–VDA method instead uses a table that assigns high (H), medium (M) or low (L) action priority to each S–O–D combination, giving severity the most weight, then occurrence, then detection. High priority requires action, or a justification of why current controls are adequate.
The AP table is part of the handbook and is not reproduced here; use the official publication or the built-in table of your FMEA software.