FMEA stands for Failure Modes and Effects Analysis, while FMECA stands for Failure Modes, Effects, and Criticality Analysis.

The FMEA/FMECA process is a systematic method used to evaluate and prioritize potential failure modes of a system, process, or product, along with their effects and criticality. The primary purpose of FMEA/FMECA in RCM is to identify and address potential weaknesses before they lead to actual failures.

The FMEA/FMECA should be done collaboratively. A cross-functional team, consisting (where possible) of designers, maintainers, safety officers and operators, led by a facilitator, should brainstorm all functions, functional failures and failure modes. An open, judgement-free environment should be fostered to gain the best results.

The difference between the FMEA and FMECA is the C - the criticality. John Moubray (one of the father's of RCM) only described a FMEA, but then went on to describe how to calculate the criticality (via a PRN, now commonly known as a RPN). Defining the consequence and criticality is always part of RCM. The question is when to do it. The FMEA/FMECA stage is a collaborative brain-storming event. We believe that such an event should not include the criticality - define the FMEA first. The criticality is dependent on the decision logic and consequences. These are added to the FMEA in a later stage, and the criticality should only be calculated when you have all the necessary data. So in the process below, omit step 5, to only perform a FMEA.

The FMEA/FMECA process addresses the first 5 questions of the RCM Process and involves the following steps:

1. Identification of Functions: List all functions (primary and secondary) the system should provide.
2. Identification of Functional Failures: For each function listed, list all functional failures - how the system can fail to fulfil its function.
3. Identification of Failure Modes: For each functional failure listed, list all possible ways (events) in which the system can fail.
4. Determination of Failure Effects: For each failure mode listed, assess the effects of each identified failure mode (What happens?)
5. Evaluation of Criticality: For each failure mode listed, assign a criticality rating based on the severity of its consequences and the likelihood of occurrence (How does it matter?)