Basic Terms

The following covers some basic FMEA terminology.

Failure

The loss of a function under stated conditions.

Failure mode

The specific manner or way by which a failure occurs in terms of failure of the item (being a part or (sub) system) function under investigation; it may generally describe the way the failure occurs. It shall at least clearly describe a (end) failure state of the item (or function in case of a Functional FMEA) under consideration. It is the result of the failure mechanism (cause of the failure mode). For example; a fully fractured axle, a deformed axle or a fully open or fully closed electrical contact are each a separate failure mode.

Failure cause and/or mechanism

Defects in requirements, design, process, quality control, handling or part application, which are the underlying cause or sequence of causes that initiate a process (mechanism) that leads to a failure mode over a certain time. A failure mode may have more causes. For example; "fatigue or corrosion of a structural beam" or "fretting corrosion in an electrical contact" is a failure mechanism and in itself (likely) not a failure mode. The related failure mode (end state) is a "full fracture of structural beam" or "an open electrical contact". The initial cause might have been "Improper application of corrosion protection layer (paint)" and /or "(abnormal) vibration input from another (possibly failed) system".

Failure effect

Immediate consequences of a failure on operation, function or functionality, or status of some item.

Indenture levels (bill of material or functional breakdown)

An identifier for system level and thereby item complexity. Complexity increases as levels are closer to one.

Local effect

The failure effect as it applies to the item under analysis.

Next higher level effect

The failure effect as it applies at the next higher indenture level.

End effect

The failure effect at the highest indenture level or total system.

Detection

The means of detection of the failure mode by maintainer, operator or built in detection system, including estimated dormancy period (if applicable)

Risk Priority Number (RPN)

Severity (of the event) * Probability (of the event occurring) * Detection (Probability that the event would not be detected before the user was aware of it)

Severity

The consequences of a failure mode. Severity considers the worst potential consequence of a failure, determined by the degree of injury, property damage, system damage and/or time lost to repair the failure.

Remarks / mitigation / actions

Additional info, including the proposed mitigation or actions used to lower a risk or justify a risk level or scenario.