Failure mode and effects analysis (FMEA) – also referred to as “failure modes“, was one of the first highly structured, systematic techniques for failure analysis. It was developed by reliability engineers in the late 1950s to study problems that might arise from malfunctions of military systems. An FMEA is often the first step of a system reliability study. It involves reviewing as many components, assemblies, and subsystems as possible to identify failure modes, and their causes and effects. For each component, the failure modes and their resulting effects on the rest of the system are recorded in a specific FMEA worksheet. An FMEA can be a qualitative analysis, but may be put on a quantitative basis when mathematical failure rate models are combined with a statistical failure mode ratio database.
A few different types of FMEA analyses exist, such as:
- Functional/System – focuses on global system functions;
- Design – focuses on components and subsystems;
- Service – focuses on service functions;
- Process – considers potential process induced failures in manufacturing and assembly processes; and
- Software – focuses on software functions and algorithms
Sometimes FMEA is extended to FMECA (failure mode, effects and criticality analysis) to indicate that criticality analysis is performed too.
FMEA is an inductive reasoning (forward logic) single point of failure analysis and is a core task in reliability engineering, safety engineering and quality engineering.
A successful FMEA activity helps identify potential failure modes based on experience with similar products and processes—or based on common physics of failure logic. It is widely used in development and manufacturing industries in various phases of the product life cycle. Effects analysis refers to studying the consequences of those failures on different system levels.
Functional analyses are needed as an input to determine correct failure modes, at all system levels, both for functional FMEA or Piece-Part (hardware) FMEA. An FMEA is used to structure Mitigation for Risk reduction based on either failure (mode) effect severity reduction or based on lowering the probability of failure or both. The FMEA is in principle a full inductive (forward logic) analysis, however the failure probability can only be estimated or reduced by understanding the failure mechanism. Ideally this probability shall be lowered to “impossible to occur” by eliminating the (root) causes. It is therefore important to include in the FMEA an appropriate depth of information on the causes of failure (deductive analysis).
Why Do FMEA / FMECA?
Major benefits derived from a properly implemented FMEA / FMECA effort are as follows:
- It provides a documented method for selecting a design with a high probability of successful operation and safety;
- A documented uniform method of assessing potential failure mechanisms, failure modes and their impact on system operation, resulting in a list of failure modes ranked according to the seriousness of their system impact and likelihood of occurrence;
- Early identification of single failure points (SFPS) and system interface problems, which may be critical to mission success and/or safety. They also provide a method of verifying that switching between redundant elements is not jeopardised by postulated single failures;
- An effective method for evaluating the effect of proposed changes to the design and/or operational procedures on mission success and safety;
- A basis for in-flight troubleshooting procedures and for locating performance monitoring and fault-detection devices; and
- Criteria for early planning of tests.
From the above list, early identifications of SFPS, input to the troubleshooting procedure and locating of performance monitoring / fault detection devices are probably the most important benefits of the FMECA. In addition, the FMECA procedures are straightforward and allow orderly evaluation of the design.
The FMEA should be updated whenever:
- A new cycle begins (new product/process);
- Changes are made to the operating conditions;
- A change is made in the design;
- New regulations are instituted; and
- Customer feedback indicates a problem.
- Development of system requirements that minimise the likelihood of failures;
- Development of designs and test systems to ensure that the failures have been eliminated or the risk is reduced to acceptable level;
- Development and evaluation of diagnostic systems; and
- To help with design choices (trade-off analysis).
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