FMECA
FMECA stands for Failure Mode, Effects and Criticality Analysis and thus for an expansion of FMEA.
“Criticality”, i.e. the criticality analysis, takes on a quantitative description, based on FMEA, of the interaction between the degree of severity and the likelihood of occurrence of the failure types identified in the FMEA and their effects. Simply put, the FMECA determines whether the system or process still functions despite the existing likelihood and severity of demonstrated failure modes.
The higher the criticality determined in the FMECA, i.e. the likelihood of failure and the severity of assumed failure types, the more urgency is required to implement corresponding countermeasures. It is ultimately a case of using this tool for preventative quality assurance and identifying and eliminating failures in production processes and systems at an early stage. With a low criticality, subsequent costs in terms of reworking, troubleshooting, and production downtime are reduced and the efficiency of all processes is noticeably increased.
On this basis, an investigation is conducted as to whether undesired effects occur (e.g. safety-critical effects) or whether sufficient diagnosis coverage already exists. This creates a basis for analysis to determine the current status compared with specified requirements. The basis for analysis is used:
- as a data and information basis for security: failure rates and basic events for fault tree analyses (FTA)
- Availability analyses
- Logistical analyses (maintenance, upkeep, spare parts, etc.)
- The determination of detection coverage. What percentage of all failures occurring in the company is detected by monitors and/or tests? for instance, for power-on test or acceptance test
- The determination of isolation coverage (diagnostic support)
“What percentage of all failures occurring in the company is assigned to the actual defective component by the monitor and/or test?”
- The determination of critical individual failures
Sequence:
Definition of the system boundaries, aims and boundary conditions
Definition of the level of detail and identification of the components, signals, and/or functions to be analyzed
Determination of failure types
Breakdown of the failure rates from a reliability prediction (or other data sources) into the failure types
Determination of failure effects
Determination of the criticality of the failure effects (only FMECA)
Determination of the failure rates at the failure effect levels (= FMES)
Determination of detection and isolation coverage based on the entered tests for failure detection
Comparison of the FMECA/FMES results with the requirements and identification of weaknesses (non-compliances)
Identification of necessary control functions (monitors) and tests, and the corresponding safe failure reactions (requirements specification)
Customer benefits/advantages FMECA:
Targeted identification of necessary control functions (monitors) and tests, including determining the failure reactions/strategies
Reduction in repair costs by optimizing detection and isolation coverage
Functional preparation of failure rates from the reliability prediction for the fault tree analysis (FTA)
Evidence documentation to fulfill the requirements of the specification or to achieve the certification
Standards:
FMEA/FMES (civil aviation): SAE ARP-4761, ABD0100.1.3
FMECA (military aviation): MIL-STD 1629
ECSS-Q-30-02A (directive)