8 Part 8: Annex
8.1 Method References
8.1.7 Fault/Reliability Analysis
Usage
Preparing Hardware Architecture, Preparing Hardware Specification, Performing Logistic Calculations and Analyses, Performing and Evaluating Safety and Security Analysis
Reference
Purpose
The objective of the »Fault/Reliability Analysis is the identification of faults and the checking of the reliability of a system. For the fault/reliability analysis the following methods may be used:
Failure Mode Analysis (FMEA/FMECA)
FMEA/FMECA is a methodical integrated part of system development and quality assurance. It is used to increase the functional reliability and the reliability of »Work Products or processes and to minimize the impact of faults. In addition to the functional and physical impact, this includes also the life cycle costs (warranty or courtesy costs, maintenance concept, product liability).
Within the framework of the analysis, a team of experienced experts from different disciplines will discuss possible failure modes, their causes, their effects and importance to the project for each individual technical or functional structural element.
Fault Tree Analysis
The fault tree analysis (according to the German standard DIN 25424) is a proven multi-purpose analysis method. It is used for modeling the functional system and quantifying the reliability of the system. Starting with the "undesired event" (system failure), the functions/failure modes of the components and the actions required to operate a system are determined "top down". The result is the Boolean model (the fault tree) that is quantified by using reliability parameters.
Reliability Models
A reliability model serves for the identification, compaction and verification of reliability requirements. Based on the user-oriented requirements and the operational environment, the system has to be described by the model completely or adaptively.
The reliability model should not only be able to provide information about the achievement of the quality targets of the users, but also about the related criteria and the intermediate objectives that have to be achieved (increase in reliability) and the impact of technical changes.
Reliability Prediction of Electronic Equipment (MIL-HDBK 217)
For many years, MIL-HDBK-217 has been a standard method for reliability prediction. The handbook includes a number of empirically developed failure rate models that are based on historical component part failure rates for a broad range of component types. Models are available for practically all electric/electronic parts and also for some electromechanical parts. All models predict reliability in relation to failures per million operating hours and assume an exponential distribution (constant failure rate) that permits the addition of failure rates in order to determine higher equipment reliabilities. The handbook includes two prediction models (the component load technique and the component counting technique) and takes into account 14 different work environments, such as attached to the ground or observed on-board. Typical factors for determining the component failure rate include a temperature factor, a performance factor, a load factor, a quality factor and an environmental factor in addition to the basic failure rate.