Question

Discuss the differences between the quality analysis methods to reduce
product defects (FMEA, FTA) and the project risk analysis equivalents.

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Answer 1

The Failure Mode, Effects and Criticality Analysis (FMECA) is a reliability evaluation/design technique which examines the potential failure modes within a system and its equipment, in order to determine the effects on equipment and system performance. Each potential failure mode is classified according to its impact on mission success and personnel/equipment safety.” It is a bottom-up method, starting at the component level, which is used to find failure modes and to identify their effects. By adding a criticality analysis, qualitative FMEA becomes quantitative FMECA (failure mode, effects and criticality analysis).

The second method for failure analysis is Fault Tree Analysis (FTA), which is a top-down method used to identify relationships between events, such as subsystem failures and their causes.“Fault Tree Analysis (FTA) is a deductive failure analysis which focuses on one particular undesired event and provides a method for determining causes of this event. In other words, a Fault Tree Analysis is a “top-down” system evaluation procedure in which a qualitative model for a particular undesired event is formed and then evaluated.”

FMEA (Failure Mode and Effects Analysis) is an inductive and bottom-up method to identify failure modes, effects and causes of technical systems.The analysis starts at the component level where the possible component failure modes are identified and it is examined what the consequences are on a higher level. FMEA analysis typically involves a diverse team of people with different backgrounds (eg mechanical design, software, production, maintenance), as this increases the probability that all failures will be identified and the effects will be estimated correctly.The FMEA can be extended to FMECA (Failure Mode, Effects and Criticality Analysis) by adding a criticality analysis. In this way, the purely qualitative FMEA can be made quantitative. In FMECA, the criticality of each failure mode is quantified by the risk priority number (RPN). The risk priority number is the product of three indicators: (a) severity indicator (S), (b) occurrence indicator (O) and (c) detection indicator of a failure (D).The larger the RPN (S x O x D) is, the greater the priority that the risk is lowered with the help of design and quality assuring actions.

Fault Tree Analysis (FTA) is a very powerful systematic way which is widely used for estimating process quality. Starting from the top event, the fault-tree method uses a Boolean algebra and a deductive logical modeling to make a graphical representation of the relations among various failure events at different levels of the process.It enables the root causes of the failure events of a process to be found. This type of logic helps to establish a detailed scheme of relationships between the events in the process that can affect its quality.