*3.1. Problems with the Existing RPN Evaluation Method*

There are numerous problems with the existing RPN evaluation method; the following issues directly affect the evaluation [4,18,19].


Overestimating RPN leads to the implementation of unnecessary countermeasures and an excessively safe system design, increasing system installation costs. In contrast, if RPN is underestimated, the appropriate measures for the effects of each failure mode are not established, risking the preventability of future accidents. This can then lead to huge time and money losses. For example, in 1998, GM in the United States received a \$4.97 billion fine to compensate the explosion of an automobile fuel tank following a traffic accident. According to the company internal report, the reliability assessment recognized that there was an explosion risk if the fuel tank was manufactured at a low cost. In spite of having access to this information, the vehicle was released without any modifications, leading to the highest payout for individuals in American history [5].

Although FMEA poses numerous problems, it is the most frequently applied reliability evaluation method across all industries because of its simple and systematic analysis. To strengthen the FMEA evaluation performance to supplement the existing problems of FMEA, researchers have investigated methods and approaches from various perspectives [21,22], including a method where, after pre-selecting the factors necessary for FMEA [23], the relationship between the failure mode and effect can be determined by applying various control methods such as fuzzy logic, neural network, functional inference theory [10–14,24–28]; a FMEA matrix, which graphically assesses the relationship between the elements of a system, failure modes, and failure effects [29,30]; methods to effectively prepare the appropriate FMEA form for a given objective [31,32]; methods to provide a worksheet that automatically generates the FMEA using past FMEA data [33]; and other approaches to derive more objective FMEA results [34].
