Risk priority number (RPN) is a widely used approach, and it is a powerful means to assess the criticality of modes in a failure modes, effects, and criticality analysis (FMECA) worksheet. In the application of the traditional FMECA, the RPN is determined to rank the failure modes; however, the method has been criticized several times for having many drawbacks and weaknesses, such as the presence of gaps in the range of admissible values, the duplicates value provided by different combinations of the base factors, and the high sensitivity to small changes. This paper analyses and compares some alternative RPN formulation proposed in the literature to overcome these limits. This paper takes into account only the alternative RPN, which proposes a powerful solution without increasing the computational complexity and remaining coherent to the classical idea included in the international standard IEC 60812. In order to compare the advantages and disadvantages of these alternative RPNs, an FMECA was developed for a heating, ventilation, and air condition (HVAC) system in railway application. The critical analysis of the comparison can provide recommendations and suggestions regarding the choice of the alternative RPN based on the type of application. Finally, this paper takes into account the scales reduction of possible values related to the parameters (i.e., occurrence, severity, and detection), which influence the assessment of the RPN. This approach allows the designers to mitigate the drawbacks related to the full scale and provide an easier and faster assessment of the scores to evaluate the criticality analysis and prioritization. INDEX TERMS FMECA, railway engineering, reliability theory, risk priority number.

This paper focuses on the development of a new logistic approach based on reliability and maintenance assessment, with the final aim of establishing a more efficient interval for the maintenance activities for Unmanned Aerial Vehicles (UAV). In the first part, we develop an architectural philosophy to obtain a more detailed reliability evaluation; then, we study the intrinsic reliability at the design stage in order to avoid severe critical issues in the UAV. In the second part, we compare different maintenance philosophies for UAVs and develop the concepts of preventive and corrective maintenance that consider the system subjected (until real “hard failure”) to partial performance degradation (“soft failure”). Finally, by evaluation of the uncertainty through the confidence interval, we determine the new soft failure limits, taking into account the general knowledge of the systems and subsystems in order to guarantee the proper preventive maintenance interval.

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The renewable energy industry has been growing\ud remarkably in the last years and the Fukushima event has\ud given a further incentive. In this context, solar radiation\ud represents one of the most accessible and clean energy\ud resources. For this reason the number and size of the\ud photovoltaic (PV) systems is growing and consequently the\ud amount of the investments and the related opportunities and\ud risks are increasing. Therefore, the optimization of electrical\ud performances of PV plants and the assessment of their\ud quality and reliability are important for both the investors\ud and the manufacturers. In a previous work some aspects,\ud fundamental for the efficiency evaluation of PV panels,\ud have been considered with particular attention to the\ud presence of pollution and dust on the panel surface. On the\ud basis of the results so obtained, an experimental activity\ud based on the electrical characterization of some PV modules\ud in presence of powder is proposed in this paper as evolution.\ud The results, in terms of power analysis, were analyzed by\ud means of a statistical approach in order to identify the\ud behavior of PV modules, with a given confidence interval.\ud The final aim is to use a PV panel as “reference panel” in\ud order to monitor the operating condition of a more complex\ud PV plant

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