Operational Availability and Obsolescence: A Usage-Oriented Approach

SUMMARY & CONCLUSIONSIn a constantly evolving technological context, the sustainability of complex systems can no longer be assessed only through the traditional indicators of reliability, maintainability, and availability (RAM). The obsolescence of components, whether hardware, software, or documentation has become a critical vulnerability factor, compromising the ability of systems to accomplish their missions over the long term. This issue is particularly critical in multifunctional systems, where the failure or unavailability of a subset of components does not necessarily result in total system shutdown but may selectively affect certain missions or functionalities.In this context, traditional approaches, which are often binary and global, prove insufficient to apprehend the differentiated effects of obsolescence. This article proposes a mission-oriented approach to estimating the operational availability of complex systems, by assessing their capacity to accomplish each specific mission within a real-world usage context. A hierarchical modeling framework is introduced, linking the functional structure (missions and functionalities) with the physical structure (systems, subsystems, components). Components are classified according to their mode of acquisition (internal or external) and their nature (repairable or consumable), in order to identify critical vulnerabilities and potential levers for action. To model the interactions between missions, functions, failures, and obsolescence, the method relies on hierarchical Petri nets. A case study focused on an industrial programmable logic controller illustrates the approach. It demonstrates that certain critical functions can remain operational despite component obsolescence and partial failure. The results highlight the value of this approach for anticipating performance degradation due to obsolescence, prioritizing maintenance actions, and guiding management decisions in a mission-oriented availability framework.