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SUMMARY & CONCLUSIONSCommon part modular assemblies composed of multiple Circuit Card Assemblies (CCAs) are increasingly being used in a variety of systems for ease of use and to streamline production. These common part modular assemblies offer an easy baseline solution for a variety of systems and applications. Each application may only require or use certain CCAs during different conditions and calculating the reliability of these components and the system is done independently of each other. Failure rate adjustments of environments and dormancy often require additional independent calculations for each system. This paper showcases the utilization of a modular model approach to analyze the reliability of the CCA modular assemblies, the benefits of this type of model, and limitations.Combining the modular assembly of CCAs into a single model allows for increased utility by permitting configuration changes in use-case, environment, and dormancy. The fictional model presented herein illustrates one modular assembly composed of three CCAs with seven unique use cases for two different systems. The model was created to illustrate the use of modularity and is not representative of any actual real-life system, thus the failure rates are not accurate or typical. With the base system model created, adding additional use cases or copying the assembly into a new system for different use cases is improved and easier. Using modular assemblies additionally allows for the creation of templates to reduce the time needed for updates. Proper planning for modular assemblies allows for ease of updating for obsolescence and design refreshes. By changing the environment factors within the model, the reliability calculation has an inherent higher fidelity than by using the MIL-HDBK-338 adjustment factors. In the modular assembly, circuit cards can be inactive (zeroed out) and active based on need during each environment use case.Overall, creating a modular based model for the CCA modular assembly provides increased utility by encompassing all the CCAs into a single model that can be adjusted for differing use cases, environmental uses, and dormancy applications instead of having individual models for each CCA to demonstrate reliability calculations. Additionally, the modular approach can give more flexibility in adding potential future use cases. Caution should be taken when the system modeled is too complex or requires more dynamic reliability calculations due to constant failure rate models. Moreover, some Reliability & Maintainability (R&M) software tools may have computational difficulty with highly complex models with extensive use cases.