System-Level CBM/PBM Aggregation: A Unified Framework for Proactive and Reactive Metrics in Redundant Architectures
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Abstract
Assessing the in-service performance of Condition-Based Maintenance (CBM) and Predictive-Based Maintenance (PBM) solutions remains a challenge, as traditional reliability formulas often fail to capture the true nature of proactive operations. First, this paper formally proves that applying classic reactive formulas to CBM/PBM KPIs (Key Performance Indicators) leads to a quantifiable underestimation of the actual Mean Time Between Failures (MTBF). While previous work established aggregation laws for "in-series" equipment configurations, this study extends the mathematical framework to "in-parallel" architectures. Indeed, such specific aggregation laws are essential for evaluating the global performance of CBM/PBM solutions applied to fault-tolerant systems involving redundancy.
Subsequently, this paper introduces a unified theory based on two distinct frames of reference: the "Operational Timeline," using the Mean Time Between Proactive Removals (MTBPR) to measure logistical workload, and the "Effectiveness Timeline," using the Mean Lifetime Reduction (MLR) correction term to account for the residual life lost due to early removal. Following a review of the laws governing MTBF and the reliability function, we demonstrate the laws applicable to key CBM/PBM indicators, including Recall and Precision-based metrics.
Finally, this framework elevates equipment-level performance into system-wide strategic indicators. Ultimately, this enables a holistic evaluation of the global performance of a CBM/PBM solution at the system or aircraft level by balancing the Proactive Aggregated Recall (PAR) for detection coverage, and the Proactive Aggregated Precision (PAP) for detection confidence.
How to Cite
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PBM, CBM, System reliability, Aggregation laws, Redundant architecture, PHM KPI, Performance metrics
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