Real-time System-wide Safety Assurance (RSSA) is a major, emerging strategic thrust for NASA aviation research. The detailed definition of RSSA requires further clarity to facilitate communication, prioritization, and progress in the research community. Over the past year, our team gathered and refined material from domain experts, NASA researchers, and prior literature to formulate key RSSA definitions and underlying concepts. We found relevant elements of RSSA in several existing fields of research, including system safety, data mining, operations modeling, and system health management. The foundational definitions and concepts presented here provide a useful and consistent reference point for RSSA research and development as it moves forward to new projects and capabilities.

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Real-time System-wide Safety Assurance (RSSA) is one of six strategic thrusts defined by NASA's Aeronautics Research Mission Directorate to articulate its vision for the future of aviation, and to drive research efforts in the near future. A framework of metrics is developed as part of work supporting the definition of an RSSA research roadmap. The bases for metric development are an RSSA descriptive model outlining the system architecture at a conceptual level, a review of previous safety metrics used to measure the impact of NASA research, and the delineation of challenges and opportunities stemming from unique systemic features in RSSA. The metrics are structured in a three-tier hierarchy that mirrors the functional decomposition of RSSA. Among them, mid-level metrics are novel and significantly distinct from prior aviation safety measures. Top-level metrics circumvent notable challenges associated with the current use of aggregate accident statistics, whereas low-level metrics are adopted from a broad review of the state of the art. All metrics are defined and discussed in detail. Qualitative validation indicates the framework meets its purpose and successfully addresses salient challenges. Aspects for further improvement and requisite future work are discussed.