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This paper explores the ramifications of key elements of the FAA's Advisory Circular (AC) 29 MG 15 (Airworthiness Approval of Rotorcraft Health Usage Monitoring Systems (HUMSs)) in terms of the current and emerging HUMS technology, including: a) end-to-end criticality assessments; b) special considerations for COTS ground equipment and software; c) credit validation for monitoring techniques, algorithms, parameters and rejection criteria; d) intervention actions associated with HUMS monitoring data; e) certification mitigation actions to lower the criticality levels (and costs) of all or part of the HUMS system. The next generation HUMSs will become smarter and more integrated, and will continue to change how aircraft are maintained. With this integration and dependence of maintenance actions on HUMSs comes increased regulation. In the United States and abroad, airworthiness authorities are furnishing guidance for the certification and fielding of HUMSs. HUMS suppliers are expanding the roles and capabilities of HUMSs. New directions include shifts to diagnosis and figure maintenance-requirement prediction, early indication of potential problems, component management, information generation, and aircraft system-wide collection and analysis. These new capabilities will change how aircraft are maintained; the decision of when to perform maintenance is being automated.