Criticality Determination of HUMS Applications for Life-Adjustment

Health and Usage Monitoring Systems installed on modern rotorcraft can be used for substantiating component life extensions leveraging actual loads and usage information, reducing uncertainty from assumed loads and usage. One challenge inhibiting fielding such extensions is lack of clearly defined methodology to robustly determine the criticality of the HUMS application. This paper proposes a semi-quantifiable methodology for determining criticality. It is applicable to both loads- and usage-based approaches for part-number-level life adjustments. The approach relies on baseline component design data and is independent of HUMS data to eliminate the possibility of a HUMS errors affecting the bounding criticality assigned to the application. It takes into account the specifics of the component, including the SN working curve, relevant component failure mode severity, and validated compensating provisions that either reduces the likelihood of the component failure mode and/or provides significant "hidden" conservatism not explicitly considered in the assigned uncompensated component failure severity level.