Probabilistic Rotorcraft Usage Spectrum Development Using Recognized Maneuvers

Presently the fatigue lives of H-53E dynamic components and airframe are based on a usage spectrum developed using pilot surveys. In order to better define the usage spectrum and to extend component and airframe fatigue life, the Integrated Mechanical Diagnostic (IMD/HUM) System is being installed on the U.S. Navy H-53 rotorcraft. So far, 157 aircraft are equipped with IMD systems and 77,680 flight hours of good data have been recorded. This paper analyzes the HUMS data using regime recognition. The wide variations in regime utilizations from rotorcraft to rotorcraft were characterized using the Normal and the Weibull probability distributions. The unique distributions parameters' mean and standard deviation, Weibull slope and Weibull characteristic values were determined for 46 regimes of the H-53E usage spectrum. The probabilistic fleet usage spectrum of various severities, 50th, 93.3th, 97.7th, and 99.9th percentiles were created using distribution parameters and damaging status of the regimes. The approach helped to create a mean plus 2 sigma spectrum and a Fleet Composite Worst Case Usage Spectrum (FCWCS) to fulfill U.S. Army ADS-79E requirements. The impact of usage spectrum severities on rotorcraft component fatigue life and reliability are assessed. The individual components Fatigue Life Expended (FLEs) were computed to determine the feasibility of Condition Based Maintenance (CBM).