Rotorcraft structural methodology has traditionally relied upon the use of three sources of conservatism for design and fatigue substantiation of rotorcraft dynamic components: fatigue strength, flight loads, and the aircraft usage spectrum. In contrast to the thousands of engineering hours typically spent quantifying component strength and loads through full scale laboratory and flight testing, definition of the usage spectrum has traditionally relied on legacy specifications, pilot surveys, and rotorcraft original equipment manufacturer (OEM) historical knowledge of rotorcraft usage. Significant and largely untapped value lies in the application of HUMS recorded flight parameter data and regime recognition (RR) algorithms to monitor fleet wide usage metrics and to support development of a data driven usage spectrum that maintains the intended conservatism of the original usage spectrum. This paper presents the methods and tools that were used to determine actual fleet usage rates for one very significant and easy to detect damaging regime for the S-92® main rotor blade using 700,000 flight hours of S-92® rotorcraft fleet HUMS data. The calculated retirement time (CRT) based on this updated usage demonstrated that the main rotor blade can be safely extended from a retirement time of 22,000 to ＞30,000 hours.
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