Downloaded from https://www.everyspec.com ADS-79D-HDBK HIs may have any combination of these statuses as determined by the failure mode monitored or the redundancy of the component. FIGURE D-2. Example color code score card The maintenance descriptions associated with the colors yellow, orange, and red for ―Maintenance Action Required‖ were obtained from Department of the Army Pamphlet (DA PAM) 738-751 ―Functional Users Manual for the Army Maintenance Management System – Aviation‖ to directly correlate the CBM information to actionable maintenance information understood by the field maintainers. The ―Time Horizon to Maintenance‖ is associated with the estimated Remaining Useful Life (RUL).
RUL is very important to the prognostics and diagnostics process for engines and transmissions. With regard to lifing, there are generally two fatigue life approaches to metal design life for critical aircraft components: ―safe life‖ and ―damage tolerant‖ designs. Fixed wing aircraft typically employ the ―damage tolerant‖ design approach wherein there exists an attribute of a metal component that permits it to retain residual strength for a period of usage without repair after the component has sustained damage from specified levels of fatigue, corrosion, or accident. Damage is allowed to progress:
(1) to an inspectable flaw size detectable within a specified probability and confidence; or (2) when the component fails in a safe manner due to a redundant load path or crack stopping design. Rotorcraft and their propulsion systems are typically designed using a ―safe life‖ approach for the metals in critical components to resist fatigue without ancillary damage and thus ensure safety. The 81