Downloaded from https://www.everyspec.com ADS-79D-HDBK For predicted RUL calculations based on life usage algorithms that measure fatigue or thermal damage, the engine manufacturer should develop models and establish life limits which follow established military and commercial standards as referenced in Appendix D. These life limits should be reserved for only the most critical and difficult to detect failure modes that are analyzed and investigated during engine qualification testing. G.7.5 Auxiliary power units. Designs of APUs over time have become more efficient and reliable. The FMECA should establish the need for monitoring fault modes and establishing CIs and HIs for the APU.
Trade studies in conjunction with the FMECA should establish the optimum design of sensors and data management, balancing the relative ease of maintenance and reliability of the specific APU and airframe with added cost of CBM data management. The process for developing CI and HI for the APU is found in Appendix D and E. Integration of the sensors, signal processing and data management for the APU with the CBM system of the aircraft should be a high priority in the design of the APU monitoring system.
Specific objectives for fault detection, mean maintenance hours to repair, and MTBF are controlled by the cognizant government engineering office, based on recommendations from the aircraft manufacturer. 135