Helicopter Health and Usage Monitoring Systems (HUMS) provide many benefits, one of which is the ability to provide real time condition of aircraft systems on-board. Providing the aircraft pilot with pending failure information increases safety and in most cases affords the pilot ample time to perform safe precautionary landings. The information displayed to the pilot must be specific as to the system affected to allow for an immediate, intelligent assessment of the aircraft condition. The predominant challenge facing system engineering is establishing parameter and signal validity prior to generating parameter exceedance alarms. Data fidelity must be carefully considered and accomplished in every aspect prior to generating onboard alarms. The United States Marine Corp CH-46E aircraft program has installed over 130 Honeywell Aircraft Integrated Maintenance Systems (AIMS), which provides a method of providing onboard alarming in three categories. (1) Non-Abort, post flight maintenance required, (2) Pilot informational displayed on the Control Display Navigation Unit, (3) Master Caution panel illumination for flight abort alarms. These three alarm categories represent the best approach to providing aircrew and maintenance personnel with system critical information for continued safe operation of the aircraft while performing maintenance in a field environment. The AIMS' current configuration has over 100 alarms programmed for cockpit display if advisory criteria are valid. System architecture requires several faulting and alarming mechanisms working together to ensure data fidelity has been met prior to generating an alarm. Several techniques are employed to validate incoming engine parameter signals, such as range checking and rate of change qualification. If signals do not pass validity, alarming is suppressed. Vibration alarming is slightly different. The alarming mechanism utilized is a time hysteresis method, which employs a band alarm with an amplitude and time duration trigger, as well as an amplitude and time duration release. If validity fails, the alarming is suppressed. The Safety aspects are obvious; however just as significant are the maintenance savings recognized from reduction of component collateral damage. . With the belief that all pilots need to know the condition of the machine they are flying at all times, on-board alarming of critical flight components is a necessary function of HUMS. Condition based maintenance starts with safe landing of the aircraft without mishap. On-board alarming will provide increased safety, reliability, and maintainability for the fleet. Savings are incalculable as prevention of the mishap is priceless.
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