Downloaded from https://www.everyspec.com ADS-79D-HDBK component conditions, commonly used references for grading component condition are employed. Some of these references are as follows: ANSI/AGMA 1010-E95 - Appearance of Gear Teeth -Terminology of Wear and Failure EPRI GS-7352 - Manual of Bearing Failures and Repair in Power Plant Equipment Wilcoxon Research - Bearing Failure: Causes and Cures Barden Precision Bearings - Bearing Failure:
Causes and Cures SKF - Bearing failures and their causes FAG – Roller Bearing Damage Recognition of Damage and Bearing Inspection After assessing the severity of the component‘s condition, engineers scoring the TDAs then consider the specific speeds, loads, temperatures, and lubrication around the component (along with L10 lives for bearings) to determine an estimated time horizon to maintenance or RUL. Currently the estimates for these RULs range from 10 to 100 operational hours, which is a detection improvement over current state-of-the-art chip detectors.
Until the CI maturity is verified and validated, the engineers‘ TDA score on the hardware condition may vary from the actual CI reading provided by the aircraft HUMS or Ground based station output. While the vast majority of the vibratory CI thresholds for US Army rotorcraft are not mature, the incorporation of the sensors and processors on fielded aircraft allows a laboratory/research environment to exist on fleet aircraft performing their missions to facilitate data gathering and threshold maturation. The flight environment provides actual fleet data versus simulated data to be obtained and analyzed for further maturing the alert thresholds.
When components are removed from the aircraft due to legacy maintenance requirements, a confirmation of hardware condition may be made against the vibratory threshold alerts developed for CIs and HIs. When a significant number of hardware confirmations demonstrate acceptable accuracy, the CIs and HIs are adjusted to provide an alert based on data yielded from the fleet aircraft. Since legacy maintenance practices remain in place for continued airworthiness of rotorcraft, the only concern for employing CBM using unvalidated CI/HI algorithms is that of removing components prematurely due to a potential false alert from the CBM system and incurring the additional maintenance costs.
To reduce the number of components removed for CBM false alerts, designated platform working groups involving US Army rotorcraft platform managers, vibration analysts, maintainers, and hardware component experts jointly decide on whether a component should be removed for tear down analysis or wait for legacy inspections and/or chip detectors to provide an indication for removal. This process for data gathering permits time to adjust maintenance alert levels built into the CI/HI algorithms.
The vibratory CBM also increases the reliability of the overall aircraft system provided the sensor hardware reliability is not mission or flight critical and does not cause unscheduled maintenance impacting aircraft readiness. Note, also, the sensors and associated algorithms may be applied to focus on specific component failure modes versus all failure modes of complex components such as a transmissions or engines. 83