Downloaded from https://www.everyspec.com ADS-79D-HDBK c. Abnormal wear is a wear rate beyond the level of normal rubbing wear caused by overload, overspeed, over age, contamination, poor lubrication, etc. Once initiated, this abnormal state continues, eventually leading to component failure. These wear cycles should be trended over time. Once a fault is initiated, it is critical to monitor not only the amount of debris but also a measure of the rate it is being generated since rate is the most useful in determining RUL estimates. It should be noted that wear metal concentrations in oil are subject to variability.
69 The rate of wear debris release is not linear with time and for many fault mechanisms, wear occurs in bursts. 70 71 Wear particle release is event driven. For instance, increased load or speed may result in increased wear events. 72 Filters remove the majority of debris particles greater than the filter pore size. Thus an oil sample only captures new wear and small, suspended, old wear. Wear metal analysis methods have particle size limitations that should be included in evaluations. For example, inductively coupled plasma (ICP) metal analyses are limited to those particles below nominally three microns.
It should also be noted that gearbox geometry may trap particles in areas that are not in the oil flow path and thus prevent them from being detected. M.5.1.3 Oil Filter Monitoring: Oil filters should be monitored to assess the level of filter blockage and prognosticate the need for filter replacement or additional mechanical system maintenance. With the move to finer filtration, Filter Debris Analysis (FDA) should be utilized for wear assessment. 73 FDA has been shown to provide earlier warning on abnormal wear conditions than sampled oil analysis due to the fact the filter captures approximately 95% of all debris, which enters the filter for the filter size rating.
74 M.5.2 Monitoring Location Options: Oil condition and debris analysis can be performed on-aircraft or off-aircraft as shown in Figure M-1 and Table M-I with the oil obtained or monitored prior to entering a filter element. M.5.2.1 Off-aircraft: In off-aircraft sampled oil analysis, a small quantity of oil is taken from the component lubrication system and analyzed off-aircraft ( off-line ). Testing may be performed in a laboratory, which is the current Army practice, or at the flight-line ( at-line ). 69 Toms, L and A. Toms., ―Machinery Oil Analysis - Methods, Automation & Benefits‖, 3rd Edition, STLE, Park Ridge, IL, 2008, ISBN: 978-0-9817512-0-7. 70 Muir, D.
and Howe B., ―In-Line Oil Debris Monitor (ODM) for the Advanced Tactical Fighting Engine‖, SAE Aerospace Atlantic Congress, 961308, May 1996 71 Miller, J.L. and D. Kitaljevich. In-line Oil Debris Monitor for Aircraft Engine Condition Assessment, IEEE, 0- 7803-5846-5, 2000. 72 Forster, N.H., K.L. Thompson, and T.N. Baldwin. "Spall Propagation Characteristics of SAE 52100 and AISI M50 Bearings‖, BINDT-CM, July 2010. 73 Toms, A. M., E. Jordan, and G.R. Humphrey. ― The Success of Filter Debris Analysis for J52 Engine Condition Based Maintenance”, Proc. 41 st AIAA, Tucson, AZ, July 2005. 74 Humphrey, G.
R., ―Filter Debris Analysis by Energy Dispersive X-Ray Fluorescence Applied to J52P408 Engines Denver X-Ray Conference , August 2007, Denver, CO. 242