Downloaded from https://www.everyspec.com ADS-79D-HDBK Additional problems inherent to off-aircraft laboratory testing include mixing up samples, transport to laboratory, and long lead time for results which may delay effective maintenance analysis and complicate logistic support of the aircraft. In addition, different instrument models or manufacturers do not correlate to one another. Consequently, these different data populations should not be compared to one another. Note also that to maintain quality data, precision laboratory instruments should be standardized daily and require periodic (generally yearly) calibrations. M.6.1.1.2 Off-aircraft Sampling:
Since improper or poor sampling techniques profoundly impact condition test data triggering a false trend alarm, sampling procedures should follow TB 43-0211 AOAP Guide for Leaders and Users and/or ASTM Sampling Practice D4057. Examples of poor sampling with off-line techniques are: stagnant sampling, sampling after component change out, sampling after oil or filter change or both, irregular sample intervals, and sampling without circulating the oil and bringing the equipment to operating temperatures. New oil should also be periodically sampled. M.6.1.1.3 Off-aircraft Quality Laboratory and Testing Practices:
The laboratory tools used to perform the condition monitoring tests influence the data. 81 Variations in analytical instrument configurations impact data reliability. Therefore, limits and trends should only be established based on results from the same make and model of test instrument. For example, trending atomic emission ICP results should be from ICPs with the same sample introduction configuration, same plasma energy, and preferably, the same manufacturer and model. Analytical instruments or test methods with poor measurement repeatability and reproducibility will result in correspondingly poor level and trend limits.
Testing repeatability should be included with any limit and trend studies. ISO17025 provides general guidance for quality laboratory operation. If data from multiple laboratories and multiple instruments (same make and model) are to be compared and included in statistical analyses, a correlation (quality assurance) program should be mandatory to ensure all instruments are providing the same quality results. And finally, inappropriate analysis techniques may hide or distort interpretational conclusions. The condition monitoring tool chosen should provide evidence of the critical failure modes under review.
To do so, the tools should provide results that are sensitive to the fault, unambiguous to the fault and statistically well behaved. See Appendix D, Minimal Guidance for Determining CIs/HIs for Propulsion Systems. M.6.1.1.4: Off-aircraft Laboratory Rotorcraft Tests: The common laboratory tests for rotorcraft are: AES (Rotrode), FTIR, AN, viscosity and water. LNF and ferrography may also be used for cleanliness ratings and more detailed examinations of particulates. The following provides a short description on the various Army laboratory tests and some of the inherent advantages and disadvantages: AES by rotating disk detects normal rubbing wear, some additives and abnormal wear.
82 It is easy to use; requires no sample preparation and is relatively easy to deploy. However 81 Toms, L and A. Toms., ―Machinery Oil Analysis - Methods, Automation & Benefits‖, 3rd Edition, STLE, Park Ridge, IL, 2008, ISBN: 978-0-9817512-0-7. 82 ASTM D6595-00, Standard Test Method for Determination of Wear Metals and Contaminants in Used Lubricating Oils or Used Hydraulic Fluids by Rotating Disc Electrode Atomic Emission Spectrometry, 2011. 247