Downloaded from https://www.everyspec.com ADS-79D-HDBK Details of the validation of the SHM/LME system should be documented in the CBM Management Plan. The capability of the system to evaluate structural health or monitor/estimate loads must be substantiated by analysis and test. Likewise, the durability of the system must be demonstrated including demonstration of any calibration/recalibration necessary to ensure that the system continues to perform in accordance with appropriate measurement standards.
The SHM/LME system must be substantiated to meet the reliability requirements presented in Appendix A for Fatigue Life Management as specified in section A.6 to prevent a catastrophic failure in order to achieve airworthiness credit that expands or eliminates current maintenance actions. The structure must be restored to ultimate strength capability when the SHM/LME system and follow on inspections reveal that the structure can no longer support ultimate loads. C.5.2 Integrated NDI methods. Alternative NDI methods are being developed based on various arrays or patterns of micro-sensors and actuators designed to detect structural health issues such as corrosion or crack detection.
Many of these technologies depend on analysis, test, or field experience to determine the most likely location for crack initiation. Others claim to detect changes (such as growing cracks) in larger structures. In either case, the probability of detection must be substantiated for each critical crack initiation site being protected (see MIL-HDBK-1823 and ASTM E2862-12 for details on establishing appropriate probabilities of detection). Every NDI system must be qualified and validated on a case by case basis. The design of experiments approach may be best to quantify various influencing variables, particularly the human factors.
These CBM systems must be evaluated for their particular human factors. Rummel provides guidelines for demonstration of NDI reliability on aircraft production parts and contains information for development of a valid repeatable NDI demonstration program. 15 Although these alternative NDI methods may not necessarily improve on the probability of detection of established NDI methods, the ability to integrate NDI methods into structure has the potential to increase structural reliability based on the frequency of inspections. Inspection intervals should be based on reliability analysis incorporating probability of detection, material property variation, and load/usage variation.
(see guidance in paragraphs A.5.4 and A.6 of this ADS, as well as the example methodology discussed in Zhao, et al., AHS Forum 67, 2011 16 ). Diagnostics should include identification of any faults in the integrated NDI method which would reduce the probability of detection from the baseline capability. To avoid establishing integrated NDI as a mission critical function, incorporation of integrated NDI should not impede the ability to perform manual NDI methods for periods of time where the integrated NDI system is inoperable.
For example, future acquisition airframes developed with integrated NDI capabilities as a requirement should continue to incorporate inspection access panels to allow for manual NDI. Validation of integrated NDI methods as applied to a particular structure should include the effects of geometry and, as applicable, the nearby presence of built up structure, joints, or fittings. By definition, integrated NDI methods must not damage or cause any change in the characteristics of the structure or component. 15 Rummel, Ward D. ―Recommended Practice for a Demonstration of Nondestructive Evaluation (NDE) Reliability On Aircraft Production Parts‖, Materials Evaluation, Volume 40, No. 9, 1982. 16 J.
Zhao, Justin Wu, M. Urban, and Douglas Tristch, ―Optimization of Inspection Planning for Probabilistic Damage Tolerance Design‖, presented at the American Helicopter Society 67 th Annual Forum, Virginia Beach, Virginia, May 1-3, 2011. 64