Downloaded from https://www.everyspec.com ADS-79D-HDBK positives (less maintenance) and false negatives (less safety issues) with the on-condition redesign; and realizing cost and schedule synergies in testing the performance of the component and monitoring device concurrently during requalification. Disadvantages of a redesign and requalification using on condition designs are associated with relatively higher costs than pursuing TBO enhancements (5.9.1) and TBO extensions (5.9.2) as well as relatively longer schedule than TBO enhancements. A second alternative is to do nothing.
Doing nothing sometimes may be the most logical alternative if a TBO is not being attained on components in the field due to reasons not appropriate for CBM resolution. No additional investment cost or schedule is needed to maintain the status quo. However, the status quo may be unacceptable to current readiness rates. Other disadvantages to doing nothing are not being able to realize any operations and sustainment savings or provide proactive maintenance. 5.9.4 Statistical considerations. There is interest in the likelihood that the monitoring system will detect a significant difference in signal when such a difference exists.
To validate the target detection and confidence levels (target detection = 90%, target confidence = 90 to 95% depending on component criticality), a statistically significant sample size (see Appendix I) for faulted and unfaulted components should take into account the required confidence and reliability guidelines within this document for flight critical components. Since a probabilistic approach is a recommended method that can be utilized to validate CBM algorithms using confidence and reliability factors, it is important to maintain a high level of quality in the probabilistic design.
It should be noted the only way to successfully attack a probabilistic design or analysis is to undermine confidence in its quality. For information addressing legal implications when employing a probabilistic approach, reference SAE AIR5113 for a compilation of experience and past precedent. If at least one of the detections in the sample size is a false positive, then evaluate to determine the root cause of the false positive. Corrective actions may involve anything from a slight upward adjustment of the CI limit to a major change in the detection algorithm.
Once corrective action is taken and prior to any further increase in TBO, additional inspections/TDAs is necessary to complete validation of the CIs/HIs. A false negative occurrence for a critical component will impact safety, and should be assessed to determine the impact on future TBO extensions or On-Condition status. Each false negative event will require a detailed investigation to determine the root cause. Once corrective action is taken and prior to any further increase in TBO, additional inspections/TDAs of possible positive detections is necessary to continue validation of the CIs/HIs.
Components used for TDA and validation may be acquired through either seeded fault testing or through naturally occurring field faults. 5.10 CBM management plan . This handbook provides the overall standards and guidance in the design of a CBM system. It is beyond the scope of this document to provide detail guidance in the implementation of any particular CBM design. A written Management Plan or part of an existing Systems Engineering Plan should be developed for each implemented CBM system that describes the details of how the specific design meets the guidance of this ADS. This Management Plan should provide the following: 28