ADS-79D-HDBK Downloaded from https://www.everyspec.com J.3 DEFINITIONS Probability of Detection (P D ): The probability that a true fault signature is detected by the CBM sensors. For CBM aircraft systems, the target probability of detection is 90% for both condition and health indicators; however, this target value may be increased or decreased pending the level of criticality associated with the fault. Probability of False Positive (P FP ): The probability that a sensor detects a fault that is not found by inspection.
For CBM systems, the target probability of false positive is 10% for both condition and health indicators; however, this target value may also be increased or decreased pending the level of criticality associated with the fault. Probability of a False Negative (P FN ): The probability that a sensor fails to detect a fault that is found by inspection. P FN is equal to one minus P D, and P FN and P FP are inversely related. For CBM systems, the target probability of false negative is 10% for both condition and health indicators; however, this target value may also be increased or decreased pending the level of criticality associated with the fault. Component Failure:
In the context of this appendix, component failure may refer to either ―complete‖ or ―near‖ failure. ―Complete‖ failure is defined as the condition in which the article under test can no longer perform its intended function and may happen as either a slow progression or a sudden, catastrophic event. ―Near‖ failure is defined as the point where the component under test reaches a degraded condition where complete failure is imminent. J.4 GENERAL GUIDANCE Test stand Seeded Fault Testing (SFT) provides a means to acquire the empirical information needed to verify the fault indication(s) in support of on-aircraft CBM validation.
SFT can be used to advance the development or refinement of CIs when the specific failure modes are not occurring naturally in the field or in the quantities desired for statistical significance due to legacy maintenance practices. SFT permits measurement and observation of a component in a controlled laboratory environment with a known faulted condition as it degrades towards failure. Further, condition and health indicators can be tested with SFT for their ability to reliably and accurately recognize fault signatures. SFT can be used for a variety of reasons. One purpose could be to down select among a candidate list of sensors or location of sensors.
Another purpose of SFT could be to develop or refine CIs and CI threshold values for achieving an acceptable tradeoff between probability of a false positive (P FP ) and false negative (P FN ) indications. Furthermore, SFT can be used to demonstrate fault signatures and their detection by CIs are suitably insensitive to variations in test specimen and operating environment. CIs should deliver consistent results across all available test specimens over the full range of expected on- aircraft operating conditions (examples: temperature, vibration). To consider and quantify variability of fielded aircraft, CIs should also be tested on multiple aircraft. 176