Downloaded from https://www.everyspec.com ADS-79D-HDBK observed for flight critical applications. For non critical applications, the RUL estimate accuracy may vary significantly lower than 90% depending on what additional maintenance and costs associated with early removals are acceptable to the maintainer and platform manager. For Army aviation CBM, the prognostics assessment is not required to be part of the onboard system. The goal of the PA module is to provide data to the Advisory Generation (AG) module with sufficient time to enable effective response by the maintenance and logistics system.
Because RUL for a given fault condition is based on the individual fault behavior as influenced by projected loads and operational use, there can be no single criteria for the lead time from fault detection to reaching the RUL. In all cases, the interval between fault detection and reaching the removal requirement threshold should be calculated in a way that provides the highest level of confidence in the RUL estimate without creating false positive rates higher than 10% for critical applications at the time of component removal.
Again, for non critical applications, the false positive rate may vary significantly higher than 10% depending on what additional maintenance and costs associated with false positives are acceptable to the maintainer and platform manager. 5.8 Advisory generation (AG). The goal of AG is to provide specific maintenance tasks or operational changes required to optimize the life of the equipment and allow continued operation. Using the information from the Health Assessment (Section 5.6) and Prognostics Assessment (Section 5.7) modules, the advisories generated for a CBM system should include: a. provisions for denying operational use (―not safe for flight‖) b.
specific maintenance actions required to sustain system operation The interval between download of data and health assessment is affected by operational use and tempo or conditions noted by the flight crew. Download intervals should consider the intended use of the CI/HI implemented by the system. If the goal of the system is to enhance maintenance, download intervals should be set by the Platform Management Office. If the intent of the system is to replace current maintenance practices, the download interval should be sufficient to diagnose whether the system is operating properly, to avoid loss of data, and to identify damage prior to failure in any case.
Defining the basis for continued operation by limiting the qualified flight envelope or operating limitations is determined by the process of granting Airworthiness Credits. Since these limitations are situation dependent, analysis by Aviation Engineering Directorate (AED) staff engineers is normally required and considered outside the scope of the CBM system to provide through automated software. 5.9 Guidelines and alternatives for modifying maintenance on legacy aircraft. A robust and effective CBM system can provide a basis for maintenance and airworthiness credits and debits that modify legacy maintenance practices and intervals.
As part of the continuous analysis of CBM data provided by the fielded systems and or seeded fault testing, CBM applications to scheduled maintenance intervals for servicing and inspection can enhance current maintenance practices to increase aircraft availability and optimize safe operations and maintenance cost. Similarly, validated CBM data can be used to modify the Time Between Overhauls (TBO) for affected components. Finally, validated CBM data can be used to transition away from current reactive maintenance practices to a proactive maintenance strategy in a manner that does not adversely impact the baseline risk associated with the aircraft‘s certification.
Involved in each of these approaches are alternatives to CBM which should be considered to realize the most beneficial gain in maintenance and airworthiness for the using service. The following subsections discuss each of the aforementioned CBM approaches and related alternatives to CBM. It is important to note that the number of test specimens necessary to validate each alternative approach will vary across the different methods. The details for determining the necessary sample size 24