ADS-79D-HDBK Downloaded from https://www.everyspec.com Sub-Section 3: The next step is to determine the methodology for credit. Here, one can choose a Mechanical Health approach, a Mechanical Health-based Prognostics approach, a Usage/Structural Health Monitoring (SHM) approach or a Usage/SHM-based Prognostics approach. In this step, the algorithm is proposed and all necessary development activities can be conducted. In order to go down the Mechanical Health and/or Usage/SHM path, the candidate HUMS system DSC must have been installed previously and must have collected the appropriate data. If the system was not previously installed, credit for the methodology cannot be acquired.
Similarly, for a Prognostics Credit, the candidate system must have a validated health credit in place for the target component. Sub-Section 4: The determination of the credit methodology leads into performing an Integrity Assessment (IA) of the methodology. This assessment should focus on the potential functional failures of the health/prognostics algorithm such as false negatives and false positives. The IA should also spell out the mitigations for these functional failures. Sub-Section 5: At this point in the process, all the preliminary items required for Maintenance Credit have been established.
Thus, this is an appropriate spot to make the decision whether or not to proceed with Verification and Validation activities, based on whether or not a catastrophic failure would occur if the credit methodology fails to perform. The determination of catastrophic failure should have been made previously when the component severity was established. The IA should have spelled out all possible functional failures of the algorithm. If the component severity is catastrophic and the IA does not provide mitigation for an algorithm failure that can misdiagnose this component, then Maintenance Credit cannot be acquired for this component.
However, if the IA has mitigation spelled out for all possible functional failures of the algorithm, then one can proceed with the next V&V steps, i.e. establishing the V&V criteria and getting the V&V plan approved. The V&V criteria should describe the plan for verification and validation. It should spell out all appropriate test cases and test plans to complete the verification and validation specifications for Maintenance Credit for the target component. The level of verification will be based on the severity of the component.
Once the criteria have been established, the V&V plan needs to be approved by aviation authority, who will determine whether the V&V plan meets the specifications for Maintenance Credit. 200