Downloaded from https://www.everyspec.com ADS-79D-HDBK sufficient regimes, such as 97% or greater of the actual flight regimes, including all highly damaging maneuvers and benign maneuvers with high frequencies of occurrence. Maneuver descriptions and tolerances should match those used during the flight load survey. Targeted regimes should be selected such that any unrecognized regimes would introduce less than 0.5% under-prediction of fatigue damage fraction based on the design usage spectrum. Also, for misidentified or unrecognized flight regimes, the system should demonstrate that it errs on the side of selecting a more severe regime.
This ensures that a component is not allowed to receive maintenance credit where it is not due and therefore allows a component to fly beyond its margin of safety. B.5.4 Validation of structural usage monitoring system (SUMS). The objective of the following is to provide guidelines for the qualification of a Structural Usage Monitoring System (SUMS) that will establish the basis for maintaining the reliability for the entire lifecycle of the aircraft in accordance with Appendix A. Fully validated SUMS should be considered an intimate part of the airworthiness process throughout the aircraft‘s lifecycle.
Accordingly, the SUMS process should be included in the airworthiness qualification process for the aircraft, including consideration of SUMS diagnostics and alternative means of achieving reliability in the event of a SUMS failure. B.5.4.1 Introduction. The design usage spectrum defines the number of occurrences or amount of time spent in different flight regimes during a block of operational flight hours. This defines the amount of time for each different configuration and the amount of time at different altitudes. Also, defined in the usage spectrum are assumed fixed number of occurrences for certain events (e.g., number of ground- air-ground (GAG) cycles per flight hour).
SUMS have the ability to measure and provide the actual usage of aircraft for utilization in fatigue damage calculations. The plan for validating SUMS should consider the components of the aircraft that are to receive maintenance credits. The regimes that are fatigue damaging to these components are documented in the fatigue substantiation and qualification databases of the aircraft. This includes all spectrum maneuvers flown at the various GW and CG loadings. Also defined is the magnitude of the fatigue damage fraction for the different regimes for usage per the design spectrum.
Fatigue damage is also identified as being from within maneuver damage, maneuver to maneuver damage, or GAG damage. To appreciate the data requirements for the usage monitoring system it is important to understand the characteristics of the loads producing the fatigue damage. For instance, damage within the maneuver can be caused by loads generated during the entry or exit portions of a maneuver. Here, the duration time of the maneuver does not correlate with the amount of fatigue damage. In contrast, when blade performance (example, stall) produces cyclic loads that are damaging, the duration of the maneuver correlates with the amount of damage.
Maneuver to maneuver damage depends on the pairing of maximum and minimum loads. The pairing can be between two peak loads from within the same maneuver, but most often the pairing involves loads from different regimes. The sequence should include a pre or post flight static event (―unloaded‖) to assure proper representation of the GAG which pairs the highest and lowest load magnitude over the entire flight. Here, an optimum usage monitoring system will aid in a realistic pairing of loads to generate appropriate cyclic and mean loads. Usage monitoring will provide data to increase certainty on the magnitude of the loads as well as the number of occurrences.
The usage monitoring system should have the ability to identify and store the sequence of regimes for maneuver to maneuver damage. Any Parametric, Regime, and Damage Fraction/Life data stored on the ground station should be stored using a common non-proprietary binary format. B.5.4.2 Development of the structural monitoring system. This effort consists of the design of the monitoring system and parameter identification and algorithm development for usage recognition. The design includes the onboard and ground software and hardware systems for collecting and storing usage data. A formal report that documents this effort will be provided to the certifying official as part 58