Downloaded from https://www.everyspec.com ADS-79D-HDBK B.5 DETAIL GUIDANCE B.5.1 Flight regime definition. Flight regimes are flight load events or states typically flown during a flight load survey to determine flight loads experienced by aircraft components and structural elements based on combining the following types of parameters: a. Aircraft configuration: On a mission by mission basis, items may be added or removed from the aircraft in a manner that might affect flight loads and aircraft center of gravity. For example, the presence of external stores, position of landing gear, weight of external or internal cargo, or fuel quantity.
These parameters are required to determine flight loads experienced by aircraft components. b. Flight environment: Altitude, outside air temperature, and other parameters that allow reasonable estimation of density altitude, which is required to determine flight loads experienced by aircraft components. c. Flight Conditions or Maneuvers: General type of maneuver, its severity (examples: speed, load factor, angle of bank, rate of climb/descent), and duration.
Prior to conducting flight load surveys and fatigue life substantiation, flight regimes in the usage spectrum are typically specified for each aircraft model based on aircraft classification, current tactics, mission profiles, and anticipated threat environment (see ADS-51-HDBK for details). As depicted in Figure B-5, these regimes form the basis of fatigue calculations and should also form the basic requirement for regime recognition algorithms. Two validation loops are shown in Figure B-5 and described in Table B-IV.
In addition to the regime recognition system‘s ability to identify usage in an operational environment and a key factor in the successful implementation of a regime recognition algorithm is whether the regime recognition matches the flight loads survey test points including consideration of flight test maneuver descriptions and tolerances used during the flight load survey. A series of flights should be performed with a test aircraft that is fully equipped with the regime measurement package (such as the DSC) and additional recording systems for capturing data needed to evaluate and tune the algorithms.
One may establish that a 0.5% under-prediction of damage fraction could introduce a 5% increase in probability of failure. To avoid under predicting damage fraction by more than 0.5%, it is recommended that the regime recognitions algorithms be required to demonstrate that they can identify 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. 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 prevents a component from being flown beyond its margin of safety. Cronkhite, et al. (1998) provides an example which cautions against the temptation to identify overly-broad flight conditions.
9 Although broad flight conditions would allow one to claim credit for identification of a high percentage of flight times with little effort, the lack of correlation between broad categories and the certification spectrum may result in fatigue damage accrual rates that do not sufficiently represent those corresponding to more refined regime categories. 9 Cronkhite, J., B. Dickson, W. Martin, and G. Collingwood DOT/FAA/AR-97/64 Operational Evaluation of a Health and Usage Monitoring System (HUMS), April 1998. 50