ISO 21785-2020 pdf download.Air cargo unit load devices一Load distribution model.
4.2 Application
4.2.1 When airworthiness testing unit load devices or conducting equivalent numeric simulation for this purpose, the test load shall be distributed (or simulated, as is the case) onto the pallet surface or the container base in accordance with the reference model defined in 413.
4.2.2 When designing aircraft cargo compartments structure and systems, it is recommended the load distribution assumptions defined in 4J.3 be used to take into account maximum allowable ULD C.G. deviation limits. However, airframe manufacturers may use for this purpose alternate assumptions, providing aircraft structure and systems compatibility with the reference load distribution model is demonstrated.
4.2.3 When developing detailed unit load devices utilization rules, operators shall use the reference load distribution model as the assumption describing the most critical C.G. eccentricity case. They shall in addition apply any requirements set forth by the aircraft type’s Weight and Balance Manual, and may also apply the requirements of Claue5.
5 Operational C.G. trade-off
5.1 General
The load distribution model in 4j3 is defined at the unit load device’s maximum gross mass acceptable in the aircraft zone concerned. When the actual IJLD gross mass is lower than this maximum, linear trade-off may be operationally used for increased C.G. eccentricity limits in proportion of the lower gross weight, in accordance with either 52 or, exceptionally where unavoidable, 53 hereafter.
The requirements of an approved aircraft Weight and Balance Manual take precedence in the event of a conflict.
5.2 One direction trade-off
When the ULD gross mass is lower than the maximum allowable at the intended aircraft position, the allowable C.G. offset in one direction only, either longitudinal or lateral, maybe increased proportionally in accordance with Figure 3.
Figure 3 ilustrates, as an example, that for a payload weighing only 50 % of the aircraft zonal or position limit, the lateral or longitudinal C.G. offset may vary up to +30 % instead of +10 % at maximum gross mass.
5.3 Two directions trade-off
When the ULD gross mass is lower than the maximum allowable at the intended aircraft position, the allowable C.G. offset in both directions simultaneously, longitudinal and lateral, may be increased in accordance with Figure 4.ISO 21785 pdf download.