Cruise CofG is calculated using a table reflecting the index change due to fuel load. The table is set up for various fuel densities. This correction is added to the ZFW Index to obtain a new index for current weight.
With this index and the actual weight you enter the Index-Weight graph (on the loadsheet) to obtain your Cruise-MAC. Weight and balance computers are used on ground to check loadsheet versus calculated weight.
Once center wing and R2/R3 are empty changes are minor.
This way you obtain a new Max Alt from the FMC. Only problem is that you do not know if it is thrust or 1.3g limited. With our engines it must be 1.3g unless we change it to 1.2g.
Max Cruise thrust is available till ISA + 30 °C.
This technique is useful outside RVSM (4000 ft steps) and in areas where RVSM is imposing you steps that are greater than 2000 ft like Russia and China.
Since Yellow manoeuvering band is calculated by FMC based on weight and speed and red tape stall margin comes from the MAWEA based on AoA you have two independent sources of information. Only problem here is that the AoA is not corrected for Mach unless you ave a software update.
Last edited by Pitch Up Authority; 20th Apr 2011 at 18:30.