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Hello Bob,
Just to confirm if weight to add and weight to shift formula can be used on charlie loading system for both forward and aft limit calculations?

You could use the formula (flow chart) to solve any problem relating to the aft limit, because the exact position of the aft limit is given on the Charlie envelope and it doesn't change with weight.

It is 3004mm aft of the datum for normal operations and 2896mm aft of the datum for utility category operations at any weight. So that's fine.

The arms of each compartment are also given in the instructions for use of the loading system.

However, you would have to use the envelope for any forward limit problem, because not enough information is given to allow you to accurately derive a formula to calculate the exact position of the forward limit at any particular weight.

You could approximate a formula by working backwards off the envelope. (it looks like the forward limit for normal category is 2744mm at 820kg and about 2889mm at 1115kg).

You could then work out a constant to apply to allow for the linear variation (about .49). The formula then becomes: Forward Limit = Present weight - 820 x .49 + 2744. (actually that formula works pretty well would you believe?).

I think I'd just hope the examiner would not be so cruel as to expect you to do that!