Unless I missed something, THS setting comes from load planning or charts as the MCDU is incapable of calculating it.
You must have missed something
The Bus MCDU is capable of calculating the T/O CG as described in posts above.
However, SOP's vary from operator to operator. AFAIR, the official Airbus way (as thaught in Toulouse) was:
- read the TO CG from the loadsheet
- look at the scale on the back of the QRH to convert TO CG value info the trim setting
- insert the obtained trim setting into TAKEOFF PERF page for reference
- set the THS after engine start
Our SOP:
- read the T/O CG from FUEL PRED page after eng start
- set the THS
The latter method is simpler/faster and eliminates the potential for error of setting the THS in the wrong direction (eg. 2 UP instead 2 DN).
On the other hand, Airbus must be the only airplane in the world, where simple things like setting the trim for takeoff get so complicated that they require a discussion...
