Ok you bus guru's here an 'off subject' question because I didn't want to start a new thread for one question.
I've been keenly reading about the auto flight system on the A320 & am puzzled that should a selected hdg be chosen for say ATC req's then the CLB mode (which I assume is managed if FMA says CLB) reverts to OP CLB meaning any previous ALT constraints in the MCDU Flt-Pln will be ignored. I understand that OP CLB does that (ignores constraints) but why would it be automatically selected when hdg only is in selected mode?
Hopefully some simple answers for an Airbus novice here
Wmk2