Chris Scott:
Thanks for your reply. I agree with the rest of your comments, except that you might wish to rethink slightly:
VS from the AD, (...) could only give a trajectory relative to the air – not the ground
Barometric VS differs from inertial (tapeline or geometric) VS when temperature differs from ISA. Another reason why the use of barometric seems odd.
PJ2:
I owe you an apology for setting you off on the wrong foot. Although I am used to defining FPA relative to the airflow, the mention of 'drift' should have alerted me to the fact that FPV on the PFD is relative to the ground.
regards,
HN39