C Star
Don't ever put your faith in knowledgeable Gentlemen... read the bleedin' FCOM for yourself... extract below. The difference between Pitch attitude and FPV on your PFD is a very good visual indication of AoA .. this works whether the FPV is level, climb or descent. Does not work the other way round, i.e. the IR cannot calculate FPV from the other two parameters.
"Each ADIRU is divided in two parts, either of which can work separately in case of failure in the other:
• The ADR part (Air Data Reference) which supplies barometric altitude, airspeed, mach, angle of attack, temperature and overspeed warnings.
• The IR part (Inertial Reference) which supplies attitude, flight path vector, track, heading, accelerations, angular rates, ground speed and aircraft position."
The IR part may well use info from the ADR part in it's calculations .. but as a practical pilot I couldn't give a rats about that... life's too short.