@
OK465;
The A/P pb apparently latches with the 2 values in 'agreement' below actual VLS.
If you can follow the
logic schematic posted by
A33Zab, you will note there are a number of variables that must meet specified values before the p/b can be effectual.
The latching of ALT 2B was a result of diverging ADR speeds. ADR2 was nominated the "median" value and when speeds hadn't returned to within 50KTS of the median in 10 secs, law reversion to ALT 2B occurred and remained for the rest of the flight.
A33Zab has previously pointed out that the FD may be engaged on the ground in V/S mode, and on AF447 the A/P was inhibited due to CAS < VLS from 02:10:08.
AP Engage is inhibited: if abs(φ) > 40°,
or θ < -10°, or θ > +22°,
or CAS < VLS,
or CAS >(VMO/MMO or VLE/VFE)
In respect of the FD Bars, they do appear to have been available when 2 ADRs (also 2 IRs) agreed within 20 KTS. The same agreement is also a provision of A/P engagement, plus FMGEC, FCPC (also
no breakout by SS or pedals), plus the φ, θ and CAS conditions being met per the schematic.