@
OK465
I tend to agree that the various colors of ALT Law are not well documented, but can only assume that Airbus Industrie have determined in their wisdom that full divulgence will conflict with their KISS policy.
Best I can judge is that the switch to ALT2B was due to diverging CAS data which set up the ADR monitoring sequence with ADR2 being voted the "median". At the end of the monitoring period the new CAS "median" was not within 50KTS of the initial "median" value. Now that certainly matches the UAS criteria, but whether that should have been displayed or annunciated is debatable. The PNF announced, "We've lost the speeds", but then failed to check the QRH for guidance and the game was lost before reaching first base.
The following discussion between
HazelNuts39 and
Takata in
AF447 - Thread No.5 should give you an insight into why the law change was ALT2B, and the implications for the remainder of the flight.
I do think that
Clandestino summed up ALL the ALT Law states quite succinctly:-
Most important is to recognize that all the technical jargon about laws signifies that the safety nets are no longer there.
and this could be quantified by the "bucket is half full" approach which is eminently preferable to the "bucket is half empty" scenario when DIRECT Law is applicable.