BEA's 2nd interim report, page 47:
In alternate or direct law, the angle-of-attack protections are no longer available
but a stall warning is triggered when the greatest of the valid angle-of-attack
values exceeds a certain threshold. In clean confi guration, this threshold depends,
in particular, on the Mach value in such a way that it decreases when the Mach
increases. It is the highest of the valid Mach values that is used to determine the
threshold. If none of the three Mach values is valid, a Mach value close to zero is
used. For example, it is of the order of 10° at Mach 0.3 and of 4° at Mach 0.8.
There is another "backup" value of 8.6 degrees that is used when all three ADR's are lost (or switched off to get the BUSS).
P.S.
On page 20 of IR#3 BEA notes that the decrease in speed corresponding to an increase of 1° in the angle of attack depends on the flight conditions: 25 kt in cruise vs 5 kt in Takeoff/Approach. It is interesting to note in the following chart that the difference near the stall warning threshold is much smaller: 9 kt at FL350 vs 7 kt at sealevel.
