Originally Posted by svarin
At the end of these 10 seconds, each PRIM will either confirm and latch Alternate 2 or revert to Normal law, based on differences between ADR values. This is the purpose of this 10 seconds checking. This happens at 02:10:15.
My take is PRIM2 reverted alone to Normal, while PRIM1 & PRIM3 latched Alternate 2. This is because PRIM2's set of ADR data, being different (only ADR2 & ADR3), would have allowed differences into the 50 kts range that triggers reversion to Normal law.
From BEA's explanation of PROBE PITOT fault message (Interim #1 p.51):
This message, transmitted by the FCDC2 (EFCS2), means that the FCPCs (or PRIMs) triggered one of the speed monitoring processes: they have detected a decrease of more than 30 kt in one second of the “polled” speed value. The three ADRs were considered valid by the EFCS2 at the time the monitoring was triggered, because the prior rejection of an ADR would have generated a class 2 fault message and there would therefore have been an asterisk in front of the source. In this case, the “polled” value is the median value.
At the time this monitoring is triggered, the FCPCs open a window during which they operate with alternate 2 law (see following graphic). The rudder deflection limitation function is also frozen, but the associated alarm is inhibited. At the end of the window, if the difference between the values polled at each end of that window is less than 50 kt, the FCPCs return to normal law. Otherwise, they continue in alternate 2 law, the rudder deflection limitation function remains unavailable and the corresponding alarm is generated.
Note: the alternate 2 control law is a load factor law for pitch and a direct law for roll. Only the load factor protection remains available. In certain cases, the high and low speed stabilities may also be lost.