Originally Posted by ZeeDoktor
Only alpha floor is lost in alternate law 2. AOA is still monitored and protection now applies to stall speed rather than AOA. Protection is lost only if VSG1 can no longer be calculated (which I think was not the case, happens when slat/flap information is not available and GWT is no longer known), or when dual ADR fail or disagree is triggered.
In our case, it looks as if at least stall protection was available until ADR disagree triggered.
I agree evasive action in the form of a turnaround is virtually unheard of (in fact it's usually discouraged for reasons we can discuss in another thread). But we don't know what picture was painted on the radar. Nor what went on with the aircraft, maybe a something evolved that prompted them to return to the nearest landing opportunity which would have been behind them (I think?)
Well. but the late triggering of "ADR disagree" at 02.12 is obviously what caused ALT2, Autopilot OFF, Autothrust OFF, Rudder limiter control, etc. And this is what happend in the first place at 02.10 because of those Pitots reading errors... There is not so much possibility for the system to switch to ALT2 in any case.
The fact that this maintenance message was transmitted much later in the ACAR sequence doesn't mean that the system was not already in error before its maintenance time stamping or you'll have to find an explanation why ALT2 was already triggered at 02.10.