Machinbird posted :
Now assuming AF447 somehow departed controlled flight while in Normal Law while cruising on autopilot
Interesting but when ? Certainly not initially at 02:10. But maybe at 02:13, when the FMGEC1 failure appeared, as determined by the AFS in a class 1 message. The AFS would only detect a fault if it was active. So by 02:13, the pilots thought it was over and the aircraft showed them the F/D bars, and they reengaged A/P with unintended consequences...
Loss of autopilot and autothrottle would be due to the ADR failures which would be caused by the departure from controlled flight.
Strongly disagree, these auto-thingies losses are due to the Probe-Pitot failure at 02:10 which put the PRIMs in a special alternate law with ADR monitoring.
Read again the BEA report : a failure message will not appear twice. If A/P was lost at 02:10, reengaged at 02:13 and lost again, its subsequent disconnection will not show a second time on ACARS (since they are
maintenance messages and not flight data monitoring messages)
Remember, the basic situation is faulty probes to scattered ADRs to alternate law. This UAS is routinely handled by all pilots in the sim
and in reality. Nobody crashes from cruise level because of this
alone.
However, voting logic, ADR selection, PRIM behaviour under manual alternate law as compared to their behaviour under A/P, all these are of the utmost relevance. The AD put forward by a poster a few days ago reveals a possible hazardous misbehaving of the A/P itself under certain ADR failures conditions. These conditions are such that the system as a whole deems appropriate to show F/D bars and allow A/P reengagement when it is unsafe to do so. This is extremely serious and so very close to our mystery here.