[omegant]

You are right about the 4 min, but there is no such a thing as a flight mode button. Normal, alternate and direct law change automatically depending the number of computers or inputs available. There is a big red ALTERNATE LAW at the HSI, also a big red STALL. The problem is not that they where in alternate law, is that they used the wrong maneuver to recover the plane.

[gcp]

From reading the reports, what you say doesn't make sense. As far as I understand, it's not possible to stall the plane in normal law. They crashed the plane because it was stalled for over 4 minutes. This implies that the plane did not go back to normal law.

Given that the plane was fully functional after the initial glitch (all inputs and all computers OK), this means they had to either force it back to normal law either via a kind of switch (the flight mode button), or pilot it into a configuration where normal law applies (essentially, recover from the stall manually). They obviously failed the latter.

An obvious question resulting from this (also asked in another thread here) is: can the autopilot recover the plane when it already is in alternate law?

[omegant]

It´s true it is not possible to stall the plane in normal mode AND stable air conditions, in fact at high altitudes is possible to lose control of the plane even in normal mode, due to sudden changes in air density or extreme turbulence. This is highly improbable but sometimes happens when changing from one mass of air to another or flying into clear air turbulence.(I know some pilots who have suffered this, flying close to the equator due to captains trying to save fuel climbing above the recommended altitude for that day, or the case of a A320 loosing 4000´ while flying above the Pyrenees due to turbulence and once again trying to save fuel going high).

Once you are at stall there is a protection in alternate mode (if I remember properly) that will pitch down the plane to help getting a recover speed (not like normal law that will prevent you from performing stall and over speed maneuvers), BUT that protection can be overridden (unfortunately in this case) by side stick input. I don´t think you could engage the autopilot in such situation even in normal law(I´ll try at my next simulator). Read my comment below about the maneuver I think they were trying to perform.

[gcp]

Once you are at stall there is a protection in alternate mode (if I remember properly) that will pitch down the plane to help getting a recover speed (not like normal law that will prevent you from performing stall and over speed maneuvers), BUT that protection can be overridden (unfortunately in this case) by side stick input.

So ironically, the correct advice is not to "fly the plane", but "DONT fly the plane" and let it fix itself.

(This is what I would have expected from a reasonably designed automated system, anyway)

I don´t think you could engage the autopilot in such situation even in normal law(I´ll try at my next simulator).

Can you clarify whether going from alternate to normal law requires a specific action, or is it automatic?

[omegant]

Well, yes in this case , but if you have obstacles ahead maybe your best option is keeping the plane close to the stall in order to climb, so you need to fly the plane. That is the reason most of this protections must have an override.

The modes are automatic, if you have all the flight computers and inputs available it will be at normal mode, if you begin loosing computers or inputs (like speed) it no longer has the capability to have that protections active so it downgrades itself, if there is a recovery of some sort (computer reset or working again pitot) it will upgrade the mode to normal by itself. The only action that can be taken is resetting computers or trying to recover a system. In fact when we want to practice alternate or direct law in the simulators, we just disconnect some flight computers. It is not that different flying in alternate or direct law than it is flying normal mode (just a bit more dizzy), unless you try something like pulling the control all the way back for 3 minutes.

Here there is a resume of the airbus flight laws:

http://www.airbusdriver.net/airbus_fltlaws.htm

Pd. mechanical backup, THAT is difficult to fly!. edit: typo