Did I understand correctly that basically air speed sensor was faulty and because of that the autopilot decided that we need more speed to avoid stall and put the nose down all the way to the ground/sea?
It seems they added a second autopilot that prevents pilots from doing truly stupid things without telling anybody. Problem? Failure modes of that autopilot can easily be lethal.
I think they may have been right in saying pilots don’t need additional training for this new feature. If the plane flew itself into the ground, and there’s nothing the pilots could have done to prevent that, they don’t need additional training.
Chances are they didn’t tell buyers of the plane because, for years, they have marketed their planes as “if the software fails, pilots can take control, unlike in Airbus planes” (counter-acting Airbus’ message that their planes were more modern)
So no: in Airbus planes the pilot can and do absolutely control everything. If needed the pilot can always go into Direct Law. When sensors fail (like the pitot tubes in AF447) Airbus planes step down to Alternate Law. “If the software fails, pilots can take control, unlike in Airbus planes” has never been true.
There is however a difference in that Boeing pilots are supposed to always have the last word without needing to deactivate protections or anything. The plane would for instance apply physical resistance on the yoke to alert the pilot that something is wrong, but pulling/pushing hard enough is enough to override the protection. Well, that was my understanding until this accident (investigation pending, of course).
See http://www.b737.org.uk/flightcontrols.htm
The pitch trim can be controlled by a number of different systems for different reasons, see the section on mach trim for an interesting one. I would be shocked if the inputs here weren't disabled by switching thd stab trim - autopilot switch to the off position.
I've mentioned in previous comments, this sounds like a trim runaway incident. The mechanism may be new but the underlying fault and the symptoms would have been the same.
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/...
> Runaway Stabilizer
> Disengage autopilot and control airplane pitch attitude with control column and main electric trim as required. If relaxing the column causes the trim to move, set stabilizer trim switches to CUTOUT. If runaway continues, hold the stabilizer trim wheel against rotation and trim the airplane manually.
When autopilot is off, you'll still have stall/overspeed protection that will pitch down/up in the corresponding condition. This protection can also be disabled by switching off some flight computer control. This is the case for both Airbus and Boeing, and the specific controls required depend on the particular plane model.
The issue at hand is ensuring that training for these situations and knowledge of the flight control computers is adequate.