As I understand it, after one airspeed sensor failed, the plane switched from "normal law" to "alternate law". In "normal law", there is no control input that can take the plane out of its safe flight envelope (i.e., you can pull all the way back at the lowest possible airspeed and not stall the plane). In "alternate law" there is no such protection. When AF447 crashed, the first officer spent most of the time pulling all the way back on the joystick, which will (and did) stall the plane. This, to me, indicates that he didn't have any idea that the plane had switched into alternate law, which seems like a UX error. I bet if all the screens switched from white-on-black to black-on-white when going into alternate law (or something more night-vision friendly) there would have been no doubt and there would have been no incident.

The other problem was that the captain and first-officer were inputting conflicting control inputs and didn't know it. The plane just averages them, and provides no indication that it's doing so. The captain sees that he's pushing all the way forward on the joystick and has to wonder why the plane is still stalling. Meanwhile, on other planes the control columns are mechanically linked, so you have to fight against the force of the other pilot which will signal you to say something like "dude let go" and regain control over the plane.

I feel like we should have fixed this in the 1980s when this happened:

https://www.youtube.com/watch?v=-kHa3WNerjU

But here we are in 2019 with basically the same problem. I fear that Boeing hasn't learned Airbus's lessons and the 737 MAX is confusing people in the same way that people were confused by the first A320s. The solution has always been "blame the pilot" but I blame the software.