How many airlines did what American and Southwest did? I understand that both of those airlines have an installed option (why it's an 'option' I have no idea, I'll let wiser heads reflect on that) that gives the pilots AoA displays. Given that AoA signal appears to figure in this back up system's operation, seems a smart move to me. What puzzles me is why any airline would not, but I am biased since I believe that pilots are supposed to fly aircraft, not guess at what an aircraft is doing.
When I look at this system from a systems perspective, it is a back up system whose intended function is to avoid a stall/accident.
Fix one problem, raise another one.
Nothing new under the sun.
I saw an interesting observation
here regarding the Brazilian Certifying authority.
The Brazilian Certifying authority did, with Boeing's involvement, require MCAS training. What that training was would be interesting. I would assume somebody from GOL, a Max operator, would know what that was. If we find out we might know whether that type of training would have helped the Lion Air crew.
I am not sure if they called for this before or after the Lion Air accident. If before, that leaves open, to me, the question of why didn't all certifying authorities, FAA, CAA, Chinese, Norwegian... all of them, make that same demand?
Again, this is my bias showing since I do not believe that something that moves the flight controls should be hidden from, or a mystery to, the pilots.