> if the AoA isn't shown anywhere in the default configuration, there is no way for the pilots to crosscheck them and see the fault. Which is why you need the AoA disagree warning message.
But the article buried the lede!
There is much bigger problem reported now in this article:
The warning wouldn't have helped even when flying with those companies that paid extra for it!
Note:
"“We were told that if the A.O.A. vane, like on Lion Air, was in a massive difference, we would receive an alert on the ground and therefore not even take off,” said Dennis Tajer, a spokesman for the union representing American Airlines pilots. “That gave us additional confidence in continuing to fly that aircraft.”
But in the last several weeks, Boeing has been saying something different. Mr. Tajer said the company recently told American pilots that the system would not alert pilots about any sensor disagreement until the aircraft is 400 feet above the ground."
Note what happens then: at the moment you are above the ground, and the MCAS activates, we already know that if you "just follow the procedure" the forces against pilot corrections could be too big to do anything. That's what can be concluded from the analysis of the Ethiopian crash.
That means the plane from the "20%" with "paid option" would still eventually crash as soon as AoA vanes fail, just there would be one more of many alerts in the cockpit for some short time before everybody dies.
The sense of "security" Boeing gave the American pilots flying for the companies who paid for that additional feature was completely false. They would have been doomed too as soon as a single AoA vane that the MCAS depended on failed: The warning worked only at the moment it was completely useless.
The U.S. MAX planes were grounded the last, yet they were in the same danger as the other planes.