The angle of attack (AOA) disagree alert only worked on an aircraft if the airline had purchased an additional, optional feature, known as the AOA indicator, Boeing said.

Basically, an optional feature decided whether 2 planes crashed or not. So, the optional feature turned out to be a necessary feature for the plane not to crash as two of them eventually did that did NOT have the optional feature.

If you look at thousands of computer applications where software is involved in mechanical and electronic things around the world like self driving cars, self driving planes or self driving ships or boats, anything moving (including stationary machines) can kill if programs aren't working properly. So, it isn't just the 737 that is a problem there are thousands and possibly millions of other problems you aren't hearing about around the world regarding software going on right now. And even if people died this information could be easily covered up by businesses or governments or not researched by anyone even when people die. Look how many people had to die (two planeloads) to find all this out in public? Imagine how many other systems are messed up as well around the world right now in the self driving automatic pilot kind of world in planes, cars, trucks and ships and other stationary machines? Artificial intelligence is only going to magnify this problem about 1000 times between now and 2100. Although with the right self diagnosing programs in place many deaths could be avoided if the right artificial intelligence program or programs  were written to help avoid these problems.

If Boeing doesn't go bankrupt now from wrongful death suits it is possible that a lot of these self diagnosing programs using artificial intelligence will start to be written there and spread from there around the world. So, the end result might be much better designed planes on every single level starting with Boeing here in the U.S. We'll see.

It is my hope that this is the case.

Begin partial quote from:
https://www.cnn.com/2019/05/05/us/boeing-737-max-disagree-alert/index.html

The angle of attack (AOA) disagree alert only worked on an aircraft if the airline had purchased an additional, optional feature, known as the AOA indicator, Boeing said.

The AOA indicator lets pilots know if one of the AOA sensors is not working, while the disagree alert shows if the sensors contradict each other.

Boeing relied on single sensor for 737 Max that had been flagged 216 times to FAA

It's not known if the lack of the alert function played a role in the crashes of Lion Air crash and Ethiopian Airlines planes, which killed 346 people. But the disagree alert could have notified pilots that a sensor was malfunctioning. In both disasters, preliminary investigations suggest faulty data from a malfunctioning AOA sensor triggered the aircraft's anti-stall software, known as MCAS, which pitched down the nose of the planes as pilots struggled for control.