1. The Maneuvering Characteristics Augmentation System (MCAS) system existed because the plane was unstable at high angles of attack.

2. The 737 MAX was unstable because Boeing wanted to milk the 737 airframe further than it should have been for financial reasons and oversized engines were mounted forward on the wings.

3. Since the plane was unstable in this way, it would pitch up when climbing. MCAS would detect this through the angle of attack (AoA sensors) and automatically engage, forcing the nose down.

4. When the single, nonredundant AoA sensor failed, MCAS would misinterpret this and try to continuously force the nose down in normal operations. Or more plainly, it would fly the plane into the ground for no reason.

5. This happened at least 3 times. In two cases, it caused crashes, killing everyone - almost 350 men, women, and children - aboard.

6. Boeing strenuously blamed the crew in the first crash, and did not ground the planes.

7. Boeing did not ground the 737 MAXes after the second crash, either. The FAA only grounded the aircraft after much of the rest of the world already had.

As you noted previously, MCAS existed to make the 737 MAX fly like prior versions of the plane. Boeing, in fact, lobbied for this outcome so it would not affect certification or require separate pilot training, which would have cost time and money. So while MCAS was documented, pilots were not required to be trained on the system, because of Boeings efforts.

One cannot put a "don't crash the plane button" on a plane, even if it is well documented. It is particularly disgraceful if the "don't crash the plane" button only exists because the plane's manufacturer added the button to increase their own profits.

I have to admit, you have made me lose my composure here a bit. I thought anyone this knowledgable about flying would not blame pilot error in the 737 MAX crashes. The plane was grounded for almost 2 years, this was arguably the greatest scandal in the production and regulation of commercial aircraft in history. Boeing paid $20 billion in fines and restitution, and pled guilty to criminal charges.

For the benefit of anyone else curious about this, good starting points are

https://en.wikipedia.org/wiki/Boeing_737_MAX_groundings

"hours after the approval for MCAS's redesign was granted, Boeing sought, and the FAA approved, the removal of references to MCAS from Boeing's flight crew operations manual (FCOM)"

"Boeing wanted the FAA to certify the airplane as another version of the long-established 737; this would limit the need for additional training of pilots, a major cost saving for airline customers. During flight tests, however, Boeing discovered that the position and larger size of the engines tended to push up the airplane nose during certain maneuvers. To counter that tendency and ensure fleet commonality with the 737 family, Boeing added MCAS so the MAX would handle similar to earlier 737 versions."

"The MAX was exempted from certain newer safety requirements, saving Boeing billions of dollars in development costs."

https://en.wikipedia.org/wiki/List_of_Boeing_737_MAX_groundi...

https://www.amazon.com/Flying-Blind-Tragedy-Fall-Boeing/dp/0...

Regarding Boeing, every person, and particularly every engineer, should read https://www.amazon.com/Flying-Blind-Tragedy-Fall-Boeing/dp/0...

The background of this is covered in the new book, Flying Blind:

https://www.amazon.com/Flying-Blind-Tragedy-Fall-Boeing/dp/0...

It talks about GE a lot as well, as both companies were destroyed by the Jack Welch "school of managers".