How the Boeing 737 Max disaster looks to a software Developer

One really essential reason those planes crashed was that each time the MCAS triggered, it acted like it was the first time. If it added 1 degree of trim last time, it adds a second this time, a third next time, up to the five degrees that runs the trim all the way to the stops.

A second reason is that, under the design still on file at the FAA, it could only add a maximum of 0.8 degrees (each time). This was raised to 2.4 degrees after testing, so only two hits could, in principle, put you almost to the stops.

A third was that the only way to override the MCAS was to turn off power to the motor that worked the trim. But above 400 knots, the strength needed to dial back the trim with the hand crank was more than actual live pilots have, especially if it is taking all their strength to pull back on the yoke.

A fourth was that, with two flight control computers, the pilot could (partly) turn off a misbehaving one, but there is no way to turn on the other one. You have to land first, to switch over, even though the other is doing all the work to be ready to fly the plane.

A fifth was that it ignored that pilots were desperately pulling back on the yoke, which could have been a clue that it was doing the wrong thing.

A sixth was that, besides comparing redundant sensors, it could have compared what the other flight computer thought it should be doing.

It doesn't need to be binary technical/non-technical; everybody is, to some degree, technical. If you can use a knife, you're technical. And it doesn't need to be this rigid specialization, I do computers / I do aviation. If we removed that divide we might start to widen and deconstrict that bottleneck, and we might even start to find more people like this author who know both, and who don't need to have an aviation SME tell them to check more than one sensor for example, because when they're writing it, and coding the part where you set or decide the value for AOA, they automatically say to themselves "hey let's add a cross-check here like I always do when I'm flying." Specialization seems like a magic bullet but it also creates a big burden of oversight & communication, I guess is my point. It's like splitting the monolith of the human world into microservices, and with the same resulting problems.

https://www.youtube.com/watch?v=SVRiktFlWxI#t=2h9m38s

Software could be proven correct, but we abandoned that, just gave up on it, it’s too hard. But we can test it. We can use science, and we can write tests that demonstrate that the software is not failing. We treat software like a science, not like mathematics.

— Robert Martin