How the Boeing 737 Max disaster looks to a software Developer
This is a very good analysis, but fatally incomplete.<p>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.<p>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.<p>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.<p>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.<p>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.<p>A sixth was that, besides comparing redundant sensors, it could have compared what the other flight computer thought it should be doing.