I studied aircraft UX as my dissertation work. I’ll admit it is a few years out of date, but unlike JavaScript libraries, aircraft don’t change that fast. Here

I studied aircraft UX as my dissertation work. I’ll admit it is a few years out of date, but unlike JavaScript libraries, aircraft don’t change that fast. Here's my understanding/analysis of the situation: 1. Boeing was under pressure to create a more fuel-efficient version of the 737NG to compete with Airbus's A320neo. The 737MAX was the result. 2. In order to be lower investment for airlines, it was critical that the 737MAX share a type rating with the 737NG. This meant that a pilot certified ("checked out") on an NG would be able to fly on the MAX without further certification. 3. To gain fuel efficiency, the MAX has larger engines. To first order, larger engines result in more efficiency: by accelerating more air by a smaller amount you leave less energy in the air that's exiting the aircraft. The larger and more efficient engines results in 14% less fuel burn. That's a major improvement! 4. The larger engines and their placement resulted in a "pitch-up moment" during certain flight regimes. What this means is that when you add a lot of power to climb, and/or during steep turns. 5. To compensate and – this is critical – to maintain the same type certification, Boeing added something called MCAS (Maneuvering Characteristics Augmentation) which nudged the nose down by trimming the stabilizer (the horizontal bit of the tail) down (which pushes the tail down and therefore the nose up). It appears to be activated without pilot input. 6. There are other mechanisms which also "trim the stab down" and there has always been a mechanism which disconnects them: pulling back hard on the yoke. This is a natural motion for pilots because in all flight regimes pulling back on the yoke pulls the nose up, which is what you want to if the nose is going down. There is a backup mechanism as well which involves flipping a pair of cutout switches and manually taking over. 7. My speculation is that because MCAS was considered critical to making the MAX fly "like" the NG, the first disconnect mechanism was removed on the MAX. This is critical bit #2: the obvious/intuitive mechanism to disable something pushing the nose down was removed. 8. Because MCAS was so important, two (?) Angle of Attack sensors were added to the MAX. These sensors appear to fail more often than they should. In aviation terms that might mean they work 99.99% of the time, not 99.999%. 9. So now you have a situation where an aircraft has a required mechanism to fly/feel like another aircraft in order to maintain a consistent type rating but which is reliant on a shaky sensor. And when the sensor fails, the mechanism has – purposefully – been made more difficult to disconnect. From what I can tell, this entire set of decisions was driven by this type certificate/rating decision. That's the key mistake. I understand why this was done from a business standpoint, but if you're going to rely on manipulating flight characteristics it had better be bulletproof. Note that I'm not against the philosophy: Airbus has been doing it successfully for 25 years starting with the A320. But this isn't bulletproof. As it stands today, I wouldn't fly on the aircraft. Pilots are following this stuff pretty closely and are incredibly well-trained, but in a high pressure, low altitude, high wingload, high AoA situation, having them fiddle around looking for switches is a huge mistake. I have never said this about an aircraft before. I expect Boeing to re-enable the yoke disconnect and for the FAA to require recertification and a new type certificate for pilots to fly the MAX. Unfortunately, for Boeing, this will make them far, far less enticing to buy.