4 ms·

Interesting stuff, thanks. But my understanding is that other jets have a similar pitch up characteristics and no one considers them to be fundamentally flawed

Interesting stuff, thanks. But my understanding is that other jets have a similar pitch up characteristics and no one considers them to be fundamentally flawed. That the 737 MAX design creates a new problem vs the 737-NG does not necessarily mean it's fundamentally flawed. I'd only consider it a fundamental flaw if MCAS can't actually be designed to compensate for the problem. An unsolvable problem due to bad design = fundamental flaw. Otherwise having to stick a windshield on the front of an airplane could be considered a fundamental flaw. But it's not considered one because of very strong laminated materials compensating for the the problem. And yet it's still a huge potential risk. Windshields have cracked, broken, clouded up, etc.

salawat 7y ago
The behavior held common with the other 737 variants is a tendency to pitch up with the application of power. All aircraft with underslung engines share this characteristic. MAX, however, has additional problems where its flyability is adversely impacted when flying at high Angles of Attack when the engine nacelles (positioned higher and in front of the wing) creates extra lift in front of the center of mass of the aircraft. This creates divergences from the normal "control feel" of the older aircraft. When at low power, and high AoA, (such as might be experienced on descent), sudden applications of power can cause pitch up, which can put the plane at an AoA that experiences this handling divergence. MCAS, in it's second form, was intended to induce a controlled mistrim to compensate for both it's original purpose (high speed, high AoA divergence from 737 NG handling), and a low speed, high AoA handling divergence. It was being modified to handle the low speed case that removed an extra G-Load based cross check, and greatly increased the authority the MCAS system commanded, due to the larger deflections required to induce attitude changes in the low speed portions of the flight envelope. The fundamental flaw I mention, is several fold. Requirementswise: A)The MAX had to be developed yesterday to allow Boeing to maintain dominance/market share in narrow body civil transport against the A320neo. (They needed it fast) B) It had to be cheap. They needed minimum overhead cost to appease airlines, and comparable fuel efficiency to the A320neo. This meant no blank slate redesign. This locked them into the 737 type cert. This meant (to an engineer): C) It had to fly exactly like a 737... Without being one (They need it to be right). In engineering, there is a common saying: You can get it done cheap You can get it done fast. You can get [everything you want] done right). Pick two. For success, they needed all three, and delivering the third was not allowed the flexibility to intrude on either of the other points of the triad areas of process. The only way this project could have ended was with a breakdown somewhere in the process. That breakdown was in communication and propagation of the significance of the aerodynamics change. That failure in communication was bundled in the "fast and cheap" directive. The "right" directive required the aerodynamics divergence, and the software control system reconfiguration to compensate for it. The cheap and fast also required that the software solution not be driven by a dual sensor system, as that wouldn't have been allowed through without simulator training by the FAA, as testified to by a whistleblower as reported in the Australian 60 minutes expose. The whole thing is just a Greek tragedy in an engineering project's clothing. Hubris, greed, equivocation, catastrophe... It's all there.
- staunch 7y ago
  Thanks for the reply. I agree that Boeing clearly made a huge mistake by rushing the process, and in doing so, did a bad job. I'm still not yet aware of any reason that they won't be able to eventually make the MAX design safe and functional. It's a very interesting example of engineering/business dynamics. I'll be happy whether the MAX flies successfully or gets totally scrapped, as long as no one else dies in a MAX from negligence.

salawat 7y ago

The behavior held common with the other 737 variants is a tendency to pitch up with the application of power. All aircraft with underslung engines share this characteristic. MAX, however, has additional problems where its flyability is adversely impacted when flying at high Angles of Attack when the engine nacelles (positioned higher and in front of the wing) creates extra lift in front of the center of mass of the aircraft. This creates divergences from the normal "control feel" of the older aircraft. When at low power, and high AoA, (such as might be experienced on descent), sudden applications of power can cause pitch up, which can put the plane at an AoA that experiences this handling divergence. MCAS, in it's second form, was intended to induce a controlled mistrim to compensate for both it's original purpose (high speed, high AoA divergence from 737 NG handling), and a low speed, high AoA handling divergence. It was being modified to handle the low speed case that removed an extra G-Load based cross check, and greatly increased the authority the MCAS system commanded, due to the larger deflections required to induce attitude changes in the low speed portions of the flight envelope. The fundamental flaw I mention, is several fold. Requirementswise: A)The MAX had to be developed yesterday to allow Boeing to maintain dominance/market share in narrow body civil transport against the A320neo. (They needed it fast) B) It had to be cheap. They needed minimum overhead cost to appease airlines, and comparable fuel efficiency to the A320neo. This meant no blank slate redesign. This locked them into the 737 type cert. This meant (to an engineer): C) It had to fly exactly like a 737... Without being one (They need it to be right). In engineering, there is a common saying: You can get it done cheap You can get it done fast. You can get [everything you want] done right). Pick two. For success, they needed all three, and delivering the third was not allowed the flexibility to intrude on either of the other points of the triad areas of process. The only way this project could have ended was with a breakdown somewhere in the process. That breakdown was in communication and propagation of the significance of the aerodynamics change. That failure in communication was bundled in the "fast and cheap" directive. The "right" directive required the aerodynamics divergence, and the software control system reconfiguration to compensate for it. The cheap and fast also required that the software solution not be driven by a dual sensor system, as that wouldn't have been allowed through without simulator training by the FAA, as testified to by a whistleblower as reported in the Australian 60 minutes expose. The whole thing is just a Greek tragedy in an engineering project's clothing. Hubris, greed, equivocation, catastrophe... It's all there.

staunch 7y ago
Thanks for the reply. I agree that Boeing clearly made a huge mistake by rushing the process, and in doing so, did a bad job. I'm still not yet aware of any reason that they won't be able to eventually make the MAX design safe and functional. It's a very interesting example of engineering/business dynamics. I'll be happy whether the MAX flies successfully or gets totally scrapped, as long as no one else dies in a MAX from negligence.