7 ms·

ELI5: why can’t the auto safety system be removed and the plane be sound? Is the design so flawed that it can’t be safely flown by a human without this system

ELI5: why can’t the auto safety system be removed and the plane be sound? Is the design so flawed that it can’t be safely flown by a human without this system that causes random catastrophic failures?

totalZero 7y ago
If there is another crash due to a manufacturing defect, expect airlines to abandon the 737 Max variants. Boeing has very little margin for error.
csours 7y ago
Briefly: It could be, but that would mean reclassifying the airplane. Maybe think about it like anti-lock brakes. Cars without ABS can be driven safely in many/most circumstances, but most drivers are accustomed to ABS. (This is necessarily a limited analogy) Also, there are government requirements per aircraft type, and removing this system would change the aircraft type, triggering a significant amount of required re-training. --- Not directly related to your question, but I think [pure speculation/psychological theory] one thing that went badly wrong here was engineers thinking about this as a convenience system. Because it was thought of as a convenience system, they didn't fully consider the safety aspect of it.
- kayfox 7y ago
  It cant, the forces have to linearly increase per FARs, so MCAS has to be a thing, same type certificate or not.
  - csours 7y ago
    Ah, that's the first time I've heard that. I'm certainly not an expert, I've just read/watched a number of reports.
    - kayfox 7y ago
      The problem with reporting around this issue is that its emotionally driven and done often by people who have little experience with how the aviation industry works. So while the exact details are accurately reported in aviation industry news, the mainstream news keeps parroting things that are false and confirmation bias keeps people from picking up when those things are false. The departure from reality in this case is pretty severe: 1. There were severe issues with pilot's performance on both flights. 2. Airline maintenance is culpable in the Lion Air flight. 3. MCAS is required irregardless of what type certificate is used. 4. Boeing's "new problems with the 737" are not as much a result of faults previously ignored, but new issues created by reassessing the risk factors related to those systems. 5. The 737 MAX is not aerodynamically unstable. 6. The 737 MAX issue has brought to light severe issues in the aviation industry that may require retraining many pilots in the industry or being way more aggressive with refresh training (also see the Atlas Air crash recently).
nexuist 7y ago
TL;DR The 737 design is super, super old and they wanted to install new engines on it that are more efficient and powerful. These engines are much bigger than the engines that were initially installed, meaning they had to be installed further up the wing in order to ensure adequate ground clearance. Unfortunately that changes the flight model of the airplane and makes it prone to pitching up, especially during take off. Pitching up too far can cause a stall and result in a crash. MCAS was designed to detect this pitch up and counter it with a pitch down. It's entirely possible, even likely I would say, that the majority of pilots would intervene before a stall is ever reached in a scenario where MCAS would kick in. I think you could fly this plane for hundreds of thousands of hours without incident without MCAS. Unfortunately, there have been cases (AF447) where the pilots were so confused/tired/inexperienced that they ignored the stall horn and let the plane stall and crash. MCAS was meant to address situations like those but tragically it only made things worse. The other thing is that Boeing didn't want to have to re-certify this aircraft with the FAA, as that would also require airlines to train their pilots for this new aircraft type. Note that the whole purpose of the MAX was to compete with the A320neo, and re-certification would have taken a long time and cost a whole lot of money. This would negate the purpose of the MAX in the first place. MCAS allowed Boeing to "pretend" the 737 MAX was the same exact airplane as the 737NG (which the MAX was based off, I believe), and thus pilots didn't need additional training outside of a 30 minute iPad session.
kawfey 7y ago
It's like if you replaced your 2015 car with a new, but heavier 2020 model. Since its heavier, but has the same braking system as the 2015 model, it has a longer braking distance. To remedy that the engineers put in a "braking characteristics augmentation system" (BCAS) to augment the braking power applied, so that it stops sooner than a person normally would. It uses a single camera and computer vision to detect obstacles ahead. The car company didn't think they need to tell its drivers about it. One day you'll be driving and all of a sudden come to a screeching halt (and maybe cause a wreck) and come to find out the camera was obscured by a precise strike of bird poop. The car company could have either A) told and trained their drivers at the dealership to brake harder than normal, B) used a two-camera backup system, or C) redesigned the brakes to accommodate for the increased vehicle weight. MCAS is basically that. It makes the MAX8 maneuver and behave just like the previous 737 models, even though the larger engine and more forward placement causes it to fly somewhat differently in certain situations. The failures came from the lack of training and understanding of the system as well as a flawed implementation using input from only a single sensor instead of two. Without MCAS, they would have required a significant amount of training and possibly re certification, which costs at least a few billion dollars more than a few hundred lines of code (but unfortunately a lot less than 346 people's lives and many many billions of dollars of follow-on debt).

totalZero 7y ago

If there is another crash due to a manufacturing defect, expect airlines to abandon the 737 Max variants. Boeing has very little margin for error.

csours 7y ago

Briefly: It could be, but that would mean reclassifying the airplane. Maybe think about it like anti-lock brakes. Cars without ABS can be driven safely in many/most circumstances, but most drivers are accustomed to ABS. (This is necessarily a limited analogy) Also, there are government requirements per aircraft type, and removing this system would change the aircraft type, triggering a significant amount of required re-training. --- Not directly related to your question, but I think [pure speculation/psychological theory] one thing that went badly wrong here was engineers thinking about this as a convenience system. Because it was thought of as a convenience system, they didn't fully consider the safety aspect of it.

kayfox 7y ago
It cant, the forces have to linearly increase per FARs, so MCAS has to be a thing, same type certificate or not.
- csours 7y ago
  Ah, that's the first time I've heard that. I'm certainly not an expert, I've just read/watched a number of reports.
  - kayfox 7y ago
    The problem with reporting around this issue is that its emotionally driven and done often by people who have little experience with how the aviation industry works. So while the exact details are accurately reported in aviation industry news, the mainstream news keeps parroting things that are false and confirmation bias keeps people from picking up when those things are false. The departure from reality in this case is pretty severe: 1. There were severe issues with pilot's performance on both flights. 2. Airline maintenance is culpable in the Lion Air flight. 3. MCAS is required irregardless of what type certificate is used. 4. Boeing's "new problems with the 737" are not as much a result of faults previously ignored, but new issues created by reassessing the risk factors related to those systems. 5. The 737 MAX is not aerodynamically unstable. 6. The 737 MAX issue has brought to light severe issues in the aviation industry that may require retraining many pilots in the industry or being way more aggressive with refresh training (also see the Atlas Air crash recently).

nexuist 7y ago

TL;DR The 737 design is super, super old and they wanted to install new engines on it that are more efficient and powerful. These engines are much bigger than the engines that were initially installed, meaning they had to be installed further up the wing in order to ensure adequate ground clearance. Unfortunately that changes the flight model of the airplane and makes it prone to pitching up, especially during take off. Pitching up too far can cause a stall and result in a crash. MCAS was designed to detect this pitch up and counter it with a pitch down. It's entirely possible, even likely I would say, that the majority of pilots would intervene before a stall is ever reached in a scenario where MCAS would kick in. I think you could fly this plane for hundreds of thousands of hours without incident without MCAS. Unfortunately, there have been cases (AF447) where the pilots were so confused/tired/inexperienced that they ignored the stall horn and let the plane stall and crash. MCAS was meant to address situations like those but tragically it only made things worse. The other thing is that Boeing didn't want to have to re-certify this aircraft with the FAA, as that would also require airlines to train their pilots for this new aircraft type. Note that the whole purpose of the MAX was to compete with the A320neo, and re-certification would have taken a long time and cost a whole lot of money. This would negate the purpose of the MAX in the first place. MCAS allowed Boeing to "pretend" the 737 MAX was the same exact airplane as the 737NG (which the MAX was based off, I believe), and thus pilots didn't need additional training outside of a 30 minute iPad session.

kawfey 7y ago

It's like if you replaced your 2015 car with a new, but heavier 2020 model. Since its heavier, but has the same braking system as the 2015 model, it has a longer braking distance. To remedy that the engineers put in a "braking characteristics augmentation system" (BCAS) to augment the braking power applied, so that it stops sooner than a person normally would. It uses a single camera and computer vision to detect obstacles ahead. The car company didn't think they need to tell its drivers about it. One day you'll be driving and all of a sudden come to a screeching halt (and maybe cause a wreck) and come to find out the camera was obscured by a precise strike of bird poop. The car company could have either A) told and trained their drivers at the dealership to brake harder than normal, B) used a two-camera backup system, or C) redesigned the brakes to accommodate for the increased vehicle weight. MCAS is basically that. It makes the MAX8 maneuver and behave just like the previous 737 models, even though the larger engine and more forward placement causes it to fly somewhat differently in certain situations. The failures came from the lack of training and understanding of the system as well as a flawed implementation using input from only a single sensor instead of two. Without MCAS, they would have required a significant amount of training and possibly re certification, which costs at least a few billion dollars more than a few hundred lines of code (but unfortunately a lot less than 346 people's lives and many many billions of dollars of follow-on debt).