15 ms·

Btw, the new "fix" for the MCAS has just been announced and discussed by a 40-year experienced pilot [1]. Turns out that while we shouldn't be doing armchair an

Btw, the new "fix" for the MCAS has just been announced and discussed by a 40-year experienced pilot [1]. Turns out that while we shouldn't be doing armchair analysis and assuming the worst of the engineering, management and executive team; the software fix released appears to be rather elementary and MCAS should have been designed with these safety checks in the first place. Why it wasn't is a huge concern and we wonder what other systems are at risk. In summary, the software fix does the following: 1. Use inputs from both AOA sensors, if they disagree by 5.5 degrees, disable MCAS. Original MCAS system used only 1 AOA sensor and switched back and forth between the two after every flight. 2. Triple redundant filters, A) Average value reasonability filter B) Catastrophic failure low-to-high transition filter C) Left vs. Right AOA deviation filter 3. Limiting MCAS stab trim so that the elevator always can provide 1.2g of nose-up pitch authority for recovery. Furthermore, electric trim with the yoke switch will override MCAS. Turns out that armchair analysis was sort of on point and goes along with the incompetency at Boeing affirmed in this reddit post - sometimes, I wonder how we, humans, collectively build extraordinary monuments while we individually rest on stilts. [1] https://youtu.be/zGM0V7zEKEQ?t=370 https://youtu.be/zGM0V7zEKEQ?t=370

ptidhomme 8y ago
> I wonder how we, humans, collectively build extraordinary monuments while we individually rest on stilts My take is that we used to have brilliant engineers in the time where computational ressources were scarce (60s, 70 , 80s...), and they thought out their design thoroughly starting with a fucking paper and pencil. Aerospace indutries still rely on the designs from these times. But now engineering seems to be : let's ask my computing power what is the good design, with little further questioning.
- Gravityloss 8y ago
  There were a lot of failures and accidents back then. But in general, designers did get more experience because there were more aircraft programs and they were way faster. So if you designed, say, landing gear, you might have done quite many during your career. It was more "agile" in that sense. Nowadays companies can not go so quickly to production. The whole business has turned into oligopolies both in the main integrators and the suppliers.
- noncoml 8y ago
  Brilliant engineers are still there. We haven’t gotten stupider as a species in 30 years. It’s the economics that changed. As people say “They don’t build stuff like they used too anymore”. First we started going cheap on the materials. Now we are going cheap on the engineers too. Why pay a senior “brilliant” engineer $$$$ when a fresh out of college “average” engineer can write the “same piece of code” for $$
  - ptidhomme 8y ago
    Indeed, and I'd add that we are going cheap because we can, thanks to computing power. As a matter of fact : computing tools make a lot of things easier and cheaper (which is good). But the setback is a tendency to "laziness" in the whole process...
  - noir_lord 8y ago
    > “They don’t build stuff like they used too anymore”. In fairness part (but far from all) of the reason we don't build stuff like we used too, is because we have much better understanding of material limits so we don't need to over-design structual elements like we used to. How that understanding of material limits feeds into design obsolescence is where I do get annoyed though. With everything we know now we could (obviously) build things better (for whatever criteria you chose) than they did 50 or 100 years ago, if that was the goal but it rarely is. My favourite piece of civil engineering in the world (because it's nearby and I've ridden over it many times) was built in 1980 though (it's the exact same age as me) and its still awe-inspiring to look at. https://upload.wikimedia.org/wikipedia/commons/b/b1/Humber_Bridge_Sunset_Wideshot.jpg https://upload.wikimedia.org/wikipedia/commons/b/b1/Humber_B...
    - dx034 8y ago
      The problem is that if a company gives customers (both b2b and b2c) the choice between a cheaper product with minimal guarantees vs. a product that is indeed better and can last longer, not enough customers will choose the better (more expensive) product to justify development cost (there are exceptions obviously). Partly, companies are even forced if the lowest bidder for pre-defined specification gets the contract. I believe there are more than enough engineers and companies that would like to build better and more durable products but demand just isn't there.
- yiyus 8y ago
  > But now engineering seems to be : let's ask my computing power what is the good design, with little further questioning. I see this quite often at the undergrad level. Even for the simplest problem that can be solved with a pencil and a couple of calculations, many students launch their finite element software and blindly trust the results, even if it is telling them something obviously wrong, like orders of magnitude larger or smaller than expected, or with the opposite sign. I acknowledge the problem, but I do not know where it comes from, or how to stop it.
  - majewsky 8y ago
    I don't find that particularly surprising. Engineering students want to learn how to build machines to find solutions to everything, so it's intuitive that they would place a high confidence in a solution provided by a machine.
    - yiyus 8y ago
      Good observation. There is a nice analogy to programming here. The same that one of the main tasks of the programmer is to handle errors, one of the main tasks of the engineer is to know the limitations of the tools he is using.
    - C1sc0cat 8y ago
      With no back checking?
      - majewsky 8y ago
        That's why I said "engineering students", not "engineers". Not blindly trusting your outputs is (or, at least, should be) part of the curriculum.
  - salawat 8y ago
    Is this for real? That's startling to me. I don't really feel like I "know" something well enough to bother with the overhead of developing computer code until I can at least get the essence of it down on paper. Computers are for enumerating and increasing confidence in proofs. I find pen and paper to be far more creativity friendly.
- Cthulhu_ 8y ago
  I think that's a bit unfair; designs have gotten so much more advanced and efficient in part thanks to computational design. The efficiency, range and maximum weight that airplanes can carry has pretty much doubled since that time. However, the original comment and the video it is a reply to explains a bit of the countering force; economy and competition. It's management that pressures the engineers to cut corners, basically. I don't doubt the Boeing engineers are some of the best people in the industry. I'm very much skeptical of management (and whipping them are shareholders) that optimize for time and by extension profits.
- robbiep 8y ago
  But we do. Look at SpaceX. Landing Rockets, crew dragon going to be half the cost of starliner. It’s just that LargeCorp eventually has the profit motive as the overriding goal and stops being innovative. It’s schumpters creative destruction in reality
- spacenick88 8y ago
  SpaceX is landing rocket stages on a drone ship after having them drop from 7400 km/h at 100 km altitude. JPL has a city car sized rover craned from a hovering lander on Mars and DeepMind has a computer win against the acting Go champion. Pretty sure that rules out the "today's engineers are bad" hypotheses.
  - ptidhomme 8y ago
    Indeed we still make great technological achievements, and thanks God there are still brilliant engineers out there. But they may not be equally distributed in the industry. And many of them (in my humble experience, at least) rely too much on computing tools and algorithms they do not completely master, expecting a "magical" answer out of them.
  - magduf 8y ago
    There absolutely are brilliant engineers out there. The problem is, they're probably not working at Boeing.
- magduf 8y ago
  We still have many brilliant engineers. The problem is that the brilliant ones from that age have all retired or died, and the brilliant ones these days didn't go into aerospace engineering, they went into other fields. Even when I was in college 25 years ago, we were making fun of the Aerospace Engineering majors as being in a dead-end field where they could look forward to few jobs and lay-offs. It's only gotten worse since then, I'm sure. The pay and career potential and job security is much better in computer science and engineering, so that's where all the brilliant engineers have been going for quite some time now.
thatoneuser 8y ago
Why do you say we shouldn't do armchair analysis right before you acknowledge that said analysis was on point? I think it's good our populace is eager to analyze. Ultimately we aren't making the decision, just forming a branch of decentralized checks. Long as witch hunts like the Boston bomber don't happen I say people should analyze till their hearts are content.
- spectramax 8y ago
  I agree with you but the general view is to avoid doing armchair analysis until official word is out. As far as armchair analysis doesn’t cause any harm, I think it’s fine!
tus87 8y ago
> 1. Use inputs from both AOA sensors, if they disagree by 5.5 degrees, disable MCAS. Great, and now you have the other problem the MCAS was supposed to mitigate (the tendency of the MAX to do backflips).
- noir_lord 8y ago
  Shrugs, if the MCAS disables with a clear notification to the pilots I think at this point most 737-Max pilots would know the procedure to deal with that. Better than the plane flying itself into the ground.
  - tus87 8y ago
    Which raises a rather obvious question ...
  - vkou 8y ago
    > Shrugs, if the MCAS disables with a clear notification to the pilots I think at this point most 737-Max pilots would know the procedure to deal with that. The plane is only certified to be 'identical to the 737' when MCAS is on, and operating correctly. If MCAS has to be disabled in response to a common mechanical problem, then the plane must be re-certified.
- cjrp 8y ago
  Although at least now you're trying to solve a more logical problem. Increasing angle of attack => counter with elevator, if not sufficient reduce thrust
  - foldr 8y ago
    Reducing thrust will increase angle of attack. The angle of attack is the angle of the wing relative to the airflow, not the angle of the plane relative to the horizon.
    - salawat 8y ago
      Yes conceptually, no because of signage error. If you were in a position MCAS would have to kick in, you were at positive AoA, reduced thrust would impart a negative AoA moment.
ozmaverick72 8y ago
The software fixes as described sound sensible and it's hard to believe they were not in the original design. Unfortunately I don't see how these changes will allow them to keep a common type rating with the 737 NG. After the updated MCAS has made its one shot trim adjustment you will now be flying an aircraft with different handling characteristics if you keep increasing the angle of attack into the stall. Surely the FAA can't sign off on the common type rating and half hour of video training ??
- peteradio 8y ago
  > Surely the FAA can't sign off on the common type rating and half hour of video training ?? What? Why not? They did a blood sacrifice and everything.
- PaulHoule 8y ago
  Having a new type rating is a fair punishment, I think, for Boeing and the airlines who have been stringing along this obsolete airliner for way too long. Note the 737 MAX was rushed out not just to fight the A320neo but also to counter this kind of jet: https://en.wikipedia.org/wiki/Airbus_A220 https://en.wikipedia.org/wiki/Airbus_A220 which is cheaper to run than the 737 MAX but also has much better passenger comfort than the 737. I was in the similar https://en.wikipedia.org/wiki/Embraer_E-Jet_family#E175 https://en.wikipedia.org/wiki/Embraer_E-Jet_family#E175 and even though it is a smaller plane, it feels more like riding in a widebody than in a 737. Canada developed a fully modern small jet on it's own dime and taking risk, then Boeing nearly killed it by offering airlines a 70% discount on the 737 MAX. Airbus bought a controlling interest in it for free because that was the only way it could survive. Common type rating is a big reason why airlines are sticking with the 1967 era 737 rather than upgrading to modern planes that will make flying much more pleasant, make less noise, use less fuel, less climate change impact, etc.
  - mcguire 8y ago
    How is the 737 obsolete?
    - 8y ago
ilogik 8y ago
> Original MCAS system used only 1 AOA sensor and switched back and forth between the two after every flight. Who the fuck thought that was a good idea??? Let's make it 10x more difficult to detect that there is a problem.
- 6nf 8y ago
  Just to explain a bit more: It uses the main pilot side AOA sensor, and pilots switch seats every flight.
  - amelius 8y ago
    So switching seats during the flight would have solved the problem?
    - philpem 8y ago
      That sounds so unlikely that most people would dismiss it as silly... I'm not a pilot, but if the controls are linked -- why would the plane need to know where the pilot is sitting (or even have a switch for it)? (Any 747 pilots reading? Can you please fill in the gaps for me?)
      - cjbprime 8y ago
        Not a pilot either. Perhaps to show different information to the pilot flying vs. assisting? E.g. only the pilot assisting needs to see checklists?
      - tellak 8y ago
        Not a 747 pilot (not sure why that matters here)... but a pilot. The flight positions are equal. The plane is designed to be flown the same from either flight position and this is routinely done. The guy saying otherwise is talking out their ass.
        philpem 8y ago
koenigdavidmj 8y ago
I thought that the flight immediately before this one had MCAS trouble too. Were both sensors busted, or was that actually an even number of cycles previous to the crash, and only the previous day?
- salawat 8y ago
  There was an extra pilot in the cockpit uninvolved with flying the plane. His participation in Crew Resource Management allowed the previous flight to correctly identify and remediate the issue before things became unrecoverable.
  - koenigdavidmj 8y ago
    I remember that, but if the issue was that one AOA instrument was broken, then only half the flights should be affected.
- tremon 8y ago
  The plane went through a maintenance cycle in-between the flights; it was suggested that the maintenance caused the chosen AoA sensor to flip twice. I'm not sure of the exact mechanics of this, but it's conceivable the maintenance crew performed a full engine or board computer boot cycle. Therefore, when the pilots started on their flight, it was the second warm-up since the previous flight, hence the same sensor was selected.
usrusr 8y ago
I wonder if the new iteration will also get an intermediate disable state, where you keep powered trim but shut out all automatic inputs. Defense in depth.
linuxftw 8y ago
> 1. Use inputs from both AOA sensors, if they disagree by 5.5 degrees, disable MCAS This can only mean that MCAS is disabled even more frequently. This is a terrible idea. This is like RAID0. The failure mode will increase greatly in complexity. MCAS might cut in and out, the plane might behave erratically. What the need to do is add a damn switch for 'disable MCAS' and tell people how and when to use the damn thing.
- magduf 8y ago
  No, they can't do that, because then they'd have to retrain the pilots, or maybe even have a different type rating, which would make them uncompetitive against the Airbus and Bombardier planes. Remember, profits are more important than passengers' lives.
  - pas 8y ago
    > because then they'd have to retrain the pilots, I think that ship has sailed already.
  - linuxftw 8y ago
    Just booked a flight. Price between two major carriers was about the same. One was a Boeing, the other Airbus. Guess who got my business?
agumonkey 8y ago
I don't get it, Boeing seemed to have a positive slope, with their plane outselling the competition. Fragile system design is hard to understand in this context. But maybe MCAS were conceived at a time where Boeing was more willing to cut corners.
garaetjjte 8y ago
>Furthermore, electric trim with the yoke switch will override MCAS. Does that mean it didn't override MCAS before? Really?
- pas 8y ago
  The point was, that they "just" put that shadow system there which will perfectly encapsulate the 737MAX to match the old 737 "interface". Now, they completely fucked that up. They did a so mindblowingly bad job, that anyone involved at the FAA who should have known about this should be in jail. Either for incompetence (negligence) or worse. They designed a system that relied on one input, operated periodically, told no one, documented nowhere, made it too powerful, always on, and un-turn-off-able, and spent the rest of the day corrupting/pleasing the FAA, then made the AoA input mismatch light an upsell feature, and finally called it a day.
- parrellel 8y ago
  Yep, this being one of the reasons the planes went splat.
morpheuskafka 8y ago
I know very little about aircraft, but wouldn't making the MCAS less powerful increase the risk of a stall? How do we know that there would be a net decrease in crashes?
- pas 8y ago
  We know nothing about how many times MCAS got engaged, maybe Boeing does. Who knows.* Furthermore, the problem seems to be that there is no explicit feedback about this from the pilots, because some of them did not even know about this. Consequently there was no widespread beta test in simulators, meaning there was not much data to base the fine tuning on. * actually, since MCAS activates only when the plane is over the critical angle (according to the AoA sensor), and there are other warnings, probably those can be counted.

ptidhomme 8y ago

> I wonder how we, humans, collectively build extraordinary monuments while we individually rest on stilts My take is that we used to have brilliant engineers in the time where computational ressources were scarce (60s, 70 , 80s...), and they thought out their design thoroughly starting with a fucking paper and pencil. Aerospace indutries still rely on the designs from these times. But now engineering seems to be : let's ask my computing power what is the good design, with little further questioning.

Gravityloss 8y ago
There were a lot of failures and accidents back then. But in general, designers did get more experience because there were more aircraft programs and they were way faster. So if you designed, say, landing gear, you might have done quite many during your career. It was more "agile" in that sense. Nowadays companies can not go so quickly to production. The whole business has turned into oligopolies both in the main integrators and the suppliers.
noncoml 8y ago
Brilliant engineers are still there. We haven’t gotten stupider as a species in 30 years. It’s the economics that changed. As people say “They don’t build stuff like they used too anymore”. First we started going cheap on the materials. Now we are going cheap on the engineers too. Why pay a senior “brilliant” engineer $$$$ when a fresh out of college “average” engineer can write the “same piece of code” for $$
- ptidhomme 8y ago
  Indeed, and I'd add that we are going cheap because we can, thanks to computing power. As a matter of fact : computing tools make a lot of things easier and cheaper (which is good). But the setback is a tendency to "laziness" in the whole process...
- noir_lord 8y ago
  > “They don’t build stuff like they used too anymore”. In fairness part (but far from all) of the reason we don't build stuff like we used too, is because we have much better understanding of material limits so we don't need to over-design structual elements like we used to. How that understanding of material limits feeds into design obsolescence is where I do get annoyed though. With everything we know now we could (obviously) build things better (for whatever criteria you chose) than they did 50 or 100 years ago, if that was the goal but it rarely is. My favourite piece of civil engineering in the world (because it's nearby and I've ridden over it many times) was built in 1980 though (it's the exact same age as me) and its still awe-inspiring to look at. https://upload.wikimedia.org/wikipedia/commons/b/b1/Humber_Bridge_Sunset_Wideshot.jpg https://upload.wikimedia.org/wikipedia/commons/b/b1/Humber_B...
  - dx034 8y ago
    The problem is that if a company gives customers (both b2b and b2c) the choice between a cheaper product with minimal guarantees vs. a product that is indeed better and can last longer, not enough customers will choose the better (more expensive) product to justify development cost (there are exceptions obviously). Partly, companies are even forced if the lowest bidder for pre-defined specification gets the contract. I believe there are more than enough engineers and companies that would like to build better and more durable products but demand just isn't there.
yiyus 8y ago
> But now engineering seems to be : let's ask my computing power what is the good design, with little further questioning. I see this quite often at the undergrad level. Even for the simplest problem that can be solved with a pencil and a couple of calculations, many students launch their finite element software and blindly trust the results, even if it is telling them something obviously wrong, like orders of magnitude larger or smaller than expected, or with the opposite sign. I acknowledge the problem, but I do not know where it comes from, or how to stop it.
- majewsky 8y ago
  I don't find that particularly surprising. Engineering students want to learn how to build machines to find solutions to everything, so it's intuitive that they would place a high confidence in a solution provided by a machine.
  - yiyus 8y ago
    Good observation. There is a nice analogy to programming here. The same that one of the main tasks of the programmer is to handle errors, one of the main tasks of the engineer is to know the limitations of the tools he is using.
  - C1sc0cat 8y ago
    With no back checking?
    - majewsky 8y ago
      That's why I said "engineering students", not "engineers". Not blindly trusting your outputs is (or, at least, should be) part of the curriculum.
- salawat 8y ago
  Is this for real? That's startling to me. I don't really feel like I "know" something well enough to bother with the overhead of developing computer code until I can at least get the essence of it down on paper. Computers are for enumerating and increasing confidence in proofs. I find pen and paper to be far more creativity friendly.
Cthulhu_ 8y ago
I think that's a bit unfair; designs have gotten so much more advanced and efficient in part thanks to computational design. The efficiency, range and maximum weight that airplanes can carry has pretty much doubled since that time. However, the original comment and the video it is a reply to explains a bit of the countering force; economy and competition. It's management that pressures the engineers to cut corners, basically. I don't doubt the Boeing engineers are some of the best people in the industry. I'm very much skeptical of management (and whipping them are shareholders) that optimize for time and by extension profits.
robbiep 8y ago
But we do. Look at SpaceX. Landing Rockets, crew dragon going to be half the cost of starliner. It’s just that LargeCorp eventually has the profit motive as the overriding goal and stops being innovative. It’s schumpters creative destruction in reality
spacenick88 8y ago
SpaceX is landing rocket stages on a drone ship after having them drop from 7400 km/h at 100 km altitude. JPL has a city car sized rover craned from a hovering lander on Mars and DeepMind has a computer win against the acting Go champion. Pretty sure that rules out the "today's engineers are bad" hypotheses.
- ptidhomme 8y ago
  Indeed we still make great technological achievements, and thanks God there are still brilliant engineers out there. But they may not be equally distributed in the industry. And many of them (in my humble experience, at least) rely too much on computing tools and algorithms they do not completely master, expecting a "magical" answer out of them.
- magduf 8y ago
  There absolutely are brilliant engineers out there. The problem is, they're probably not working at Boeing.
magduf 8y ago
We still have many brilliant engineers. The problem is that the brilliant ones from that age have all retired or died, and the brilliant ones these days didn't go into aerospace engineering, they went into other fields. Even when I was in college 25 years ago, we were making fun of the Aerospace Engineering majors as being in a dead-end field where they could look forward to few jobs and lay-offs. It's only gotten worse since then, I'm sure. The pay and career potential and job security is much better in computer science and engineering, so that's where all the brilliant engineers have been going for quite some time now.

thatoneuser 8y ago

Why do you say we shouldn't do armchair analysis right before you acknowledge that said analysis was on point? I think it's good our populace is eager to analyze. Ultimately we aren't making the decision, just forming a branch of decentralized checks. Long as witch hunts like the Boston bomber don't happen I say people should analyze till their hearts are content.

spectramax 8y ago
I agree with you but the general view is to avoid doing armchair analysis until official word is out. As far as armchair analysis doesn’t cause any harm, I think it’s fine!

tus87 8y ago

> 1. Use inputs from both AOA sensors, if they disagree by 5.5 degrees, disable MCAS. Great, and now you have the other problem the MCAS was supposed to mitigate (the tendency of the MAX to do backflips).

noir_lord 8y ago
Shrugs, if the MCAS disables with a clear notification to the pilots I think at this point most 737-Max pilots would know the procedure to deal with that. Better than the plane flying itself into the ground.
- tus87 8y ago
  Which raises a rather obvious question ...
- vkou 8y ago
  > Shrugs, if the MCAS disables with a clear notification to the pilots I think at this point most 737-Max pilots would know the procedure to deal with that. The plane is only certified to be 'identical to the 737' when MCAS is on, and operating correctly. If MCAS has to be disabled in response to a common mechanical problem, then the plane must be re-certified.
cjrp 8y ago
Although at least now you're trying to solve a more logical problem. Increasing angle of attack => counter with elevator, if not sufficient reduce thrust
- foldr 8y ago
  Reducing thrust will increase angle of attack. The angle of attack is the angle of the wing relative to the airflow, not the angle of the plane relative to the horizon.
  - salawat 8y ago
    Yes conceptually, no because of signage error. If you were in a position MCAS would have to kick in, you were at positive AoA, reduced thrust would impart a negative AoA moment.

ozmaverick72 8y ago

The software fixes as described sound sensible and it's hard to believe they were not in the original design. Unfortunately I don't see how these changes will allow them to keep a common type rating with the 737 NG. After the updated MCAS has made its one shot trim adjustment you will now be flying an aircraft with different handling characteristics if you keep increasing the angle of attack into the stall. Surely the FAA can't sign off on the common type rating and half hour of video training ??

peteradio 8y ago
> Surely the FAA can't sign off on the common type rating and half hour of video training ?? What? Why not? They did a blood sacrifice and everything.
PaulHoule 8y ago
Having a new type rating is a fair punishment, I think, for Boeing and the airlines who have been stringing along this obsolete airliner for way too long. Note the 737 MAX was rushed out not just to fight the A320neo but also to counter this kind of jet: https://en.wikipedia.org/wiki/Airbus_A220 https://en.wikipedia.org/wiki/Airbus_A220 which is cheaper to run than the 737 MAX but also has much better passenger comfort than the 737. I was in the similar https://en.wikipedia.org/wiki/Embraer_E-Jet_family#E175 https://en.wikipedia.org/wiki/Embraer_E-Jet_family#E175 and even though it is a smaller plane, it feels more like riding in a widebody than in a 737. Canada developed a fully modern small jet on it's own dime and taking risk, then Boeing nearly killed it by offering airlines a 70% discount on the 737 MAX. Airbus bought a controlling interest in it for free because that was the only way it could survive. Common type rating is a big reason why airlines are sticking with the 1967 era 737 rather than upgrading to modern planes that will make flying much more pleasant, make less noise, use less fuel, less climate change impact, etc.
- mcguire 8y ago
  How is the 737 obsolete?
  - 8y ago

ilogik 8y ago

> Original MCAS system used only 1 AOA sensor and switched back and forth between the two after every flight. Who the fuck thought that was a good idea??? Let's make it 10x more difficult to detect that there is a problem.

6nf 8y ago
Just to explain a bit more: It uses the main pilot side AOA sensor, and pilots switch seats every flight.
- amelius 8y ago
  So switching seats during the flight would have solved the problem?
  - philpem 8y ago
    That sounds so unlikely that most people would dismiss it as silly... I'm not a pilot, but if the controls are linked -- why would the plane need to know where the pilot is sitting (or even have a switch for it)? (Any 747 pilots reading? Can you please fill in the gaps for me?)
    - cjbprime 8y ago
      Not a pilot either. Perhaps to show different information to the pilot flying vs. assisting? E.g. only the pilot assisting needs to see checklists?
    - tellak 8y ago
      Not a 747 pilot (not sure why that matters here)... but a pilot. The flight positions are equal. The plane is designed to be flown the same from either flight position and this is routinely done. The guy saying otherwise is talking out their ass.
      - philpem 8y ago

koenigdavidmj 8y ago

I thought that the flight immediately before this one had MCAS trouble too. Were both sensors busted, or was that actually an even number of cycles previous to the crash, and only the previous day?

salawat 8y ago
There was an extra pilot in the cockpit uninvolved with flying the plane. His participation in Crew Resource Management allowed the previous flight to correctly identify and remediate the issue before things became unrecoverable.
- koenigdavidmj 8y ago
  I remember that, but if the issue was that one AOA instrument was broken, then only half the flights should be affected.
tremon 8y ago
The plane went through a maintenance cycle in-between the flights; it was suggested that the maintenance caused the chosen AoA sensor to flip twice. I'm not sure of the exact mechanics of this, but it's conceivable the maintenance crew performed a full engine or board computer boot cycle. Therefore, when the pilots started on their flight, it was the second warm-up since the previous flight, hence the same sensor was selected.

usrusr 8y ago

I wonder if the new iteration will also get an intermediate disable state, where you keep powered trim but shut out all automatic inputs. Defense in depth.

linuxftw 8y ago

> 1. Use inputs from both AOA sensors, if they disagree by 5.5 degrees, disable MCAS This can only mean that MCAS is disabled even more frequently. This is a terrible idea. This is like RAID0. The failure mode will increase greatly in complexity. MCAS might cut in and out, the plane might behave erratically. What the need to do is add a damn switch for 'disable MCAS' and tell people how and when to use the damn thing.

magduf 8y ago
No, they can't do that, because then they'd have to retrain the pilots, or maybe even have a different type rating, which would make them uncompetitive against the Airbus and Bombardier planes. Remember, profits are more important than passengers' lives.
- pas 8y ago
  > because then they'd have to retrain the pilots, I think that ship has sailed already.
- linuxftw 8y ago
  Just booked a flight. Price between two major carriers was about the same. One was a Boeing, the other Airbus. Guess who got my business?

agumonkey 8y ago

I don't get it, Boeing seemed to have a positive slope, with their plane outselling the competition. Fragile system design is hard to understand in this context. But maybe MCAS were conceived at a time where Boeing was more willing to cut corners.

garaetjjte 8y ago

>Furthermore, electric trim with the yoke switch will override MCAS. Does that mean it didn't override MCAS before? Really?

pas 8y ago
The point was, that they "just" put that shadow system there which will perfectly encapsulate the 737MAX to match the old 737 "interface". Now, they completely fucked that up. They did a so mindblowingly bad job, that anyone involved at the FAA who should have known about this should be in jail. Either for incompetence (negligence) or worse. They designed a system that relied on one input, operated periodically, told no one, documented nowhere, made it too powerful, always on, and un-turn-off-able, and spent the rest of the day corrupting/pleasing the FAA, then made the AoA input mismatch light an upsell feature, and finally called it a day.
parrellel 8y ago
Yep, this being one of the reasons the planes went splat.

morpheuskafka 8y ago

I know very little about aircraft, but wouldn't making the MCAS less powerful increase the risk of a stall? How do we know that there would be a net decrease in crashes?

pas 8y ago
We know nothing about how many times MCAS got engaged, maybe Boeing does. Who knows.* Furthermore, the problem seems to be that there is no explicit feedback about this from the pilots, because some of them did not even know about this. Consequently there was no widespread beta test in simulators, meaning there was not much data to base the fine tuning on. * actually, since MCAS activates only when the plane is over the critical angle (according to the AoA sensor), and there are other warnings, probably those can be counted.