6 ms·

Yep, 3 sensors can fail too. Less often however. These sensors exist to solve a problem with the MAX design. Changing and moving the engines increased the like

by cletus 8y ago

Yep, 3 sensors can fail too. Less often however. These sensors exist to solve a problem with the MAX design. Changing and moving the engines increased the likelihood of a stall when the engines could push the nose up (as I understand it). Fine. But here's the kicker: this should be something that pilots should be trained on. They should be aware of how the MAX is different to the previous 737s and know what to do to disable this system if it causes problems. But that might be the end of a common type rating, which is something the airlines (and apparently Boeing) didn't want. The whole 737 MAX situation just looks like a giant clusterf--- that was a kneejerk reaction to the unexpected success of the A320neo to which Boeing had no answer and to avoid years-long development delays and losing more customers to Airbus, it really looks like they made shortcuts. And that's so damaging to their brand it really defies belief.

xiphias2 8y ago
I was hoping to have the damage in the Boing brand reflected more significantly in the share prices.
- jdc 8y ago
  Maybe the problem hasn't been shouted from a high enough rooftop yet.
  - bdamm 8y ago
    Or more likely it doesn't really matter, and in a couple years nobody will really remember this about Boeing. They'll go back to being a big airplane producer that has a stunning safety record, which they are despite this issue.
    - Tsubasachan 8y ago
      The airline industry is growing and there are only two manufacturers who can build hundreds of planes on time. Airbus is already near full capacity. It would be impossible NOT to buy Boeing if you want planes.
    - carlmr 8y ago
      Which is also the correct thing to do. Despite our president and some NYTimes columnists being scared of automation (apparently they only agree when they're wrong), automation has saved so many lives that a failure like this doesn't affect the big picture. Yes, mistakes were made, yes, we should find ways to avoid this happening in the future, no, automation isn't the enemy. Without automation in flying at the current number of airplanes in the sky we'd probably have one or two crashes a day. The fact that 2 crashes in half a year make the news is thanks to the amazing safety of modern airplanes.
      - magduf 8y ago
        Automation is definitely not the enemy. However, automation that is designed in a criminally negligent manner is. People who create such designs should be put in prison, and we should not be using products from them ever again.
        carlmr 8y ago
        Have fun using any product. If your company gets big enough the probability that one of its products was faulty because of negligence slowly approaches 100%. Any big company has a scandal, learns from it, the people that learned the lesson leave at some point, a new generation of employees makes a similar mistake again, wash rinse, repeat. You probably can't fly any airplanes if you will not use any airplanes from a company that had a scandal like this.
        jdc 8y ago
        AFAIK the automation had no good reason to be there first place, unless you consider racing Airbus for contracts a good reason. I mean, the simpler the better especially when lives are at stake, right?
AareyBaba 8y ago
I am puzzled by the apparent lack of a "this plane is heading straight into the ground" sensor that should have overridden the MCAS.
- bdonlan 8y ago
  The MCAS is designed to prevent an aerodynamic stall; a situation where the plane is pointed too far up and as a result starts heading straight for the ground. It does do by detecting the plane pointing too far up, and pushing it back down. If it did not function when the plane was descending rapidly it would not be fit for its designed purpose.
  - deleted 8y ago
    [deleted]
  - AceyMan 8y ago
    > The MCAS is designed to prevent an aerodynamic stall [...] This has become a trope and is flatly incorrect. MCAS was cooked up to maintain the handling characteristics required by the certification specifications. The standard requires stick resistance to increase as the critical (stall) angle of attack is approached. The MAX violated that requirement due to the aerodynamics of the new engine cowls, so MCAS was Boeing's (?crap) implementation of "artificial feel" to meet the spec. Yes, while the spec exists presumably to prevent the pilots from themselves taking the ship into a stall, MCAS doesn't change wing or aircraft performance in a material way that would be meant by "prevent a stall."
    - linuxftw 8y ago
      There seem to be a handful of people spreading this talking point here. In every authoritative source, MCAS is described as anti-stall system.
      - AceyMan 8y ago
        I believe the critical passage is here in CFR 14 §25.175¹ (2) With the landing gear retracted at low speed, the stick force curve must have a stable slope at all speeds within a range which is the greater of 15 percent of the trim speed plus the resulting free return speed range, or 50 knots plus the resulting free return speed range, above and below the trim speed (except that the speed range need not include speeds less than 1.3 VSR1, nor speeds greater than the minimum speed of the applicable speed range prescribed in paragraph (b)(1), nor speeds that require a stick force of more than 50 pounds)[...] The crucial phrase is "stick force curve", which is the characteristic MCAS was created to tweak. As far as 'authoritative sources' go, I'll just mention the Gell-Mann amnesia effect.² (me: non-active aircraft dispatcher) ¹—https://www.ecfr.gov/cgi-bin/text-idx?node=14:1.0.1.3.11#se14.1.25_1175 https://www.ecfr.gov/cgi-bin/text-idx?node=14:1.0.1.3.11#se1... ²—https://en.wikipedia.org/wiki/Gell-Mann_amnesia_effect?wprov=sfla1 https://en.wikipedia.org/wiki/Gell-Mann_amnesia_effect?wprov...
chungleong 8y ago
If there were specific steps that the pilots could have taken to avert disaster, why not just incorporate them into the flight software? Why resorting instead to "reprogramming" the pilot? That's what training is: programming of the human brain. One can't teach others without having first learned the lesson oneself. I'm not convinced Boeing has. I'm not convinced the company had adequately consider all possible scenarios and how pilots would react in them based on their intuition.
- phire 8y ago
  Even if it has enough sensprs, the flight software has no situational awareness. This is by design. The flight software is deliberately kept simple enough that the pilots can be trained to understand the full workings of the flight software and what it will do in any situation. The entire flight control algorithm is probably only a few hundred lines of psudocode. It's a catch 22: We are fully capable of designing a plane that safely flys itself from airport to airport without any pilots, to handle most emergency situations. We have been able to do so since the 80s. But we are not able to put a pilot in the loop on such a plane without massive safety implications. To have a pilot in the loop, the software has to be kept super simple so the pilot can diagnose it in an emergency and take the correct action. Either we have the flight software that is situational aware and authorised to take any action, or we have a super simple software and a pilot in the loop. There is no safe middle ground.
  - alistairSH 8y ago
    Not sure about the "able to do so since the 80s" part, but generally, I agree. It's the same problem we see with Tesla, Uber, etc and autonomous cars. If it's to be truly autonomous, it needs to do so without ANY human intervention. As soon as a human is added to the loop, the system needs to be understandable by any human operator. In the case of the MAX, even with Redundancy sensors, there is the possibility enough of them fail that the plane doesn't "know" how to resolve the problem. So, control must be returned to the pilot with enough time and enough information to avert disaster.
    - 8y ago
hvidgaard 8y ago
If all three AoA sensors are mounted to the side, they're likely to freeze at the same pitch if they do freeze. So unless you have multiple different ways to measuring AoA three sensors do not protect against this failure mode better than two does.
Aser 8y ago
The pilots were trained on how to deal with a runaway trim stabiliser. The procedure hasn't changed from the old 737, the only thing that has changed is that it is that the failure mode is more likely to occurr on the 737 MAX. From the article: “A properly trained pilot should be able to solve an MCAS anomaly or any uncommanded flight-control input through procedures that are taught to all 737 pilots,” said Menza, noting that the emergency information Boeing distributed in December reiterated those procedures. Here's a video of a competent 737 pilot showing those exact procedures: https://www.youtube.com/watch?v=xixM_cwSLcQ https://www.youtube.com/watch?v=xixM_cwSLcQ Obviously the MCAS system is badly designed, but any automation system can fail and pilots need to know how to deal with it.
- cjbprime 8y ago
  It doesn't present as runaway trim, though. It's a small change in the trim, repeated every few seconds, which can be counteracted on the control column but will eventually add up. Small trim changes are usually happening all the time.
  - alistairSH 8y ago
    This is my understanding. In a typical run-away trim, the trim wheel will move a great distance. It's very noticeable, both audibly (the wheel makes a clack-clack-clack noise) and visibly (there are white paint flashes on the wheel). And, obviously, the plane nose goes up or down by more than expected. The correct remedy is to disable the auto trim control via switches on the panel (located near the trim wheels). The MCAS will adjust the trim in small increments every 10 (or is it 20?) seconds. Yes, a pilot should notice this, but because it's intermittent, it's more likely they don't "see" it as run-away trim, and just a slightly abnormal trim (EDIT - problem made worse because pilots were not informed MCAS existed - it's not a failure more they have trained on). They may attempt to remedy this with the manual trim control (a rocker switch on the control yoke). This does NOT disable MCAS, it only re-trim the plane. MCAS will re-engage due to faulty AoA sensors repeatedly until either the pilot disables all auto-trim with the switch on the panel OR the plane runs into the ground.
erentz 8y ago
> These sensors exist to solve a problem with the MAX design. No, the sensors existed before the MAX they are used by the autopilot system. With the MAX they are now also used by the MCAS system.

by cletus 8y ago

xiphias2 8y ago

I was hoping to have the damage in the Boing brand reflected more significantly in the share prices.

jdc 8y ago
Maybe the problem hasn't been shouted from a high enough rooftop yet.
- bdamm 8y ago
  Or more likely it doesn't really matter, and in a couple years nobody will really remember this about Boeing. They'll go back to being a big airplane producer that has a stunning safety record, which they are despite this issue.
  - Tsubasachan 8y ago
    The airline industry is growing and there are only two manufacturers who can build hundreds of planes on time. Airbus is already near full capacity. It would be impossible NOT to buy Boeing if you want planes.
  - carlmr 8y ago
    Which is also the correct thing to do. Despite our president and some NYTimes columnists being scared of automation (apparently they only agree when they're wrong), automation has saved so many lives that a failure like this doesn't affect the big picture. Yes, mistakes were made, yes, we should find ways to avoid this happening in the future, no, automation isn't the enemy. Without automation in flying at the current number of airplanes in the sky we'd probably have one or two crashes a day. The fact that 2 crashes in half a year make the news is thanks to the amazing safety of modern airplanes.
    - magduf 8y ago
      Automation is definitely not the enemy. However, automation that is designed in a criminally negligent manner is. People who create such designs should be put in prison, and we should not be using products from them ever again.
      - carlmr 8y ago
        Have fun using any product. If your company gets big enough the probability that one of its products was faulty because of negligence slowly approaches 100%. Any big company has a scandal, learns from it, the people that learned the lesson leave at some point, a new generation of employees makes a similar mistake again, wash rinse, repeat. You probably can't fly any airplanes if you will not use any airplanes from a company that had a scandal like this.
        jdc 8y ago
        AFAIK the automation had no good reason to be there first place, unless you consider racing Airbus for contracts a good reason. I mean, the simpler the better especially when lives are at stake, right?

AareyBaba 8y ago

I am puzzled by the apparent lack of a "this plane is heading straight into the ground" sensor that should have overridden the MCAS.

bdonlan 8y ago
The MCAS is designed to prevent an aerodynamic stall; a situation where the plane is pointed too far up and as a result starts heading straight for the ground. It does do by detecting the plane pointing too far up, and pushing it back down. If it did not function when the plane was descending rapidly it would not be fit for its designed purpose.
- deleted 8y ago
  [deleted]
- AceyMan 8y ago
  > The MCAS is designed to prevent an aerodynamic stall [...] This has become a trope and is flatly incorrect. MCAS was cooked up to maintain the handling characteristics required by the certification specifications. The standard requires stick resistance to increase as the critical (stall) angle of attack is approached. The MAX violated that requirement due to the aerodynamics of the new engine cowls, so MCAS was Boeing's (?crap) implementation of "artificial feel" to meet the spec. Yes, while the spec exists presumably to prevent the pilots from themselves taking the ship into a stall, MCAS doesn't change wing or aircraft performance in a material way that would be meant by "prevent a stall."
  - linuxftw 8y ago
    There seem to be a handful of people spreading this talking point here. In every authoritative source, MCAS is described as anti-stall system.
    - AceyMan 8y ago
      I believe the critical passage is here in CFR 14 §25.175¹ (2) With the landing gear retracted at low speed, the stick force curve must have a stable slope at all speeds within a range which is the greater of 15 percent of the trim speed plus the resulting free return speed range, or 50 knots plus the resulting free return speed range, above and below the trim speed (except that the speed range need not include speeds less than 1.3 VSR1, nor speeds greater than the minimum speed of the applicable speed range prescribed in paragraph (b)(1), nor speeds that require a stick force of more than 50 pounds)[...] The crucial phrase is "stick force curve", which is the characteristic MCAS was created to tweak. As far as 'authoritative sources' go, I'll just mention the Gell-Mann amnesia effect.² (me: non-active aircraft dispatcher) ¹—https://www.ecfr.gov/cgi-bin/text-idx?node=14:1.0.1.3.11#se14.1.25_1175 https://www.ecfr.gov/cgi-bin/text-idx?node=14:1.0.1.3.11#se1... ²—https://en.wikipedia.org/wiki/Gell-Mann_amnesia_effect?wprov=sfla1 https://en.wikipedia.org/wiki/Gell-Mann_amnesia_effect?wprov...

chungleong 8y ago

If there were specific steps that the pilots could have taken to avert disaster, why not just incorporate them into the flight software? Why resorting instead to "reprogramming" the pilot? That's what training is: programming of the human brain. One can't teach others without having first learned the lesson oneself. I'm not convinced Boeing has. I'm not convinced the company had adequately consider all possible scenarios and how pilots would react in them based on their intuition.

phire 8y ago
Even if it has enough sensprs, the flight software has no situational awareness. This is by design. The flight software is deliberately kept simple enough that the pilots can be trained to understand the full workings of the flight software and what it will do in any situation. The entire flight control algorithm is probably only a few hundred lines of psudocode. It's a catch 22: We are fully capable of designing a plane that safely flys itself from airport to airport without any pilots, to handle most emergency situations. We have been able to do so since the 80s. But we are not able to put a pilot in the loop on such a plane without massive safety implications. To have a pilot in the loop, the software has to be kept super simple so the pilot can diagnose it in an emergency and take the correct action. Either we have the flight software that is situational aware and authorised to take any action, or we have a super simple software and a pilot in the loop. There is no safe middle ground.
- alistairSH 8y ago
  Not sure about the "able to do so since the 80s" part, but generally, I agree. It's the same problem we see with Tesla, Uber, etc and autonomous cars. If it's to be truly autonomous, it needs to do so without ANY human intervention. As soon as a human is added to the loop, the system needs to be understandable by any human operator. In the case of the MAX, even with Redundancy sensors, there is the possibility enough of them fail that the plane doesn't "know" how to resolve the problem. So, control must be returned to the pilot with enough time and enough information to avert disaster.
  - 8y ago

hvidgaard 8y ago

If all three AoA sensors are mounted to the side, they're likely to freeze at the same pitch if they do freeze. So unless you have multiple different ways to measuring AoA three sensors do not protect against this failure mode better than two does.

Aser 8y ago

The pilots were trained on how to deal with a runaway trim stabiliser. The procedure hasn't changed from the old 737, the only thing that has changed is that it is that the failure mode is more likely to occurr on the 737 MAX. From the article: “A properly trained pilot should be able to solve an MCAS anomaly or any uncommanded flight-control input through procedures that are taught to all 737 pilots,” said Menza, noting that the emergency information Boeing distributed in December reiterated those procedures. Here's a video of a competent 737 pilot showing those exact procedures: https://www.youtube.com/watch?v=xixM_cwSLcQ https://www.youtube.com/watch?v=xixM_cwSLcQ Obviously the MCAS system is badly designed, but any automation system can fail and pilots need to know how to deal with it.

cjbprime 8y ago
It doesn't present as runaway trim, though. It's a small change in the trim, repeated every few seconds, which can be counteracted on the control column but will eventually add up. Small trim changes are usually happening all the time.
- alistairSH 8y ago
  This is my understanding. In a typical run-away trim, the trim wheel will move a great distance. It's very noticeable, both audibly (the wheel makes a clack-clack-clack noise) and visibly (there are white paint flashes on the wheel). And, obviously, the plane nose goes up or down by more than expected. The correct remedy is to disable the auto trim control via switches on the panel (located near the trim wheels). The MCAS will adjust the trim in small increments every 10 (or is it 20?) seconds. Yes, a pilot should notice this, but because it's intermittent, it's more likely they don't "see" it as run-away trim, and just a slightly abnormal trim (EDIT - problem made worse because pilots were not informed MCAS existed - it's not a failure more they have trained on). They may attempt to remedy this with the manual trim control (a rocker switch on the control yoke). This does NOT disable MCAS, it only re-trim the plane. MCAS will re-engage due to faulty AoA sensors repeatedly until either the pilot disables all auto-trim with the switch on the panel OR the plane runs into the ground.

erentz 8y ago

> These sensors exist to solve a problem with the MAX design. No, the sensors existed before the MAX they are used by the autopilot system. With the MAX they are now also used by the MCAS system.