6 ms·

That's not very surprising to anyone who has been following along. The more interesting question is why they failed to identify the trim runaway condition, or i

That's not very surprising to anyone who has been following along. The more interesting question is why they failed to identify the trim runaway condition, or if they did indeed identify it, why the procedure failed to correct it? This is significantly different to the Lion air incident where you can easily give the pilots the benefit of the doubt because the failure mode hadn't been previously identified. The details of MCAS and the procedure to handle it was communicated to all operators months before this accident.

tapland 8y ago
Maybe time was an issue? Saw in an earlier post that the issue had to be mitigated within 40 seconds of it occurring.
- sokoloff 8y ago
  40 seconds is an eternity to accomplish the memory items on runaway stab trim non-normal checklist. It’s literally “control column - hold firmly” (already a given, since MCAS only affects manual flight and the increased back pressure required is the cue that something is amiss), “autopilot and autothrottle - disengage” (click-click, click-click), (if runaway continues) “stab trim cutout switches - cutout (both)”, (if runaway continues) “trim wheel x grasp and hold” All of those are “above the line, memory items” which the crew must be able to recall and execute prior to referencing the checklists in the QRH. Boeing has some significant fault here, but I’d expect a full performance crew to handle this emergency and suspect the CVR and FDR data will show them in a less than fully flattering light, especially after Lion Air, the emergency AD, safety memos, and general publicity surrounding the previous crash.
  - dba7dba 8y ago
    Main stream media made it sound like 40 seconds is way too short of a time to troubleshoot the issue. But now that you state it that way, I gotta agree with you it's not Only Boeings fault. Sure they are big significant part of the issue. But not the only part.
    - chopin 8y ago
      40s is only enough if you know what to do right away from the start of the situation. A failing sensor may confront the pilots with many (unrelated to a trim runaway) warnings (like unreliable airspeed, stick shaker, alt disagree). That has been the case for Lion Air at least.
      - sokoloff 8y ago
        Take a car analogy. Suppose your car starts drifting into oncoming traffic. Maybe the road crown changed, maybe your alignment changed from a debris strike, maybe you have a tire going down, maybe you have a crosswind. In all those cases, your reaction is the same and instinctive regardless of whether or not you know the root cause. Flying an airplane manually on instruments, the pilot sees the airplane undershooting the pitch target and pulls back on the control column every bit as naturally as the car driver above. When the pitch target is correct and the control force high, use the stab trim to take the force away. This is every bit as much a continual process as the driver lane keeping. If MCAS is trimming against you every time you let go of the trim, you get feedback that this is likely a trim issue. Keep flying the airplane and trimming as needed. This is not a case where the airplane automation fails and an airplane suddenly gets “dumped” onto a pilot who has to regain control and figure things out. It’s obvious that the time and space available was not enough for that Lion Air or that Ethiopian Air flight, so you have real world evidence to support your point. I acknowledge that fact, of course.
    - karlkatzke 8y ago
      As someone who's done a bunch of human factors design training for critical situations in a previous career as a UI/UX designer and now works as a systems engineer doing a bunch of alerting, 40 seconds is too short of a time to troubleshoot the issue. When this situation happens, five things happen at once. MASTER CAUTION (whoop, whoop noises and a big red light!), ALT DISAGREE alert on the MFD, Incorrect Airspeed on the MFD, the stick shaker goes off, and by the way, if you take the time to look down at the throttle section of the dashboard with all those other alerts going off, you'd see that there is suddenly a lot of trim on the APL trim indicator but the trim wheel doesn't actually move (which would provide an audible 'click click click' that would probably trigger that there was a problem with trim. Each of those things has a separate memory checklist that you have to run down, and subtract ten seconds to register them, prioritize, communicate with the other pilot, and start executing them. The worst part here is that they've added another alert and then changed how the airplane will fly in the middle of an emergency. While the extra alert narrows down the number of branches from the "prioritization" part of the checklist, I'm not sure that's "fixing" the problem.
  - ricardobeat 8y ago
    Going from previous discussion, apparently it would be hard for pilots to recognise it as trim runaway. The last description mentions: stall warning going off, column shake, incorrect airspeed (on one side, due to the faulty sensor), trim wheel doesn’t move, plus the fact MCAS operates in 10s intervals. Has the information disclosed to pilots after the LyonAir incident been made public?
    - ams6110 8y ago
      Yes, easy to imagine a chaotic situation causing distraction, or hyper focus on the wrong thing, etc. What I have gathered from reading other forums about this, many pilots say they would interpret any significant undesired trim as a runaway condition, regardless of whether it was happening in intervals or it was literally continuous. Others say that depending on training, and the policies of the operator, a much more literal reading of procedures is enforced. I don't fly, but apparently trim is a very fundamental control for a pilot. It's easy to recognize when the aircraft is out of trim, and reacting to it is about as natural as it is for a driver of a car to use the steering wheel to keep the car centered in a lane. So my assumption is, that with the AoA disagreement, and resulting multiple alerts and chaos in the cockpit, the pilots lost awareness of what the trim was doing. I'm wondering if there's not a deeper problem within the air data systems. Why are the AoA sensors on new aircraft failing? They are just simple vanes, normally very reliable. The same ones are used on many different aircraft. So I don't think the actual sensor is a problem. But maybe there's something different downstream of the sensor itself. I would think if there were persistent problems with bad AoA data in 737s generally, it would have been addressed. Because the stick shakers, unreliable air speed, and everything else would still be happening regardless of MCAS.
      - VBprogrammer 8y ago
        > I'm wondering if there's not a deeper problem within the air data systems. ... Because the stick shakers, unreliable air speed, and everything else would still be happening regardless of MCAS. This is a very good point. If the AoA sensor failed say climbing through cloud at 5000ft on auto-pilot, dropping control of the aircraft to a pilot who's busy thinking about what he's going to have for lunch, with half a dozen alerts going off, an AF447 type incident could easily happen MCAS or no MCAS.
  - tyingq 8y ago
    The layperson in me wants to know why things like trim don't have a meter/display that shows the actual setting. Seeing +6/-6 seems like it might trigger recognition of runaway adjustment.
    - userbinator 8y ago
      It does... http://www.b737.org.uk/images/throttlequadrant.jpg http://www.b737.org.uk/images/throttlequadrant.jpg See the scale with "APL NOSE UP" and "APL NOSE DOWN" next to the trim wheels. Whether the pilots noticed it (or the attitude indicator pointing nose-down, or the rapidly decreasing altimeter...) is the question.
      - deleted 8y ago
        [deleted]
      - tyingq 8y ago
        Ah, so that indicator would have been abnormally in the "nose down" area after MCAS over adjusted it. Interesting. Information overload, and nobody looked because that amount of auto adjustment wasn't anticipated. And also means they didn't correlate the fairly noisy/visual turning off the wheels to get it in that position.
        DougBTX 8y ago
        There was a PDF incident report going around earlier with a chart showing a graph of the inputs from MCAS and the pilots over a period of time. There was a "nose down" command from MCAS, followed by a "nose up" command from the pilot, then a "nose down" command from MCAS, a "nose up" command from the pilot... repeated about 20 times in a row...
        mhandley 8y ago
        The full preliminary report from the LionAir crash is here: https://www.flightradar24.com/blog/wp-content/uploads/2018/10/2018-035-PK-LQP-Preliminary-Report.pdf https://www.flightradar24.com/blog/wp-content/uploads/2018/1... I've put the relevant figure showing the trim adjustments here: http://nrg.cs.ucl.ac.uk/mjh/lionair.png http://nrg.cs.ucl.ac.uk/mjh/lionair.png
  - alistairSH 8y ago
    I wonder if the difference in behavior between the trim buttons on the stick and trim cutout switches on the panel was the problem? If I've read correctly, the former only temporarily disengages MCAS. The pilots may have repeatedly hit the button on the stick, but then 20s later, MCAS re-engages and sends the plane nose down again. I agree that the procedure calls for flipping the switch on the panel. But, not sure that's actually what the pilots were doing. In the image below, you can see the electric trim control on the stick in the left portion, and the manual trim cut-out switch on the panel in the top right. https://theaircurrent.com/wp-content/uploads/2018/11/737-max-trim-control.jpg https://theaircurrent.com/wp-content/uploads/2018/11/737-max...
- cm2187 8y ago
  I am not talking about these specific pilots about which I know nothing. But not every single commercial pilot is passionate about his job. For some it is just a day job and until they are asked to do a particular training, may not even be aware that MCAS even exists. Think professional developers (granted the bar is infinitely lower). You would assume no one would introduce a SQL injection vulnerability in new code given all we know and all that happened. Well... Also some commercial pilot on HN provided another element of answer. When you are in an emergency situation, you don't have the time to sit back and think, you revert to experience, muscle memory and training. Even if it may have crossed these guys mind that it was the same problem than Lion air, they may not necessarily know the procedure to fix it while trying to keep the plane from crashing at the same time. Just speculating.
  - VBprogrammer 8y ago
    That would be a huge failing on behalf of the airline. There was an emergency airworthiness directive which should have brought this to the attention to all pilots of these aircraft even if they somehow missed all of the other coverage.
    - chopin 8y ago
      But this directive said "handle like a trim runaway". However MCAS may present itself differently from a trim runaway when failing. Furthermore a failing sensor may activate the stick shaker and the last thing a pilot is trained to do is pull up in such a situation. So you might get: - unreliable airspeed warning - stick shaker (=stall is imminent) So you don't know your airspeed (otherwise you can conclude you're safe for your current pitch and vertical speed) and a stall warning. The last thing you do is to look for horizontal trim.
      - VBprogrammer 8y ago
        The full list of potential indications is included in the AD. It also describes the operation of the trim system under MCAS control. You can see them in the Lion Air preliminary report linked above. Pilots are trained to deal with partial panel situations. The mantra is pitch + power = performance. In VMC this should be well within the capibilities of a normal pilot, put the nose on the horizon and set something like 65% power.
- in_cahoots 8y ago
  That 40 second quote is a bit misleading. As I understand it, if the pilots do absolutely nothing then they only have 40 seconds until MCAS has adjusted the trim the maximum amount. But the Lion Air flight flew for several minutes with the MCAS firing; the pilot manually counter-intervened each time. It was only when he handed control to a co-pilot that the plane nosedived. Theoretically they could have flown indefinitely while they debugged the problem.
  - Rooster61 8y ago
    > Theoretically they could have flown indefinitely while they debugged the problem. Not true. From what I have read, MCAS runs in 10 second intervals, with the amount of trim added increasing with each successive run. Once the trim has reached a certain point, it over-powers the amount of control the pilot has by putting pressure on the yoke (this controls elevators, which have less overall influence on the aircraft than the trim at full bore). We know that the pilots on the previous flight with the 3rd deadheading pilot were attempting to right the plane using yoke pressure, and at one point the first officer mentioned that the yoke was "too heavy to hold back". That indicates that MCAS had pushed the trim past the point at which the pilots could physically overcome it's influence using the elevators. (source here: https://www.reuters.com/article/us-ethiopia-airplane-regulator-insight/regulators-knew-before-crashes-that-737-max-trim-control-was-confusing-in-some-conditions-document-idUSKCN1RA0DP https://www.reuters.com/article/us-ethiopia-airplane-regulat...)
    - VBprogrammer 8y ago
      The pilot can run the trim in the other direction using the normal switches on the yoke. You can see that if you look at the trim position graph in the Lion Air accident. For some reason before the crash the pattern of repeatedly correcting changes, possibly because he handed control to the first officer.
      - Rooster61 8y ago
        "The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said. It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s center console rather than an electric thumb switch on the control yoke. " So, yes and no. It gives SOME control over the trim, but if the trim keeps getting bumpped progressively higher by the MCAS, it will eventually outstrip the yoke control. My guess is that that change you mentioned is the threshold at which their yoke trim control became insufficient.
- deleted 8y ago
  [deleted]
snarf21 8y ago
A major factor in this is that they were told that this plane flies exactly the same as the previous 737. If you do the same "right" things you always do, how are supposed to know things are going badly when you've been lied to from the jump?

tapland 8y ago

Maybe time was an issue? Saw in an earlier post that the issue had to be mitigated within 40 seconds of it occurring.

sokoloff 8y ago
40 seconds is an eternity to accomplish the memory items on runaway stab trim non-normal checklist. It’s literally “control column - hold firmly” (already a given, since MCAS only affects manual flight and the increased back pressure required is the cue that something is amiss), “autopilot and autothrottle - disengage” (click-click, click-click), (if runaway continues) “stab trim cutout switches - cutout (both)”, (if runaway continues) “trim wheel x grasp and hold” All of those are “above the line, memory items” which the crew must be able to recall and execute prior to referencing the checklists in the QRH. Boeing has some significant fault here, but I’d expect a full performance crew to handle this emergency and suspect the CVR and FDR data will show them in a less than fully flattering light, especially after Lion Air, the emergency AD, safety memos, and general publicity surrounding the previous crash.
- dba7dba 8y ago
  Main stream media made it sound like 40 seconds is way too short of a time to troubleshoot the issue. But now that you state it that way, I gotta agree with you it's not Only Boeings fault. Sure they are big significant part of the issue. But not the only part.
  - chopin 8y ago
    40s is only enough if you know what to do right away from the start of the situation. A failing sensor may confront the pilots with many (unrelated to a trim runaway) warnings (like unreliable airspeed, stick shaker, alt disagree). That has been the case for Lion Air at least.
    - sokoloff 8y ago
      Take a car analogy. Suppose your car starts drifting into oncoming traffic. Maybe the road crown changed, maybe your alignment changed from a debris strike, maybe you have a tire going down, maybe you have a crosswind. In all those cases, your reaction is the same and instinctive regardless of whether or not you know the root cause. Flying an airplane manually on instruments, the pilot sees the airplane undershooting the pitch target and pulls back on the control column every bit as naturally as the car driver above. When the pitch target is correct and the control force high, use the stab trim to take the force away. This is every bit as much a continual process as the driver lane keeping. If MCAS is trimming against you every time you let go of the trim, you get feedback that this is likely a trim issue. Keep flying the airplane and trimming as needed. This is not a case where the airplane automation fails and an airplane suddenly gets “dumped” onto a pilot who has to regain control and figure things out. It’s obvious that the time and space available was not enough for that Lion Air or that Ethiopian Air flight, so you have real world evidence to support your point. I acknowledge that fact, of course.
  - karlkatzke 8y ago
    As someone who's done a bunch of human factors design training for critical situations in a previous career as a UI/UX designer and now works as a systems engineer doing a bunch of alerting, 40 seconds is too short of a time to troubleshoot the issue. When this situation happens, five things happen at once. MASTER CAUTION (whoop, whoop noises and a big red light!), ALT DISAGREE alert on the MFD, Incorrect Airspeed on the MFD, the stick shaker goes off, and by the way, if you take the time to look down at the throttle section of the dashboard with all those other alerts going off, you'd see that there is suddenly a lot of trim on the APL trim indicator but the trim wheel doesn't actually move (which would provide an audible 'click click click' that would probably trigger that there was a problem with trim. Each of those things has a separate memory checklist that you have to run down, and subtract ten seconds to register them, prioritize, communicate with the other pilot, and start executing them. The worst part here is that they've added another alert and then changed how the airplane will fly in the middle of an emergency. While the extra alert narrows down the number of branches from the "prioritization" part of the checklist, I'm not sure that's "fixing" the problem.
- ricardobeat 8y ago
  Going from previous discussion, apparently it would be hard for pilots to recognise it as trim runaway. The last description mentions: stall warning going off, column shake, incorrect airspeed (on one side, due to the faulty sensor), trim wheel doesn’t move, plus the fact MCAS operates in 10s intervals. Has the information disclosed to pilots after the LyonAir incident been made public?
  - ams6110 8y ago
    Yes, easy to imagine a chaotic situation causing distraction, or hyper focus on the wrong thing, etc. What I have gathered from reading other forums about this, many pilots say they would interpret any significant undesired trim as a runaway condition, regardless of whether it was happening in intervals or it was literally continuous. Others say that depending on training, and the policies of the operator, a much more literal reading of procedures is enforced. I don't fly, but apparently trim is a very fundamental control for a pilot. It's easy to recognize when the aircraft is out of trim, and reacting to it is about as natural as it is for a driver of a car to use the steering wheel to keep the car centered in a lane. So my assumption is, that with the AoA disagreement, and resulting multiple alerts and chaos in the cockpit, the pilots lost awareness of what the trim was doing. I'm wondering if there's not a deeper problem within the air data systems. Why are the AoA sensors on new aircraft failing? They are just simple vanes, normally very reliable. The same ones are used on many different aircraft. So I don't think the actual sensor is a problem. But maybe there's something different downstream of the sensor itself. I would think if there were persistent problems with bad AoA data in 737s generally, it would have been addressed. Because the stick shakers, unreliable air speed, and everything else would still be happening regardless of MCAS.
    - VBprogrammer 8y ago
      > I'm wondering if there's not a deeper problem within the air data systems. ... Because the stick shakers, unreliable air speed, and everything else would still be happening regardless of MCAS. This is a very good point. If the AoA sensor failed say climbing through cloud at 5000ft on auto-pilot, dropping control of the aircraft to a pilot who's busy thinking about what he's going to have for lunch, with half a dozen alerts going off, an AF447 type incident could easily happen MCAS or no MCAS.
- tyingq 8y ago
  The layperson in me wants to know why things like trim don't have a meter/display that shows the actual setting. Seeing +6/-6 seems like it might trigger recognition of runaway adjustment.
  - userbinator 8y ago
    It does... http://www.b737.org.uk/images/throttlequadrant.jpg http://www.b737.org.uk/images/throttlequadrant.jpg See the scale with "APL NOSE UP" and "APL NOSE DOWN" next to the trim wheels. Whether the pilots noticed it (or the attitude indicator pointing nose-down, or the rapidly decreasing altimeter...) is the question.
    - deleted 8y ago
      [deleted]
    - tyingq 8y ago
      Ah, so that indicator would have been abnormally in the "nose down" area after MCAS over adjusted it. Interesting. Information overload, and nobody looked because that amount of auto adjustment wasn't anticipated. And also means they didn't correlate the fairly noisy/visual turning off the wheels to get it in that position.
      - DougBTX 8y ago
        There was a PDF incident report going around earlier with a chart showing a graph of the inputs from MCAS and the pilots over a period of time. There was a "nose down" command from MCAS, followed by a "nose up" command from the pilot, then a "nose down" command from MCAS, a "nose up" command from the pilot... repeated about 20 times in a row...
        mhandley 8y ago
        The full preliminary report from the LionAir crash is here: https://www.flightradar24.com/blog/wp-content/uploads/2018/10/2018-035-PK-LQP-Preliminary-Report.pdf https://www.flightradar24.com/blog/wp-content/uploads/2018/1... I've put the relevant figure showing the trim adjustments here: http://nrg.cs.ucl.ac.uk/mjh/lionair.png http://nrg.cs.ucl.ac.uk/mjh/lionair.png
- alistairSH 8y ago
  I wonder if the difference in behavior between the trim buttons on the stick and trim cutout switches on the panel was the problem? If I've read correctly, the former only temporarily disengages MCAS. The pilots may have repeatedly hit the button on the stick, but then 20s later, MCAS re-engages and sends the plane nose down again. I agree that the procedure calls for flipping the switch on the panel. But, not sure that's actually what the pilots were doing. In the image below, you can see the electric trim control on the stick in the left portion, and the manual trim cut-out switch on the panel in the top right. https://theaircurrent.com/wp-content/uploads/2018/11/737-max-trim-control.jpg https://theaircurrent.com/wp-content/uploads/2018/11/737-max...
cm2187 8y ago
I am not talking about these specific pilots about which I know nothing. But not every single commercial pilot is passionate about his job. For some it is just a day job and until they are asked to do a particular training, may not even be aware that MCAS even exists. Think professional developers (granted the bar is infinitely lower). You would assume no one would introduce a SQL injection vulnerability in new code given all we know and all that happened. Well... Also some commercial pilot on HN provided another element of answer. When you are in an emergency situation, you don't have the time to sit back and think, you revert to experience, muscle memory and training. Even if it may have crossed these guys mind that it was the same problem than Lion air, they may not necessarily know the procedure to fix it while trying to keep the plane from crashing at the same time. Just speculating.
- VBprogrammer 8y ago
  That would be a huge failing on behalf of the airline. There was an emergency airworthiness directive which should have brought this to the attention to all pilots of these aircraft even if they somehow missed all of the other coverage.
  - chopin 8y ago
    But this directive said "handle like a trim runaway". However MCAS may present itself differently from a trim runaway when failing. Furthermore a failing sensor may activate the stick shaker and the last thing a pilot is trained to do is pull up in such a situation. So you might get: - unreliable airspeed warning - stick shaker (=stall is imminent) So you don't know your airspeed (otherwise you can conclude you're safe for your current pitch and vertical speed) and a stall warning. The last thing you do is to look for horizontal trim.
    - VBprogrammer 8y ago
      The full list of potential indications is included in the AD. It also describes the operation of the trim system under MCAS control. You can see them in the Lion Air preliminary report linked above. Pilots are trained to deal with partial panel situations. The mantra is pitch + power = performance. In VMC this should be well within the capibilities of a normal pilot, put the nose on the horizon and set something like 65% power.
in_cahoots 8y ago
That 40 second quote is a bit misleading. As I understand it, if the pilots do absolutely nothing then they only have 40 seconds until MCAS has adjusted the trim the maximum amount. But the Lion Air flight flew for several minutes with the MCAS firing; the pilot manually counter-intervened each time. It was only when he handed control to a co-pilot that the plane nosedived. Theoretically they could have flown indefinitely while they debugged the problem.
- Rooster61 8y ago
  > Theoretically they could have flown indefinitely while they debugged the problem. Not true. From what I have read, MCAS runs in 10 second intervals, with the amount of trim added increasing with each successive run. Once the trim has reached a certain point, it over-powers the amount of control the pilot has by putting pressure on the yoke (this controls elevators, which have less overall influence on the aircraft than the trim at full bore). We know that the pilots on the previous flight with the 3rd deadheading pilot were attempting to right the plane using yoke pressure, and at one point the first officer mentioned that the yoke was "too heavy to hold back". That indicates that MCAS had pushed the trim past the point at which the pilots could physically overcome it's influence using the elevators. (source here: https://www.reuters.com/article/us-ethiopia-airplane-regulator-insight/regulators-knew-before-crashes-that-737-max-trim-control-was-confusing-in-some-conditions-document-idUSKCN1RA0DP https://www.reuters.com/article/us-ethiopia-airplane-regulat...)
  - VBprogrammer 8y ago
    The pilot can run the trim in the other direction using the normal switches on the yoke. You can see that if you look at the trim position graph in the Lion Air accident. For some reason before the crash the pattern of repeatedly correcting changes, possibly because he handed control to the first officer.
    - Rooster61 8y ago
      "The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said. It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s center console rather than an electric thumb switch on the control yoke. " So, yes and no. It gives SOME control over the trim, but if the trim keeps getting bumpped progressively higher by the MCAS, it will eventually outstrip the yoke control. My guess is that that change you mentioned is the threshold at which their yoke trim control became insufficient.
deleted 8y ago
[deleted]

snarf21 8y ago

A major factor in this is that they were told that this plane flies exactly the same as the previous 737. If you do the same "right" things you always do, how are supposed to know things are going badly when you've been lied to from the jump?