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Cockpit voice recorder of Lion Air jet depicts pilots' frantic search for fix

304 points by petethomas 8y ago

cjbprime 8y ago
This appears to answer the question of why, given that there is a "memory item" for dealing with runaway trim that would have helped, it wasn't followed by the crew: > “They didn’t seem to know the trim was moving down,” the third source said. “They thought only about airspeed and altitude. That was the only thing they talked about.” If this is true, not only did the pilots not realize the trim was the cause of the dive and try to fix it, it seems that they didn't even realize the trim wheel was moving. "Runaway trim" would be something they trained for, but has a presentation so vastly different (of a visibly spinning trim wheel causing quick descent) as to not be recognizably the same emergency to these pilots. Of course, this crew had no way of knowing that there was a system on the plane that could slowly make erroneous trim changes over a long period with autopilot off, and it makes sense that they might miss it happening while focusing on their stall alerts and speeds and trying to come up with an explanation and also trying to retain control.
- RidingPegasus 8y ago
  Was the trim wheel not visibly spinning out of their control? Simply because the symptoms are different should mean that stopping it via taking manual control is a recurring option.
  - cjbprime 8y ago
    The spin was not visible to these pilots presumably because it was happening in small increments with a delay between them.
    - acqq 8y ago
      Exactly. It was not "runaway" in the sense of "continuously doing the same." Something was happening, from the point of view of the pilot and co-pilot "at random." (Not to mention that on the previous models exactly such pattern was effectively impossible to happen). The faulty non-redundant sensor was producing false reading and that was the input to the to the pilots completely unknown MCAS which then moved the nose down based on the difference between the input and MCAS' expected target, turning "the correction" on only from time to time. The presence of the third, off-duty pilot on the flight before additionally explains even better how in that case the crash was avoided. While the pilot and co-pilot were at the controls, the third one, looking from behind, didn't have the direct duties to do, so he had enough time to both just observe everything that was going on and the less immediate stress to allow him to come to the solution that worked. Like when one programmer spends half an hour on something "not working" and complains to the colleague who just takes a look and immediately sees what the first one hasn't for half an hour. Additionally the movement of the trim wheel is actually easier to follow from the place in the back (see https://news.ycombinator.com/item?id=19440045 https://news.ycombinator.com/item?id=19440045 ). And there's also a possibility that the false sensor reading and MCAS together produced a slightly different differential signal which resulted in more obvious manifestation of the problem. Possibly both elements contributed to the lucky outcome in that previous flight. In the old times of civil aviation there was the third person on duty in the cockpit, the "flight-engineer." As the planes got more computerized controls, they started to be certified to fly with two-pilot crews. The computerized systems, when working, do reduce the chance of the crash and overall number of accidents did decrease simply because the humans were on the average less often in control, and therefore there was less chance to do anything wrong. The problem is when the unreported computerized controls secretly depend on the single sensor that can be faulty. And when they actively confuse the pilot and ruin the flight instead of helping him.
      - kayfox 8y ago
        "Runaway" in the sense of "its moving in a undesired and unexpected direction and continues to do so despite attempts to stop it".
        jeremysmyth 8y ago
    - ahoka 8y ago
      If anyone wonders this is how it looks like: https://youtu.be/-X01uY0bJs0?t=48 https://youtu.be/-X01uY0bJs0?t=48
      - TheSpiceIsLife 8y ago
        And sounds? The trim wheels moving also makes a sound?
        deleted 8y ago
        [deleted]
        ekianjo 8y ago
        From the videos I have seen in cockpit it does seem to make a sound as it rolls.
        WalterBright 8y ago
        Yes. The ratcheting sound is deliberate, so the pilots don't need to see the wheels spin to know the trim is running. Also note that there's a white stripe on the wheel so it's easy to see it is running.
        jacobush 8y ago
        Someone else in the thread said newer models don't make a sound.
        michaelt 8y ago
        You'll note in that video, the left-hand pilot has a headset on, presumably the right-hand pilot does too. Headsets are seen in other videos [1] of the cockpit. So even if the spinning trim wheels make noise, they may not have heard it. (My google image search shows some pilots wearing two-ear headsets, some wearing one-ear headsets, some wearing two-ear headsets with side not on their ear, and some not wearing headsets. But some of those are pilots posing for photos, and presumably pilots don't let people visit the cockpit during critical stages of the flight) [1] https://youtu.be/wz2Q3COfveg?t=409 https://youtu.be/wz2Q3COfveg?t=409
  - frenchy 8y ago
    I doubt it would have been "out of control", it would have just been slow changes over time as trim increased. The pilots might not have been fighting it much either, if they thought that airspeed was the problem, and not pitch.
    - Someone1234 8y ago
      The graph on page 14 of this report[0] is pretty telling about how slow the changes were... Note Trim Manual, Trim Automatic, and Pitch Trim Position. [0] https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-LQP_PRELIMINARY.pdf https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-...
      - acqq 8y ago
        Thanks! Page 23 of the PDF or 14 as printed at the bottom. Sadly it's hard to compare with the previous flight (pg. 25 or 16) as for it they published the graph of the whole flight instead of only the part until the (at the time still secret) MCAS was turned off (or probably more correctly, the motor controlled by the MCAS, which actually steered the "trim").
  - crooked-v 8y ago
    Part of the problem is that the MCAS system has a 20-second delay after the last time the pilot touched controls for the flaps, and it adjusts itself to a new position and then stops. There are no other indicators that it's happening, and since it's noncontinuous and has a delay, it would be easy to miss the only visual sign of the trim wheel readjusting itself once, especially since the wheel itself is by the pilot's thigh outside of forward line of sight. In a normal runaway trim situation, by comparison, the trim wheel continues obviously spinning as long as the problem is going on, so it only takes a single glance at any time to notice it.
    - oasisbob 8y ago
      I'm not sure that's accurate. Other descriptions of the MCAS system state that it will continually modify the trim on the horizontal stabilizer for up to 10 seconds at a time. http://www.b737.org.uk/mcas.htm http://www.b737.org.uk/mcas.htm
      - inferiorhuman 8y ago
        To summarise; MCAS will trim the Stabilizer down for 10 seconds (2.5 deg nose down) and pause for 5 seconds and repeat if the conditions (high angle of attack, flaps up and autopilot disengaged) continue to be met. Using electric pitch trim will only pause MCAS, to deactivate it you need to switch off the STAB TRIM SUTOUT switches.
      - usrusr 8y ago
        Well, the point is that the experience from MCAS trying to be clever and subtle is very different from what one would expect in an old-school runaway trim situation caused by, say, a stuck relay. Easy to chase down a wrong line of inquiry when the symptoms only appear sporadically and can be temporarily stopped by a whole range of actions that won't permanently fix it.
  - dukoid 8y ago
    To my understanding, the trim wheels are moving frequently for small adjustments -- and it's possible to switch the wheel movement off if this becomes too annoying.
    - losvedir 8y ago
      Also not a pilot but I don't think you can switch the wheel off. You can, however, disable the electric motors that spin the wheel, which is what the checklist for runaway trim tells you to do, and what was supposed to have been done here.
      - WalterBright 8y ago
        The spinning wheels are directly connected to the stab trim via cables. If the trim motors fail, the pilots can turn those wheels by hand (there's a folding crank on them) to manually adjust the trim.
    - VBprogrammer 8y ago
      It's running for 10 seconds at a time for 2.5 units of trim out of a possible ~15. That's quite a big trim change. I find it hard to believe that it's not noticed because of the 'boiling a frog' situation. It not possible to disable wheel movement. It's mechanically linked to the jackscrew.
  - verytrivial 8y ago
    The Lion Air directive has instructions on page 41 of their preliminary report that include: 5. If the runaway continues after the autopilot is disengaged: STAB TRIM CUTOUT switches (both) ... CUTOUT If the runaway continues: Stabilizer trim wheel .... *Grasp and hold* This may be an overabundance of caution, or to cover other runaway events, but it reads like "you may need to physically fight the computer even when it has been disabled". Not exactly heartening. EDIT: A comment below points out haptic feedback to disengage as a reason to grab-and-hold. https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-LQP_PRELIMINARY.pdf https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-...
    - mlindner 8y ago
      That's incorrect, these have haptic feedback, once you grasp it, it's not going to fight you. It looks for resistance and if it sees the resistance it doesn't continue.
      - verytrivial 8y ago
        Ah, Okay, thanks. What remaining automation would be driving the trim wheel in this case that grab-and-hold would countermand?
      - heavenlyblue 8y ago
        You are still fighting it, aren't you?
      - userbinator 8y ago
        Really? Here's a video of someone doing it, and it certainly looks like it tries to fight you (and the trim motor continues running) but there's a clutch that starts slipping: https://www.youtube.com/watch?v=cQirIH_DuAs https://www.youtube.com/watch?v=cQirIH_DuAs
    - ProAm 8y ago
      > you may need to physically fight the computer This is the future I look forward to. AI/ML/Autopilot/Companies moving fast and breaking things.... Boeing took that one literally.
- l33tman 8y ago
  This is not true, on the released FDR data, it shows clearly that the pilot flying corrected the MCAS system's trim down adjustments at every cycle (each 10 seconds) for most of the level flight. So at least the PF must have been aware of this. It's a bit weird if they didn't talk about it though, maybe it was obvious to both pilots and they were concentrating on if they were keeping altitude and airspeed at all (the most important factors that would keep them flying).
  - mannykannot 8y ago
    This got my attention too. For at least 6 minutes, the crew were coping with the problem - the aircraft was holding altitude and speed, if erratically, and they must have been getting the trim back to approximately where it should have been, or else MCAS would have driven the stabilizer to the point where it overrode the elevator authority. In about the last minute of that recording, the pattern changes: the pilot trim inputs decreased and became much shorter, and the stick forces changed from going up and down to a sustained, high, back-force. The article says that near the end, the captain handed over control to the 1st officer so he could look for answers. I am speculating wildly here, but could that coincide with the change in the pattern of the pilot's responses? Could it be that the 1st officer did not attempt to re-trim, or did not do it completely? Did he try to trim manually, but perhaps could not because of the load on the stabilizer? [1]. IIRC, according to Dominic Gates, it would only take two cycles of MCAS intervention until the stabilizer had reached a point where full nose-up elevator could not keep the airplane level. The chart was published in one of Dominic Gates' Seattle Times articles, but I am not in a position to find it right now... [1] https://news.ycombinator.com/item?id=19400157 https://news.ycombinator.com/item?id=19400157
    - VBprogrammer 8y ago
      Anyone who's ever piloted an aircraft would try to re-trim against pitch forces. It's inconceivable that the pilot for some reason just failed to do that. I'm not sure exactly what force it takes to get full nose up elevator at flying speed but it will be in the range of dozens of kilograms. I personally wonder if there is potentially a thermal cut-off on the trim motor which could have been activated by this trimming and re-triming. Or even an outright failure of some part of the system.
- dvdkhlng 8y ago
  I'm just wondering: it looks like the absolute trim angle is not visible anywhere in the cockpit? The trim wheel takes multiple revolutions to adjust trim between min/max limits, so looking at the wheel itself, you can only every see changes, not values. Unless you notice the change while it happens, you won't have any indication as to the unusual trim angle? Thinking about that I wonder whether there was even a measurement signal that the computers could rely on to determine the current state of the trim angle in absolute terms. Given how the MCAS did incremental changes without stopping before reaching the mechanical limits, I do imagine that there might have been no hardware feedback to assess the current trim state, thereby making it impossible hardware-wise to limit MCAS to a sensible (and safe) range of angles. [edit] Looking at the lion air crash report [1] p.14 ff it seems like also the black box only recorded trim changes, not absolute trim state. [1] https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-LQP_PRELIMINARY.pdf https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-...
  - VBprogrammer 8y ago
    There is a trim position indication. It's to the left and right of the throttles. It's a critical thing to check before starting the takeoff roll. You can see it on the copilot's side here by the trim wheel. http://www.b737.org.uk/images/stabtrim_200.jpg http://www.b737.org.uk/images/stabtrim_200.jpg
    - dvdkhlng 8y ago
      Yes, thinking about that, not having any pilot-visible indication would be quite some point of failure at lift-off. Still wondering whether MCAS and other automatation systems have a representation of that position indication. I can't currently come up with an idea of how to implement that in an easy, yet error-resilient way. Usually you would initially drive into a reference position, then integrate the motor's actions to arive at an absolute value, but integration would potentially add up subsequent errors, and obviously you can't re-do the referencing step while in the air.
      - VBprogrammer 8y ago
jve 8y ago
In the other news, on the previous day on the same plane there was a retired pilot flying in cockpit who correctly diagnosed problem & told how to disable malfunctioning system: https://www.bloomberg.com/news/articles/2019-03-19/how-an-extra-man-in-cockpit-saved-a-737-max-that-later-crashed https://www.bloomberg.com/news/articles/2019-03-19/how-an-ex...
- gojomo 8y ago
  That's the most amazing revelation to me so far. The same plane had an identical uncontrolled-dive problem the day before, which required an emergency power cut to the improperly-engaged motor, and somehow that incident didn't ground the plane or even result in any effective advisory to the next crew. Further, the Bloomberg story reports: "The Indonesia safety committee report said the plane had had multiple failures on previous flights and hadn’t been properly repaired." Lots of blame to go around here.
  - deleted 8y ago
    [deleted]
  - acqq 8y ago
    > Lots of blame to go around here. Only if the faulty sensor was listed as "critical." Boeing didn't declare it as such and reported to nobody the way it was used in the unreported MCAS. That the MCAS even exists and that a single faulty sensor was enough to mess with the flight erratically enough to confuse the pilots was somehow acknowledged by Boeing only after the first crash. It took the second crash for most observers to recognize that just blaming the pilot or maintenance won't keep the planes from not crashing.
    - icebraining 8y ago
      Even if they didn't know about the MCAS, they still knew the plane had had an uncontrolled-dive problem from an unknown cause. How is it responsible to fly it without understanding the issue? Boeing is still fully culpable, but the airline should have debugged the issue before using the plane again.
mikejb 8y ago
I'm trying to imagine the horror the pilots (and passengers) were feeling. Imagine your car slowly starting to shift sideways into incoming traffic, and no matter how hard you pull the steering wheel, you can't get it back. Horrifying.
- SmellyGeekBoy 8y ago
  This is why I refuse to listen to these things when they're released. The thought of eavesdropping in on someone's frantic hopeless fight for survival just doesn't sit right with me.
  - isolli 8y ago
    Agreed. It reminds me of the final scene of Grizzly Man, when Herzog listens to the audio recording of the bear enthusiast and his girlfriend being mauled to death. Herzog puts the headphones down, visibly shaken, and comments (paraphrasing): nobody should have to listen to that.
    - Darthy 8y ago
      He actually says to the mother: Jewel, you must never listen to this.
      - aeorgnoieang 8y ago
        Wasn't it the girlfriend?
        mikejb 8y ago
        The girlfriend was on location and apparently the one who turned on the camera (but did not remove the lens cap, making it an audio-only recording). She was killed and partially eaten together with Treadwell. Edit: The tape is actually owned by Jewel Palovak who this scene is also with; She's a former girlfriend of Treadwell, not his (or his girlfriends) mother.
    - 8y ago
CyberFonic 8y ago
One of the factors that has been quickly glossed over is the low level of experience of some of the pilots in both the Indonesian and Ethopian accidents. In the USA, due to much higher levels of experience pilots have been correcting for the MCAS actions effectively and complaining about it to NASA (in order to avoid being branded as whistle-blowers by their airlines).
- deleted 8y ago
  [deleted]
- dannyw 8y ago
  I’d be highly concerned of the competency of any pilot who complains to NASA.
  - mhandley 8y ago
    NASA runs the airline safety reporting system ASRS, which is where pilots anonymously report potential safety issues.
  - taejo 8y ago
    NASA is indeed where pilots confidentially report aviation safety problems: https://asrs.arc.nasa.gov/ https://asrs.arc.nasa.gov/ It is, after all, the National Aeronautics and Space Administration.
    - LoSboccacc 8y ago
      Bob Ebeling should have used that for the shuttle.
  - tialaramex 8y ago
    You think people using the provided incident reporting anonymity scheme are... Incompetent? Or you yourself are actually incompetent because you thought that you should comment about this without knowing that NASA runs ASRS which is exactly what this is for?
- 8y ago
zw123456 8y ago
The thing I don't understand about that MCAS system is why it would continue to drive the nose of the plane down even when the pilot is reefing on the stick to pull up. The cruise control in my car automatically disengages when I hit the brakes, it doesn't continue to accelerate to keep the car going 60 while I am jamming on the brakes, in an emergency, I don't have time to find the off switch. Similarly, I would think that in an emergency, it should automatically disengage if the pilot pulls hard on the stick, in an emergency, the pilot doesn't have time to read the manual to find the off switch for the thing. It seems crazy to me that they wouldn't have a safety override like that.
- StreamBright 8y ago
  Flight augmentation systems work a different way. Those take into consideration all inputs and average it out. Same when two pilots give different instructions.
  - piquadrat 8y ago
    > Same when two pilots give different instructions. That's only true for Airbus (and probably contributed to the loss of Air France 447, https://en.wikipedia.org/wiki/Air_France_Flight_447 https://en.wikipedia.org/wiki/Air_France_Flight_447). In Boeing airplanes, the movement of the two yokes is synchronized.
    - neuronic 8y ago
      > In Boeing airplanes, the movement of the two yokes is synchronized. So in case of two equally strong and equally determined pilots you still get averaging of opposing control inputs.
      - wikibob 8y ago
        No, the failure mode is not two pilots consciously fighting against each other. The failure mode is two pilots who are UNAWARE they are commanding contradicting inputs. Airbus negligently averages these inputs. This is legacy tech debt because the physical design didn’t leave room to link the two controls. Now they are stuck because they feel they can’t change and have some planes that (dangerously) average the inputs, and some that are physically linked. When controls are physically linked, if one pilot thinks he should nose up, and the other tries to nose down, they can yell “what are you doing” at each other and this create an accurate mental model of what the other is intending. Think of this every time you fly Airbus. It’s very similar to debugging a production technology issue. Imagine you decide to restore the database to a snapshot from 1 hour ago, and at the same time someone else tries to restore to an earlier snapshot from 12 hours ago. Should the system average these inputs and restore from 6.5 hours ago? No, obviously not.
programmer_dude 8y ago
What I don't understand whenever I read anything related to the MCAS system is why does it not check if the plane is in a dangerous nose dive using other sensors the plane might have? Does the average plane not have a gyroscope? My sub 500 dollar phone has both a gyroscope and an inertial measurement unit (accelerometer).
- dannyw 8y ago
  Because MCAS never assumes the input sensors could be faulty.
  - pishpash 8y ago
    Sounds like a shitty and incompetent design. Grounding the plane was the right decision.
    - ody4242 8y ago
      Totally agree.
    - achandlerwhite 8y ago
      I agree, but I see the reasoning. MCAS failure leads to runaway trim for which there is an established and well known procedure to fix--in the checklist almost 50 years. For a problem with trim you flip the trim cutout switch. Doesn't matter if the problem stems from MCAS, autopilot, crossed wires, the magentic pole flipping, jammed electric motor, whatever. It's like explaining to a computer user that rebooting will fix aproblem--they don't need to know the exact cause but just how to recover from it.
  - _archon_ 8y ago
    It's worse than this. MCAS is designed to only look at one of the two AoA sensors. If this happens to be faulty, it doesn't know, because it's not comparing the sensor to the other one. Instead of a system which can notice and account for disagreeing sensors and fail gracefully, we have a system which is a designed single point of failure and fails... lethally.
pts_ 8y ago
Airline by Michael Crichton played out in real.
- docdeek 8y ago
  *Airframe. I miss Crichton...
bookofjoe 8y ago
Best book I've ever read on the root cause ("tight coupling") of accidents: https://en.wikipedia.org/wiki/Normal_Accidents https://en.wikipedia.org/wiki/Normal_Accidents From its Wikipedia entry: >"Normal Accidents: Living with High-Risk Technologies" is a 1984 book by Yale sociologist Charles Perrow, which provides a detailed analysis of complex systems from a sociological perspective. It was the first to "propose a framework for characterizing complex technological systems such as air traffic, marine traffic, chemical plants, dams, and especially nuclear power plants according to their riskiness." Perrow argues that multiple and unexpected failures are built into society's complex and tightly coupled systems. Such accidents are unavoidable and cannot be designed around. His analysis also applies to anesthesia disasters, I learned the hard way during my 38 years in the O.R. Highly recommended.
- mjburgess 8y ago
  I think this perspective on accidents needs far more emphasis. Many accidents are unavoidable and not the result of some person failing to do some thing. The world isn't a story, people don't have much agency, and events do not happen because people want them to. These "narrative explanations" are mythological just-so stories that attribute the complex interaction of systems to individuals, organizations, etc. in naive agency-based ways.
  - rusk 8y ago
    Yes, but, its no excuse for relaxing operational rigor. Those who fail to learn from history are doomed to repeat it. And if you repeatedly ignore the lessons of experience then you are to blame.
    - bookofjoe 8y ago
      "History is written by the victors."—attributed to Winston Churchill. https://www.quora.com/Winston-Churchill-said-that-history-was-written-by-the-victors-Do-you-agree-with-that-statement https://www.quora.com/Winston-Churchill-said-that-history-wa...
mclightning 8y ago
Why is it kept in a water-filled box in the image on the news article? Feels freaky like it is a living animal kept alive in an aquarium. edit> https://www.quora.com/Why-are-black-boxes-put-into-water-after-they-are-rescued-from-the-accident-site https://www.quora.com/Why-are-black-boxes-put-into-water-aft...
- lawlessone 8y ago
  once it has been submerged taking it back out of the water will cause it to rust in the air.
lawlessone 8y ago
>The manufacturer has said there is a documented procedure to handle the situation. A different crew on the same plane the evening before encountered the same problem but solved it after running through three checklists, according to the November report. They shouldn't have to do this routinely.
- achandlerwhite 8y ago
  Agree, if the AoA sensor had been properly maintained and/or the MCAS was able to better handle a faulty sensor this could be mitigated. Also pilots should be made aware of the characteristics of the resulting mode of stabilizer trim runaway.
mlindner 8y ago
How did the pilots not think about trim controls... This is BASIC piloting. If you are experiencing pressure on the control stick you adjust trim. How were the pilots this inept?
- matz1 8y ago
  It's Indonesian and this particular budget airline locally has been famous for having many issues. But it's cheap.
binarnosp 8y ago
The book "Aviation Psychology: Practice and Research" by Klaus-Martin Goeters is an eye opener on the problems that the architects of complex control systems that interface with humans must take into account. And the kind of problem that MCAS exhibited is clearly explained in the book. The book doesn't talk only about control system design, but also about training, hiring, etc.
YeGoblynQueenne 8y ago
>> On the same aircraft the evening before the crash, a captain at Lion Air’s full-service sister carrier, Batik Air, was riding along in the cockpit and solved the similar flight control problems, two of the sources said. His presence on that flight, first reported by Bloomberg, was not disclosed in the preliminary report. Like that bug that there's only one person in the company who knows about and how to fix it, but she's always working on something else? That's just awful.
peteradio 8y ago
I'm becoming most curious about these AoA sensors. What is going on with them? Is there a problem in the manufacturing process?
- achandlerwhite 8y ago
  I believe it was installed incorrectly and poorly maintained by the airline.
vgoh1 8y ago
Wow. This is a failure from so many parties. The pilots for not knowing the correct procedure. Boeing (who should bear the majority of the blame) for allowing sensors that are not properly redundant, purchasing sensors that appear to fault on a regular basis, not properly training, and not making sure that a problem that was well understood can never happen again, the airline for not informing the next crew of problems from previous flights, the regulators of the United States and Ethiopia for allowing these mistakes to happen.
- mtw 8y ago
  We should look at the root cause, which is Boeing installing much more powerful engines on an old frame that wasn't designed for it. They haven't properly done it.
zaroth 8y ago
The previous flight had exactly the same issue. This is what that pilot wrote in the logs; After parking, the PIC informed the engineer about the aircraft problem and entered IAS (Indicated Air Speed) and ALT (altitude) Disagree and FEEL DIFF PRESS (Feel Differential Pressure) light problem on the Aircraft Flight Maintenance Log (AFML). The PIC also reported the flight condition through the electronic reporting system of the company A-SHOR. The event was reported as follows: Airspeed unreliable and ALT disagree shown after takeoff, STS also running to the wrong direction, suspected because of speed difference, identified that CAPT instrument was unreliable and handover control to FO. Continue NNC of Airspeed Unreliable and ALT disagree. Decide to continue flying to CGK at FL280, landed safely runway 25L. STS is the speed trim system. The pilot didn’t explicitly note that they set STAB TRIM to CUT OUT to correct the problem, perhaps because he thought it was obvious? But then reading the log of the previous flight; After three automatic AND trim occurrences, the SIC commented that the control column was too heavy to hold back. At 14:25:46 UTC, the PIC declared “PAN PAN” to the Denpasar Approach controller due to instrument failure and requested to maintain runway heading. At 14:28:28 UTC, the PIC moved the STAB TRIM switches to CUT OUT. The PIC re-engaged the STAB TRIM switches to NORMAL, but almost immediately the problem re-appeared. The PIC then moved the STAB TRIM switches back to CUT OUT and continued with manual trim without auto-pilot until the end of the flight. This implies it took almost three minutes for the previous crew to figure out the STAB TRIM needed to be CUT OUT after finding the trim is so wrong that they can’t hold the stick back. Clearly this is not a memory item for these pilots. [1] - https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-LQP_PRELIMINARY.pdf https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-...
- VBprogrammer 8y ago
  I haven't checked but I'd bet STS is speed trim system (Aka Mach trim). Interesting that he came up with a reasonable mental model of what was wrong even though Boeing hadn't given them any details.
- Someone1234 8y ago
  MCAS problems weren't a memory item for any pilot, the memory item is Runaway Stabilizer and exhibits different behaviour to MCAS. Which is to say that they'll be receiving sim training for Runaway Stabilizer, learn what to expect (wheel moves continuously, hard nose down, etc), and then in real life have MCAS cause the same issue but in a substantively different way (change, delay, change, delay, etc). Without the benefit of hindsight why not try the Memory Item: Engine Surge / Stall or Uncommanded Roll? Both of which could exhibit as an uncommanded nose down. The reality of the situation is that some pilots immediately went straight for Runaway Stabilizer whereas others did not. That's a problem. That's a TRAINING problem. The type rating should have included additional training against the Runaway Stabilizer Memory Item for MCAS so "I've seen this before" is second nature.
veryworried 8y ago
Where can we listen to the recording??
Trisell 8y ago
Again we are seeing a more systematic issue that commercial pilots don’t have stick and rudder skills. Automation has taken over 95% of the job. They push the throttles up to take off power, pull back on the stick, and then punch the auto-pilot and sit back and enjoy the ride. Then they don’t fly or input anything into flying until landing where they again fly the plane for the last 3-5 minutes of the flight. I would be interested to see the experience level/age of the pilots. As I think the retiring generation of pilot was much more equipped to deal with this type of issue. Then the new generation of pilot. I included an article lamenting this decreased skill we are seeing. It’s refering to the Miracle on the Hudson. But I think it applies here as well. [1] [1]https://nymag.com/news/features/53788/index1.html https://nymag.com/news/features/53788/index1.html
- throwaway663 8y ago
  Afaik autopilot has always played a large role, I used to have a few beers, amoungst company, with a retired SA first officer or engineer - someone in the cockpit anyway, they basically mastered sleeping upright once they reached desired altitude, helpful as they were all hungover as fuck. I'm sure they were all capable though. Autopilot handled 95% of flight even back then - 20 years ago I'd gather given his age. Wasn't a bullshiter about anything else so I'd (I at least) take his account as accurate, esp when hearing about the arms cargo etc.. and meeting other pilots that would visit
- _s 8y ago
  This is rather inflammatory at best, and pretty derogatory to the vast majority of pilots who spend upwards of $100,000 to gain the skills necessary for an ATPL, spending anywhere from 1000-2500 hours flying aircraft older than yourself using technology that predates WW2, and even WW1 in some cases. Stick and rudder skills is all you have to get through the first 100 or so hours of your flying career. What you're seeing is a consequence of companies willing to skimp on training and certifications, pressuring authorities and manufacturers to find workarounds, and keeping the folks actually flying the thing in the dark about it.
petilon 8y ago
This is the most revelatory news for me: The MAX has larger engines than previous 737s, and they are in a slightly different position. As a result, the plane has a tendency to pitch its nose up. To keep that from getting out of control if pilots flying manually aren’t attentive, MCAS automatically pushes the nose down if the sensor says the nose is too high. See: https://www.wsj.com/articles/what-you-need-to-know-about-flying-on-a-boeing-737-max-11552334508 https://www.wsj.com/articles/what-you-need-to-know-about-fly... In other words, Boeing fixed a hardware flaw with software. I am no aeronautical engineer, but this seems wrong to me. The hardware needs to be correct in and of itself. The software layer should be for enhancing the capabilities of the hardware, not for fixing fundamental flaws in hardware.
- achandlerwhite 8y ago
  Not a really a hardware flaw--a design choice/hardware compromise so that existing 737 infrastructure could be used. The low ground clearance of a 737 is one of its main selling points. It's customers have a large investment in infrastructure around this capability--Think of things like loading ramps, luggage carts, servicing vehicles, etc.
  - petilon 8y ago
    So in other words they designed it this way in order to make the 737 MAX is cheaper to operate, and therefore easier to sell. That's terrible. Boeing traded off safety for profits.
    - achandlerwhite 8y ago
      Yes cost is a factor. The alternative might not be feasible economically. I don't think the failure here was reusing the 737 design, but the downstream due diligence of implying no significant changes. I also think airline training is a factor--both Boeing for the new systems and the airliners because runaway stabilizer trim has been in the aircraft emergency checklist for over 50 years and every pilot should know it. That same procedure would have saved these planes.
linsomniac 8y ago
AvE over on youtube has some speculation about what caused these crashes, and sums it up with: This was clearly a training issue, but now everyone is talking about it and every pilot is going to have this at the top of their mind. Would I hesitate to get on a Max 8 right now? Not for a second, pardner. It's like how right after a bad health dept report is probably one of the safest times to go to a particular restaurant. http://www.youtube.com/watch?v=1XCU__OEftU http://www.youtube.com/watch?v=1XCU__OEftU
m23khan 8y ago
I don't get one thing -- why didn't the Lion Air pilots just shut off the Autopilot and take manual control of the aircraft?
- paulmd 8y ago
  This problem specifically only manifests when the autopilot is off. It's designed to prevent the pilots from stalling out the airplane without realizing it, which only happens in manual flight. Enabling the autopilot cuts out MCAS.

304 points by petethomas 8y ago

This appears to answer the question of why, given that there is a "memory item" for dealing with runaway trim that would have helped, it wasn't followed by the crew: > “They didn’t seem to know the trim was moving down,” the third source said. “They thought only about airspeed and altitude. That was the only thing they talked about.” If this is true, not only did the pilots not realize the trim was the cause of the dive and try to fix it, it seems that they didn't even realize the trim wheel was moving. "Runaway trim" would be something they trained for, but has a presentation so vastly different (of a visibly spinning trim wheel causing quick descent) as to not be recognizably the same emergency to these pilots. Of course, this crew had no way of knowing that there was a system on the plane that could slowly make erroneous trim changes over a long period with autopilot off, and it makes sense that they might miss it happening while focusing on their stall alerts and speeds and trying to come up with an explanation and also trying to retain control.

RidingPegasus 8y ago
Was the trim wheel not visibly spinning out of their control? Simply because the symptoms are different should mean that stopping it via taking manual control is a recurring option.
- cjbprime 8y ago
  The spin was not visible to these pilots presumably because it was happening in small increments with a delay between them.
  - acqq 8y ago
    Exactly. It was not "runaway" in the sense of "continuously doing the same." Something was happening, from the point of view of the pilot and co-pilot "at random." (Not to mention that on the previous models exactly such pattern was effectively impossible to happen). The faulty non-redundant sensor was producing false reading and that was the input to the to the pilots completely unknown MCAS which then moved the nose down based on the difference between the input and MCAS' expected target, turning "the correction" on only from time to time. The presence of the third, off-duty pilot on the flight before additionally explains even better how in that case the crash was avoided. While the pilot and co-pilot were at the controls, the third one, looking from behind, didn't have the direct duties to do, so he had enough time to both just observe everything that was going on and the less immediate stress to allow him to come to the solution that worked. Like when one programmer spends half an hour on something "not working" and complains to the colleague who just takes a look and immediately sees what the first one hasn't for half an hour. Additionally the movement of the trim wheel is actually easier to follow from the place in the back (see https://news.ycombinator.com/item?id=19440045 https://news.ycombinator.com/item?id=19440045 ). And there's also a possibility that the false sensor reading and MCAS together produced a slightly different differential signal which resulted in more obvious manifestation of the problem. Possibly both elements contributed to the lucky outcome in that previous flight. In the old times of civil aviation there was the third person on duty in the cockpit, the "flight-engineer." As the planes got more computerized controls, they started to be certified to fly with two-pilot crews. The computerized systems, when working, do reduce the chance of the crash and overall number of accidents did decrease simply because the humans were on the average less often in control, and therefore there was less chance to do anything wrong. The problem is when the unreported computerized controls secretly depend on the single sensor that can be faulty. And when they actively confuse the pilot and ruin the flight instead of helping him.
    - kayfox 8y ago
      "Runaway" in the sense of "its moving in a undesired and unexpected direction and continues to do so despite attempts to stop it".
      - jeremysmyth 8y ago
  - ahoka 8y ago
    If anyone wonders this is how it looks like: https://youtu.be/-X01uY0bJs0?t=48 https://youtu.be/-X01uY0bJs0?t=48
    - TheSpiceIsLife 8y ago
      And sounds? The trim wheels moving also makes a sound?
      - deleted 8y ago
        [deleted]
      - ekianjo 8y ago
        From the videos I have seen in cockpit it does seem to make a sound as it rolls.
      - WalterBright 8y ago
        Yes. The ratcheting sound is deliberate, so the pilots don't need to see the wheels spin to know the trim is running. Also note that there's a white stripe on the wheel so it's easy to see it is running.
        jacobush 8y ago
        Someone else in the thread said newer models don't make a sound.
      - michaelt 8y ago
        You'll note in that video, the left-hand pilot has a headset on, presumably the right-hand pilot does too. Headsets are seen in other videos [1] of the cockpit. So even if the spinning trim wheels make noise, they may not have heard it. (My google image search shows some pilots wearing two-ear headsets, some wearing one-ear headsets, some wearing two-ear headsets with side not on their ear, and some not wearing headsets. But some of those are pilots posing for photos, and presumably pilots don't let people visit the cockpit during critical stages of the flight) [1] https://youtu.be/wz2Q3COfveg?t=409 https://youtu.be/wz2Q3COfveg?t=409
- frenchy 8y ago
  I doubt it would have been "out of control", it would have just been slow changes over time as trim increased. The pilots might not have been fighting it much either, if they thought that airspeed was the problem, and not pitch.
  - Someone1234 8y ago
    The graph on page 14 of this report[0] is pretty telling about how slow the changes were... Note Trim Manual, Trim Automatic, and Pitch Trim Position. [0] https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-LQP_PRELIMINARY.pdf https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-...
    - acqq 8y ago
      Thanks! Page 23 of the PDF or 14 as printed at the bottom. Sadly it's hard to compare with the previous flight (pg. 25 or 16) as for it they published the graph of the whole flight instead of only the part until the (at the time still secret) MCAS was turned off (or probably more correctly, the motor controlled by the MCAS, which actually steered the "trim").
- crooked-v 8y ago
  Part of the problem is that the MCAS system has a 20-second delay after the last time the pilot touched controls for the flaps, and it adjusts itself to a new position and then stops. There are no other indicators that it's happening, and since it's noncontinuous and has a delay, it would be easy to miss the only visual sign of the trim wheel readjusting itself once, especially since the wheel itself is by the pilot's thigh outside of forward line of sight. In a normal runaway trim situation, by comparison, the trim wheel continues obviously spinning as long as the problem is going on, so it only takes a single glance at any time to notice it.
  - oasisbob 8y ago
    I'm not sure that's accurate. Other descriptions of the MCAS system state that it will continually modify the trim on the horizontal stabilizer for up to 10 seconds at a time. http://www.b737.org.uk/mcas.htm http://www.b737.org.uk/mcas.htm
    - inferiorhuman 8y ago
      To summarise; MCAS will trim the Stabilizer down for 10 seconds (2.5 deg nose down) and pause for 5 seconds and repeat if the conditions (high angle of attack, flaps up and autopilot disengaged) continue to be met. Using electric pitch trim will only pause MCAS, to deactivate it you need to switch off the STAB TRIM SUTOUT switches.
    - usrusr 8y ago
      Well, the point is that the experience from MCAS trying to be clever and subtle is very different from what one would expect in an old-school runaway trim situation caused by, say, a stuck relay. Easy to chase down a wrong line of inquiry when the symptoms only appear sporadically and can be temporarily stopped by a whole range of actions that won't permanently fix it.
- dukoid 8y ago
  To my understanding, the trim wheels are moving frequently for small adjustments -- and it's possible to switch the wheel movement off if this becomes too annoying.
  - losvedir 8y ago
    Also not a pilot but I don't think you can switch the wheel off. You can, however, disable the electric motors that spin the wheel, which is what the checklist for runaway trim tells you to do, and what was supposed to have been done here.
    - WalterBright 8y ago
      The spinning wheels are directly connected to the stab trim via cables. If the trim motors fail, the pilots can turn those wheels by hand (there's a folding crank on them) to manually adjust the trim.
  - VBprogrammer 8y ago
    It's running for 10 seconds at a time for 2.5 units of trim out of a possible ~15. That's quite a big trim change. I find it hard to believe that it's not noticed because of the 'boiling a frog' situation. It not possible to disable wheel movement. It's mechanically linked to the jackscrew.
- verytrivial 8y ago
  The Lion Air directive has instructions on page 41 of their preliminary report that include: 5. If the runaway continues after the autopilot is disengaged: STAB TRIM CUTOUT switches (both) ... CUTOUT If the runaway continues: Stabilizer trim wheel .... *Grasp and hold* This may be an overabundance of caution, or to cover other runaway events, but it reads like "you may need to physically fight the computer even when it has been disabled". Not exactly heartening. EDIT: A comment below points out haptic feedback to disengage as a reason to grab-and-hold. https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-LQP_PRELIMINARY.pdf https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-...
  - mlindner 8y ago
    That's incorrect, these have haptic feedback, once you grasp it, it's not going to fight you. It looks for resistance and if it sees the resistance it doesn't continue.
    - verytrivial 8y ago
      Ah, Okay, thanks. What remaining automation would be driving the trim wheel in this case that grab-and-hold would countermand?
    - heavenlyblue 8y ago
      You are still fighting it, aren't you?
    - userbinator 8y ago
      Really? Here's a video of someone doing it, and it certainly looks like it tries to fight you (and the trim motor continues running) but there's a clutch that starts slipping: https://www.youtube.com/watch?v=cQirIH_DuAs https://www.youtube.com/watch?v=cQirIH_DuAs
  - ProAm 8y ago
    > you may need to physically fight the computer This is the future I look forward to. AI/ML/Autopilot/Companies moving fast and breaking things.... Boeing took that one literally.
l33tman 8y ago
This is not true, on the released FDR data, it shows clearly that the pilot flying corrected the MCAS system's trim down adjustments at every cycle (each 10 seconds) for most of the level flight. So at least the PF must have been aware of this. It's a bit weird if they didn't talk about it though, maybe it was obvious to both pilots and they were concentrating on if they were keeping altitude and airspeed at all (the most important factors that would keep them flying).
- mannykannot 8y ago
  This got my attention too. For at least 6 minutes, the crew were coping with the problem - the aircraft was holding altitude and speed, if erratically, and they must have been getting the trim back to approximately where it should have been, or else MCAS would have driven the stabilizer to the point where it overrode the elevator authority. In about the last minute of that recording, the pattern changes: the pilot trim inputs decreased and became much shorter, and the stick forces changed from going up and down to a sustained, high, back-force. The article says that near the end, the captain handed over control to the 1st officer so he could look for answers. I am speculating wildly here, but could that coincide with the change in the pattern of the pilot's responses? Could it be that the 1st officer did not attempt to re-trim, or did not do it completely? Did he try to trim manually, but perhaps could not because of the load on the stabilizer? [1]. IIRC, according to Dominic Gates, it would only take two cycles of MCAS intervention until the stabilizer had reached a point where full nose-up elevator could not keep the airplane level. The chart was published in one of Dominic Gates' Seattle Times articles, but I am not in a position to find it right now... [1] https://news.ycombinator.com/item?id=19400157 https://news.ycombinator.com/item?id=19400157
  - VBprogrammer 8y ago
    Anyone who's ever piloted an aircraft would try to re-trim against pitch forces. It's inconceivable that the pilot for some reason just failed to do that. I'm not sure exactly what force it takes to get full nose up elevator at flying speed but it will be in the range of dozens of kilograms. I personally wonder if there is potentially a thermal cut-off on the trim motor which could have been activated by this trimming and re-triming. Or even an outright failure of some part of the system.
dvdkhlng 8y ago
I'm just wondering: it looks like the absolute trim angle is not visible anywhere in the cockpit? The trim wheel takes multiple revolutions to adjust trim between min/max limits, so looking at the wheel itself, you can only every see changes, not values. Unless you notice the change while it happens, you won't have any indication as to the unusual trim angle? Thinking about that I wonder whether there was even a measurement signal that the computers could rely on to determine the current state of the trim angle in absolute terms. Given how the MCAS did incremental changes without stopping before reaching the mechanical limits, I do imagine that there might have been no hardware feedback to assess the current trim state, thereby making it impossible hardware-wise to limit MCAS to a sensible (and safe) range of angles. [edit] Looking at the lion air crash report [1] p.14 ff it seems like also the black box only recorded trim changes, not absolute trim state. [1] https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-LQP_PRELIMINARY.pdf https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-...
- VBprogrammer 8y ago
  There is a trim position indication. It's to the left and right of the throttles. It's a critical thing to check before starting the takeoff roll. You can see it on the copilot's side here by the trim wheel. http://www.b737.org.uk/images/stabtrim_200.jpg http://www.b737.org.uk/images/stabtrim_200.jpg
  - dvdkhlng 8y ago
    Yes, thinking about that, not having any pilot-visible indication would be quite some point of failure at lift-off. Still wondering whether MCAS and other automatation systems have a representation of that position indication. I can't currently come up with an idea of how to implement that in an easy, yet error-resilient way. Usually you would initially drive into a reference position, then integrate the motor's actions to arive at an absolute value, but integration would potentially add up subsequent errors, and obviously you can't re-do the referencing step while in the air.
    - VBprogrammer 8y ago

jve 8y ago

In the other news, on the previous day on the same plane there was a retired pilot flying in cockpit who correctly diagnosed problem & told how to disable malfunctioning system: https://www.bloomberg.com/news/articles/2019-03-19/how-an-extra-man-in-cockpit-saved-a-737-max-that-later-crashed https://www.bloomberg.com/news/articles/2019-03-19/how-an-ex...

gojomo 8y ago
That's the most amazing revelation to me so far. The same plane had an identical uncontrolled-dive problem the day before, which required an emergency power cut to the improperly-engaged motor, and somehow that incident didn't ground the plane or even result in any effective advisory to the next crew. Further, the Bloomberg story reports: "The Indonesia safety committee report said the plane had had multiple failures on previous flights and hadn’t been properly repaired." Lots of blame to go around here.
- deleted 8y ago
  [deleted]
- acqq 8y ago
  > Lots of blame to go around here. Only if the faulty sensor was listed as "critical." Boeing didn't declare it as such and reported to nobody the way it was used in the unreported MCAS. That the MCAS even exists and that a single faulty sensor was enough to mess with the flight erratically enough to confuse the pilots was somehow acknowledged by Boeing only after the first crash. It took the second crash for most observers to recognize that just blaming the pilot or maintenance won't keep the planes from not crashing.
  - icebraining 8y ago
    Even if they didn't know about the MCAS, they still knew the plane had had an uncontrolled-dive problem from an unknown cause. How is it responsible to fly it without understanding the issue? Boeing is still fully culpable, but the airline should have debugged the issue before using the plane again.

mikejb 8y ago

I'm trying to imagine the horror the pilots (and passengers) were feeling. Imagine your car slowly starting to shift sideways into incoming traffic, and no matter how hard you pull the steering wheel, you can't get it back. Horrifying.

SmellyGeekBoy 8y ago
This is why I refuse to listen to these things when they're released. The thought of eavesdropping in on someone's frantic hopeless fight for survival just doesn't sit right with me.
- isolli 8y ago
  Agreed. It reminds me of the final scene of Grizzly Man, when Herzog listens to the audio recording of the bear enthusiast and his girlfriend being mauled to death. Herzog puts the headphones down, visibly shaken, and comments (paraphrasing): nobody should have to listen to that.
  - Darthy 8y ago
    He actually says to the mother: Jewel, you must never listen to this.
    - aeorgnoieang 8y ago
      Wasn't it the girlfriend?
      - mikejb 8y ago
        The girlfriend was on location and apparently the one who turned on the camera (but did not remove the lens cap, making it an audio-only recording). She was killed and partially eaten together with Treadwell. Edit: The tape is actually owned by Jewel Palovak who this scene is also with; She's a former girlfriend of Treadwell, not his (or his girlfriends) mother.
  - 8y ago

CyberFonic 8y ago

One of the factors that has been quickly glossed over is the low level of experience of some of the pilots in both the Indonesian and Ethopian accidents. In the USA, due to much higher levels of experience pilots have been correcting for the MCAS actions effectively and complaining about it to NASA (in order to avoid being branded as whistle-blowers by their airlines).

deleted 8y ago
[deleted]
dannyw 8y ago
I’d be highly concerned of the competency of any pilot who complains to NASA.
- mhandley 8y ago
  NASA runs the airline safety reporting system ASRS, which is where pilots anonymously report potential safety issues.
- taejo 8y ago
  NASA is indeed where pilots confidentially report aviation safety problems: https://asrs.arc.nasa.gov/ https://asrs.arc.nasa.gov/ It is, after all, the National Aeronautics and Space Administration.
  - LoSboccacc 8y ago
    Bob Ebeling should have used that for the shuttle.
- tialaramex 8y ago
  You think people using the provided incident reporting anonymity scheme are... Incompetent? Or you yourself are actually incompetent because you thought that you should comment about this without knowing that NASA runs ASRS which is exactly what this is for?
8y ago

zw123456 8y ago

The thing I don't understand about that MCAS system is why it would continue to drive the nose of the plane down even when the pilot is reefing on the stick to pull up. The cruise control in my car automatically disengages when I hit the brakes, it doesn't continue to accelerate to keep the car going 60 while I am jamming on the brakes, in an emergency, I don't have time to find the off switch. Similarly, I would think that in an emergency, it should automatically disengage if the pilot pulls hard on the stick, in an emergency, the pilot doesn't have time to read the manual to find the off switch for the thing. It seems crazy to me that they wouldn't have a safety override like that.

StreamBright 8y ago
Flight augmentation systems work a different way. Those take into consideration all inputs and average it out. Same when two pilots give different instructions.
- piquadrat 8y ago
  > Same when two pilots give different instructions. That's only true for Airbus (and probably contributed to the loss of Air France 447, https://en.wikipedia.org/wiki/Air_France_Flight_447 https://en.wikipedia.org/wiki/Air_France_Flight_447). In Boeing airplanes, the movement of the two yokes is synchronized.
  - neuronic 8y ago
    > In Boeing airplanes, the movement of the two yokes is synchronized. So in case of two equally strong and equally determined pilots you still get averaging of opposing control inputs.
    - wikibob 8y ago
      No, the failure mode is not two pilots consciously fighting against each other. The failure mode is two pilots who are UNAWARE they are commanding contradicting inputs. Airbus negligently averages these inputs. This is legacy tech debt because the physical design didn’t leave room to link the two controls. Now they are stuck because they feel they can’t change and have some planes that (dangerously) average the inputs, and some that are physically linked. When controls are physically linked, if one pilot thinks he should nose up, and the other tries to nose down, they can yell “what are you doing” at each other and this create an accurate mental model of what the other is intending. Think of this every time you fly Airbus. It’s very similar to debugging a production technology issue. Imagine you decide to restore the database to a snapshot from 1 hour ago, and at the same time someone else tries to restore to an earlier snapshot from 12 hours ago. Should the system average these inputs and restore from 6.5 hours ago? No, obviously not.

programmer_dude 8y ago

What I don't understand whenever I read anything related to the MCAS system is why does it not check if the plane is in a dangerous nose dive using other sensors the plane might have? Does the average plane not have a gyroscope? My sub 500 dollar phone has both a gyroscope and an inertial measurement unit (accelerometer).

dannyw 8y ago
Because MCAS never assumes the input sensors could be faulty.
- pishpash 8y ago
  Sounds like a shitty and incompetent design. Grounding the plane was the right decision.
  - ody4242 8y ago
    Totally agree.
  - achandlerwhite 8y ago
    I agree, but I see the reasoning. MCAS failure leads to runaway trim for which there is an established and well known procedure to fix--in the checklist almost 50 years. For a problem with trim you flip the trim cutout switch. Doesn't matter if the problem stems from MCAS, autopilot, crossed wires, the magentic pole flipping, jammed electric motor, whatever. It's like explaining to a computer user that rebooting will fix aproblem--they don't need to know the exact cause but just how to recover from it.
- _archon_ 8y ago
  It's worse than this. MCAS is designed to only look at one of the two AoA sensors. If this happens to be faulty, it doesn't know, because it's not comparing the sensor to the other one. Instead of a system which can notice and account for disagreeing sensors and fail gracefully, we have a system which is a designed single point of failure and fails... lethally.

pts_ 8y ago

Airline by Michael Crichton played out in real.

docdeek 8y ago
*Airframe. I miss Crichton...

bookofjoe 8y ago

Best book I've ever read on the root cause ("tight coupling") of accidents: https://en.wikipedia.org/wiki/Normal_Accidents https://en.wikipedia.org/wiki/Normal_Accidents From its Wikipedia entry: >"Normal Accidents: Living with High-Risk Technologies" is a 1984 book by Yale sociologist Charles Perrow, which provides a detailed analysis of complex systems from a sociological perspective. It was the first to "propose a framework for characterizing complex technological systems such as air traffic, marine traffic, chemical plants, dams, and especially nuclear power plants according to their riskiness." Perrow argues that multiple and unexpected failures are built into society's complex and tightly coupled systems. Such accidents are unavoidable and cannot be designed around. His analysis also applies to anesthesia disasters, I learned the hard way during my 38 years in the O.R. Highly recommended.

mjburgess 8y ago
I think this perspective on accidents needs far more emphasis. Many accidents are unavoidable and not the result of some person failing to do some thing. The world isn't a story, people don't have much agency, and events do not happen because people want them to. These "narrative explanations" are mythological just-so stories that attribute the complex interaction of systems to individuals, organizations, etc. in naive agency-based ways.
- rusk 8y ago
  Yes, but, its no excuse for relaxing operational rigor. Those who fail to learn from history are doomed to repeat it. And if you repeatedly ignore the lessons of experience then you are to blame.
  - bookofjoe 8y ago
    "History is written by the victors."—attributed to Winston Churchill. https://www.quora.com/Winston-Churchill-said-that-history-was-written-by-the-victors-Do-you-agree-with-that-statement https://www.quora.com/Winston-Churchill-said-that-history-wa...

mclightning 8y ago

Why is it kept in a water-filled box in the image on the news article? Feels freaky like it is a living animal kept alive in an aquarium. edit> https://www.quora.com/Why-are-black-boxes-put-into-water-after-they-are-rescued-from-the-accident-site https://www.quora.com/Why-are-black-boxes-put-into-water-aft...

lawlessone 8y ago
once it has been submerged taking it back out of the water will cause it to rust in the air.

lawlessone 8y ago

>The manufacturer has said there is a documented procedure to handle the situation. A different crew on the same plane the evening before encountered the same problem but solved it after running through three checklists, according to the November report. They shouldn't have to do this routinely.

achandlerwhite 8y ago
Agree, if the AoA sensor had been properly maintained and/or the MCAS was able to better handle a faulty sensor this could be mitigated. Also pilots should be made aware of the characteristics of the resulting mode of stabilizer trim runaway.

mlindner 8y ago

How did the pilots not think about trim controls... This is BASIC piloting. If you are experiencing pressure on the control stick you adjust trim. How were the pilots this inept?

matz1 8y ago
It's Indonesian and this particular budget airline locally has been famous for having many issues. But it's cheap.

binarnosp 8y ago

The book "Aviation Psychology: Practice and Research" by Klaus-Martin Goeters is an eye opener on the problems that the architects of complex control systems that interface with humans must take into account. And the kind of problem that MCAS exhibited is clearly explained in the book. The book doesn't talk only about control system design, but also about training, hiring, etc.

YeGoblynQueenne 8y ago

>> On the same aircraft the evening before the crash, a captain at Lion Air’s full-service sister carrier, Batik Air, was riding along in the cockpit and solved the similar flight control problems, two of the sources said. His presence on that flight, first reported by Bloomberg, was not disclosed in the preliminary report. Like that bug that there's only one person in the company who knows about and how to fix it, but she's always working on something else? That's just awful.

peteradio 8y ago

I'm becoming most curious about these AoA sensors. What is going on with them? Is there a problem in the manufacturing process?

achandlerwhite 8y ago
I believe it was installed incorrectly and poorly maintained by the airline.

vgoh1 8y ago

Wow. This is a failure from so many parties. The pilots for not knowing the correct procedure. Boeing (who should bear the majority of the blame) for allowing sensors that are not properly redundant, purchasing sensors that appear to fault on a regular basis, not properly training, and not making sure that a problem that was well understood can never happen again, the airline for not informing the next crew of problems from previous flights, the regulators of the United States and Ethiopia for allowing these mistakes to happen.

mtw 8y ago
We should look at the root cause, which is Boeing installing much more powerful engines on an old frame that wasn't designed for it. They haven't properly done it.

zaroth 8y ago

The previous flight had exactly the same issue. This is what that pilot wrote in the logs; After parking, the PIC informed the engineer about the aircraft problem and entered IAS (Indicated Air Speed) and ALT (altitude) Disagree and FEEL DIFF PRESS (Feel Differential Pressure) light problem on the Aircraft Flight Maintenance Log (AFML). The PIC also reported the flight condition through the electronic reporting system of the company A-SHOR. The event was reported as follows: Airspeed unreliable and ALT disagree shown after takeoff, STS also running to the wrong direction, suspected because of speed difference, identified that CAPT instrument was unreliable and handover control to FO. Continue NNC of Airspeed Unreliable and ALT disagree. Decide to continue flying to CGK at FL280, landed safely runway 25L. STS is the speed trim system. The pilot didn’t explicitly note that they set STAB TRIM to CUT OUT to correct the problem, perhaps because he thought it was obvious? But then reading the log of the previous flight; After three automatic AND trim occurrences, the SIC commented that the control column was too heavy to hold back. At 14:25:46 UTC, the PIC declared “PAN PAN” to the Denpasar Approach controller due to instrument failure and requested to maintain runway heading. At 14:28:28 UTC, the PIC moved the STAB TRIM switches to CUT OUT. The PIC re-engaged the STAB TRIM switches to NORMAL, but almost immediately the problem re-appeared. The PIC then moved the STAB TRIM switches back to CUT OUT and continued with manual trim without auto-pilot until the end of the flight. This implies it took almost three minutes for the previous crew to figure out the STAB TRIM needed to be CUT OUT after finding the trim is so wrong that they can’t hold the stick back. Clearly this is not a memory item for these pilots. [1] - https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-LQP_PRELIMINARY.pdf https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-...

VBprogrammer 8y ago
I haven't checked but I'd bet STS is speed trim system (Aka Mach trim). Interesting that he came up with a reasonable mental model of what was wrong even though Boeing hadn't given them any details.
Someone1234 8y ago
MCAS problems weren't a memory item for any pilot, the memory item is Runaway Stabilizer and exhibits different behaviour to MCAS. Which is to say that they'll be receiving sim training for Runaway Stabilizer, learn what to expect (wheel moves continuously, hard nose down, etc), and then in real life have MCAS cause the same issue but in a substantively different way (change, delay, change, delay, etc). Without the benefit of hindsight why not try the Memory Item: Engine Surge / Stall or Uncommanded Roll? Both of which could exhibit as an uncommanded nose down. The reality of the situation is that some pilots immediately went straight for Runaway Stabilizer whereas others did not. That's a problem. That's a TRAINING problem. The type rating should have included additional training against the Runaway Stabilizer Memory Item for MCAS so "I've seen this before" is second nature.

veryworried 8y ago

Where can we listen to the recording??

Trisell 8y ago

Again we are seeing a more systematic issue that commercial pilots don’t have stick and rudder skills. Automation has taken over 95% of the job. They push the throttles up to take off power, pull back on the stick, and then punch the auto-pilot and sit back and enjoy the ride. Then they don’t fly or input anything into flying until landing where they again fly the plane for the last 3-5 minutes of the flight. I would be interested to see the experience level/age of the pilots. As I think the retiring generation of pilot was much more equipped to deal with this type of issue. Then the new generation of pilot. I included an article lamenting this decreased skill we are seeing. It’s refering to the Miracle on the Hudson. But I think it applies here as well. [1] [1]https://nymag.com/news/features/53788/index1.html https://nymag.com/news/features/53788/index1.html

throwaway663 8y ago
Afaik autopilot has always played a large role, I used to have a few beers, amoungst company, with a retired SA first officer or engineer - someone in the cockpit anyway, they basically mastered sleeping upright once they reached desired altitude, helpful as they were all hungover as fuck. I'm sure they were all capable though. Autopilot handled 95% of flight even back then - 20 years ago I'd gather given his age. Wasn't a bullshiter about anything else so I'd (I at least) take his account as accurate, esp when hearing about the arms cargo etc.. and meeting other pilots that would visit
_s 8y ago
This is rather inflammatory at best, and pretty derogatory to the vast majority of pilots who spend upwards of $100,000 to gain the skills necessary for an ATPL, spending anywhere from 1000-2500 hours flying aircraft older than yourself using technology that predates WW2, and even WW1 in some cases. Stick and rudder skills is all you have to get through the first 100 or so hours of your flying career. What you're seeing is a consequence of companies willing to skimp on training and certifications, pressuring authorities and manufacturers to find workarounds, and keeping the folks actually flying the thing in the dark about it.

petilon 8y ago

This is the most revelatory news for me: The MAX has larger engines than previous 737s, and they are in a slightly different position. As a result, the plane has a tendency to pitch its nose up. To keep that from getting out of control if pilots flying manually aren’t attentive, MCAS automatically pushes the nose down if the sensor says the nose is too high. See: https://www.wsj.com/articles/what-you-need-to-know-about-flying-on-a-boeing-737-max-11552334508 https://www.wsj.com/articles/what-you-need-to-know-about-fly... In other words, Boeing fixed a hardware flaw with software. I am no aeronautical engineer, but this seems wrong to me. The hardware needs to be correct in and of itself. The software layer should be for enhancing the capabilities of the hardware, not for fixing fundamental flaws in hardware.

achandlerwhite 8y ago
Not a really a hardware flaw--a design choice/hardware compromise so that existing 737 infrastructure could be used. The low ground clearance of a 737 is one of its main selling points. It's customers have a large investment in infrastructure around this capability--Think of things like loading ramps, luggage carts, servicing vehicles, etc.
- petilon 8y ago
  So in other words they designed it this way in order to make the 737 MAX is cheaper to operate, and therefore easier to sell. That's terrible. Boeing traded off safety for profits.
  - achandlerwhite 8y ago
    Yes cost is a factor. The alternative might not be feasible economically. I don't think the failure here was reusing the 737 design, but the downstream due diligence of implying no significant changes. I also think airline training is a factor--both Boeing for the new systems and the airliners because runaway stabilizer trim has been in the aircraft emergency checklist for over 50 years and every pilot should know it. That same procedure would have saved these planes.

linsomniac 8y ago

AvE over on youtube has some speculation about what caused these crashes, and sums it up with: This was clearly a training issue, but now everyone is talking about it and every pilot is going to have this at the top of their mind. Would I hesitate to get on a Max 8 right now? Not for a second, pardner. It's like how right after a bad health dept report is probably one of the safest times to go to a particular restaurant. http://www.youtube.com/watch?v=1XCU__OEftU http://www.youtube.com/watch?v=1XCU__OEftU

m23khan 8y ago

I don't get one thing -- why didn't the Lion Air pilots just shut off the Autopilot and take manual control of the aircraft?

paulmd 8y ago
This problem specifically only manifests when the autopilot is off. It's designed to prevent the pilots from stalling out the airplane without realizing it, which only happens in manual flight. Enabling the autopilot cuts out MCAS.