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Ethiopian Max Crash Simulator Scenario Stuns Pilots

194 points by inferiorhuman 8y ago

tus87 8y ago
> and underscores the importance of pilots understanding severe runaway trim recovery procedures. So we're back to blaming the pilots?
- pageandrew 8y ago
  There were pilot crews that were able to successfully fend off MCAS's murderous tendencies, and there were pilot crews that were not. Ignoring this learning opportunity for better general pilot education would be a mistake. Pilots being better trained is always a good thing.
  - jfk13 8y ago
    IIUC, those who did overcome the problem in the simulator lost around 8,000 feet of altitude in the process (despite presumably going into the simulator already knowing what they were going to be facing). It's not clear to me that the Ethiopian plane ever had enough altitude (above the ground) to allow for such a recovery.
    - cjbprime 8y ago
      If I recall, it did stay at around 12k altitude for a stable period of flight where MCAS was being successfully neutralized. It's in the Ethiopian report. The airspeed was way above limit, though, which would make everything harder, including the manual retrimming.
      - bronson 8y ago
        Remember that they left an airport about 7000 feet up and headed over mountains. It's unlikely the plane was ever more than a few thousand feet above ground level. Page 26 in Ethiopia's report: https://fearoflanding.com/files/2019/04/Preliminary-Report-B737-800MAX-ET-AVJ.pdf https://fearoflanding.com/files/2019/04/Preliminary-Report-B...
        cjbprime 8y ago
        Thanks, I'd forgotten the numbers. They aren't quite as bad as you say. The Ethiopian report shows their radar elevation around 14k feet before the descent, so it seems they made it to around 7k feet AGL for a few minutes. Not enough to be able to give up 8k feet during a recovery, I agree.
- d1str0 8y ago
  Nobody is saying that. That’s not even what this out of context quote is saying.
- jfk13 8y ago
  Sounds more like we're blaming the manufacturer for concealing the fact that pilots needed to be specifically (re-)trained for this plane if they were to have a chance of handling it successfully.
  - blunte 8y ago
    Exactly. But such training should not be necessary because this problem was created by Boeing. Pilots really should have extensive emergency training, but that doesn't mean it's ok for the manufacturer to Add a new failure case to a previously fine aircraft.
    - olliej 8y ago
      [edit: leaving this here because I wrote so much :D I totally misread/interpreted the comment I was replying to, and am entirely in agreement :D ] In this case the "fix" is called the "roller coaster", but Boeing has removed the documentation regarding this from the manuals - specifically the Pilots could have 100% perfect recall of the entire 737-MAX documentation and it wouldn't have helped. This is 100% Boeing's responsibility: * They designed a system that overrode pilot control so that they could avoid a requirement to retrain pilots. MCAS existed specifically to maintain the perception of identical flight behaviour entirely to avoid the need for recertification and training. That is the only reason MCAS existed. * They had minimal (no?) documentation indicating it existed * They made a warning system to report that the system was faulty - literally they shipped a broken safety system: the warning was intended to be freely available, but it was incorrectly tied to a costly system, so even though it was meant to be a standard feature, it was not present. * The recommended recovery technique from their documentation was not physically possible, even when you knew exactly what you were meant to do. * The only technique to recover - the roller coaster - had been deliberately removed from the training and flight manuals. The pilots who managed to recover were only able to recover because they knew of the "solution" from old manuals that were published online after both crashes had occurred, by some non-Boeing website. Even then the pilots in the article said that they didn't believe it would be possible to recover once you got below 5000 feet. Now, exactly how was this in any way the pilot's fault? They were fully trained, they had clearly read the manuals provided by Boeing (they knew they were mean to be using the manual wheel thing), the warning system was non-functional due to a construction/software error in Boeing's control software, etc.
- daveguy 8y ago
  That's pretty much the opposite, right? That the pilots would need to know an extreme emergency procedure. In other words you'd need a Sully level pilot to survive (and unsurvivable below a certain speed and height). If you ask me that's a damning indictment when a flawed autopilot results in a state like that.
  - namirez 8y ago
    Except Sully actually screwed up and put the passengers life in danger by trying to land on water and rather than returning to the airport. https://www.cbsnews.com/news/ntsb-sully-could-have-made-it-back-to-laguardia/ https://www.cbsnews.com/news/ntsb-sully-could-have-made-it-b...
    - cjbprime 8y ago
      I don't know how you could read the article you linked and come away with that conclusion.
    - YokoZar 8y ago
      The link you included says the opposite of what you're implying. > under the circumstances the captain's decision to ditch into the Hudson River was the better choice, documents released Tuesday by a federal safety panel said > He also would have had no way of knowing that he would be successful, and therefore would have been risking the possibility of a catastrophic crash in a densely populated area.
    - Someone1234 8y ago
      This was disproven. And is a major plot point in the movie about Flight 1549 (Sully). From Wikipedia: > The NTSB used flight simulators to test the possibility that the flight could have returned safely to LaGuardia or diverted to Teterboro; only seven of the thirteen simulated returns to La Guardia succeeded, and only one of the two to Teterboro. > Furthermore, the NTSB report called these simulations unrealistic: "The immediate turn made by the pilots during the simulations did not reflect or account for real-world considerations, such as the time delay required to recognize the bird strike and decide on a course of action." A further simulation, in which a 35-second delay was inserted to allow for those, crashed.
- salawat 8y ago
  No, we're back to, "why the heck didn't Boeing honor the regulatory requirement for simulator training, and tell American it was the best you could do?" Clearly, the condition is recoverable, with simulator training. Throw in a triple redundant AoA sensor on top of the training, plus the inclusion of MCAS implementation details in the training material, and things would likely have had a much higher chance of being dealt with without loss of life. Would Boeing have had a harder sell? Yes. Would there have been a non-zero chance of losing out on the order? Yes. Would 300+ people currently be pulp? I think not. I have a great deal of respect for the skill pilots develop. They are only human however, and are therefore subject to the same weakness of not being omniscient. If MCAS was the bullet, Boeing's opaque communication, and refusal to not game aviation certification regulations was the gun. Of that, I'm fairly certain. What plays the trigger pull in this sordid affair is the last thing that remains to be declared, but there are some seriously bright neon signs pointing at either somewhere in Chicago, or at the culture as a whole at Boeing. Let the digging continue. Let's see how deep the rabbit hole goes.
  - blunte 8y ago
    TFA said it was likely not recoverable under 5000 AGL.
    - deleted 8y ago
      [deleted]
    - salawat 8y ago
      Didn't read the entire thing. Going to register later. I actually wonder whether anyone with access to the simulator has tried pulsing the trim switches in sub 4 second intervals. Which depending on how the trim switches work, (I.e. are they continuously coupled, or do they act by moving around a discrete set-point) might be able to fend off MCAS by constantly resetting the time until reactivation long enough to give the trim system time to neutralize. If something like that were done, a recovery below 5000AGL may be possible. It's not by a long shot the most intuitive approach out there, and it doesn't generalize well, but for the specific MCAS behavior that's been revealed it may work. (If there's any 737 pilots out there with insight, I'd be giddy if you'd offer some perspective.)
deleted 8y ago
[deleted]
virtuexru 8y ago
Article is behind a paywall unfortunately. Any help? :)
- bxio 8y ago
  Registration wall and the ol' HN Hug of Death, not a good combination.
- jfk13 8y ago
  AFAICS it's a registration-wall, not actually a pay-wall.
  - newnewpdro 8y ago
    Isn't this just splitting hairs over which currency is paid?
- amluto 8y ago
  This might be the same article: https://theworldnews.net/us-news/ethiopian-max-crash-simulator-scenario-stuns-pilots https://theworldnews.net/us-news/ethiopian-max-crash-simulat... The original link seems dead. edit: nope, my link is no good either.
  - Animats 8y ago
    Is there video of the simulation?
    - mimixco 8y ago
      Yes. Here: https://m.youtube.com/watch?feature=youtu.be&v=QytfYyHmxtc https://m.youtube.com/watch?feature=youtu.be&v=QytfYyHmxtc
- simcop2387 8y ago
  Found a forum thread about it from some aviation enthusiasts [1]. Some choice excerpts they made: ‘A simulator session flown by a U.S.-based Boeing 737 MAX crew that mimicked a key portion of the Flight 302 accident sequence suggests that the crew faced a near-impossible task of getting their 737 MAX back under control, and underscores the importance of pilots understanding severe runaway trim recovery procedures.’ ‘What the U.S. crew found -. Keeping the aircraft level required significant aft-column pressure by the captain, and aerodynamic forces prevented the first officer from moving the trim wheel a full turn. They resorted to a little-known procedure to regain control.’ (YoYo Roller Coaster) The excessive descent rates during the first two steps meant the crew got as low as 2,000 ft. during the recovery. ... ‘The simulator session underscored the importance of reacting quickly to uncommanded stabilizer movements and avoiding a severe out-of-trim condition, one of the pilots involved said. “I donʼt think the situation would be survivable at 350 kt. and below 5,000 ft,” this pilot noted.’ “This is the sort of simulator experience airline crews need to gain an understanding of how runaway trim can make the aircraft very difficult to control, and how important it is to rehearse use of manual trim inputs,” [1] https://www.pprune.org/rumours-news/621478-ethiopian-max-crash-simulator-scenario-stuns-pilots.html https://www.pprune.org/rumours-news/621478-ethiopian-max-cra...
danols 8y ago
I am not very concerned with this particular problem anymore since it will get a satisfactory solution due to its publicity. What I am worried about and think should get more focus is other potential issues and corners that has been cut by the Boeing management. I have note read a single thing that Boeing has handled well in this massive disaster. This lack of judgement, short term profit seeking & cover up mentality is what media should spend more time on. It feels to me that they used up a lot of their trust capital to be allowed to perform any type of self-certification
- adreamingsoul 8y ago
  That is also expected in our Capitalistic system. Greed, profit, and share-holder value is often more important then the end-user. Boeing is not the only company that subscribes to that religion.
  - geff82 8y ago
    I doubt that in a non-capitalistic system the 737 MAX would not have had similar problems as in no system resources are infinite. Budgets, even in the most socialist country, are limited. The question is just WHO limits the budget: private enterprises (or their shareholders), co-ops or politicians.
    - adreamingsoul 8y ago
      Appreciate the feedback!
    - objektif 8y ago
      How is this a resource problem particularly. Airbus a coporation from the land of semi-socialist countries have similiar reaoirce constraints.
  - chimpburger 8y ago
    Psychopaths in leadership/management create problems in all economic systems. Don't blame capitalism. Evil people are evil. There are good people at Boeing but psychopaths have a natural ability to gain power in all kinds of social structures.
mcyukon 8y ago
"WASHINGTON—A simulator session flown by a U.S.-based Boeing 737 MAX crew that mimicked a key portion of the Ethiopian Airlines Flight 302 (ET302) accident sequence suggests that the Ethiopian crew faced a near-impossible task of getting their 737 MAX 8 back under control, and underscores the importance of pilots understanding severe runaway trim recovery procedures. Details of the session, shared with Aviation Week, were flown voluntarily as part of routine, recurrent training. Its purpose: practice recovering from a scenario in which the aircraft was out of trim and wanting to descend while flying at a high rate of speed. This is what the ET302 crew faced when it toggled cutout switches to de-power the MAX’s automatic stabilizer trim motor, disabling the maneuvering characteristics augmentation system (MCAS) that was erroneously trimming the horizontal stabilizer nose-down. In such a scenario, once the trim motor is de-powered, the pilots must use the hand-operated manual trim wheels to adjust the stabilizers. But they also must keep the aircraft from descending by pulling back on the control columns to deflect the elevator portions of the stabilizer upward. Aerodynamic forces from the nose-up elevator deflection make the entire stabilizer more difficult to move, and higher airspeed exacerbates the issue. The U.S. crew tested this by setting up a 737-Next Generation simulator at 10,000 ft., 250 kt. and 2 deg. nose up stabilizer trim. This is slightly higher altitude but otherwise similar to what the ET302 crew faced as it de-powered the trim motors 3 min. into the 6 min. flight, and about 1 min. after the first uncommanded MCAS input. Leading up to the scenario, the Ethiopian crew used column-mounted manual electric trim to counter some of the MCAS inputs, but did not get the aircraft back to level trim, as the 737 manual instructs before de-powering the stabilizer trim motor. The crew also did not reduce their unusually high speed. What the U.S. crew found was eye-opening. Keeping the aircraft level required significant aft-column pressure by the captain, and aerodynamic forces prevented the first officer from moving the trim wheel a full turn. They resorted to a little-known procedure to regain control. The crew repeatedly executed a three-step process known as the roller coaster. First, let the aircraft’s nose drop, removing elevator nose-down force. Second, crank the trim wheel, inputting nose-up stabilizer, as the aircraft descends. Third, pull back on the yokes to raise the nose and slow the descent. The excessive descent rates during the first two steps meant the crew got as low as 2,000 ft. during the recovery. The Ethiopian Ministry of Transport preliminary report on the Mar. 10 ET302 accident suggests the crew attempted to use manual trim after de-powering the stabilizer motors, but determined it “was not working,” the report said. A constant trust setting at 94% N1 meant ET302’s airspeed increased to the 737 MAX’s maximum (Vmo), 340 kt., soon after the stabilizer trim motors were cut off, and did not drop below that level for the remainder of the flight. The pilots, struggling to keep the aircraft from descending, also maintained steady to strong aft control-column inputs from the time MCAS first fired through the end of the flight. The U.S. crew’s session and a video posted recently by YouTube’s Mentour Pilot that shows a similar scenario inside a simulator suggest that the resulting forces on ET302’s stabilizer would have made it nearly impossible to move by hand. Neither the current 737 flight manual nor any MCAS-related guidance issued by Boeing in the wake of the October 2018 crash of Lion Air Flight 610 (JT610), when MCAS first came to light for most pilots, discuss the roller-coaster procedure for recovering from severe out-of-trim conditions. The 737 manual explains that “effort required to manually rotate the stabilizer trim wheels may be higher under certain flight conditions,” but does not provide details. The pilot who shared the scenario said he learned the roller coaster procedure from excerpts of a 737-200 manual posted in an online pilot forum in the wake of the MAX accidents. It is not taught at his airline. Boeing’s assumption was that erroneous stabilizer nose-down inputs by MCAS, such as those experienced by both the JT610 and ET302 crews, would be diagnosed as runaway stabilizer. The checklist to counter runaway stabilizer includes using the cutout switches to de-power the stabilizer trim motor. The ET302 crew followed this, but not until the aircraft was severely out of trim following the MCAS inputs triggered by faulty angle-of-attack (AOA) data that told the system the aircraft’s nose was too high. Unable to move the stabilizer manually, the ET302 crew moved the cutout switches to power the stabilizer trim motors—something the runaway stabilizer checklist states should not be done. While this enabled their column-mounted electric trim input switches, it also re-activated MCAS, which again received the faulty AOA data and trimmed the stabilizer nose down, leading to a fatal dive. The simulator session underscored the importance of reacting quickly to uncommanded stabilizer movements and avoiding a severe out-of-trim condition, one of the pilots involved said. “I don’t think the situation would be survivable at 350 kt. and below 5,000 ft,” this pilot noted. The ET302 crew climbed through 5,000 ft. shortly after de-powering the trim motors, and got to about 8,000 ft.—the same amount of altitude the U.S. crew used up during the roller-coaster maneuvers—before the final dive. A second pilot not involved in the session but who reviewed the scenario’s details said it highlighted several training opportunities. “This is the sort of simulator experience airline crews need to gain an understanding of how runaway trim can make the aircraft very difficult to control, and how important it is to rehearse use of manual trim inputs,” this pilot said. While Boeing’s runaway stabilizer checklist does not specify it, the second pilot recommended a maximum thrust of 75% N1 and a 4 deg. nose-up pitch to keep airspeed under control. Boeing is developing modifications to MCAS, as well as additional training. Simulator sessions are expected to be integrated into recurrent training, and may be required by some regulators, and opted for by some airlines, before pilots are cleared to fly MAXs again. The MAX fleet has been grounded since mid-March, a direct result of the two accidents."
bengoodger 8y ago
Is anyone concerned that even in the face of re-training, that two aircraft could find themselves in this position within the first year of operations? Let's say you were on one of these aircraft and the pilots were able to recover. How terrifying would that be? This is the designed behavior?
argc 8y ago
Would a possible recovery method be to roll the plane somewhat so that when the nose is forced down, it doesn't take the plane directly toward the ground?
- nosianu 8y ago
  No. Now a substantial part of the lift no longer points up because you use it for turning instead. That's why when you turn you have to increase lift (i.e. you pull back a bit, or adjust trim if it's a shallow turn that takes a while to complete) or the nose drops, to compensate for the loss of lift by not using all of it to remain at the original altitude. Remember that unless you have negative or zero g you always have positive lift even with a nose pointed down, so taking away some of it won't help you, you'll just help gravity. You could slow down (forward speed) - if you can, that is. Banking won't help your descend rate all else remaining equal.
- pjc50 8y ago
  You'd need to turn it all the way over, which is likely to upset the passengers.
  - lutorm 8y ago
    Well, I'm sure they'd prefer being upset over being dead... although the likelihood of successfully rolling over and flying a negative-g recovery in a transport airplane seem dubious at best. Transport category airplanes are only certified to -1G so an inverted pullout would definitely exceed those limits.
    - salawat 8y ago
      I believe every teenage flight enthusiast has dreamed of doing this maneuver.
    - rqqt 7y ago
      See Boeing 707 barrel roll by Tex JohnSton.
  - 8y ago
fulafel 8y ago
How do these simulators work? What is the underlying model that gives sim users assurance that the simulated behaviour corresponds to real world aerodynamics and eg engine behaviour?
- QuotedForTruth 8y ago
  There are several levels of "Full Flight Simulators" [1] defined by the FAA: "There are currently four levels of full flight simulator, levels A - D, level D being the highest standard and being eligible for zero flight time (ZFT) training of civil pilots when converting from one airliner type to another." The requirements and process for testing simulators for certification is documented as well [2]. Its not clear from the article exactly what simulator they were using though. [1] https://en.wikipedia.org/wiki/Full_flight_simulator https://en.wikipedia.org/wiki/Full_flight_simulator [2] https://www.faa.gov/about/initiatives/nsp/media/14CFR60_Searchable_Version.pdf https://www.faa.gov/about/initiatives/nsp/media/14CFR60_Sear...
theclaw 8y ago
> The U.S. crew tested this by setting up a 737-Next Generation simulator at 10,000 ft., 250 kt. and 2 deg. nose up stabilizer trim. This is slightly higher altitude but otherwise similar to what the ET302 crew faced as it de-powered the trim motors 3 min. into the 6 min. flight, and about 1 min. after the first uncommanded MCAS input That's not slightly higher, that's a lot higher. The graphs in the preliminary report [0] note that the flight starts at around 7,500 ft. since Addis Ababa Bole International Airport is 7,625 ft. above sea level [1]. Their radar altitude "about 1 min. after the first uncommanded MCAS input" was ~1,000 ft. The highest they got above ground was around 6,500 ft. around 5 mins 30 seconds into the flight. > The excessive descent rates during the first two steps meant the crew got as low as 2,000 ft. during the recovery. If you assume they meant they were 10,000 ft. above sea level in the first quote, then this quote means they'd be 5,625 ft. under ground at their lowest point. [0] http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+B737-800MAX+%2C%28ET-AVJ%29.pdf http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+... [1] https://en.wikipedia.org/wiki/Addis_Ababa_Bole_International_Airport https://en.wikipedia.org/wiki/Addis_Ababa_Bole_International... edit: oops, refs.
- erentz 8y ago
  So if you run into this problem at 7,500’ above ground level you might just be okay. This is why having the ability to disable MCAS without disabling electric assisted trim is so important and such a big factor in this accident. Additionally its raised another possible accident scenario: The runaway trim cutouts were put in place after electric trim in case the switch (or some other aspect of the electric trim) got stuck in an on position that would cause the trim to go to full deflection one direction or the other, hence runaway trim. And hence if you notice this happening you cutout the power to the electric trim completely. But now we know you can’t manually trim the aircraft above certain speeds with some trim levels. Should there be an expectation you can? What if runaway trim happens and ran to full deflection before a pilot cut it out. That would be equivalent to the same conditions experienced in this accident - the pilots now needing to manually trim but being unable to. So on top of needing separate cutouts for the MCAS and electric trim, should the manual trim not be investigated for installing some higher ratio gearing/pulleys to enable over coming the forces experienced here?
Merrill 8y ago
Besides retraining, it seems that there must be upper-body strength tests that 737 MAX pilots will have to pass to ensure that they will be able to manually trim the stabilizer. Are such tests part of flight crew physicals?
- pricechild 8y ago
  Not in Europe at least. Here's the UK's version: https://www.caa.co.uk/Commercial-industry/Pilot-licences/Applications/Medical/Medical-examination-information/ https://www.caa.co.uk/Commercial-industry/Pilot-licences/App... (there's a broken link which should point to https://www.caa.co.uk/Aeromedical-Examiners/Medical-standards/Guidelines-and-resources/Guidance-on-performing-medical-examinations/ https://www.caa.co.uk/Aeromedical-Examiners/Medical-standard... )
- wyldfire 8y ago
  Poe's law 'n all that -- are you serious? I mean, yes, I've seen the video, but presumably it won't be safe to require pilots to execute the manual trim, yeah? IMO either the design is unsafe and must change or there exists a way to safely fly without ever needing manual trim.
  - Merrill 8y ago
    I'm serious. If the final backup system is to revert to mechanical cranks, pulleys, and cables to move the horizontal stabilizer, then the pilots have to be able to exert sufficient torque and power on the control wheels to do so.
zaroth 8y ago
I made the prediction a month ago and I’ll make it again. MCAS won’t ever fly again. I think the plane will fly without MCAS with a new type rating, and where pilots specifically train on the stick feel during a power on stall. They needed the 737 with new engines to fly like the old 737 in order to maintain the type rating and avoid training. Now that they obviously have lost that and require substantial training, I don’t see any reason to keep the system. Some people think the plane is unflyable / inherently unstable without MCAS. I’ve only flown about 15 hours in my life, and a Cessna at that so I’m not qualified to offer an expert opinion. But my intuition is that if that were true, if MCAS was not just a bandaid to maintain a type rating, but rather a safety critical system essential for flightworthiness, it would never have shipped in its current form in the first place. Or rather, the 737 MAX would not have been viable to begin with. If it is the case that 737 MAX is not actually airworthy without a functioning MCAS then Boeing has fucked up an order of magnitude worse than even they appear to have at this point.
- VBprogrammer 8y ago
  Unflyable or unstable isn't nearly the same thing as uncertifiable. People have flown a whole lot of time in uncertifiable aircraft (see the whole experimental aircraft sector) but transport category aircraft are supposed to exhibit as full proof as possible behaviour. I bet you it flies again with MCAS. I'll also bet it flies with barely a few hours of conversion training and that there aren't any accidents directly related to the updated MCAS system.
  - lutorm 8y ago
    This isn't true though, it seems perfectly possible to certificate transport-category airplanes with sketchy stall characteristics, since T-tail planes can end up in unrecoverable situations by blanketing the tail in a stall. Twin-engine planes also are not required to be recoverable from an engine failure at speeds below Vmc. I don't know what the certification requirements are, but it seems they rely on being able to guarantee that you never get below a certain speed since in multi-engine airplanes there's always a low power/high thrust regime that's potentially uncontrollable.
mtw 8y ago
What does this mean for Boeing's responsibility? Is there a case that they were negligent for this plane and partially responsible for the crash?
- mcguire 8y ago
  This is all largely irrelevant until the actual accident reports are finished. Yes, it's possible that Boeing will be partially (or even fully, although I doubt it) responsible.
corey_moncure 8y ago
Kind of sad that they don't report AGL or AMSL along with the elevations here. How is anyone supposed to make sense of this reporting?
VBprogrammer 8y ago
One thing I don't understand is how the pilots can override the operation of the electric trim system by holding the manual trim wheels and yet the electric trim appears to be able to overcome airloads on the jackscrew that the pilots can't. In light aircraft the design of autopilot servos normally includes a clutch so that the pilot can override the servos. But that limits the force that the servo can apply. I guess it could have some kind of torsion sensing system which cuts the power to the trim motor but I've been unable to find this detailed anywhere.
- janoc 8y ago
  Well, the "Stabilizer wheel - grasp and hold" item of the procedure doesn't necessarily mean the crew will be able to override it. That's the last ditch option on the checklist, when everything else has failed, even turning the motors off (there could be e.g. a short circuit powering the motor). There is no clutch on the 737, AFAIK, because the forces are such that it wouldn't work. Here is a good video by an actual 737 captain explaining how the runaway stab trim procedure works and what you have to do. https://www.youtube.com/watch?v=xixM_cwSLcQ https://www.youtube.com/watch?v=xixM_cwSLcQ And this simulator video shows both how the 737 horizontal stabilizer is controlled and what kind of forces are on the trim wheel and control column when severely out of trim: https://www.youtube.com/watch?v=aoNOVlxJmow https://www.youtube.com/watch?v=aoNOVlxJmow Should give you an idea what were the Ethiopian pilots facing when unable to use the electric trim, plane trimmed nose heavy by MCAS and at high speed ...
- lutorm 8y ago
  My impression is that, at least partly, it's a result of the trim wheel being connected through a very long mechanical linkage to the tail, while the motor is right there. The pilots also don't have great mechanical leverage to turn a fairly small wheel in the direction they have to.
- rasz 8y ago
  From what I understand disabling MCAS kills electric trim and leaves you with this https://youtu.be/aoNOVlxJmow?t=11m59s https://youtu.be/aoNOVlxJmow?t=11m59s
fujitzu 8y ago
TLDR; 1: multi billion dollar U.S. aviation company that employs thousands of employees statewide screws up 2: the aviation company offers to send consultants to "help" investigate the cause of the crash, and not falsify or change the narrative of the story in of the African operated flight whatsoever 3: the reputable Airlines that used their plane, decided to do their own untampered investigation and found the aviation company at fault 4: leaks get out via a few ethical employees at the aviation company that the plane was not tested properly and was rushed to market to compete with a rival European aviation company 5: CEO semi apologizes and the company has nightmare of pr
mimixco 8y ago
You can watch the simulation in this video by 60 Minutes Australia: https://m.youtube.com/watch?feature=youtu.be&v=QytfYyHmxtc https://m.youtube.com/watch?feature=youtu.be&v=QytfYyHmxtc
- rasz 8y ago
  do you mean this? https://youtu.be/aoNOVlxJmow?t=11m59s https://youtu.be/aoNOVlxJmow?t=11m59s
uxhacker 8y ago
Link to the forum post explaining how to execute the yo-yo manoeuvre, mentioned in the article. What is interesting was one pilot mentioned that the yo-yo procedure dates all the way back to the 707 for a runaway trim. The 737 was derived from the 707 and 727. The 707 was the first Jet Airliner. Edited for links : referance to 737-200 Manuel https://www.pprune.org/tech-log/619326-boeing-advice-aerodynamically-relieving-airloads-using-manual-stabilizer-trim.html#post10414805 https://www.pprune.org/tech-log/619326-boeing-advice-aerodyn... https://www.pprune.org/tech-log/619326-boeing-advice-aerodynamically-relieving-airloads-using-manual-stabilizer-trim.html https://www.pprune.org/tech-log/619326-boeing-advice-aerodyn...
- pmyteh 8y ago
  A little pedantic, but: the 707 was one of the first jet airliners. Britain's de Havilland Comet beat it into service by six years, and the Soviet Union's Tupolev Tu-104 by two.
- dingaling 8y ago
  The 707 is interesting as the UK air Registration Board refused to certify it in its original form. It had insufficient rudder authority in the case of certain engine-out scenarios because Boeing hadn't implemented full rudder boost, and the pilots therefore couldn't overcome yaw. That had killed two crews in training. In order to save the big BOAC order Boeing had to fit full boost and a tail strake, which they quietly adopted for all subsequent 707s Then there was the 727 that had four fatal crashes within six months of entering service, which was put down to inadequate training. But it was later found that the high fatality rate was because Boeing had routed fuel lines along the belly, which severed in a hard landing and caused immediate fires. And they severed easily because bizarrely they were aluminium, in order to bring the weight within target...
wiremine 8y ago
This is slightly off topic, but I read write ups like this and wonder how flight simulators like this work. Do they have to program in the details of the accident, or is it just a standard Max 737 simulator?
- tk75x 8y ago
  In flight simulators, every aspect of the environment is able to be controlled by the user. Programming in the details of the accident involves setting up the same conditions as were present during the accident including altitude, airspeed, etc. Then the user/instructor would activate specific malfunctions that will cause the plane to behave like it did during the accident. Now the pilot is, for all intents and purposes, flying the same plane in the same conditions that the pilots were during the accident.
Animats 8y ago
The 777 and 787 are full fly by wire. The control system has all the sensor inputs, all the actuator outputs, and a model of how the aircraft is supposed to behave. If the aircraft isn't doing what's expected, the flight control system will fault and drop to a dumber control mode, giving the pilot more control rather than driving control surfaces to their limits trying to correct the wrong problem. Those systems are managing trim, like MCAS, plus a lot more.[1] MCAS is dumb. It has few inputs and one output. It has no overall model of aircraft behavior. It just detects a bad angle of attack and cranks the trim to bring the nose down. The 777 is supposed to handle like a 737. The cockpit controls are reasonably similar, although different enough that transition training is required. Unfortunately, there's no "small 777", a gap in Boeing's product line the 737 Max was supposed to fill. (Or small 757, 767, or 787 variants. How did they go half a century without a new sub-200 seat aircraft?) [1] https://www.linkedin.com/pulse/analysis-boeing-777-fly-by-wire-system-jaime-beneyto-g%C3%B3mez-de-barreda https://www.linkedin.com/pulse/analysis-boeing-777-fly-by-wi...
bayareanative 8y ago
This focus on MCAS only is tantamount to a red-herring because there are many more changes to the 737 NG and MAX that the FAA allowed with little or no oversight. The absurdly-crude Ducommun critical structural parts debacle gained almost no media attention in 2010, and several people have died due to fuselages breaking-up in runway overruns and hard landings where previous and similar aircraft maintained fuselage integrity. 737 NG, MAX, 787 and all other Boeing aircraft developed in the past 25 years need to be seriously reexamined for safety risks and deficiencies.
bayareanative 8y ago
Mentour Pilot's channel: https://www.youtube.com/channel/UCwpHKudUkP5tNgmMdexB3ow https://www.youtube.com/channel/UCwpHKudUkP5tNgmMdexB3ow

194 points by inferiorhuman 8y ago

> and underscores the importance of pilots understanding severe runaway trim recovery procedures. So we're back to blaming the pilots?

pageandrew 8y ago
There were pilot crews that were able to successfully fend off MCAS's murderous tendencies, and there were pilot crews that were not. Ignoring this learning opportunity for better general pilot education would be a mistake. Pilots being better trained is always a good thing.
- jfk13 8y ago
  IIUC, those who did overcome the problem in the simulator lost around 8,000 feet of altitude in the process (despite presumably going into the simulator already knowing what they were going to be facing). It's not clear to me that the Ethiopian plane ever had enough altitude (above the ground) to allow for such a recovery.
  - cjbprime 8y ago
    If I recall, it did stay at around 12k altitude for a stable period of flight where MCAS was being successfully neutralized. It's in the Ethiopian report. The airspeed was way above limit, though, which would make everything harder, including the manual retrimming.
    - bronson 8y ago
      Remember that they left an airport about 7000 feet up and headed over mountains. It's unlikely the plane was ever more than a few thousand feet above ground level. Page 26 in Ethiopia's report: https://fearoflanding.com/files/2019/04/Preliminary-Report-B737-800MAX-ET-AVJ.pdf https://fearoflanding.com/files/2019/04/Preliminary-Report-B...
      - cjbprime 8y ago
        Thanks, I'd forgotten the numbers. They aren't quite as bad as you say. The Ethiopian report shows their radar elevation around 14k feet before the descent, so it seems they made it to around 7k feet AGL for a few minutes. Not enough to be able to give up 8k feet during a recovery, I agree.
d1str0 8y ago
Nobody is saying that. That’s not even what this out of context quote is saying.
jfk13 8y ago
Sounds more like we're blaming the manufacturer for concealing the fact that pilots needed to be specifically (re-)trained for this plane if they were to have a chance of handling it successfully.
- blunte 8y ago
  Exactly. But such training should not be necessary because this problem was created by Boeing. Pilots really should have extensive emergency training, but that doesn't mean it's ok for the manufacturer to Add a new failure case to a previously fine aircraft.
  - olliej 8y ago
    [edit: leaving this here because I wrote so much :D I totally misread/interpreted the comment I was replying to, and am entirely in agreement :D ] In this case the "fix" is called the "roller coaster", but Boeing has removed the documentation regarding this from the manuals - specifically the Pilots could have 100% perfect recall of the entire 737-MAX documentation and it wouldn't have helped. This is 100% Boeing's responsibility: * They designed a system that overrode pilot control so that they could avoid a requirement to retrain pilots. MCAS existed specifically to maintain the perception of identical flight behaviour entirely to avoid the need for recertification and training. That is the only reason MCAS existed. * They had minimal (no?) documentation indicating it existed * They made a warning system to report that the system was faulty - literally they shipped a broken safety system: the warning was intended to be freely available, but it was incorrectly tied to a costly system, so even though it was meant to be a standard feature, it was not present. * The recommended recovery technique from their documentation was not physically possible, even when you knew exactly what you were meant to do. * The only technique to recover - the roller coaster - had been deliberately removed from the training and flight manuals. The pilots who managed to recover were only able to recover because they knew of the "solution" from old manuals that were published online after both crashes had occurred, by some non-Boeing website. Even then the pilots in the article said that they didn't believe it would be possible to recover once you got below 5000 feet. Now, exactly how was this in any way the pilot's fault? They were fully trained, they had clearly read the manuals provided by Boeing (they knew they were mean to be using the manual wheel thing), the warning system was non-functional due to a construction/software error in Boeing's control software, etc.
daveguy 8y ago
That's pretty much the opposite, right? That the pilots would need to know an extreme emergency procedure. In other words you'd need a Sully level pilot to survive (and unsurvivable below a certain speed and height). If you ask me that's a damning indictment when a flawed autopilot results in a state like that.
- namirez 8y ago
  Except Sully actually screwed up and put the passengers life in danger by trying to land on water and rather than returning to the airport. https://www.cbsnews.com/news/ntsb-sully-could-have-made-it-back-to-laguardia/ https://www.cbsnews.com/news/ntsb-sully-could-have-made-it-b...
  - cjbprime 8y ago
    I don't know how you could read the article you linked and come away with that conclusion.
  - YokoZar 8y ago
    The link you included says the opposite of what you're implying. > under the circumstances the captain's decision to ditch into the Hudson River was the better choice, documents released Tuesday by a federal safety panel said > He also would have had no way of knowing that he would be successful, and therefore would have been risking the possibility of a catastrophic crash in a densely populated area.
  - Someone1234 8y ago
    This was disproven. And is a major plot point in the movie about Flight 1549 (Sully). From Wikipedia: > The NTSB used flight simulators to test the possibility that the flight could have returned safely to LaGuardia or diverted to Teterboro; only seven of the thirteen simulated returns to La Guardia succeeded, and only one of the two to Teterboro. > Furthermore, the NTSB report called these simulations unrealistic: "The immediate turn made by the pilots during the simulations did not reflect or account for real-world considerations, such as the time delay required to recognize the bird strike and decide on a course of action." A further simulation, in which a 35-second delay was inserted to allow for those, crashed.
salawat 8y ago
No, we're back to, "why the heck didn't Boeing honor the regulatory requirement for simulator training, and tell American it was the best you could do?" Clearly, the condition is recoverable, with simulator training. Throw in a triple redundant AoA sensor on top of the training, plus the inclusion of MCAS implementation details in the training material, and things would likely have had a much higher chance of being dealt with without loss of life. Would Boeing have had a harder sell? Yes. Would there have been a non-zero chance of losing out on the order? Yes. Would 300+ people currently be pulp? I think not. I have a great deal of respect for the skill pilots develop. They are only human however, and are therefore subject to the same weakness of not being omniscient. If MCAS was the bullet, Boeing's opaque communication, and refusal to not game aviation certification regulations was the gun. Of that, I'm fairly certain. What plays the trigger pull in this sordid affair is the last thing that remains to be declared, but there are some seriously bright neon signs pointing at either somewhere in Chicago, or at the culture as a whole at Boeing. Let the digging continue. Let's see how deep the rabbit hole goes.
- blunte 8y ago
  TFA said it was likely not recoverable under 5000 AGL.
  - deleted 8y ago
    [deleted]
  - salawat 8y ago
    Didn't read the entire thing. Going to register later. I actually wonder whether anyone with access to the simulator has tried pulsing the trim switches in sub 4 second intervals. Which depending on how the trim switches work, (I.e. are they continuously coupled, or do they act by moving around a discrete set-point) might be able to fend off MCAS by constantly resetting the time until reactivation long enough to give the trim system time to neutralize. If something like that were done, a recovery below 5000AGL may be possible. It's not by a long shot the most intuitive approach out there, and it doesn't generalize well, but for the specific MCAS behavior that's been revealed it may work. (If there's any 737 pilots out there with insight, I'd be giddy if you'd offer some perspective.)

deleted 8y ago

[deleted]

virtuexru 8y ago

Article is behind a paywall unfortunately. Any help? :)

bxio 8y ago
Registration wall and the ol' HN Hug of Death, not a good combination.
jfk13 8y ago
AFAICS it's a registration-wall, not actually a pay-wall.
- newnewpdro 8y ago
  Isn't this just splitting hairs over which currency is paid?
amluto 8y ago
This might be the same article: https://theworldnews.net/us-news/ethiopian-max-crash-simulator-scenario-stuns-pilots https://theworldnews.net/us-news/ethiopian-max-crash-simulat... The original link seems dead. edit: nope, my link is no good either.
- Animats 8y ago
  Is there video of the simulation?
  - mimixco 8y ago
    Yes. Here: https://m.youtube.com/watch?feature=youtu.be&v=QytfYyHmxtc https://m.youtube.com/watch?feature=youtu.be&v=QytfYyHmxtc
simcop2387 8y ago
Found a forum thread about it from some aviation enthusiasts [1]. Some choice excerpts they made: ‘A simulator session flown by a U.S.-based Boeing 737 MAX crew that mimicked a key portion of the Flight 302 accident sequence suggests that the crew faced a near-impossible task of getting their 737 MAX back under control, and underscores the importance of pilots understanding severe runaway trim recovery procedures.’ ‘What the U.S. crew found -. Keeping the aircraft level required significant aft-column pressure by the captain, and aerodynamic forces prevented the first officer from moving the trim wheel a full turn. They resorted to a little-known procedure to regain control.’ (YoYo Roller Coaster) The excessive descent rates during the first two steps meant the crew got as low as 2,000 ft. during the recovery. ... ‘The simulator session underscored the importance of reacting quickly to uncommanded stabilizer movements and avoiding a severe out-of-trim condition, one of the pilots involved said. “I donʼt think the situation would be survivable at 350 kt. and below 5,000 ft,” this pilot noted.’ “This is the sort of simulator experience airline crews need to gain an understanding of how runaway trim can make the aircraft very difficult to control, and how important it is to rehearse use of manual trim inputs,” [1] https://www.pprune.org/rumours-news/621478-ethiopian-max-crash-simulator-scenario-stuns-pilots.html https://www.pprune.org/rumours-news/621478-ethiopian-max-cra...

danols 8y ago

I am not very concerned with this particular problem anymore since it will get a satisfactory solution due to its publicity. What I am worried about and think should get more focus is other potential issues and corners that has been cut by the Boeing management. I have note read a single thing that Boeing has handled well in this massive disaster. This lack of judgement, short term profit seeking & cover up mentality is what media should spend more time on. It feels to me that they used up a lot of their trust capital to be allowed to perform any type of self-certification

adreamingsoul 8y ago
That is also expected in our Capitalistic system. Greed, profit, and share-holder value is often more important then the end-user. Boeing is not the only company that subscribes to that religion.
- geff82 8y ago
  I doubt that in a non-capitalistic system the 737 MAX would not have had similar problems as in no system resources are infinite. Budgets, even in the most socialist country, are limited. The question is just WHO limits the budget: private enterprises (or their shareholders), co-ops or politicians.
  - adreamingsoul 8y ago
    Appreciate the feedback!
  - objektif 8y ago
    How is this a resource problem particularly. Airbus a coporation from the land of semi-socialist countries have similiar reaoirce constraints.
- chimpburger 8y ago
  Psychopaths in leadership/management create problems in all economic systems. Don't blame capitalism. Evil people are evil. There are good people at Boeing but psychopaths have a natural ability to gain power in all kinds of social structures.

mcyukon 8y ago

"WASHINGTON—A simulator session flown by a U.S.-based Boeing 737 MAX crew that mimicked a key portion of the Ethiopian Airlines Flight 302 (ET302) accident sequence suggests that the Ethiopian crew faced a near-impossible task of getting their 737 MAX 8 back under control, and underscores the importance of pilots understanding severe runaway trim recovery procedures. Details of the session, shared with Aviation Week, were flown voluntarily as part of routine, recurrent training. Its purpose: practice recovering from a scenario in which the aircraft was out of trim and wanting to descend while flying at a high rate of speed. This is what the ET302 crew faced when it toggled cutout switches to de-power the MAX’s automatic stabilizer trim motor, disabling the maneuvering characteristics augmentation system (MCAS) that was erroneously trimming the horizontal stabilizer nose-down. In such a scenario, once the trim motor is de-powered, the pilots must use the hand-operated manual trim wheels to adjust the stabilizers. But they also must keep the aircraft from descending by pulling back on the control columns to deflect the elevator portions of the stabilizer upward. Aerodynamic forces from the nose-up elevator deflection make the entire stabilizer more difficult to move, and higher airspeed exacerbates the issue. The U.S. crew tested this by setting up a 737-Next Generation simulator at 10,000 ft., 250 kt. and 2 deg. nose up stabilizer trim. This is slightly higher altitude but otherwise similar to what the ET302 crew faced as it de-powered the trim motors 3 min. into the 6 min. flight, and about 1 min. after the first uncommanded MCAS input. Leading up to the scenario, the Ethiopian crew used column-mounted manual electric trim to counter some of the MCAS inputs, but did not get the aircraft back to level trim, as the 737 manual instructs before de-powering the stabilizer trim motor. The crew also did not reduce their unusually high speed. What the U.S. crew found was eye-opening. Keeping the aircraft level required significant aft-column pressure by the captain, and aerodynamic forces prevented the first officer from moving the trim wheel a full turn. They resorted to a little-known procedure to regain control. The crew repeatedly executed a three-step process known as the roller coaster. First, let the aircraft’s nose drop, removing elevator nose-down force. Second, crank the trim wheel, inputting nose-up stabilizer, as the aircraft descends. Third, pull back on the yokes to raise the nose and slow the descent. The excessive descent rates during the first two steps meant the crew got as low as 2,000 ft. during the recovery. The Ethiopian Ministry of Transport preliminary report on the Mar. 10 ET302 accident suggests the crew attempted to use manual trim after de-powering the stabilizer motors, but determined it “was not working,” the report said. A constant trust setting at 94% N1 meant ET302’s airspeed increased to the 737 MAX’s maximum (Vmo), 340 kt., soon after the stabilizer trim motors were cut off, and did not drop below that level for the remainder of the flight. The pilots, struggling to keep the aircraft from descending, also maintained steady to strong aft control-column inputs from the time MCAS first fired through the end of the flight. The U.S. crew’s session and a video posted recently by YouTube’s Mentour Pilot that shows a similar scenario inside a simulator suggest that the resulting forces on ET302’s stabilizer would have made it nearly impossible to move by hand. Neither the current 737 flight manual nor any MCAS-related guidance issued by Boeing in the wake of the October 2018 crash of Lion Air Flight 610 (JT610), when MCAS first came to light for most pilots, discuss the roller-coaster procedure for recovering from severe out-of-trim conditions. The 737 manual explains that “effort required to manually rotate the stabilizer trim wheels may be higher under certain flight conditions,” but does not provide details. The pilot who shared the scenario said he learned the roller coaster procedure from excerpts of a 737-200 manual posted in an online pilot forum in the wake of the MAX accidents. It is not taught at his airline. Boeing’s assumption was that erroneous stabilizer nose-down inputs by MCAS, such as those experienced by both the JT610 and ET302 crews, would be diagnosed as runaway stabilizer. The checklist to counter runaway stabilizer includes using the cutout switches to de-power the stabilizer trim motor. The ET302 crew followed this, but not until the aircraft was severely out of trim following the MCAS inputs triggered by faulty angle-of-attack (AOA) data that told the system the aircraft’s nose was too high. Unable to move the stabilizer manually, the ET302 crew moved the cutout switches to power the stabilizer trim motors—something the runaway stabilizer checklist states should not be done. While this enabled their column-mounted electric trim input switches, it also re-activated MCAS, which again received the faulty AOA data and trimmed the stabilizer nose down, leading to a fatal dive. The simulator session underscored the importance of reacting quickly to uncommanded stabilizer movements and avoiding a severe out-of-trim condition, one of the pilots involved said. “I don’t think the situation would be survivable at 350 kt. and below 5,000 ft,” this pilot noted. The ET302 crew climbed through 5,000 ft. shortly after de-powering the trim motors, and got to about 8,000 ft.—the same amount of altitude the U.S. crew used up during the roller-coaster maneuvers—before the final dive. A second pilot not involved in the session but who reviewed the scenario’s details said it highlighted several training opportunities. “This is the sort of simulator experience airline crews need to gain an understanding of how runaway trim can make the aircraft very difficult to control, and how important it is to rehearse use of manual trim inputs,” this pilot said. While Boeing’s runaway stabilizer checklist does not specify it, the second pilot recommended a maximum thrust of 75% N1 and a 4 deg. nose-up pitch to keep airspeed under control. Boeing is developing modifications to MCAS, as well as additional training. Simulator sessions are expected to be integrated into recurrent training, and may be required by some regulators, and opted for by some airlines, before pilots are cleared to fly MAXs again. The MAX fleet has been grounded since mid-March, a direct result of the two accidents."

bengoodger 8y ago

Is anyone concerned that even in the face of re-training, that two aircraft could find themselves in this position within the first year of operations? Let's say you were on one of these aircraft and the pilots were able to recover. How terrifying would that be? This is the designed behavior?

argc 8y ago

Would a possible recovery method be to roll the plane somewhat so that when the nose is forced down, it doesn't take the plane directly toward the ground?

nosianu 8y ago
No. Now a substantial part of the lift no longer points up because you use it for turning instead. That's why when you turn you have to increase lift (i.e. you pull back a bit, or adjust trim if it's a shallow turn that takes a while to complete) or the nose drops, to compensate for the loss of lift by not using all of it to remain at the original altitude. Remember that unless you have negative or zero g you always have positive lift even with a nose pointed down, so taking away some of it won't help you, you'll just help gravity. You could slow down (forward speed) - if you can, that is. Banking won't help your descend rate all else remaining equal.
pjc50 8y ago
You'd need to turn it all the way over, which is likely to upset the passengers.
- lutorm 8y ago
  Well, I'm sure they'd prefer being upset over being dead... although the likelihood of successfully rolling over and flying a negative-g recovery in a transport airplane seem dubious at best. Transport category airplanes are only certified to -1G so an inverted pullout would definitely exceed those limits.
  - salawat 8y ago
    I believe every teenage flight enthusiast has dreamed of doing this maneuver.
  - rqqt 7y ago
    See Boeing 707 barrel roll by Tex JohnSton.
- 8y ago

fulafel 8y ago

How do these simulators work? What is the underlying model that gives sim users assurance that the simulated behaviour corresponds to real world aerodynamics and eg engine behaviour?

QuotedForTruth 8y ago
There are several levels of "Full Flight Simulators" [1] defined by the FAA: "There are currently four levels of full flight simulator, levels A - D, level D being the highest standard and being eligible for zero flight time (ZFT) training of civil pilots when converting from one airliner type to another." The requirements and process for testing simulators for certification is documented as well [2]. Its not clear from the article exactly what simulator they were using though. [1] https://en.wikipedia.org/wiki/Full_flight_simulator https://en.wikipedia.org/wiki/Full_flight_simulator [2] https://www.faa.gov/about/initiatives/nsp/media/14CFR60_Searchable_Version.pdf https://www.faa.gov/about/initiatives/nsp/media/14CFR60_Sear...

theclaw 8y ago

> The U.S. crew tested this by setting up a 737-Next Generation simulator at 10,000 ft., 250 kt. and 2 deg. nose up stabilizer trim. This is slightly higher altitude but otherwise similar to what the ET302 crew faced as it de-powered the trim motors 3 min. into the 6 min. flight, and about 1 min. after the first uncommanded MCAS input That's not slightly higher, that's a lot higher. The graphs in the preliminary report [0] note that the flight starts at around 7,500 ft. since Addis Ababa Bole International Airport is 7,625 ft. above sea level [1]. Their radar altitude "about 1 min. after the first uncommanded MCAS input" was ~1,000 ft. The highest they got above ground was around 6,500 ft. around 5 mins 30 seconds into the flight. > The excessive descent rates during the first two steps meant the crew got as low as 2,000 ft. during the recovery. If you assume they meant they were 10,000 ft. above sea level in the first quote, then this quote means they'd be 5,625 ft. under ground at their lowest point. [0] http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+B737-800MAX+%2C%28ET-AVJ%29.pdf http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+... [1] https://en.wikipedia.org/wiki/Addis_Ababa_Bole_International_Airport https://en.wikipedia.org/wiki/Addis_Ababa_Bole_International... edit: oops, refs.

erentz 8y ago
So if you run into this problem at 7,500’ above ground level you might just be okay. This is why having the ability to disable MCAS without disabling electric assisted trim is so important and such a big factor in this accident. Additionally its raised another possible accident scenario: The runaway trim cutouts were put in place after electric trim in case the switch (or some other aspect of the electric trim) got stuck in an on position that would cause the trim to go to full deflection one direction or the other, hence runaway trim. And hence if you notice this happening you cutout the power to the electric trim completely. But now we know you can’t manually trim the aircraft above certain speeds with some trim levels. Should there be an expectation you can? What if runaway trim happens and ran to full deflection before a pilot cut it out. That would be equivalent to the same conditions experienced in this accident - the pilots now needing to manually trim but being unable to. So on top of needing separate cutouts for the MCAS and electric trim, should the manual trim not be investigated for installing some higher ratio gearing/pulleys to enable over coming the forces experienced here?

Merrill 8y ago

Besides retraining, it seems that there must be upper-body strength tests that 737 MAX pilots will have to pass to ensure that they will be able to manually trim the stabilizer. Are such tests part of flight crew physicals?

pricechild 8y ago
Not in Europe at least. Here's the UK's version: https://www.caa.co.uk/Commercial-industry/Pilot-licences/Applications/Medical/Medical-examination-information/ https://www.caa.co.uk/Commercial-industry/Pilot-licences/App... (there's a broken link which should point to https://www.caa.co.uk/Aeromedical-Examiners/Medical-standards/Guidelines-and-resources/Guidance-on-performing-medical-examinations/ https://www.caa.co.uk/Aeromedical-Examiners/Medical-standard... )
wyldfire 8y ago
Poe's law 'n all that -- are you serious? I mean, yes, I've seen the video, but presumably it won't be safe to require pilots to execute the manual trim, yeah? IMO either the design is unsafe and must change or there exists a way to safely fly without ever needing manual trim.
- Merrill 8y ago
  I'm serious. If the final backup system is to revert to mechanical cranks, pulleys, and cables to move the horizontal stabilizer, then the pilots have to be able to exert sufficient torque and power on the control wheels to do so.

zaroth 8y ago

I made the prediction a month ago and I’ll make it again. MCAS won’t ever fly again. I think the plane will fly without MCAS with a new type rating, and where pilots specifically train on the stick feel during a power on stall. They needed the 737 with new engines to fly like the old 737 in order to maintain the type rating and avoid training. Now that they obviously have lost that and require substantial training, I don’t see any reason to keep the system. Some people think the plane is unflyable / inherently unstable without MCAS. I’ve only flown about 15 hours in my life, and a Cessna at that so I’m not qualified to offer an expert opinion. But my intuition is that if that were true, if MCAS was not just a bandaid to maintain a type rating, but rather a safety critical system essential for flightworthiness, it would never have shipped in its current form in the first place. Or rather, the 737 MAX would not have been viable to begin with. If it is the case that 737 MAX is not actually airworthy without a functioning MCAS then Boeing has fucked up an order of magnitude worse than even they appear to have at this point.

VBprogrammer 8y ago
Unflyable or unstable isn't nearly the same thing as uncertifiable. People have flown a whole lot of time in uncertifiable aircraft (see the whole experimental aircraft sector) but transport category aircraft are supposed to exhibit as full proof as possible behaviour. I bet you it flies again with MCAS. I'll also bet it flies with barely a few hours of conversion training and that there aren't any accidents directly related to the updated MCAS system.
- lutorm 8y ago
  This isn't true though, it seems perfectly possible to certificate transport-category airplanes with sketchy stall characteristics, since T-tail planes can end up in unrecoverable situations by blanketing the tail in a stall. Twin-engine planes also are not required to be recoverable from an engine failure at speeds below Vmc. I don't know what the certification requirements are, but it seems they rely on being able to guarantee that you never get below a certain speed since in multi-engine airplanes there's always a low power/high thrust regime that's potentially uncontrollable.

mtw 8y ago

What does this mean for Boeing's responsibility? Is there a case that they were negligent for this plane and partially responsible for the crash?

mcguire 8y ago
This is all largely irrelevant until the actual accident reports are finished. Yes, it's possible that Boeing will be partially (or even fully, although I doubt it) responsible.

corey_moncure 8y ago

Kind of sad that they don't report AGL or AMSL along with the elevations here. How is anyone supposed to make sense of this reporting?

VBprogrammer 8y ago

One thing I don't understand is how the pilots can override the operation of the electric trim system by holding the manual trim wheels and yet the electric trim appears to be able to overcome airloads on the jackscrew that the pilots can't. In light aircraft the design of autopilot servos normally includes a clutch so that the pilot can override the servos. But that limits the force that the servo can apply. I guess it could have some kind of torsion sensing system which cuts the power to the trim motor but I've been unable to find this detailed anywhere.

janoc 8y ago
Well, the "Stabilizer wheel - grasp and hold" item of the procedure doesn't necessarily mean the crew will be able to override it. That's the last ditch option on the checklist, when everything else has failed, even turning the motors off (there could be e.g. a short circuit powering the motor). There is no clutch on the 737, AFAIK, because the forces are such that it wouldn't work. Here is a good video by an actual 737 captain explaining how the runaway stab trim procedure works and what you have to do. https://www.youtube.com/watch?v=xixM_cwSLcQ https://www.youtube.com/watch?v=xixM_cwSLcQ And this simulator video shows both how the 737 horizontal stabilizer is controlled and what kind of forces are on the trim wheel and control column when severely out of trim: https://www.youtube.com/watch?v=aoNOVlxJmow https://www.youtube.com/watch?v=aoNOVlxJmow Should give you an idea what were the Ethiopian pilots facing when unable to use the electric trim, plane trimmed nose heavy by MCAS and at high speed ...
lutorm 8y ago
My impression is that, at least partly, it's a result of the trim wheel being connected through a very long mechanical linkage to the tail, while the motor is right there. The pilots also don't have great mechanical leverage to turn a fairly small wheel in the direction they have to.
rasz 8y ago
From what I understand disabling MCAS kills electric trim and leaves you with this https://youtu.be/aoNOVlxJmow?t=11m59s https://youtu.be/aoNOVlxJmow?t=11m59s

fujitzu 8y ago

TLDR; 1: multi billion dollar U.S. aviation company that employs thousands of employees statewide screws up 2: the aviation company offers to send consultants to "help" investigate the cause of the crash, and not falsify or change the narrative of the story in of the African operated flight whatsoever 3: the reputable Airlines that used their plane, decided to do their own untampered investigation and found the aviation company at fault 4: leaks get out via a few ethical employees at the aviation company that the plane was not tested properly and was rushed to market to compete with a rival European aviation company 5: CEO semi apologizes and the company has nightmare of pr

mimixco 8y ago

You can watch the simulation in this video by 60 Minutes Australia: https://m.youtube.com/watch?feature=youtu.be&v=QytfYyHmxtc https://m.youtube.com/watch?feature=youtu.be&v=QytfYyHmxtc

rasz 8y ago
do you mean this? https://youtu.be/aoNOVlxJmow?t=11m59s https://youtu.be/aoNOVlxJmow?t=11m59s

uxhacker 8y ago

Link to the forum post explaining how to execute the yo-yo manoeuvre, mentioned in the article. What is interesting was one pilot mentioned that the yo-yo procedure dates all the way back to the 707 for a runaway trim. The 737 was derived from the 707 and 727. The 707 was the first Jet Airliner. Edited for links : referance to 737-200 Manuel https://www.pprune.org/tech-log/619326-boeing-advice-aerodynamically-relieving-airloads-using-manual-stabilizer-trim.html#post10414805 https://www.pprune.org/tech-log/619326-boeing-advice-aerodyn... https://www.pprune.org/tech-log/619326-boeing-advice-aerodynamically-relieving-airloads-using-manual-stabilizer-trim.html https://www.pprune.org/tech-log/619326-boeing-advice-aerodyn...

pmyteh 8y ago
A little pedantic, but: the 707 was one of the first jet airliners. Britain's de Havilland Comet beat it into service by six years, and the Soviet Union's Tupolev Tu-104 by two.
dingaling 8y ago
The 707 is interesting as the UK air Registration Board refused to certify it in its original form. It had insufficient rudder authority in the case of certain engine-out scenarios because Boeing hadn't implemented full rudder boost, and the pilots therefore couldn't overcome yaw. That had killed two crews in training. In order to save the big BOAC order Boeing had to fit full boost and a tail strake, which they quietly adopted for all subsequent 707s Then there was the 727 that had four fatal crashes within six months of entering service, which was put down to inadequate training. But it was later found that the high fatality rate was because Boeing had routed fuel lines along the belly, which severed in a hard landing and caused immediate fires. And they severed easily because bizarrely they were aluminium, in order to bring the weight within target...

wiremine 8y ago

This is slightly off topic, but I read write ups like this and wonder how flight simulators like this work. Do they have to program in the details of the accident, or is it just a standard Max 737 simulator?

tk75x 8y ago
In flight simulators, every aspect of the environment is able to be controlled by the user. Programming in the details of the accident involves setting up the same conditions as were present during the accident including altitude, airspeed, etc. Then the user/instructor would activate specific malfunctions that will cause the plane to behave like it did during the accident. Now the pilot is, for all intents and purposes, flying the same plane in the same conditions that the pilots were during the accident.

Animats 8y ago

The 777 and 787 are full fly by wire. The control system has all the sensor inputs, all the actuator outputs, and a model of how the aircraft is supposed to behave. If the aircraft isn't doing what's expected, the flight control system will fault and drop to a dumber control mode, giving the pilot more control rather than driving control surfaces to their limits trying to correct the wrong problem. Those systems are managing trim, like MCAS, plus a lot more.[1] MCAS is dumb. It has few inputs and one output. It has no overall model of aircraft behavior. It just detects a bad angle of attack and cranks the trim to bring the nose down. The 777 is supposed to handle like a 737. The cockpit controls are reasonably similar, although different enough that transition training is required. Unfortunately, there's no "small 777", a gap in Boeing's product line the 737 Max was supposed to fill. (Or small 757, 767, or 787 variants. How did they go half a century without a new sub-200 seat aircraft?) [1] https://www.linkedin.com/pulse/analysis-boeing-777-fly-by-wire-system-jaime-beneyto-g%C3%B3mez-de-barreda https://www.linkedin.com/pulse/analysis-boeing-777-fly-by-wi...

bayareanative 8y ago

This focus on MCAS only is tantamount to a red-herring because there are many more changes to the 737 NG and MAX that the FAA allowed with little or no oversight. The absurdly-crude Ducommun critical structural parts debacle gained almost no media attention in 2010, and several people have died due to fuselages breaking-up in runway overruns and hard landings where previous and similar aircraft maintained fuselage integrity. 737 NG, MAX, 787 and all other Boeing aircraft developed in the past 25 years need to be seriously reexamined for safety risks and deficiencies.

bayareanative 8y ago

Mentour Pilot's channel: https://www.youtube.com/channel/UCwpHKudUkP5tNgmMdexB3ow https://www.youtube.com/channel/UCwpHKudUkP5tNgmMdexB3ow