11 ms·

Boeing 737 Max Simulators Are in High Demand, But Flawed

136 points by howard941 7y ago

tlb 7y ago
How would you accurately simulate the force needed to turn the trim wheel under aerodynamic loads that vary with elevator position? It sounds like a very tricky mechanical setup.
- krallja 7y ago
  Brakes, or a strong motor.
  - jayalpha 7y ago
    crank handle with a translation?
  - dbcurtis 7y ago
    The way I would approach it (based on mechantronics I have done for robots) is to back up the control wheel with an encoded motor. (Position/rotation encoder on the tail shaft.) The encoder will give you wheel position, the motor allows you to apply arbitrary torque to the wheel to simulate the feedback forces felt by the pilot. Typically, that would be done by measuring motor current and writing a control loop that controlled for target wheel position (based on encoder) and target maximum motor current (as a proxy for torque). Then the simulator would give out the simulated results of wheel position and torque, which the control loop would attempt to follow with its control law. Alternatively, you could put an actual torque sensor between the motor and the control wheel, which might buy you some accuracy at considerably more expense. For a flight simulator, expense is unlikely to be an issue -- I tend not to have that luxury, and typically don't need that much accuracy anyway. These kind of control systems are all over modern aircraft, much less simulators. Any new grad control systems engineer should be able to knock something like this out.
    - blattimwind 7y ago
      > The way I would approach it (based on mechantronics I have done for robots) is to back up the control wheel with an encoded motor. (Position/rotation encoder on the tail shaft.) The encoder will give you wheel position, the motor allows you to apply arbitrary torque to the wheel to simulate the feedback forces felt by the pilot. Typically, that would be done by measuring motor current and writing a control loop that controlled for target wheel position (based on encoder) and target maximum motor current (as a proxy for torque). Then the simulator would give out the simulated results of wheel position and torque, which the control loop would attempt to follow with its control law. Or you just buy a COTS servo that does all that for you. Just saying, hardly a need to reinvent these particular wheels...
      - dbcurtis 7y ago
        Yeah, good point. I'm sure there are servos that have the required specs. I'm just not in the habit of looking at catalogs where the prices are that high :) Maybe I should switch to building flight simulators so that I can order the good stuff :)
        rasz 7y ago
        racing sim guys already figured it out http://opensimwheel.wikidot.com/ http://opensimwheel.wikidot.com/
- mikeash 7y ago
  The mechanical part seems easy enough. Tricky to calculate the appropriate force, but I’m sure the aerodynamics people are more than up to the task.
- ackfoo 7y ago
  No need to do so. The aerodynamic forces on the manual trim wheel on Ethiopia 302 were excessive because they were flying about 50kts overspeed. The simulator is not supposed to teach what it feels like to fly the plane when it is so far outside of its certified flight envelope that even test pilots have not been there. Instead, the simulator is supposed to teach you how to fly the plane and respond to emergencies so that the aircraft does not depart from the flight envelope to the point where a single failure or control input will cause a crash. Simulating the sensations of flying the 737 Max upside-down would also require a tricky mechanical setup, but no one feels that such a thing is necessary or appropriate. Natalie Kitroeff is the chief anti-Boeing cheerleader at NYT. She has a bachelor in International Affairs from Princeton. I can see no evidence that she has a technical degree, or enough understanding of aerodynamics or any other technical matter to comment on whether someone fixed the drip in her kitchen sink properly. She is the poster child for post-facts non-technical journalism. The facts of Ethiopian 302 are abundantly clear from the preliminary report: a single component, the AOA sensor, failed causing a common and easily-remedied runaway electric trim condition for which there was a clear and comprehensive memory checklist that, had it been followed, would have resolved this problem without even the slightest inconvenience to passengers. The fact is, the pilots did not know how to fly the plane manually. The CVR indicates that they had poor cockpit resource management. Their training was hopelessly inadequate. The right seat pilot arrived in the 737 Max type with 98 hours total flight time. They turned the inevitable failure of a single component into a disaster. Natalie Kitroeff is either a clickbait journalist with no understanding or regard for the simple facts of the matter, or else she is part of a purposeful effort to undermine Boeing, create chaos, and destabilize America and the West. The facts are clear and unequivocal. All the trolls on here should read the preliminary report. Take a few minutes to look at the data from the FDR. Then put away the torches and pitchforks and stop supporting the fact-free idiots attacking what is almost the last company that actually makes stuff in the USA.
- deleted 7y ago
  [deleted]
- matthewdgreen 7y ago
  This previous story (https://news.ycombinator.com/item?id=19902068 https://news.ycombinator.com/item?id=19902068) implies that the simulators try to simulate the forces, and in a particular simulation even the simulator crew wasn't able to move the wheel: "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."
  - A2017U1 7y ago
    So how accurate is it?
- RockyMcNuts 7y ago
  If pilots are trained in how to recognize the emergency and what to do, and they are instructed that in an actual emergency the forces on the trim wheel (presumably what they are referring to) will vary, they will respond appropriately. Simulators can't exactly replicate extreme conditions, upsets and whatnot. If you're training for trim runaway it would be helpful to simulate the full forces but I'm not sure if it reflects a worrying lack of preparedness. The most important fix is that the MCAS should not be able to put the trim in an extreme position, the fact that it did is quite worrying. This particular article seems much ado about very little.
  - karmelapple 7y ago
    Did you see this previous article? https://news.ycombinator.com/item?id=19902068 https://news.ycombinator.com/item?id=19902068 There seems to be massive issues with the force required.
    - RockyMcNuts 7y ago
      That seems like a different issue. Root problem seems to be: Software puts trim in an extreme position. It should never do that. Aviation Week article: if you are in an electric trim runaway, you need to turn off electric trim, then in order to turn the trim wheel manually, you need to nose down to reduce aerodynamic forces. Seems necessary to train for which it suggests was not the case. NYT article: Simulator doesn't simulate the forces on the trim wheel correctly (although Aviation Week suggests they were able to simulate something useful) The NYT article really seems like the least of the problems.
- ctchocula 7y ago
  Mentour Pilot has a video where he does that exact simulation for a 737NG flight simulator in order to show how difficult it is to trim manually [1]. [1] https://www.youtube.com/watch?v=aoNOVlxJmow https://www.youtube.com/watch?v=aoNOVlxJmow
jayalpha 7y ago
"who will need to approve them before the plane can start flying again." Yes, thanks. I guess I pass for now.
bumby 7y ago
A good software assurance program in a flight environment should also be ensuring simulators are of high enough fidelity for testing and training. As this story develops, it sure seems like there are either gaps in Boeings QA program or there is a culture that overrides quality concerns
- crocal 7y ago
  > A good software assurance program in a flight environment should also be ensuring simulators are of high enough fidelity for testing and training. Actually, "must" not "should". Aeronautics certification standards require tools such as simulators to be qualified for their intended use. Similar requirement have been introduced in recent release of railway standards.
  - bumby 7y ago
    I agree with you're correcting my imprecise wording, but it still seems like there's an issue with the certification process if this particular "must" didn't get built in. I guess my question is: why didn't the QA flag get raised on this or if it did, why wasn't it given any credence? I'm not trying to armchair quarterback this, but I'm legitimately curious if this issue is one the certification process is expected to catch
    - bbayer 7y ago
      Certification process is generic enough to apply it to different types of aircrafts. There is no specific requirements for different subsystems introduced by manufacturer. Simulation fidelity is tested against real world data but it is not possible to collect data for every condition that might occur during flight. You may refer to FAA FSS Level-D QTG document for further reference. [1] [1]: https://www.faa.gov/about/initiatives/nsp/media/14CFR60_Searchable_Version.pdf https://www.faa.gov/about/initiatives/nsp/media/14CFR60_Sear...
    - salawat 7y ago
      Concerns were raised, but also dismissed or otherwise culturally disincentivize by management. There are whistkeblowers currently willing to testify as much, based on information released to Australia's 60 Minutes 737 Expose.
FabHK 7y ago
Small nitpick: I don't think MCAS is well characterised as an "anti-stall system".
- dbcurtis 7y ago
  Hmmm.... "power dive" sounds like opposite of stall to me.
- avar 7y ago
  From https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Augmentation_System#Operation https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Au... > "The system is explicitly designed to override pilot action and prevent them from regaining control authority, in order to avoid an inadvertent stall." If it's not an anti-stall system what would you characterize it as?
  - danharaj 7y ago
    The purpose of a system is what it does, not what it was designed to do.
  - FabHK 7y ago
    Good question. Not sure the "flight envelope protection" description in the Wikipedia article is good. If I'm not mistaken, MCAS was put in to fulfil certification requirements stipulated in 14 CFR § 25.173 - Static longitudinal stability, and § 25.175 Demonstration of static longitudinal stability, which states that "The stick force curve must have a stable slope". The MAX has a curved slope in some regions of the flight envelope, due to the fact that the nacelles generate lift in front of the centre of gravity. (It is not clear to me whether the slope of the stick force at high AoA in a MAX without MCAS goes negative, or just decreases (while staying positive)). Note the Wikipedia article you quote also says: > It is thus distinct from an anti-stall device, such as stick pusher which physically moves the pilot's control column forward when the airplane is approaching a stall.[5] See also here [1]: > Numerous reports have incorrectly said that MCAS is a stall prevention, or stall recovery, system. It is a Maneuvering Characteristics Augmentation System and would not be expected to activate during any normal flight conditions. Or here: >> It does seem MCAS is closely related to protecting the plane from entering a stall scenario. > Only in the sense that it is giving the pilots the feedback, through the stick force, about how close the plane is to a stall, that the pilots are used to from previous 737 models. The point of MCAS is that without it, the stick force feedback as a function of angle of attack would be different from what the pilots were used to, so they might misjudge how close to a stall they were. [1] https://www.pilotsofamerica.com/community/threads/engineers-take-on-the-737-max-design.118273/ https://www.pilotsofamerica.com/community/threads/engineers-... [2] https://www.physicsforums.com/threads/boeing-737-max-mcas-system.967958/page-3 https://www.physicsforums.com/threads/boeing-737-max-mcas-sy...
FabHK 7y ago
Question: > In a tense meeting with the American Airlines pilots union after the crash, a Boeing vice president, Mike Sinnett, said he was confident that pilots were equipped to deal with problems, according to an audio recording review by The New York Times. A top Boeing test pilot, Craig Bomben, agreed, saying, “I don’t know that understanding the system would have changed the outcome of this.” Should that be Craig Bomben "disagreed"?
- voxic11 7y ago
  No he is agreeing that the pilots were as well equipped as they could have been, because he believes understanding the system wouldn't have made a difference anyways.
  - FabHK 7y ago
    Hmm, I see. So the Boeing VP was claiming that a pilot following procedures properly would've saved the plane, and (at that time, after the first crash) the test pilot (also from Boeing) agreed. Makes sense now, thanks.
    - UnoriginalGuy 7y ago
      And then a second crash occurred where they followed Boeing's procedure, it didn't work, were forced to diverge and then crashed. Boeing's procedure only works if you catch it quickly. If you let MCAS trim the aircraft too much it is difficult to recover, particularly at low altitude.
      - chaboud 7y ago
        That's how it seems. 1. Both stab trim cut switches now cut electronic horizontal stabilizer trim control and automated control together. 2. And manual control does not function at high airspeeds. 3. So... A planeload of people is screwed... That seems like a really risky set of design choices.
  - droithomme 7y ago
ackfoo 7y ago
This is the stupidest article to date about the 737 Max. It betrays a complete misunderstanding of the purpose and use of a simulator. Written by a non-technical click-bait journalist unqualified to comment on the matter at a cocktail party, let alone the NYT. Of course simulators are flawed if your moron-level understanding is that they should simulate perfectly all possible flight conditions. They don't simulate flying upside-down, or drilling it into a mountainside at Mach 2, or what happens when the tail gets ripped off, either. That is because there is limited data available to program the simulator for conditions that are so far outside the flight envelope that the test pilots have not tested them, nor is there any valid reason to create such a simulation, except for forensic reasons when the NTSB asks the generally-academic question, "At what point after the aircraft departed the flight envelope did it become completely unrecoverable?" The purpose of a simulator is to train pilots to respond to emergencies while keeping the aircraft within the flight envelope. There is an infinite number of possible attitudes and conditions outside the flight envelope that can theoretically be achieved by gross negligence, but it would be impossibly costly and counter-productive to train pilots for all of them because they should never be encountered. Unlike your home flight simulator, we don't program simulators to fly under the Golden Gate Bridge for the simple reason that commercial pilots should never, ever find themselves in such a situation. That does not mean that the simulators are flawed.
droithomme 7y ago
> Boeing has maintained that simulator training is not necessary for the 737 Max and regulators do not require it, but many airlines bought the multimillion-dollar machines to give their pilots more practice. Boeing is only arguing this because if they say simulator training is necessary, then the plane must be recertified. Their executive MBA analyst and stock watcher types under no circumstances will tolerate recertification, therefore regardless of facts, their position must be that simulator training is not necessary. Even though it obviously is. Key point to observing this and everything else about this debacle is that Boeing has no concern whatsoever for safety, professionalism or lives, and is only interested in their own profit, executive bonuses, and stock dividend gains and will do absolutely anything to protect those, even though it inevitably is going to lead to another crash and more deaths. At which point they will again start by doing everything they can to blame the pilot and the culture of whatever country he hails from, as well as paying shills to post nonsense and attack pilots, engineers and others who question their narrative publicly.
- MaxBarraclough 7y ago
  But that's only half the story. The other half is that the FAA -- which is meant to be the counterweight to those perverse incentives -- is no longer credible. (I've made this point before [0] but it bears repeating here.) [0] https://news.ycombinator.com/item?id=19888207 https://news.ycombinator.com/item?id=19888207
  - SilasX 7y ago
    That’s not making the point; that’s just asserting it.
    - virtual_void 7y ago
      I’m confused as to the difference. No snark intended. I’m likely missing something.
      - febeling 7y ago
gist 7y ago
> Since the two fatal crashes of the Boeing 737 Max, airlines around the world have moved to buy flight simulators to train their pilots. They don’t always work. Boeing recently discovered that the simulators could not accurately replicate the difficult conditions Typical article which does not address the entire context of the issue. In other words it isolates what a 737 simulator can't do without regard to what a typical simulator (for another aircraft or by even a different manufacturer) is or is not able to do. [1] The idea is to make the manufacture look like a total ignorant screw up in every way to create anger and compelling content. [1] This is like a news story talking about what a company fails to do and then gets hacked without talking at all about how likely the same thing happens at another company.
- FabHK 7y ago
  Are you suggesting that most simulators get control forces wrong for things that can realistically occur within the recoverable flight envelope after one single sensor fails? I'd have thought that that is something you'd want to get right.
forgetcolor 7y ago
Why does MCAS have to take control of trim at all? Would it not be sufficient to alert the pilot of an imminent stall situation so they can adjust the angle of attack themselves? Is it because doing so would put the MAX too far afield from the old 737 such that it would require simulator training?
- ralph84 7y ago
  Yes. MCAS is designed to make the Max handle like previous 737s when manually flying at high angle of attack. Without MCAS the handling would be different enough to require simulator training.
  - VBprogrammer 7y ago
    The behaviour is not certifiable, no amount of simulator training can fix that.
- cjbprime 7y ago
  There's an airworthiness rule requiring monotonically increasing yoke backpressure as the plane approaches a stall. It appears that the MAX violates this rule aerodynamically due to extra lift at high power generated by the high and forward nacelles, combined with the yoke being mechanically coupled. It can get easier to induce a stall as the plane approaches critical AoA. This isn't directly the same thing as saying the MAX will stall itself: if you aren't pulling back on the yoke near critical AoA then you don't stall. It's just easier to stall with the yoke than regulations say it must be. MCAS "fixes" that handling issue. I don't think an audible warning would be sufficient to turn unairworthy behavior into airworthy, so if all the assumptions above are correct, that's why it has to use trim -- or a stick pusher, but perhaps that wouldn't have enough control authority and also I'm not sure the MAX has a stick pusher, as opposed to just a stick shaker. It's a very mechanical cockpit, in general the forces you feel are coupled to aerodynamics, in stark contrast to an Airbus (or even more modern Boeing airframes).
  - cmurf 7y ago
    Maybe it's 25.173(c) https://www.law.cornell.edu/cfr/text/14/25.173 https://www.law.cornell.edu/cfr/text/14/25.173 In the working case, MCAS presumably triggers at a particular AoA, trims nose down (but is this a fixed amount and what is it?) which in effect requires more stick back pressure to maintain the angle of attack. Thing is, it seems like MCAS, again in the working case, has a trigger AoA and will incrementally nose down until it goes below some defined angle of attack - which is not really a stick force moderator alone. It's acting as a kind of AoA guardian.
heisenbit 7y ago
Considering how fast and strong the trim wheel is spinning under MCAS control the simulator may be unsafe to use. Touching a wheel spinning so fast is outright dangerous.
- weaksauce 7y ago
  you only trim with the wheel when the power is cut to the trim motors.
- tjohns 7y ago
  The trim wheel spins like that anyway under normal operation, both due to pilot input and while on autopilot. More importantly, you don't grab the trim wheel while it's moving... If the aircraft is operating normally, you use the trim switch on the yoke. The only time you'd spin the trim wheel by hand is if you've had to cutout the electric trim motor... and once that's done it's not going to move on its own anyway.
  - tgsovlerkhgsel 7y ago
    > once that's done it's not going to move on its own anyway. Unless the short is somewhere where you don't expect it to be, which is why a memory item if the runaway trim continues is STABILIZER TRIM WHEEL - GRASP and HOLD
    - Doxin 7y ago
      They teach pilots a specific way to grab the trim wheel for that scenario as to not break their wrists. It still can (and occasionally does) cause abrasive wounds to the hands however.
inamberclad 7y ago
Every simulator is flawed, some are useful.
nameisu 7y ago
idk why any sane pilot still wants to fly these
bronco21016 7y ago
I’m not sure where the misconception comes from about simulator training being equal to the aircraft being a new type certificate. The DC-9/MD-80 series/B717 are all the same DC-9 type certificate despite spanning many decades, longer than the 737 even. Pilots receive a DC-9 type certificate to fly any variant, however, for obvious reasons, the FAA requires what’s known as differences training in a simulator to transition between the different aircraft. I can’t possibly imagine that the FAA is or any aviation governing body is going to jump from iPad distance learning to full on new type certificate. B737 type rated pilots will receive 2-3 sessions in the MAX simulator and be sent on their way flying 737NG and MAX variants and the aircraft will go on to have a normal safety record. The more concerning aspect of this entire situation is finding where the system broke down to prevent this additional training to begin with and how do we fix the breaks in that system.
- ozmaverick72 7y ago
  They will have to fix the simulator first. As I understand it they can't currently simulate the handling of the aircraft under MCAS failure modes. If they correct the simulator and require pilots to train for the handling of MCAS failures then I have to problem with the reintroduction of the max on the same type certificate. From what we are hearing in the press it sounds like Boeing is still pressing for nothing more that a dumb iPad lesson. If the FAA falls for that they will loose all credibility in my eyes.
  - wjnc 7y ago
    Has the whole world subscribed to FAA oversight or would other regulators be able to pick their own fight with Boeing?
    - lrem 7y ago
      EU has its own oversight that has, at least at some point in the past, been pretty much copying FAA word-for-word. Other countries obviously have their own, but also leaned on FAA for its influence. Yet another aspect of soft power of the US.
- 7y ago

136 points by howard941 7y ago

tlb 7y ago

How would you accurately simulate the force needed to turn the trim wheel under aerodynamic loads that vary with elevator position? It sounds like a very tricky mechanical setup.

krallja 7y ago
Brakes, or a strong motor.
- jayalpha 7y ago
  crank handle with a translation?
- dbcurtis 7y ago
  The way I would approach it (based on mechantronics I have done for robots) is to back up the control wheel with an encoded motor. (Position/rotation encoder on the tail shaft.) The encoder will give you wheel position, the motor allows you to apply arbitrary torque to the wheel to simulate the feedback forces felt by the pilot. Typically, that would be done by measuring motor current and writing a control loop that controlled for target wheel position (based on encoder) and target maximum motor current (as a proxy for torque). Then the simulator would give out the simulated results of wheel position and torque, which the control loop would attempt to follow with its control law. Alternatively, you could put an actual torque sensor between the motor and the control wheel, which might buy you some accuracy at considerably more expense. For a flight simulator, expense is unlikely to be an issue -- I tend not to have that luxury, and typically don't need that much accuracy anyway. These kind of control systems are all over modern aircraft, much less simulators. Any new grad control systems engineer should be able to knock something like this out.
  - blattimwind 7y ago
    > The way I would approach it (based on mechantronics I have done for robots) is to back up the control wheel with an encoded motor. (Position/rotation encoder on the tail shaft.) The encoder will give you wheel position, the motor allows you to apply arbitrary torque to the wheel to simulate the feedback forces felt by the pilot. Typically, that would be done by measuring motor current and writing a control loop that controlled for target wheel position (based on encoder) and target maximum motor current (as a proxy for torque). Then the simulator would give out the simulated results of wheel position and torque, which the control loop would attempt to follow with its control law. Or you just buy a COTS servo that does all that for you. Just saying, hardly a need to reinvent these particular wheels...
    - dbcurtis 7y ago
      Yeah, good point. I'm sure there are servos that have the required specs. I'm just not in the habit of looking at catalogs where the prices are that high :) Maybe I should switch to building flight simulators so that I can order the good stuff :)
      - rasz 7y ago
        racing sim guys already figured it out http://opensimwheel.wikidot.com/ http://opensimwheel.wikidot.com/
mikeash 7y ago
The mechanical part seems easy enough. Tricky to calculate the appropriate force, but I’m sure the aerodynamics people are more than up to the task.
ackfoo 7y ago
No need to do so. The aerodynamic forces on the manual trim wheel on Ethiopia 302 were excessive because they were flying about 50kts overspeed. The simulator is not supposed to teach what it feels like to fly the plane when it is so far outside of its certified flight envelope that even test pilots have not been there. Instead, the simulator is supposed to teach you how to fly the plane and respond to emergencies so that the aircraft does not depart from the flight envelope to the point where a single failure or control input will cause a crash. Simulating the sensations of flying the 737 Max upside-down would also require a tricky mechanical setup, but no one feels that such a thing is necessary or appropriate. Natalie Kitroeff is the chief anti-Boeing cheerleader at NYT. She has a bachelor in International Affairs from Princeton. I can see no evidence that she has a technical degree, or enough understanding of aerodynamics or any other technical matter to comment on whether someone fixed the drip in her kitchen sink properly. She is the poster child for post-facts non-technical journalism. The facts of Ethiopian 302 are abundantly clear from the preliminary report: a single component, the AOA sensor, failed causing a common and easily-remedied runaway electric trim condition for which there was a clear and comprehensive memory checklist that, had it been followed, would have resolved this problem without even the slightest inconvenience to passengers. The fact is, the pilots did not know how to fly the plane manually. The CVR indicates that they had poor cockpit resource management. Their training was hopelessly inadequate. The right seat pilot arrived in the 737 Max type with 98 hours total flight time. They turned the inevitable failure of a single component into a disaster. Natalie Kitroeff is either a clickbait journalist with no understanding or regard for the simple facts of the matter, or else she is part of a purposeful effort to undermine Boeing, create chaos, and destabilize America and the West. The facts are clear and unequivocal. All the trolls on here should read the preliminary report. Take a few minutes to look at the data from the FDR. Then put away the torches and pitchforks and stop supporting the fact-free idiots attacking what is almost the last company that actually makes stuff in the USA.
deleted 7y ago
[deleted]
matthewdgreen 7y ago
This previous story (https://news.ycombinator.com/item?id=19902068 https://news.ycombinator.com/item?id=19902068) implies that the simulators try to simulate the forces, and in a particular simulation even the simulator crew wasn't able to move the wheel: "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."
- A2017U1 7y ago
  So how accurate is it?
RockyMcNuts 7y ago
If pilots are trained in how to recognize the emergency and what to do, and they are instructed that in an actual emergency the forces on the trim wheel (presumably what they are referring to) will vary, they will respond appropriately. Simulators can't exactly replicate extreme conditions, upsets and whatnot. If you're training for trim runaway it would be helpful to simulate the full forces but I'm not sure if it reflects a worrying lack of preparedness. The most important fix is that the MCAS should not be able to put the trim in an extreme position, the fact that it did is quite worrying. This particular article seems much ado about very little.
- karmelapple 7y ago
  Did you see this previous article? https://news.ycombinator.com/item?id=19902068 https://news.ycombinator.com/item?id=19902068 There seems to be massive issues with the force required.
  - RockyMcNuts 7y ago
    That seems like a different issue. Root problem seems to be: Software puts trim in an extreme position. It should never do that. Aviation Week article: if you are in an electric trim runaway, you need to turn off electric trim, then in order to turn the trim wheel manually, you need to nose down to reduce aerodynamic forces. Seems necessary to train for which it suggests was not the case. NYT article: Simulator doesn't simulate the forces on the trim wheel correctly (although Aviation Week suggests they were able to simulate something useful) The NYT article really seems like the least of the problems.
ctchocula 7y ago
Mentour Pilot has a video where he does that exact simulation for a 737NG flight simulator in order to show how difficult it is to trim manually [1]. [1] https://www.youtube.com/watch?v=aoNOVlxJmow https://www.youtube.com/watch?v=aoNOVlxJmow

jayalpha 7y ago

"who will need to approve them before the plane can start flying again." Yes, thanks. I guess I pass for now.

bumby 7y ago

A good software assurance program in a flight environment should also be ensuring simulators are of high enough fidelity for testing and training. As this story develops, it sure seems like there are either gaps in Boeings QA program or there is a culture that overrides quality concerns

crocal 7y ago
> A good software assurance program in a flight environment should also be ensuring simulators are of high enough fidelity for testing and training. Actually, "must" not "should". Aeronautics certification standards require tools such as simulators to be qualified for their intended use. Similar requirement have been introduced in recent release of railway standards.
- bumby 7y ago
  I agree with you're correcting my imprecise wording, but it still seems like there's an issue with the certification process if this particular "must" didn't get built in. I guess my question is: why didn't the QA flag get raised on this or if it did, why wasn't it given any credence? I'm not trying to armchair quarterback this, but I'm legitimately curious if this issue is one the certification process is expected to catch
  - bbayer 7y ago
    Certification process is generic enough to apply it to different types of aircrafts. There is no specific requirements for different subsystems introduced by manufacturer. Simulation fidelity is tested against real world data but it is not possible to collect data for every condition that might occur during flight. You may refer to FAA FSS Level-D QTG document for further reference. [1] [1]: https://www.faa.gov/about/initiatives/nsp/media/14CFR60_Searchable_Version.pdf https://www.faa.gov/about/initiatives/nsp/media/14CFR60_Sear...
  - salawat 7y ago
    Concerns were raised, but also dismissed or otherwise culturally disincentivize by management. There are whistkeblowers currently willing to testify as much, based on information released to Australia's 60 Minutes 737 Expose.

FabHK 7y ago

Small nitpick: I don't think MCAS is well characterised as an "anti-stall system".

dbcurtis 7y ago
Hmmm.... "power dive" sounds like opposite of stall to me.
avar 7y ago
From https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Augmentation_System#Operation https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Au... > "The system is explicitly designed to override pilot action and prevent them from regaining control authority, in order to avoid an inadvertent stall." If it's not an anti-stall system what would you characterize it as?
- danharaj 7y ago
  The purpose of a system is what it does, not what it was designed to do.
- FabHK 7y ago
  Good question. Not sure the "flight envelope protection" description in the Wikipedia article is good. If I'm not mistaken, MCAS was put in to fulfil certification requirements stipulated in 14 CFR § 25.173 - Static longitudinal stability, and § 25.175 Demonstration of static longitudinal stability, which states that "The stick force curve must have a stable slope". The MAX has a curved slope in some regions of the flight envelope, due to the fact that the nacelles generate lift in front of the centre of gravity. (It is not clear to me whether the slope of the stick force at high AoA in a MAX without MCAS goes negative, or just decreases (while staying positive)). Note the Wikipedia article you quote also says: > It is thus distinct from an anti-stall device, such as stick pusher which physically moves the pilot's control column forward when the airplane is approaching a stall.[5] See also here [1]: > Numerous reports have incorrectly said that MCAS is a stall prevention, or stall recovery, system. It is a Maneuvering Characteristics Augmentation System and would not be expected to activate during any normal flight conditions. Or here: >> It does seem MCAS is closely related to protecting the plane from entering a stall scenario. > Only in the sense that it is giving the pilots the feedback, through the stick force, about how close the plane is to a stall, that the pilots are used to from previous 737 models. The point of MCAS is that without it, the stick force feedback as a function of angle of attack would be different from what the pilots were used to, so they might misjudge how close to a stall they were. [1] https://www.pilotsofamerica.com/community/threads/engineers-take-on-the-737-max-design.118273/ https://www.pilotsofamerica.com/community/threads/engineers-... [2] https://www.physicsforums.com/threads/boeing-737-max-mcas-system.967958/page-3 https://www.physicsforums.com/threads/boeing-737-max-mcas-sy...

FabHK 7y ago

Question: > In a tense meeting with the American Airlines pilots union after the crash, a Boeing vice president, Mike Sinnett, said he was confident that pilots were equipped to deal with problems, according to an audio recording review by The New York Times. A top Boeing test pilot, Craig Bomben, agreed, saying, “I don’t know that understanding the system would have changed the outcome of this.” Should that be Craig Bomben "disagreed"?

voxic11 7y ago
No he is agreeing that the pilots were as well equipped as they could have been, because he believes understanding the system wouldn't have made a difference anyways.
- FabHK 7y ago
  Hmm, I see. So the Boeing VP was claiming that a pilot following procedures properly would've saved the plane, and (at that time, after the first crash) the test pilot (also from Boeing) agreed. Makes sense now, thanks.
  - UnoriginalGuy 7y ago
    And then a second crash occurred where they followed Boeing's procedure, it didn't work, were forced to diverge and then crashed. Boeing's procedure only works if you catch it quickly. If you let MCAS trim the aircraft too much it is difficult to recover, particularly at low altitude.
    - chaboud 7y ago
      That's how it seems. 1. Both stab trim cut switches now cut electronic horizontal stabilizer trim control and automated control together. 2. And manual control does not function at high airspeeds. 3. So... A planeload of people is screwed... That seems like a really risky set of design choices.
- droithomme 7y ago

ackfoo 7y ago

This is the stupidest article to date about the 737 Max. It betrays a complete misunderstanding of the purpose and use of a simulator. Written by a non-technical click-bait journalist unqualified to comment on the matter at a cocktail party, let alone the NYT. Of course simulators are flawed if your moron-level understanding is that they should simulate perfectly all possible flight conditions. They don't simulate flying upside-down, or drilling it into a mountainside at Mach 2, or what happens when the tail gets ripped off, either. That is because there is limited data available to program the simulator for conditions that are so far outside the flight envelope that the test pilots have not tested them, nor is there any valid reason to create such a simulation, except for forensic reasons when the NTSB asks the generally-academic question, "At what point after the aircraft departed the flight envelope did it become completely unrecoverable?" The purpose of a simulator is to train pilots to respond to emergencies while keeping the aircraft within the flight envelope. There is an infinite number of possible attitudes and conditions outside the flight envelope that can theoretically be achieved by gross negligence, but it would be impossibly costly and counter-productive to train pilots for all of them because they should never be encountered. Unlike your home flight simulator, we don't program simulators to fly under the Golden Gate Bridge for the simple reason that commercial pilots should never, ever find themselves in such a situation. That does not mean that the simulators are flawed.

droithomme 7y ago

> Boeing has maintained that simulator training is not necessary for the 737 Max and regulators do not require it, but many airlines bought the multimillion-dollar machines to give their pilots more practice. Boeing is only arguing this because if they say simulator training is necessary, then the plane must be recertified. Their executive MBA analyst and stock watcher types under no circumstances will tolerate recertification, therefore regardless of facts, their position must be that simulator training is not necessary. Even though it obviously is. Key point to observing this and everything else about this debacle is that Boeing has no concern whatsoever for safety, professionalism or lives, and is only interested in their own profit, executive bonuses, and stock dividend gains and will do absolutely anything to protect those, even though it inevitably is going to lead to another crash and more deaths. At which point they will again start by doing everything they can to blame the pilot and the culture of whatever country he hails from, as well as paying shills to post nonsense and attack pilots, engineers and others who question their narrative publicly.

MaxBarraclough 7y ago
But that's only half the story. The other half is that the FAA -- which is meant to be the counterweight to those perverse incentives -- is no longer credible. (I've made this point before [0] but it bears repeating here.) [0] https://news.ycombinator.com/item?id=19888207 https://news.ycombinator.com/item?id=19888207
- SilasX 7y ago
  That’s not making the point; that’s just asserting it.
  - virtual_void 7y ago
    I’m confused as to the difference. No snark intended. I’m likely missing something.
    - febeling 7y ago

gist 7y ago

> Since the two fatal crashes of the Boeing 737 Max, airlines around the world have moved to buy flight simulators to train their pilots. They don’t always work. Boeing recently discovered that the simulators could not accurately replicate the difficult conditions Typical article which does not address the entire context of the issue. In other words it isolates what a 737 simulator can't do without regard to what a typical simulator (for another aircraft or by even a different manufacturer) is or is not able to do. [1] The idea is to make the manufacture look like a total ignorant screw up in every way to create anger and compelling content. [1] This is like a news story talking about what a company fails to do and then gets hacked without talking at all about how likely the same thing happens at another company.

FabHK 7y ago
Are you suggesting that most simulators get control forces wrong for things that can realistically occur within the recoverable flight envelope after one single sensor fails? I'd have thought that that is something you'd want to get right.

forgetcolor 7y ago

Why does MCAS have to take control of trim at all? Would it not be sufficient to alert the pilot of an imminent stall situation so they can adjust the angle of attack themselves? Is it because doing so would put the MAX too far afield from the old 737 such that it would require simulator training?

ralph84 7y ago
Yes. MCAS is designed to make the Max handle like previous 737s when manually flying at high angle of attack. Without MCAS the handling would be different enough to require simulator training.
- VBprogrammer 7y ago
  The behaviour is not certifiable, no amount of simulator training can fix that.
cjbprime 7y ago
There's an airworthiness rule requiring monotonically increasing yoke backpressure as the plane approaches a stall. It appears that the MAX violates this rule aerodynamically due to extra lift at high power generated by the high and forward nacelles, combined with the yoke being mechanically coupled. It can get easier to induce a stall as the plane approaches critical AoA. This isn't directly the same thing as saying the MAX will stall itself: if you aren't pulling back on the yoke near critical AoA then you don't stall. It's just easier to stall with the yoke than regulations say it must be. MCAS "fixes" that handling issue. I don't think an audible warning would be sufficient to turn unairworthy behavior into airworthy, so if all the assumptions above are correct, that's why it has to use trim -- or a stick pusher, but perhaps that wouldn't have enough control authority and also I'm not sure the MAX has a stick pusher, as opposed to just a stick shaker. It's a very mechanical cockpit, in general the forces you feel are coupled to aerodynamics, in stark contrast to an Airbus (or even more modern Boeing airframes).
- cmurf 7y ago
  Maybe it's 25.173(c) https://www.law.cornell.edu/cfr/text/14/25.173 https://www.law.cornell.edu/cfr/text/14/25.173 In the working case, MCAS presumably triggers at a particular AoA, trims nose down (but is this a fixed amount and what is it?) which in effect requires more stick back pressure to maintain the angle of attack. Thing is, it seems like MCAS, again in the working case, has a trigger AoA and will incrementally nose down until it goes below some defined angle of attack - which is not really a stick force moderator alone. It's acting as a kind of AoA guardian.

heisenbit 7y ago

Considering how fast and strong the trim wheel is spinning under MCAS control the simulator may be unsafe to use. Touching a wheel spinning so fast is outright dangerous.

weaksauce 7y ago
you only trim with the wheel when the power is cut to the trim motors.
tjohns 7y ago
The trim wheel spins like that anyway under normal operation, both due to pilot input and while on autopilot. More importantly, you don't grab the trim wheel while it's moving... If the aircraft is operating normally, you use the trim switch on the yoke. The only time you'd spin the trim wheel by hand is if you've had to cutout the electric trim motor... and once that's done it's not going to move on its own anyway.
- tgsovlerkhgsel 7y ago
  > once that's done it's not going to move on its own anyway. Unless the short is somewhere where you don't expect it to be, which is why a memory item if the runaway trim continues is STABILIZER TRIM WHEEL - GRASP and HOLD
  - Doxin 7y ago
    They teach pilots a specific way to grab the trim wheel for that scenario as to not break their wrists. It still can (and occasionally does) cause abrasive wounds to the hands however.

inamberclad 7y ago

Every simulator is flawed, some are useful.

nameisu 7y ago

idk why any sane pilot still wants to fly these

bronco21016 7y ago

I’m not sure where the misconception comes from about simulator training being equal to the aircraft being a new type certificate. The DC-9/MD-80 series/B717 are all the same DC-9 type certificate despite spanning many decades, longer than the 737 even. Pilots receive a DC-9 type certificate to fly any variant, however, for obvious reasons, the FAA requires what’s known as differences training in a simulator to transition between the different aircraft. I can’t possibly imagine that the FAA is or any aviation governing body is going to jump from iPad distance learning to full on new type certificate. B737 type rated pilots will receive 2-3 sessions in the MAX simulator and be sent on their way flying 737NG and MAX variants and the aircraft will go on to have a normal safety record. The more concerning aspect of this entire situation is finding where the system broke down to prevent this additional training to begin with and how do we fix the breaks in that system.

ozmaverick72 7y ago
They will have to fix the simulator first. As I understand it they can't currently simulate the handling of the aircraft under MCAS failure modes. If they correct the simulator and require pilots to train for the handling of MCAS failures then I have to problem with the reintroduction of the max on the same type certificate. From what we are hearing in the press it sounds like Boeing is still pressing for nothing more that a dumb iPad lesson. If the FAA falls for that they will loose all credibility in my eyes.
- wjnc 7y ago
  Has the whole world subscribed to FAA oversight or would other regulators be able to pick their own fight with Boeing?
  - lrem 7y ago
    EU has its own oversight that has, at least at some point in the past, been pretty much copying FAA word-for-word. Other countries obviously have their own, but also leaned on FAA for its influence. Yet another aspect of soft power of the US.
7y ago