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Thread: Boeing 737 Max

  1. #961
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    Quote Originally Posted by triumph406 View Post
    ... Not sure how the 'insiders' here are going to explain this away. Although like everything else they'll come up with something, no matter how implausible.
    OMG just *who* is paying for him (Forkner) to SAY those things!

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    This is a interesting report. Seems that it is viewed as criminal. Yet the article discusses this and goes on to say that Forkner says he was talking about the simulator. That is scary because if a simulator is not valid then how can things be checked properly? With all the flights of this plane it is notable that American pilots were able to overcome the problem.

    Experience and environment of experience likely does play a role in the issue of competence. Training was not provided and information about MCAS was not provided and there is over 300 people dead. I believe that the seriousness of responsibility is not appreciated by people who worked to approve this plane.

    Fact is in this case there may have to be criminal liability here. If this happens it will make clear the punishment for not stepping forward and also the punishment for pressure and manipulation by the company in the process.

    Just saying this should play out for sure and the man has a lawyer which he needs. He may have been just talking about the simulator yet once fixed the problem should have showed up.

    More headaches come the more that we learn. The process should have caught this.

    Article; Boeing Pilot Complained of ‘Egregious’ Issue With 737 Max in 2016 - The New York Times

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    A problem in the sim in 2016 does not necessarily mean that was the same software that was certified for flight.

    That was a year before certification and the first deliveries.

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    Quote Originally Posted by jancollc View Post
    A problem in the sim in 2016 does not necessarily mean that was the same software that was certified for flight.

    That was a year before certification and the first deliveries.
    More will be brought out. That makes sense.

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    Quote Originally Posted by Trueturning View Post
    .... I believe that the seriousness of responsibility is not appreciated by people who worked to approve this plane.
    Well the CEO of the corporation appreciates it. The board fired his ass.

    And yes, about a billion posts back of you care to look, the simulation packages that were used for training, did NOT capture the behavior
    of the mcas system.

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    Quote Originally Posted by jim rozen View Post
    Well the CEO of the corporation appreciates it. The board fired his ass.

    And yes, about a billion posts back of you care to look, the simulation packages that were used for training, did NOT capture the behavior
    of the mcas system.
    I think the one this fellow was using was not for training though because the system had yet to be approved at that point. If the simulator were right then the problem should be noted and addressed.

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    Quote Originally Posted by jim rozen View Post
    ,,,And yes, about a billion posts back of you care to look, the simulation packages that were used for training, did NOT capture the behavior
    of the mcas system.
    If it says that in this thread it's incorrect.

    What the simulators failed to do was accurately simulate the aerodynamic stresses on the horizontal stab, which makes the manual trim wheel too difficult to operate at extreme airspeeds.

    In the sim, you could trim manually no matter how fast you were going. In the real world, there is a point where the aerodynamic force on the stab makes it impossible to hand crank the trim wheel.

    Updating all the sims will be part of the process in getting the MAX back in the air.

    Also, you just can't expect the simulators will replicate every possible situation. There will always be conditions that the simulators don't accurately model. Wind gusts for example.

    Why would an airline develop a training program for speeds beyond the certified maximums? You'll never do that on purpose.

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    Quote Originally Posted by jancollc View Post
    What the simulators failed to do was accurately simulate the aerodynamic stresses on the horizontal stab, which makes the manual trim wheel too difficult to operate at extreme airspeeds.....
    And the stabilizer got into that coffin corner because..... of magic, right? Or, maybe the magic involved sounded like...

    MCAS, eh?

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    You trying to be funny I guess?

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    Quote Originally Posted by Tyrone Shoelaces View Post
    Putting to one side the terrible and tragic deaths of all the passengers and aircrew ...
    To put a more realistic viewpoint on it, there are over seven billion people on the planet. Supply and demand - a human life is worth about a buck thirty-seven.

    It's too bad about the planes tho.

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    Quote Originally Posted by jim rozen View Post
    And the stabilizer got into that coffin corner because..... of magic, right? Or, maybe the magic involved sounded like...

    MCAS, eh?
    In the one case the stabilizer got into that coffin corner because the crew left the power at full thrust and allowed the MCAS to active twenty times.

    The airplane just didn't do it by itself.

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    Quote Originally Posted by jancollc View Post
    If it says that in this thread it's incorrect.

    What the simulators failed to do was accurately simulate the aerodynamic stresses on the horizontal stab, which makes the manual trim wheel too difficult to operate at extreme airspeeds.

    In the sim, you could trim manually no matter how fast you were going. In the real world, there is a point where the aerodynamic force on the stab makes it impossible to hand crank the trim wheel.

    .
    In the 1970's the trim wheel for a large aircraft operated a redundant cable system that went to a hydraulics closet that contained hydraulic servos for the wing and stabilizer control surface actuators. The closet location was chosen to keep the hydraulic lines from the engine driven pumps as short as possible. The servo assemblies included a "feel box" which was designed to give the pilot a false sense of the aerodynamic forces acting on the control surfaces. Without the "feel box" there would be no force required by the pilot to move any of the control surfaces. The 737 control system would have been designed in the late 1960's.

    The "feel box" design was a critical part of the aircraft certification. The aircraft companies avoided any revisions to the box design when they made derivatives of the original aircraft. This avoided having to go through a complete aircraft certification with the derivative design.

    The L1011 used redundant hydraulic pistons for their geared stabilizer/elevator design . Boeing and McDonald Douglas used redundant ball screws to set the trim. The ball screw system included brakes to lock the stabilizer screws in place. The elevator control surface would have been driven by redundant hydraulic pistons.


    There are no forces acting on the pilots controls except those set by the "feel box". The largest plane at that time, that I am aware of, that still used direct cable control of the control surfaces was the Lockheed P3. This plane had power assist devices similar to the power steering in a car. The hydraulic boost system was not practical for larger planes.

    The cable systems are vulnerable to a complete failure should the plane depressurize and the fuselage floor pressure fuses fail to open. The fuselage floor would then buckle and damage the cables running through the floor structure.

    Modern designs use fly by wire with electric motors driving the ball screws. There are no aerodynamic forces acting on the pilot's controls. There are only software simulated forces.

    My knowledge on this subject is derived from a brief period of employment at Lockheed. The design rules would not have been much different at Boeing. Except for one thing.

    In the 1970's the FAA required triple redundant controls and sensors for any operation that could reduce aircraft safety. There were, for example, three completely independent hydraulic systems, three flight control computers,three inertial navigation systems, and three pitot air speed sensors in case one froze up. In some instances triple redundancy was not considered adequate. The L-1011 had four independent hydraulic systems for example. There was some clever redundant software logic that would allow the redundant sensor signals to vote. The computer required two out of the three signals to agree.

    The design goals of flight software back then included reducing the pilots work load and insuring that the flight controls were mistake proof.

    The standards used by the FAA appear to have changed significantly in the last 45 years.


    I have not read all of the previous posts. Someone may have already described these design standards.
    Last edited by Robert R; 10-22-2019 at 02:56 AM.

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    Quote Originally Posted by jancollc View Post
    If it says that in this thread it's incorrect.

    What the simulators failed to do was accurately simulate the aerodynamic stresses on the horizontal stab, which makes the manual trim wheel too difficult to operate at extreme airspeeds.

    In the sim, you could trim manually no matter how fast you were going. In the real world, there is a point where the aerodynamic force on the stab makes it impossible to hand crank the trim wheel.

    Updating all the sims will be part of the process in getting the MAX back in the air.

    Also, you just can't expect the simulators will replicate every possible situation. There will always be conditions that the simulators don't accurately model. Wind gusts for example.

    Why would an airline develop a training program for speeds beyond the certified maximums? You'll never do that on purpose.
    So the SIM is going to be updated to reflect aerodynamic forces correctly?

    That will be comforting for the pilot when he can’t crank the handwheel and he knows he’s about to crash the simulator.

    He'll turn to his simulator co-pilot and say, "well at least the sim flies like the MAX now" As they auger into the ground.

    A great prelude to flying MAX’s that are returned to service.

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    Quote Originally Posted by triumph406 View Post
    That will be comforting for the pilot when he can’t crank the handwheel ...
    If the stupid son of a bitch refuses to drop the throttles back so he is not travelling fifty knots over the max speed, yeah, then it's possible that the hand cranks will be too hard to turn.

    But in situations where there is a real pilot in the cockpit (as happened with Lion Air in the flight just previous to the crash, same plane), it's not a giant problem.

    You are supposed to have a clue before they give you one of those things to fly. Or at least I thought they were.

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    Quote Originally Posted by Robert R View Post

    The design goals of flight software back then included reducing the pilots work load and insuring that the flight controls were mistake proof.

    The standards used by the FAA appear to have changed significantly in the last 45 years.

    I remember an interview I watched years ago and Joe Sutter (Chief Engineer of the design of the 747) was describing how they put triple redundancy into the flight system.
    He laughed when talking about newer aircraft saying (paraphrase) "well I don't think new designs are as safe"

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    Quote Originally Posted by Robert R View Post
    In the 1970's the trim wheel for a large aircraft operated a redundant cable system that went to a hydraulics closet that contained hydraulic servos for the wing and stabilizer control surface actuators.

    The "feel box" design was a critical part of the aircraft certification. The aircraft companies avoided any revisions to the box design when they made derivatives of the original aircraft. This avoided having to go through a complete aircraft certification with the derivative design.

    There are no forces acting on the pilots controls except those set by the "feel box". The largest plane at that time, that I am aware of, that still used direct cable control of the control surfaces was the Lockheed P3. This plane had power assist devices similar to the power steering in a car. The hydraulic boost system was not practical for larger planes.
    The elevator feel system on the 737 provides feedback to the control column. This is not the issue- the pilots can always move the control column no matter how fast the aircraft is going. There are conditions where the elevator feel computer increases the forces on the control column, but never to a point where a human cannot overcome it. I related to this in the first page of this thread- A friend who flies B737NG experienced this when he lost an alpha vane.

    MCAS controls stab trim, not the elevator.

    The horizontal stab is trimmed by the jackscrew. The manual trim wheel is connected by cables to the jackscrew, so that when power is cutoff to the electric trim motors the pilots can still operate the stab trim manually.

    The aerodynamic forces on the horizontal stab will affect the amount of force it takes to MANUALLY crank the trim wheel. When the electric trim is cutout, it's only the cables turning the jackscrew. There is no power assist.

    It has no bearing on the elevator feel system.

    The simulators were not accurately modeling the aerodynamic forces on the horizontal stab at excessive speeds- IOW no one knew at what point the force needed to manually trim the horizontal stab was greater than the pilots could apply.

    What they discovered from the ET302 crash was this: When the aircraft is flying faster than it's maximum design speed, and the horizontal stab trim is already at it's limit, the aero force acting on the horizontal stab is too much for the pilots to overcome with the trim wheels.

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    Might the aeroplane have been travelling 50 knots too fast because the MCAS had forced it into a dive?

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    Quote Originally Posted by Mark Rand View Post
    Might the aeroplane have been travelling 50 knots too fast because the MCAS had forced it into a dive?
    See also "coffin corner" above. Most likely caused by magic. NOT repeat NOT anything that sounds remotely like

    MCAS.

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    Quote Originally Posted by jim rozen View Post
    See also "coffin corner" above. Most likely caused by magic. NOT repeat NOT anything that sounds remotely like

    MCAS.
    See also post 971 above. Most likely caused by untrained, inexperienced and unskilled drivers. NOT repeat NOT anything that sounds remotely like

    PILOTS.

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    I think that one of the takeaways from these crashes will be better training for crews to recognize the symptoms of bad air data, and better cockpit warnings. It's a recurring theme, the number of crashes involving failed AOA vanes and/or pitot icing is a pretty long list.

    We've talked about it before- we want crews to follow the procedures precisely- any deviation turns them into test pilots with a plane full of passengers.

    The first crash (JT610), they were flying a plane that was not airworthy because one stick shaker was active continuously. The second crash (ET302), they rotated into the stick shaker.

    Both flights has the IAS DISAGREE warning, which should have triggered the checklist. Set pitch to 10 degrees and power to 80%. Both flights would have been stable at those settings. ET302 would have still been at takeoff flaps, and MCAS would never have activated. They could have just turned around and landed the plane without incident.

    JT610 should have never taken off, but the same situation was presented to the crews. IAS DISAGREE. Set pitch to 10 degrees, power to 80%, they would have been at F5 so no MCAS. Turn it around and live to fly another day.

    Both crews failed to follow the procedure, both crews tried to continue the flight when they should have aborted and sorted out the problems on the ground. In each case, the plane was telling them they had bad air data, but they failed to recognize the problem.

    I'm not exonerating Boeing for the faults in the MCAS design- those are real. But airline crashes are never single-factor causes. It's always a combination of factors- often any one of which if you changed, the crash would have been averted.

    Here's an example of the crew getting it right in a similar situation:

    http://www.bst-tsb.gc.ca/eng/rapport...1/a11o0031.pdf


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