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Thread: OT: not about 737MAX, but yeah, it kinda IS about that.

  1. #11
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    TRe: my post that stated stall indicators were required...
    Quote Originally Posted by rzbill View Post
    Just a slight correction. While that is true for some classes of aircraft operating under some sets of FAA regulations, it is not true for all aircraft. There are 10s of thousands of aircraft that operate safely without a stall warning system (including mine).


    A comment on a different post about the autopilot disconnect. In my opinion, the ability and knowledge to diasable an autopilot is critical. I have that same kill switch and have had to use it when the autopilot did not do what it was supposed to. (Predominantly because of a programming button pushng error by me). One must be able to kill the autopilot quickly and simply. Disconnection and hand flying is the safe alternative in many cases.
    Sorry about that. I've heard the warning horn in many of the small planes that I've ridden in. I did a check for FAA regulations on the subject before posting, and failed to notice that the regulation that I was reading was for a certain class of aircraft. Limited experience in the area under discussion plus single source of corroboration to validate that world view is often a formula for mistakes in posts.

    Dan
    At the end of the project, there is a profound difference between spare parts and extra parts.

  2. #12
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    Quote Originally Posted by danlb View Post
    ... Limited experience in the area under discussion plus single source of corroboration to validate that world view is often a formula for mistakes in posts.

    Dan
    That's when I like to keep my mouth shut and my ears open.

    It's the reason we have one mouth and two ears.

  3. #13
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    No worries Dan, I was referring to two sets of aircraft that a majority of folks may not be exposed to but are still quite common within the aviation world. First would be older factory built aircraft that were originally "approved" on earlier sets of rules (prior to 1969) and can possibly still be built that way but I would have to review the FARs to be clear on that, and secondly craft built under the 'Experimental' set of rules in FAR part 23. Obviously the older craft are essentially a 'fixed' set that will not increase in size however I believe it is true that there are more home fabricated 'experimental class' than factory built private aircraft being producted in the US at this time. I could be wrong on this since I have not seen the stats in a while but in any case the experimentals are a large growing class within general aviation.

    For those that are not familiar, the Extra 300 that 3Phase mentioned is a fire breathing aerobatic plane. Certified for factory construction under German flight rules and operated in the US generally under the FAA subclass "Experimental Exhibition".
    Last edited by rzbill; 04-02-2019 at 12:47 PM.
    Bill Pendergrass
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  4. #14
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    Quote Originally Posted by lynnl View Post
    That's when I like to keep my mouth shut and my ears open.

    It's the reason we have one mouth and two ears.
    +1, and it's nauseatingly unpleasant to smell

    Work hard play hard

  5. #15
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    When a wing stalls, you reduce the angle of attack away from the critical angle of attack, that is all. You need to add power to increase speed so the wing will make enough lift to support flight at a given weight. Angle of attack and airspeed have a direct relation. Poor stall recovery technique is dropping the nose too much, as you also lose a lot of altitude. In case of the 747, add max power and lower the nose a few degrees while keeping wings level. Because the center of thrust on a 747 or any other airplane with wing mounted engines, is below the actual CoG, the nose will want to pitch up a little. Should be able to enter a stall, recover with less than 300ft of altitude lost.
    The MAX has under specific stall conditions, a poor ability to recover, hence why the engineers wanted to automate a recovery before it became too deep.
    Last edited by RB211; 04-02-2019 at 01:05 PM.

  6. #16
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    Quote Originally Posted by J Tiers View Post
    Nose down IS THE stall recovery technique.... A stall is excess angle of attack (wing angle with respect to airflow) and is associated with slow speed relative to the air density at your altitude. A "low energy" position. As you go slower, you need increased angle of attack, or else flaps.

    So, nose down means increasing speed, and increasing energy, as well as a decreasing angle of attack.

    The MCAS automatically trimmed the nose down, which seems to be the issue in the crashes... it did not need to because there was no stall, the sensor, which is known to be a possible issue (see link), was giving bad data.

    But, there was a switch to shut down the system, and that switch was apparently not used.

    https://www.bloomberg.com/amp/news/a...-later-crashed
    You should know that those switches cut off hydraulic power to the stab trim, keeping the stab stuck in that position. I've had the pleasure of flying an airplane that would get a sticky elevator trim that required a ton of forward yoke pressure until the airplane slowed down enough that the trim would unfreaze. Just one of the many ways Flight Express tried to kill me flying canceled checks for banks while building time.
    Last airline, I flew a CL65, better known as a CRJ. It had two disconnects for the yoke pitch and roll incase they became jammed. In the Sim, they would jam both, require us to pull the handles, now one pilot would have pitch control, the other one had roll, and we had to bring it back and land it, was always fun.
    We also practiced runaway stab trims and disconnecting the trim, being forced to fly it back with a ton of yoke pressure required beyond the airspeed the stab trim ended being set to.

  7. #17
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    Quote Originally Posted by RB211 View Post
    You should know that those switches cut off hydraulic power to the stab trim, keeping the stab stuck in that position. I've had the pleasure of flying an airplane that would get a sticky elevator trim that required a ton of forward yoke pressure until the airplane slowed down enough that the trim would unfreaze. Just one of the many ways Flight Express tried to kill me flying canceled checks for banks while building time.
    ......
    Others elsewhere, who have apparently flown them say that the cutoff does not take away trim, that there are two inputs to trim and the manual trim is still active with at least one form of cutoff. However, if the switch is to cut off a runaway trim, then it makes sense that all inputs to it would be cut off.

    One stated that there are two motors for the trim, and that actual power to one is cut off by the switch in question. That makes sense on the basis of SPOF, at least.

    I have obviously zero experience of that A/C, have not even ridden in one, so I do not know any of it of my own knowledge.
    1601

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  8. #18
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    A friend is a long time American Airlines pilot. He told me his pilot's union's preliminary info was that the Lion Air pilot was trying to read the manual and the first officer was trying to level the plane against the MCAS system. It takes 90 lbs of pressure on the control column to defeat the MCAS downward bias. He had no info on why the angle-of-attack sensors ( a pair of vanes) were not working properly.

    RWO

  9. #19
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    There are several points that seem to be misunderstood, although my only source of info is the airliners.net thread and linked articles.

    1. MCAS was added to the 737MAX because the larger engines had to be mounted further forward because of insufficient ground clearance, thus causing greater tendency to raise the nose.

    2. The larger engines for the MAX are more powerful and about 15% more efficient, which was a decision based on profitability.

    3. Boeing introduced MCAS to make the plane similar enough to the (NG?) version with the original engines, so that a separate type designation and training would not be needed, thus cutting costs and speeding up the production to compete with the Airbus (IIRC).

    4. Information about MCAS was deliberately withheld or minimized to maintain the illusion of "no difference". There was just a short iPod presentation given to pilots.

    5. The AoA reading for MCAS was from a single sensor, and possibly randomly switched between the two that were mounted. There was no discrepancy warning - that was an extra cost "option" that was only ordered by a few airlines.

    6. The original specifications for MCAS was that it would only supply 1.25 degrees adjustment each time it operated, at 5 second intervals. But there was a poorly documented change that gave it four times as much adjustment, full 5 degrees.

    7. The recommended procedure for runaway flap control was based on observation of continuous operation to maximum, and not where it turned on and off, which is what MCAS did with the faulty sensor.

    8. The electronic flap control would override the MCAS control, and was much stronger and faster than manually operating the trim wheels. So the proper method would be to achieve proper trim using the electronic control, and then disable autopilot (and MCAS).

    9. On the fatal Lion Air flight, the pilot had successfully regained control against the improper operation of MCAS by repeatedly using the electronic control. But he may not have fully explained what he was doing to the FO when he handed over control to research the problem, and he did not do enough to restore control.

    10. There is also some evidence that airspeed was incorrectly indicated, so the pilots unknowingly increased speed beyond what was safe at low altitude, possibly causing damage to the flaps and control mechanism.

    11. Apparently there were no (or very few) simulators specifically for the 737MAX with MCAS, and possibly no scenario tested for AoA or airspeed failures.

    12. Regarding pilot experience and flight hours, it has been suggested that many such hours were logged while operating the plane on full autopilot, which is equivalent to just being a passenger.

  10. #20
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    Heavy automation and lack of training is a disaster waiting to happen. And it happened. Twice.

    That and it is obvious that Boeing changed the flight envelope on the 737. To save certification costs and training costs they added some systems so it would fly like a regular 737. The 737 Max is not a 737, it is a new airplane and should have required all the checks and balances that go along with a new airplane.

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