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Thread: Lion Air 737-Max missing, presumed down in the sea near CGK (Jakarta)

  1. #61
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    Quote Originally Posted by Evan View Post
    Where is that coming from?
    https://www.flightradar24.com/blog/f...-flight-jt610/

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    Quote Originally Posted by vaztr View Post
    Are we ruling out rudder hard over - it is a 737
    I think investigators have already ruled it out, per the preliminary analysis of the FDR. But I don't know that for sure.

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    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    I don't remember. The wording was not "uncommanded" but sudden, there are reports in avherald about the problems they had with the airspeed and altitude data, the STS, and the control feel system. The FDR that contains 1800 (!!!!) parameters for the last several flights will probably tell.
    Big distinction between "sudden" and "uncommanded"... I will be very surprised if anything here was uncommanded. There's had been a lot of chatter about STS. That system has been around on the NG's without ever causing anything like an uncommanded sudden loss of altitude.

    STS basically uses the autopilot servo on the (antiquated and overly-complex) elevator to add a small bit of opposing trim force, to compensate for things like underslung thrust at high power, light weight and aft CoG. It was needed to certify the NG, to meet the FAR requirement for minimum trim force. It's not HAL9000.

    If STS were "operating in the wrong direction", it would be subtracting required trim force. You have mentioned, I think, that on a conventional aircraft with control feedback, you can fly by letting the aircraft speak to you, by feel, as opposed to following UAS pitch/power procedure and QRH values. Perhaps this crew also felt that way. Perhaps they also failed to realize that there are stealth factors on modern (and awkwardly modernized) jets that the engineers took into consideration when they wrote those procedures, and thus they should always be adhered to for reasons you might not be aware of...

    On the other hand, forget STS. What happens when you are without reliable airspeeds and you decide to depart level pitch/power flight, to enter a turn back to base, when you are flying 20kts slower than you think?

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    Quote Originally Posted by Evan View Post
    What happens when you are without reliable airspeeds and you decide to depart level pitch/power flight, to enter a turn back to base, when you are flying 20kts slower than you think?
    The aircraft might respond with a fairly typical and not overly sudden phugoid behavior- in particular the behavior normally associated with turning while a little slow.

    Electrons shoot through the windows at near-light-speed hitting carbon-based analysis systems which are reasonably good at determining attitude.

    Laws of physics, including FAMILIAR power, attitude and performance settings remain unchanged.

    AOA-based stall warning systems remain functional.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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    Thank you. I would say that a sudden change from about +2500 fpm to about -3500 fpm in about 20 seconds (that's -6000 fpm per second or -100 fps or an acceleration -3.1g which corresponds to a load factor of -2.1) would be a sudden, very likely uncompounded, fall. And since it happens 3.5 minutes after lift off with the plane barely above 5000 ft, I would say that this qualifies as shortly after take-off too.

    There were testimony from different passengers saying that the plane suddenly started to fall out of the sky and that they thought that was the end and all these typical comments that normally don't mean much in the sense of reliable data for an investigation, but some times it does if it is consistent with other hard data.

    One could say that perhaps this was the result not of a real fall but of a false altitude and vertical speed indication caused by unreliable air data, but the way the GROUNDspeed varies during the incident makes me think this was not the case.

    If the plane really experimented an acceleration anywhere close to that, it should have been grounded for a through inspection since it exceeds the required design limit load by quite a bit.

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    I hesitated before sticking my neck out and posting. My flying experience is mainly in gliders ( 5000+ hours) instructor rating and more 300k+ cross country flights than I can count.I have seen many young men use their gliding experience as a stepping stone to a career in civil or military aviation.In many cases they have reported positive feedback from their professional instructors in terms of their flying skills and especially in terms of their sensitivity to and to the control of the the attitude of the aircraft. In this accident ( ok not proved yet) and in others,for example AF447, when systems fail the pilots involved seem unable to call upon the basic skill of establishing and maintaining their aircraft in a stable attitude giving themselves time to sort out the systems problem.

    I acknowledge freely that the " systems" and the pilots mastery of them have contributed enormously to today's remarkable standards of flight safety. I suppose that I am asking, in the extremely rare event of the systems failing, if the training equips the pilots to revert to basic principles.

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    "5000+ hours) instructor rating and more 300k+ cross country" Now that is impressive! A touch unbelievable too!!

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    Quote Originally Posted by BoeingBobby View Post
    "5000+ hours) instructor rating and more 300k+ cross country" Now that is impressive! A touch unbelievable too!!
    Why? 5K hours and 300K cross country flight gives you an average of exactly 1 minute per cross country flight (if all the 5k hours were used for cross country). Anything remarkable there?
    (let me bet it's a typo and the 300k should be 300)

    The 5000 hours is not unheard of for GA instructors. If you instruct 4 hours per day 150 days a year you make it in 8 years. Let me guess the guy is slightly more than 30 y/o.

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    Quote Originally Posted by Evan View Post
    You have mentioned, I think, that on a conventional aircraft with control feedback, you can fly by letting the aircraft speak to you, by feel, as opposed to following UAS pitch/power procedure and QRH values.
    You took short excerpts of 3 totally different comments that I made, mixed them together, put them totally out of context, and voila!!!

    On the other hand, forget STS. What happens when you are without reliable airspeeds and you decide to depart level pitch/power flight, to enter a turn back to base, when you are flying 20kts slower than you think?
    When you are flying at more than 300 kts? Nothing. I am more concerned with overspeed than with stall here.

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    The K in 300k is kilometres.Once you have been bitten by the gliding bug, the challenge is to fly cross country to a pre- determined turning point. In the case of 300k, the point will be at 150k and then to return to base.Typically,on a good day when thermals are strong, with a cloudbase of 4/5000ft you would hope to accomplish the task in less than 5 hours. I hope that this makes things clearer.

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    Quote Originally Posted by Gabriel View Post
    Thank you. I would say that a sudden change from about +2500 fpm to about -3500 fpm in about 20 seconds (that's -6000 fpm per second or -100 fps or an acceleration -3.1g which corresponds to a load factor of -2.1) would be a sudden, very likely uncompounded, fall. And since it happens 3.5 minutes after lift off with the plane barely above 5000 ft, I would say that this qualifies as shortly after take-off too.
    Would maintenance have downloaded the FDR from the previous flight to troubleshoot this? Would they have a record of that? One key question here is whether they were on autopilot when the sudden plunge occurred. An undetected air data anomaly can cause this to happen on autoflight, as it did on those Qantas A330's and that Malaysia B777 some years ago. Boeing does have a history with shady cross-comparator behavior on avionics. Turkish 1951 experienced a cross-comparator fail on the autothust unit which led it to rule a single malfunctioning radalt valid and retard thrust way... too... early...

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    Quote Originally Posted by Gabriel View Post
    Why? 5K hours and 300K cross country flight gives you an average of exactly 1 minute per cross country flight (if all the 5k hours were used for cross country). Anything remarkable there?
    (let me bet it's a typo and the 300k should be 300)

    The 5000 hours is not unheard of for GA instructors. If you instruct 4 hours per day 150 days a year you make it in 8 years. Let me guess the guy is slightly more than 30 y/o.
    Thought he was saying 300000 hours cross country. Remember Gabe that I also have a commercial glider rating.

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    Quote Originally Posted by Aviation Herald
    On Nov 7th 2018 Boeing issued an Operations Manual Bulletin (OMB) to all Boeing 737 MAX Operators stating that the investigation into the crash of PK-LQP found one of the Angle of Attack Sensors had provided incorrect readings, which could cause the aircraft's trim system to uncommandedly trim nose down in order to avoid a stall during manual flight. The OMB directs "operators to existing flight crew procedures to address circumstances where there is erroneous input from an AOA sensor." The OMB reiterates the Stabilizer Runaway non-normal checklist.

    The flight Crew Operations Manual Bulletin TBC-19 reads:

    The Indonesian National Transportation Safety Committee has indicated that Lion Air flight 610 experienced erroneous AOA data. Boeing would like to call attention to an AOA failure condition that can occur during manual flight only.

    This bulletin directs flight crews to existing procedures to address this condition. In the event of erroneous AOA data, the pitch trim system can trim the stabilizer nose down in increments lasting up to 10 seconds. The nose down stabilizer trim movement can be stopped and reversed with the use of the electric stabilizer trim switches but may restart 5 seconds after the electric stabilizer trim switches are released. Repetitive cycles of uncommanded nose down stabilizer continue to occur unless the stabilizer trim system is deactivated through use of both STAB TRIM CUTOUT switches in accordance with the existing procedures in the Runaway Stabilizer NNC. It is possible for the stabilizer to reach the nose down limit unless the system inputs are counteracted completely by pilot trim inputs and both STAB TRIM CUTOUT switches are moved to CUTOUT.

    Additionally, pilots are reminded that an erroneous AOA can cause some or all of the following indications and effects:

    - Continuous or intermittent stick shaker on the affected side only.
    - Minimum speed bar (red and black) on the affected side only.
    - Increasing nose down control forces.
    - Inability to engage autopilot.
    - Automatic disengagement of autopilot.
    - IAS DISAGREE alert.
    - ALT DISAGREE alert.
    - AOA DISAGREE alert (if the AOA indicator option is installed)
    - FEEL DIFF PRESS light.

    In the event an uncommanded nose down stabilizer trim is experienced on the 737-8 /-9, in conjunction with one or more of the above indications or effects, do the Runaway Stabilizer NNC ensuring that the STAB TRIM CUTOUT switches are set to CUTOUT and stay in the CUTOUT position for the remainder of the flight.
    Now, wait a tick... am I to understand that there is no cross-comparator redundancy on the AoA sensors? Because... that would be an accident waiting to happen.

    In manual flight, the NG (and I assume the MAX) will command a forward column trim force 4X the normal one and will continue to trim the THS (incrementally?) to a full nose down position. You don't want a single sensor failure to cause this to happen.
    Onside stickshaker activation, fine, but not this.

    If the pilots have good situational awareness, they can stop this by using the trim cutoff switches. Normally, electrical trim can also be stopped by pulling or pushing against the trim direction, but maybe not in the excessive AoA regime. They can also just grab the trim wheel and stop it.
    SItuational awareness should come from the stickshaker, the sudden column force and the trim wheel activation. Hopefully the AoA indicator is now standard on the MAX. It probably isn't...
    But also... it results in an airspeed and altitude disagree warning. Just to help scramble your situational awareness I guess. And no AoA indicator: no AoA disagree warning. Brilliant.

    Hopefully the report will tell us that a single failure cannot cause an uncommanded full-nose-down stabilizer trim.

  14. #74
    Senior Member 3WE's Avatar
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    Quote Originally Posted by Gabriel View Post
    ***I would say that a sudden change from about +2500 fpm to about -3500 fpm in about 20 seconds Gabbieaeroengineeringmath***
    I don't like seeing math on short-period radar data (like less than 5 min)...I've seen too many crazy "readouts" on ordinary flights from Flightaware/Flightradar/etc.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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    Quote Originally Posted by pegasus View Post
    ...if the training equips the pilots to revert to basic principles.
    Total ass hat parlour talk...as I became more proficient at MSFS, I found myself shift from hand flying to "playing mind games" while using the autopilot...what does my descent rate need to be...I'll just dial it in and not worry about control inputs, trim, nor phugoid variations in the descent rates...Why chase needles, just switch on a nav function...and then maybe hand fly the bitter end.

    Then, in the real world I see pilots who overwhelmingly twist knobs as they fly precise vectors and standard procedures and use navigation systems.

    I don't think they lack training or lack KNOWLEDGE, but I sometimes wonder if they just totally get out of the habit of flying.

    I know that's a wrong statement as so many folks commit to "hand flying below 10,000 feet" (or many variants of that rule)…

    Even then- you get people who totally lock in on the flight director- and their brain disconnects...and we even see folks chase bad flight director indications when 'traditional instruments' are clearly and correctly screaming foul...

    You are SOOOOOOOOO SOOOOOO so so so so so so used to vanilla flying and knob twisting that you just don't pick up on weird stuff fast enough...

    (And acknowledging that folks get good simulator and CRM training)…

    Not sure what I'm saying other than maybe it's NOT the training, but that you can get comfortable with your YEARS of routines and then excrement transpires.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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    Quote Originally Posted by 3WE View Post
    I don't like seeing math on short-period radar data (like less than 5 min)...I've seen too many crazy "readouts" on ordinary flights from Flightaware/Flightradar/etc.
    It's not radar, it's ADS-B. It is the plane reporting its altitude and vertical speed.

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    Boeing would like to call attention to an AOA failure condition that can occur during manual flight only....

    Additionally, pilots are reminded that an erroneous AOA can cause some or all of the following indications and effects:
    - Automatic disengagement of autopilot.

    So it can put itself in this failure mode!

  18. #78
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    Quote Originally Posted by vaztr View Post
    Boeing would like to call attention to an AOA failure condition that can occur during manual flight only....

    Additionally, pilots are reminded that an erroneous AOA can cause some or all of the following indications and effects:
    - Automatic disengagement of autopilot.

    So it can put itself in this failure mode!
    Two different issues.
    The 737MAX has two AoA vanes.
    The loss of autoflight is because the autoflight must always have multiple sensors in agreement on air data. It will not rely on a single source that might be erroneous, so, if one vane doesn't match the other, no autoflight. Also, the NG uses AoA vane data to calibrate other air data values, which also wouldn't match.
    The uncommanded stabilizer trim (see the AvHerald repost above) that we are discussing here occurs, of course, in manual flight only, and apparently it does not require agreement on air data, although I pray that's not true...

    The A320 has three AoA vanes, so a single failure can be fail-passive. The A350 and—I think— the A380 have four.

  19. #79
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    From the most recent statements, it seems like what we are looking at is a ground repair to correct pitot probe issues that resulted in a damaged, defective or otherwise malfunctioning AoA vane. The pitot issues on the previous four flights might not have played a role in the crash.
    The maintenance log mentions flushing the pitots. Hopefully this was done by the book, in a way to avoid water ingress into the AoA vanes. Otherwise, they could have iced up, although maybe not at 5000ft in Indonesia...

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    Quote Originally Posted by Evan View Post
    From the most recent statements, it seems like what we are looking at is a ground repair to correct pitot probe issues that resulted in a damaged, defective or otherwise malfunctioning AoA vane. The pitot issues on the previous four flights might not have played a role in the crash.
    The maintenance log mentions flushing the pitots.
    There was more than that in the previous flights...

    Apart from the remark of unreliable airspeed and altitude, which prompted the flushing of the captain's static ports, an entry for elevator feel computer light illuminated was written down by the flight crew of [the previous flight], maintenance opened and cleaned a cannon plug connector for the elevator feel computer
    Combine with this:

    Additionally, pilots are reminded that an erroneous AOA can cause some or all of the following indications and effects:

    - ...
    - FEEL DIFF PRESS light.
    And with this (re: ADS-B data from previous flight):

    I would say that a sudden change from about +2500 fpm to about -3500 fpm in about 20 seconds (that's -6000 fpm per second or -100 fps or an acceleration -3.1g which corresponds to a load factor of -2.1) would be a sudden, very likely uncompounded, fall. And since it happens 3.5 minutes after lift off with the plane barely above 5000 ft, I would say that this qualifies as shortly after take-off too.

    There were testimony from different passengers saying that the plane suddenly started to fall out of the sky and that they thought that was the end and all these typical comments that normally don't mean much in the sense of reliable data for an investigation, but some times it does if it is consistent with other hard data.

    One could say that perhaps this was the result not of a real fall but of a false altitude and vertical speed indication caused by unreliable air data, but the way the GROUNDspeed varies during the incident makes me think this was not the case.

    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
    --- Defend what you say with arguments, not by imposing your credentials ---

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