Boeing’s automatic trim for the 737 MAX was not disclosed to the Pilots

By Bjorn Fehrm

November 14, 2018, © Leeham News.: The automatic trim Boeing introduced on the 737 MAX, called MCAS, was news to us last week. Graver, it was news to the Pilots flying the MAX since 18 months as well.

Boeing and its oversight, the FAA, decided the Airlines and their Pilots had no need to know. The Lion Air accident can prove otherwise.

The background to Boeing’s 737 MAX automatic trim

The automatic trim we described last week has a name, MCAS, or Maneuvering Characteristics Automation System.

It’s unique to the MAX because the 737 MAX no longer has the docile pitch characteristics of the 737NG at high Angles Of Attack (AOA). This is caused by the larger engine nacelles covering the higher bypass LEAP-1B engines.

The nacelles for the MAX are larger and placed higher and further forward of the wing, Figure 1.

Figure 1. Boeing 737NG (left) and MAX (right) nacelles compared. Source: Boeing 737 MAX brochure.

By placing the nacelle further forward of the wing, it could be placed higher. Combined with a higher nose landing gear, which raises the nacelle further, the same ground clearance could be achieved for the nacelle as for the 737NG.

The drawback of a larger nacelle, placed further forward, is it destabilizes the aircraft in pitch. All objects on an aircraft placed ahead of the Center of Gravity (the line in Figure 2, around which the aircraft moves in pitch) will contribute to destabilize the aircraft in pitch.

Figure 2. The 737-800 (yellow) overlaid on the 737 MAX 8 (purple), with the line denoting the CG in pitch. Source: Leeham Co. and 737 ACAP.

The 737 is a classical flight control aircraft. It relies on a naturally stable base aircraft for its flight control design, augmented in selected areas. Once such area is the artificial yaw damping, present on virtually all larger aircraft (to stop passengers getting sick from the aircraft’s natural tendency to Dutch Roll = Wagging its tail).

Until the MAX, there was no need for artificial aids in pitch. Once the aircraft entered a stall, there were several actions described last week which assisted the pilot to exit the stall. But not in normal flight.

The larger nacelles, called for by the higher bypass LEAP-1B engines, changed this. When flying at normal angles of attack (3° at cruise and say 5° in a turn) the destabilizing effect of the larger engines are not felt.

The nacelles are designed to not generate lift in normal flight. It would generate unnecessary drag as the aspect ratio of an engine nacelle is lousy. The aircraft designer focuses the lift to the high aspect ratio wings.

But if the pilot for whatever reason manoeuvres the aircraft hard, generating an angle of attack close to the stall angle of around 14°, the previously neutral engine nacelle generates lift. A lift which is felt by the aircraft as a pitch up moment (as its ahead of the CG line), now stronger than on the 737NG. This destabilizes the MAX in pitch at higher Angles Of Attack (AOA). The most difficult situation is when the manoeuvre has a high pitch ratio. The aircraft’s inertia can then provoke an over-swing into stall AOA.

To counter the MAX’s lower stability margins at high AOA, Boeing introduced MCAS. Dependent on AOA value and rate, altitude (air density) and Mach (changed flow conditions) the MCAS, which is a software loop in the Flight Control computer, initiates a nose down trim above a threshold AOA.

It can be stopped by the Pilot counter-trimming on the Yoke or by him hitting the CUTOUT switches on the center pedestal. It’s not stopped by the Pilot pulling the Yoke, which for normal trim from the autopilot or runaway manual trim triggers trim hold sensors. This would negate why MCAS was implemented, the Pilot pulling so hard on the Yoke that the aircraft is flying close to stall.

It’s probably this counterintuitive characteristic, which goes against what has been trained many times in the simulator for unwanted autopilot trim or manual trim runaway, which has confused the pilots of JT610. They learned that holding against the trim stopped the nose down, and then they could take action, like counter-trimming or outright CUTOUT the trim servo. But it didn’t. After a 10 second trim to a 2.5° nose down stabilizer position, the trimming started again despite the Pilots pulling against it. The faulty high AOA signal was still present.

How should they know that pulling on the Yoke didn’t stop the trim? It was described nowhere; neither in the aircraft’s manual, the AFM, nor in the Pilot’s manual, the FCOM. This has created strong reactions from airlines with the 737 MAX on the flight line and their Pilots. They have learned the NG and the MAX flies the same. They fly them interchangeably during the week.

They do fly the same as long as no fault appears. Then there are differences, and the Pilots should have been informed about the differences.

277 Comments on “Boeing’s automatic trim for the 737 MAX was not disclosed to the Pilots

  1. In figure 2 it shows the same center of gravity for the NG as the Max. I find this a bit surprising as I would have expected that mounting heavy engines further forward would have cause a shift forward in the center of gravity that would not have been offset by the longer tailcone, which I’m assuming is relatively light even with APU installed.

    Based on what is coming out about the automatic trim, Boeing must be counting its lucky stars that this incident happened to Lion Air and not to an American aircraft. If this had happened in the US, I’m pretty sure the fleet would have been grounded by the FAA and the class action lawyers would be lined up outside the door to get their many pounds of flesh.

    This is quite the wake-up call for Boeing.

    • If the FAA is not going to comprehensively review the certification for the 737 MAX, I would not be surprised if EASA would start taking a closer look at the aircraft and why the FAA seemingly missed the seemingly inadequate testing of the automatic trim when they decided to certified the 737 MAX 8.

      • One wonders if there are any OTHER goodies in the new/improved/yet identical handling latest iteration of this old bird that Boeing did not disclose so that pilots need not be retrained.
        EASA & FAA likely already are asking some pointed questions and will want to verify any statements made by the manufacturer.
        Depending on the answers pilot training requirements are likely to change materially.

        • The reused 737 fuselage design has also been repeated extended without extending the wheel base. This means the tail of the plane is alot longer than originally intended and forces pilots to land at higher than intended speeds since the plane has to land with a flatter pitch angle so the tail doesnt strike the ground. The higher speeds mean potentially harder landings and alot harder braking, over heating of the brakes.

          • Also a non-trivial number of tail strikes on 737s. No idea of stats, but my impression is very much that the stretched airliners smack tails a lot more than shorter planes.

            At least one accident report on this I read cited the PICs familiarity with a shorter config; one day he flew a long plane and immediately smack the tail on landing. Same controls and behavior encourage these sorts of things.

          • They don’t use the brakes just after touch down upon landing. The aircraft is slowed by reversing engines thrusters to a very low speed. Before attempting to use brakes. Inhaling brakes at landing speed would quickly burn them and the tires out from the heat produced. And could set the aircraft aflame.

        • The exaust heat from the new GE engines, i believe, will be the next problem. The Nacelles is positioned so high that heatrd exaust has no where to escape while sitting in line waiting to taxi out for take off. Compare it to a regular 737- 100 or 200 for an example. Thats hot air were taking about and with flaps set for take off damage could be done to the aluminum under wings plus fuel and hydraulic lines. Not to mention melting grease for flap control. Time will tell.

          • Probably wouldn’t need all these electronic corrections if the narrow wings provided adequate lift.

        • When they put new features such as these and not inform the pilots they should put the people on the plane that think it is a good idea not to inform the pilots and such of these systems that take control away from the pilot. If they are willing to put the lives of other on the line they should be willing to do the same with their lives.

    • CG will vary based on loading. I’d guess the line is the rear-most allowed CG.

    • If it happened to Lion Air and not an U.S. airline it is simply that Lion Air should have repaired!

      Indeed it is useless to let the pilots know when an air carrier is serious.

      Lion Air is your answer

    • I noticed the same thing, too. As shown, that line is likely the aerodynamic center (ac). AC is often confused with the cg, and its location does not vary that much within aircrafts with similar wing designs.

      The difference in distance btw the ac and cg determines an aircraft’s pitch characteristics and informs the design of the horizontal stabilizer and elevator.

      • Great view. AC line is shown in the picture, and not the CG line.

      • Is this term Aerodynamic Center the same as the Center of Pressure/Center of lift? If so and it behaves the same, then the picture really doesn’t depict what it intends to, as the lines would then be in different places on each model. The diagram should have shown a different CG line and AC line for each aircraft outline, the distinction being a greater difference between the two for the 737 max, if I’m following correctly.

        • They don’t use the brakes just after touch down upon landing. The aircraft is slowed by reversing engines thrusters to a very low speed. Before attempting to use brakes. Inhaling brakes at landing speed would quickly burn them and the tires out from the heat produced. And could set the aircraft aflame.

          • not true…as there is autobrake feature set from 1 to 3 with max position..which activates immediately upon touchdown, to help slow down the aircraft soonest possible especially on short runways…just like the airspeed spoilers which can be set on auto (armed) to immediately activate upon touchdown…also to help slow down the speed the soonest possible…

          • The autobarke kicks in after the aircraft is on ground. Reversers are not always used. The primary way to stop the aircraft is the brakes.

        • Yes and the max engines are bigger around and heavier, than the next gen 737, and further forward. And working as a jet mech a&p and have a private multi instr. It seems nobody has talked about that the max should have a further aft weight and balance range. Also way you balance flight controls , you balance them mostly with a little more weight ahead of the pivot point with lead or hard metal.Also , I think and nobody has talked about doing wind tunnel tests , with the max at 150 to 500 mph , and jet engines running from idle to 100% n1, and see how much drag those new engines can cause!

      • The line shown is the CG. I say that because it fall between the outer and inner fuel tanks. In flight the outer wing tanks are used first and as it’s used off, fuel from inner tanks is pumped pumped into outer tanks to keep the CG in it’s proper place. This type of fuel management is required on sweeps back wings to keep the craft trimed during flight.

    • Hi Bruce, expect product liability litigation in the US courts even if the accident occured outside the US. Boeing is domiciled in the US and US courts have jurisdiction.

      In my opinion, even the FAA should be a defendant for certifying the aircraft and endangering the lives of the unsuspecting public.

      Take time to read this article i published last year and let me know what you think.

      Sebina Muwanga

      • Well, in practice there appears to be enough political pressure and internal career sensitivity to nearly paralyze the FAA from making any rapid changes or major innovations on its own. Ironically, risk aversion and cost avoidance are probably among the combination of things that led to this mishap. I fear if the administration had to contend with financial liability for its actions (or inactions) as well it would become all but incapacitated.

        • Like the angle of attack sensors could be monitored by simple rheostats and not esds sensedive software
 And don’t weld your bumpers on your truck without disconnecting your battery Ground or your engine computer can fry

    • hi dears
      I think that even the pilot didnt knew about the MCAS ; this case can be corrected by only applying the boeing check list (QRH) stabilizer runaway.
      the pilot when they noticed that stabilizer are trimming without a knewn input ( from pilot or from Auto pilot ) ; shout put the cut out sw in the off position according to QRH.

      • Please note that the first actions pulling back on the yoke to stop it.

        Also keep in mind the aircraft is screaming stall and the stick shaker is activated.

        Pulling back on the yoke in that case is the WRONG thing to do if you are stalled.

        The Pilot has to then determine which system is lading.

        At the same time its chaning its behavior from previous training, every 5 seconds, it does it again.

        There also was another issue taking place at the same time.

        So now you have two systems lying to you, one that is actively trying to kill you.

        If the Pitot static system is broken, you also have several key instruments feeding you bad data (VSI, altitude and speed)

        • Most pilots could do a refresher course on the old book stick-and-rudder. It always comes down to is there a plane slowing down while you have the stick pulled or pushed you can sense the airspeed other ways by like the engine starts to slow down a bit as you put more load on it the sound of the air going over the fuselage it should be flown like it’s in manual at all times and just letting the computer help you do more efficient flying

          • EVERY PILOT SHOULD READ STICK AND RUDDER ALD LIVE BY IT! Autopilot should not be engaged until cruise altitude is reached.

          • Stick & Rudder does not apply when you are forced to use software … That is a main point of this article.

      • It was a memory item years and years ago, so, old farts like me would know about the cutout switches.

      • Except you have to hand crank quickly to correct the nose down trim after cutout switch is thrown. How fast can you hand crank? Perhaps not fast enough.

      • Hello Don Gerling,

        Regarding: “Do the trim wheels move when MCAS is activated for whatever reason?”

        The following is from a post by Tech-guru further down in these comments.

        “Which ever motor moves the stab, the cockpit wheel has to move as it is back driven by cable. There is no other way to move the STAB. Visual cues are present for MCAS opn.”

      • excellent point to bring to this discussion….if the trm wheels move then they would give the pilots a sense of ‘auto corrective action” that the aircraft is taking…and that is to be interpreted ‘opposite’ to how the wheels are moving…..
        i.e., if the wheels are moving forward then the the aircraft is indeed stalling or approaching a stall & is in a stage of correcting that situation….while if the wheels are moving backward, then the aircraft is nose diving or pitching down and the wheels are trying to counter that by moving backwards…
        The bottom line is…the B737 Max with its new larger engines, fitted onto the same airframe craft of the B737-800 and B737NG…simply produced an aerodynamically UNSTABLE craft, which problem SHOULD NOT HAVE BEEN CORRECTED BY A SOFTWARE….BUT BY INTRODUCING CORRECTIVE AERODYNAMIC BLADE FINS ON THE OUTER COVER OF THE NEW ENGINE THAT WILL CREATE A COUNTER AERODYNAMIC EFFECT TO ELIMINATE THE UPWARD PITCHING TENDENCY OF THE AIRCRAFT….
        Of course this would have resolved the main aerodynamic instability of the aircraft as a whole…This would have also been doable as Boeing did not want to redesign the whole landing gear (main and front) structures, their anchoring & stowing up challenges with the available under belly space on the B737NG fuselage…and lose the market in selling against the Airbus 320 & 321NEO….
        Unfortunately, resolving basic aerodynamic stability issues as this was not done in the correct engineering manner, procedure, and ethics…You have something that doesn’t fly naturally, you make it fly naturally….you balance it aerodynamically…by introducing aerodynamic surface features to overcome that….you don’t rely on a computer to ‘keep correcting’ that situation through assumed readings that can easily be affected by malfunctioning sensors…and up until you run out of altitude…!!!


      • totally agree with you….if the B737Max cannot be made ‘naturally’ aerodynamically safe to fly…without any ‘auto corrective electronic feature’ as the MCAS…otherwise one of four options…
        .1. …introduce aerodynamic corrective features onto the fuselage or engine outer covers, (which may be retracted once the aircraft is at cruising speed)…these counter the pitch up tendency at low speeds with high AoA (at takeoffs).

        .2. redesign the whole main wing structure that holds the main landing gears to allow for a higher ground clearance for these new engines…but then that would create another new problem with heavier materials, (longer gear shafts)…(further anchored away from the fuselage)….this will affect the AC & the CG as well….

        .3….simply not install this new engine on the same fuselage of the B737NG & 737-800……!!!

        .4. simply keep the B737NG as the latest in their line and come up with a similar main structured aircraft as the 737NG but with higher ground clearance to accommodate for the new engine size which will also allow future introductions of larger & more efficient engines to be matched to such fuselage design.

    • The longer moment “arm” from the CG to the newly extended tailcone can compensate for a lot of added weight up front given the engines are so much closer to the CG.

      • correct but this does not fall within the fact that those new engines had to be placed a bit higher up along the horizontal plane of the aerodynamic lift of the wing ( to escape the ground clearance limitations)….meaning the nacils of those engines ended up within the zone of the upward lift moment of the high air pressure that is building up at the front edge of the wings….which is why there is that tendency for the aircraft to pitch up since the forward positioning of those new engines with a larger nasle acted as an extension of the front edge of the wings…just like slats would….producing an upward lift moment enhancing that of the wings…!!

    • Which figure shows who owns the patent for remote control chips on planes, trains, cars and boats?

    • Well it happened again, son, and you’re forgetting what the 28000 lbs of thrust on either side does to the pitching moment of the airplane..

      • absolutely…..simple aerodynamic physics…which unfortunately was not corrected in the correct manner……but by repetitive corrective electronic impulses from a computer….and unfortunately not to fly by wire system….but which had to still be interpreted & transferred into hydraulic forces to control the elevators…

    • The problem with instabilitet should solved by basic aerodynamic changes? There are no vortex generator on the enginees. Should it be possible to improve the lift and move the center of lift backwards at High AoA? I guess there is a separation behind the enginees early at the Grey zone and strong drag from the enginees contributing to the undesirable momentum

      • The problem is that the engine nacelle is designed for 0 lift at normal flight attitude. At high AOA, with the wing near stall, the nacelle is at max lift, so induces a nose-up pitch, much stronger than in previous models due to a) larger nacelles, and b) longer moment arm due to the more forward position.

        In short, if you get close to stall, the engines push you over the limit… Oopsie. Enters the Fly-By-Wire fix. Which relies on sensors, which can fail, which can lead to… A monster-class clusterfcuk, that will be taught to the next generation of engineers: “You Shall Beware Of Unintended Consequences When Changing A Bolt On A Design That Works”.

        You actually don’t want vortex generators on the Max’s nacelles, spoilers would be more useful…

    • The center of gravity didn’t change. The aerodynamics did. The higher engine mounting along with the tail cone keep the cog the same.

    • When MCAS is trimming, does the trim WHEEL turn, like in normal yoke switch trimming?

    • One on each side. But look at my answers in last weeks article why there can be no checking of one against the other. There can be other plausibility checks but not restricted to between the two.

      • They do compare AoA signals as there is an AoA signal disagree message displayed on the PFD if there is difference between the two signals. This does not explain why this system took action on the info from one defective AoA sensor.

        • If I am tracking this right, the AOA can disagree depending on the aircraft attitude and which side is seeing stall and which is not in a real stall.

          If they can’t cross connect the AOS to confirm each other, then you have to come up with another means (still chewing on that one)

          If the Pitot static system also has gone, you have multiple instrument lying to you while one is trying to kill you.

          Even if you figure out to turn trim off and stops one, you have to get the sterilizer back to normal;l with hand wheel, but you still are trying to sort out the VSI, speed and compare it to attitude on the PFD (only the Artificial Horizon portion is right)

          The plane continues to scream stall, your last resort is the Backup Insure Display and its in the center where you cna’t see it all that well from what I can see.

        • Does anyone know here if the 10 second
          interjection of the MCAS is a reassessment of angle of attack or based on each sensor alternating info to the system?

      • Both the x 29 and the space shuttle use for computers and four sets of sensors so that there’s multiple multiple redundancy. there should also be a big ass freaking light on the dash of the aircraft that says the computer has problems do you want to switch to fully automatic, and you should be able to do that in a second. if the two AOA sensors disagreed the pilots are going to stick and rudder mode and you should be paying attention to RPM and AirSpeed and attitude if you have any kind of visual reference

        • The auto portion is what failed. Just follow the flight manual and turn the electric trim off. Manually trim the aircraft and return for landing. I have done it many times in the simulator.

      • I am not an aviation expert, but have some basic understanding of aircraft. For decades, pilots have relied upon an attitude indicator or “artificial horizon” instrument, based upon a simple gyroscope.
        My layman’s understanding is that AOA signals should be fairly consistent with an aircraft’s attitude as indicated by a gyroscope. Would it make sense for MCAS to have a gyro input to allow for some “sanity checking” of AOA signals? If, for example, an AOA sensor indicates a high AOA while the gyro says the aircraft is in level flight, the AOA signal would be suspect, IMHO. If two AOA sensors give conflicting inputs, it would make sense to only use the input that correlates best with the gyro input.

        • The aircraft may climb on a 16 deg slope at 8 deg AoA. The gyro would show 24 deg. It can descent on 3.5 deg slope AoA 8 deg. The AoA is tightly associated with weight and IAS/CAS and turning rate.

      • I believe the sensors are shaped as miniture wings with a port in each that samples the vacuum pressure simular to a static port. And at high AOA the vacuum drops off as it would on the wings upper camber. It makes sense that the two sensors, sensing are connected together. I googled the trim system two days ago and that’s the conclusion I came away with.

    • my understanding is there are two AOA sensors but as long as one gives high AOA reading then MCAS kicks in to trim down

      • Imagine the MAX would hit a bird shortly after takeoff and one AOA Sensor is jammed to a high angle indication. There would be no time to react. This system is just plain dangerous. I am wondering, what control issues Boeing wanted to achieve (=hide) with this undocumented system. A manufacturer usually does not give anything away for free.

        • Yes, the talk at the time was that every improvement had to buy it’s way onto the airplane with an increase in fuel burn. How quickly does a stall happen without pilot action? Must have been quick to necessitate this auto system.

          • You also have to account for the issue at stall and probably the FAA requiring a solution.

            Those trump buy ins.

        • No , as I understood, this system will not act until flaps retraction, so not so shortly after take-off (over 1000 ft and 200 KIAS)

          • Add in it won’t do it in auto pilot either (manual only)

            Ted: Its not how fast it gets, its the characteristics of the aircraft and someone (FAA?) being unhappy with them.

            It does not have to be a serious control issue, if its barely h over the norm by whoever decides that, a solution wold be implemented.

            As has been pointed out, a great deal of human stupidity goes into things as well as brilliance.

            Read the book “To Engineer is Human”.

    • 2, one on each side.
      IMU a single one going overboard is sufficient for the observed effect.

  2. If proven to be the cause of the crash, or at least a contributing factor, then Boeing will have the egg on the face for many years, additional to the liabilities

  3. Bjorn:

    The last line is a bit off in English, it would read better that the pilots should have been told of the change, the right correction and trained in it.

    As it reads it has shades of the pilots were at fault, again its a bit subtle in English as far as idiomatic expressions go.

  4. This is a chilling quote from SW Management:

    “Because the system is only designed to operate in rare conditions while pilots are manually flying, “pilots should never see” the system in operation, according to the Southwest memo. As a result, Boeing chose not to include a description of it in the extensive manuals it prepared for the Max models, said the memo.”

    This has so many aspects of stunning to it, I am close to incoherence.

    • It makes one wonder why they made this decision? Why did they chose to bury a important change to flight control? Boeing begrudgingly was forced to update this plane because of the competition. They had been tweaking an older design for decades. Maybe they did something that they just shouldn’t have done…

      • Had Boeing disclosed the change, it would have required additional pilot training which which was one of the important design considerations “sold” to the airlines. As the article mentions some pilots fly the two models interchangeably as it has been represented that both are identical from the pilot’s perspective.

        • Its not a huge change, add into the Rudder Trim runaway.

          It can be a huge change unexpected and with other problems compounding.

          A 1% change that can cause a 100% loss.

  5. Thanks for explaining that Bjorn.
    The next question I have, is how much is it reasonable to expect the pilot to remember and do in a crisis,even if it is written down somewhere?Did Boeing neglect to inform the pilots about this in order to make the common type rating easier?

    • Grubbie: I can partly answer that.

      Pilots are trained to immediately deal with emergency issues (engine loss etc)

      Then there is a follow up detailed instructions for follow on actions (if any).

      Simulators are wonderful things because you can train lethal scenes without lethal results.

      In this case, with NO pilot training let alone in the manuals, pilots have to either be really quick in the situation or you get the result you do. Some are better at it than others (Sullenbergers along with other aspects elected to turn on his APU even though it was not part of the engine out checklist)

      The other one was to ditch, too many pilots try to turn back even though we are trained not to.

      What I can tell you from personal expereince is having got myself into a spin without any training, I was locked up logic wise (panic) as suddenly nothing was working the way it should.

      I was lucky I was high enough and my brain kicked back into cold logic mode and I knew the counter to a spin from reading)

      Another 500 feet and I would not be here to post.

      While I did parts of the spin recovery wrong, fortunately in that aircraft it did not care, right rudder was enough to stop it.

  6. It’s starting to look as if Boeing will not be able to just pay victims’ relatives in the form of “condolence money”, without admitting liability.

    • Im pretty sure, even though its an Indonesian Airline, any whiff of fault with the plane itself will have lawyers taking Boeing on in US courts.

  7. Astonishing to say the least. It is quite unlike Boeing. They are normally very good in the documentation and training. It makes everyone wonder how such vital change on the MAX aircraft was omitted from books as weel as in crew training.
    Your explanation is very good as to why you need this damn MCAS. But can you also tell us how just one faulty sensor can trigger this MCAS. In all other Boeing models like B777, the two AOA sensor signals are compared with a calculated AOA and choose the mid value within the ADIRU. It eliminates a drastic mistake of following a wrong sensor input.

    • Hi Tech-Gury,

      it’s not sure it’s a one sensor fault. One sensor was changed amid information there was a 20 degree diff between the two sides. But then it happened again. I think we might be informed something else is at the root of this, which could also trip such a plausibility check you mention. We just don’t know. What we know is the MCAS function was triggered without the aircraft being close to stall.

      • If it’s certain that the MCAS was doing unhelpful things, that coupled with the fact that no one was telling pilots anything about it suggests to me that this is already effectively an open-and-shut case so far as liability, regulatory remedies are concerned.

        The tecnical root cause is also important, but probably irrelevant so far as estbalishing the ultimate reason behind the crash.

      • American has instructed its pilots to turn it off.

        They did not say how they were doing that.

          • That gets into the trim system vs the program portion the AOA is involved in.

            Have to re-read it and see if it sorts out, but it seems the de-activate removes electric trim which would mean manual trim all the time.

            Not sure how that would impact things as the trim wheel is handy but…………………….

        • But the MCAS is not there on the whim of some engineer. Based on what Bjorn is saying the reason for the MCAS is that the aircraft is divergent in pitch once a critical AOA has been exceeded. Turning it means you are disabling a mechanism Boeing determined was needed to prevent the aircraft from leaving its envelope It would be similar to turning off the stick pusher on a T tail susceptible to deep stall.

          Think of the liability American is transferring to itself.

          • IANAPP, but if one has a piloting team trained on an aircraft with one handling characteristic, and I’m asking them to fly one that has a similar (but different) flying characteristic + a system that can go wrong in a very nasty way, I think I too might be switching off that system.

            Whether that now remains within the type certification is a another problem, but I think I’d rather trust my humans to be aware of and fly in accordance with a different flying characteristic than demand they fly with a system with a nasty, counterinuitive fault characteristic that no one has trained them on.

          • jbeeko:

            I would say that is not correct. The so called instability is not the same as loss of stability.

            Its amazing what code writers will do to make a simple operation so complex as to boggle the mind.

            So, if the FAA guy raises an eyebrow, well we can fix that easily.

            Where it falls apart is review and actually implementation.

            The process should not allow that without a through washing of the logic, inputs, consequences of a failure etc.

            If you don’t come close to a stall it does not affect anything and they don’t fly 737s in stall other than the Simulator.

            It would be interesting to see what Boeing is doing on the test runs with the MAX.

  8. If this proves to be the reason, Boeing is guilty of criminal negligence here. To not anticipate AOA failure at low altitude and expect the pilots to react with no training is really quite appalling. Those dead people were guinea pigs, Boeing, negligent. The 737 MAX, a warmed over death trap.

    • If it happened to Lion Air and not an U.S. airline it is simply that Lion Air should have repaired!

      Indeed it is useless to let the pilots know when an air carrier is serious.

      Lion Air is your answer

      • Mark: While I agree Boeing is criminally negligent in their whole aspect of this, the 737 is not a flying death trap.

        Boeing at least was complicit, the aircraft while an old design works and works well with about an equal crash rate with the A320.

        Not the first time Boeing has done denial.

        Nor the first time a cross linked confirmation on a critical safety item was done .

        Boeing had it disabled and likely never enabled again.

        • The way this plane came to market makes me very uneasy, a late response to A320 NEO, a rush to market, tweaking an ancient design that never envisioned large diameter engines.

          • The NG is no different as it too had not only larger, but strut engine vs the contoured in tube design of the original 737.

            It does not seem haste is an issue here.

            Some horribly poor thinking and agreement it was a good idea let alone a method to deal with it let alone no one flying knowing it was there.

            Airbus has its share of unfortunate results as a result of automation and modes that have crashed aircraft.

            There response is vastly superior to Boeing.

            I admire the work they did on AF447.

          • @tw
            What’s the consensus on AF447. Pilot/crew error mostly?

          • “The NG is no different as it too had not only larger, but strut engine vs the contoured in tube design of the original 737.”

            The MAX fan cowling sits further out _and_ higher up front.
            It’s drag will cause a pitch up earlier than
            the NG installation.

            “It does not seem haste is an issue here.”
            Think again.

          • Ivory:

            On the surface AF447 was crew failure.

            As a (best described as former) Pilot (small aircraft) I was appalled at their reaction as it goes against evering you were taught (the basics still apply up to pax aircraft, fighters are a different game)

            At the heart is it was a system disaster. They should have been tested and corrected and clearly never were.

            At the time they were doing rote training, the pilots knew the drill and you did not have to revert to your basic airman ship to pass. You simply did the procedure by rote (and debrief emphasized the procedure)

            The system was excited about take off and landings and to stay current, you had to have (3 or 5) in your currency period.

            They started asking the questions after AF447., what pilot can’t do a landing? You do one a flight, same as takeoff.

            What we see is for unknown reasons of human physiology, suddenly presented with no speed, some pilots pull back on the controls.

            That one is bizarre, as you are trained to push over if you loose speed, not pull up (that is almost beaten into so to speak, its a sure way to die as lower altitudes). To this day no one has explained i9t. It seems (to me) to be some deep human reaction to a crisis)

            One of my fellow pilots got into a situation where he had to push over close the ground. But he did it though he said his body was screaming to pull back.

            As AF447 was no where close to the ground, that makes zero logic, but most people are not logical though they can be trained to be.

            the other wrong response is to push forward. While that is the right thing to do if you loose speed, if you are cruising along, there is no way you are going to stop cold short of running into a mountain and have NO speed. Ergo, the logic is, maintain as is and sort it out, if you hit a mountain at 35k, the world has ended anyway, you are dead.

            The training is shifting (mandated) to throwing the odd ball combos at pilots to see if they understand how to react at a basic aircraft level.

            Also pilots were told not to fly by hand. You loose feel for the aircraft when that happens .

            The idea is to throw curve balls at Pilots now and challenge them in their understanding of the basic aircraft ops and doing the right thing in non rote solutions.

            It has not evolved down to all airlines and operations, but that is the direction and its the right one.

            In my case I was fortunate that I was able to fly and trust instruments 100%. Usually the training drill was to mild upset and then ask the student to recover under the hood on instruments alone, loss of instruments etc.

            As that was boring, my instructor asked if I was ok with some wild gyration to throw me and see what I could do.

            I agreed. So under the hood I went until he said, ok, you got it. He would not tell me what he did but we did some truly bizarre stuff before he gave it to me in a full stall, steep dive, dive and turn,

            He never was able to unsettle me.

            I was not a natural pilot, but I loved the challenge of instruments and trusted them (with the cross checks) . Don’t get me wrong, as a pilot I was certainly adequate, but I would not put myself at the top except the instrument end (which all my instructors commented on) . That is some kind of natural ability and boat training on course running when I was a kid and who knows. Kind of runs in the family in various ways.

            We also went up one day totally socked in and did a complete flight in the clouds. No shenanigans, but you could feel the vertigo that you did not under the hood.

            I was able to ignore that, but your sense are screaming the instruments are wrong. It was different than being under the hood. I could do it right, but it was a shift, felt good to do it and know it would lurk there and try to divert you.

            But, the more you fly them, the more the terror goes to a small back corner of your mind.

            And that is what training should do, challenge you, teach you the core basics and catch any bad habits or reactions that are wrong.

    • The standard for criminal negligence is pretty high.

      We need to hear what the excellent poster AP Robert has to say as this is up his alley.

      • The standard is high. Were there to be such a prosecution, I fear the liability might fall between Boeing who are effectively self certifying with FAA blessing, and the FAA which no longer has the resources to extensively and vigorously check up on what Boeing does.

        I suspect the real causes are the budgetary politics behind why the FAA doesn’t have the necessary teeth, and the financial reasons why Boeing stretched an old design so far as to introduce a flight characteristic that probably shouldn’t be there in the first place and then didn’t seek to properly remedy that or even require pilots to be trained for or made aware of it.

        Money and politics. Regulation should be isolated from both. If this does boil down to insufficient regulation, it’s the US politicians that ought to be prosecuted.

        I’ve no idea whether the EASA has gaps in its processes or coverage, but if there’s any hint of blunt teeth they ought to be sharpened. Right now one has to wonder if half the world’s certification system is doing a good enough job, and what else is there that Boeing pilots haven’t been told? If the other half, ESASA, has problems too and some other incident occurs, the aviation industry is going to be getting a whole load of bad publicity globally. Safety is illusory if there’s no one checking.

        That’s not good for jobs.

  9. Thanks for explaining. An inflammable topic & conclusion. On a more abstract level, one could ask how far automation of controls of an existing conventional design allows for grandfathering certification of the total system.

    • Good point.
      Also, questions on whether the flight simulators have the features programmed in. I would assume that they built in the forward COG into the training.

      • We can’t assume anything at this point.

        Arguing against that if they do upset training per standard now, they would be in the stall area and its not been reported that this occurred.

        If its not documented then how can Sim mfgs put it in?

        And by the way, if its not there, then all Sim have to get it installed or they are illegal configuration for the MAX.

        For it to be legal, the Simulator has to be 100% accurate.

        I have seen the issue and the warnings issued when it was found to be out of compliance. Yanking of certification is next.

        I would guess FAA has to allow time for this to be put in, interesting that they are the ones that approved it (even if by oversight)

        But we need to wait for 100% surety.

  10. We ALL know why they did this. They did it to preserve the same type rating and reduce transition costs. The FAA needs to yank the same type rating for MAX, as it is really a significantly different airplane. Treating it as the same type is DANGEROUS and the death toll has already started to mount. Shame on Boeing.

    • Its not just the addition of new automation to the Max without telling the pilots.
      As Southwest showed with rapid retirement of all its ‘Classic 737’ fleet detailed in LNR.

      “As far back as 2005, Boeing faced structural issues with the Classic fleet. Boeing outlined the problems, and the fixes, in an 82-page Power Point that described issues with lap joints and “potential scribe line damage.”
      Inspections were mandated and significant repairs were needed to address the issues…..
      Other photos, also of Southwest aircraft, show cracks in the fuselage.

      The fleet of Southwest Classics underwent repairs years ago. Because Southwest remained the original owner, Boeing was on the hook for the costly and time-consuming repairs, a former Boeing employee with knowledge of the situation says……
      The 737NG also has issues. Line Numbers 1-871 have crown skin cracking problems, according to a second Boeing document, this one issued in 2012. This issues begin to emerge at 35,000 cycles….”

      • That has no relevance to this case, apples and oranges.
        You might as well mention the A380 wing crack problem.

        • Serious problems with the 737 that arent generally known?
          Every relevance , just it doesnt have Max suffix.

          • Nobody knew about the crack problem until it happened. Computer modeling had predicted 60,000 cycles before problems would become like. It was a design defect that no one knew about, it wasn’t hidden.
            Again no relevance except for the Boeing name.

          • No one knew ?
            Did you read the story link at all. Cracking became major issues for the 737 classic generation and was repeated for the later 737 NG.
            There that’s word again 737… Maybe why it’s relevant, not just Boeing name. Oh and you say computer modelling said it would be OK……right. let’s it’s not the same people doing the computer modelling on the new fangled MCAS..Maybe they should have called it what it is- automated pitch control

          • 60,000 cycles from the get go taking the word of the manufacturer
            30,000 cycles to start with and
            expansion as fatique experience comes in.

          • Did you read my reply at all? No one knew that the plane would be experiencing cracks so early. Unlike in the MAX case where they knew from the get go of a potential problem.

    • Mark:

      You keep with the hyperbole.

      Death tole is mounting? Its stopped at 189, that is no longer mounting.

      Is there a lot to deal with, yes. And for that 189, there are going to be thousands of wives, husbands, sons daughters, relatives and friends tragically affected by this. That is truly ugly. It is on Boeing and the FAA.

      Where were you with AF447? That to is a flaw. You can design the system to put itself into the right mode with loss of speeds.

      One issue does not mean the 737MAX is a death trap.

      It does not absolve Boeing or the FAA.

    • Well, indeed you are correct . Boeing wanted a common type rating and this little add on system allowed them to do that. Otherwise the new engines might need a new wing, pylons and fuselage adjustments for the CG differences.

  11. I’d be interested to know what happens with Airbus and bombardier aircraft in a similar scenario.

    • Airbus A32X and Bombardier A220 series planes are naturally unstable aircraft – and along with the new Embraer E2 series which had its wing moved forward to make it unstable- and the whole aircraft rely on FBW to enable them to fly.

      • That isn’t true. The aircraft are naturally stable throughout the flight regime, however the normal laws provide additional augmentation to lower workload and improve the flight characteristics. The normal laws/mode (depending on your flavor of FBW) would prevent you getting to an aerodymanic stall.

        A mismatch in air data indications (which has been the focus here) would possibly cause a degradation to alternate or direct modes, which are closer to command by wire and would allow the pilot to fly manually, even using pitch and power tables if air data is completely unusable.

      • not naturally unstable, just reduced stability margins, which allows for reduced empennage size and loading, reducing drag, improving fuel economy.

  12. Does the NG have pitch instability at high AOA as well? Maybe this was a problem that didn’t need a solution.
    Is the lift on the engines on the MAX so great that it does not naturally recover from a stall without the MCAS? What would be the behavior of the aircraft if stalled without the MCAS?

    • Ted: The answer is no, it has to do with the engines and from what I am reading, almost a niggling issue that a Pilot would have no issue dealing with (you would put the nose down in a stall yourself)

      MAX only, engine location on the two types is different enough to have added some control issues though it seems miner or irrelevant.

      • This indicates the ‘breadth of the training’ the US pilots received

        “APA spokesman Dennis Tajer said Monday that the detail on the MCAS system “is new information for us.”

        He said his training on moving from the old 737 NG model cockpit to the new 737 MAX consisted of little more than a one-hour session on an iPad. The airline doesn’t have simulators specific to the MAX model.”

      • > almost a niggling issue
        More than that. There will be documents outlining why this system is needed to keep the aircraft safe at the edges of the envelope. And those documents are probably compelling otherwise they would have never added the MCAS. So now they will not be able to recommend it be disabled.

        The only way forward is training on how to handle inappropriate activation of the MCAS.

        • jbeeko:

          We will have to see, its going to come out slowly as a lot of Silos are about to get their walls blown in.

          As a pilot my interpretation of the trigger to put it in seems very nebulous.

          You can add in we don’t have to tell people because they will never be in that positions!

          If you do stall, your first action is to drop the nose.

          While I await the info with a lot of impatience, it sure seems twisted beyond need to me.

          The new training refers to it as unloading the wing. If you are dong that anyway?

  13. Pprune has a vidio of a simulator B737 classic stabilizer runaway which is easy to find on the web.It shows the pilot holding the yoke back, wheels running and alarms going off.It looks terrifying to me!Do the wheels visibly (and audibly)run like that with MCAS?

    • Now in a scenario of conflicting signals such as in the Lion Air case, where you experience a stick shaker and stall warnings among other things, would you do what he was doing?

      It all happened at 5000 ft, which is not a lot of room to recover from if you trusted the wrong warnings to heed.

  14. Here is the procedure for Runaway trim from my companies MAX QRH. The revision Date is July 2017.

    1 Control column. . . . . . . . . . . . . . . . . Hold firmly
    2 Autopilot (if engaged) . . . . . . . . . . . . .Disengage
    Do not re-engage the autopilot.
    Control aircraft pitch attitude manually with
    control column and main electric trim as
    3 Autothrottle (if engaged). . . . . . . . . . .Disengage
    Do not re-engage the autothrottle.
    4 If the runaway stops after the autopilot is
    ■ ■ ■ ■
    5 If the runaway continues after the autopilot is
    switches (both) . . . . . . . . . . . . . . . . CUTOUT
    If the runaway continues:
    trim wheel . . . . . . . . . . Grasp and hold
    6 Stabilizer . . . . . . . . . . . . . . . . . . . Trim manually
    7 Anticipate trim requirements.
    – – – – – – – – – – – – – –

    That procedure WILL stop MCAS or any trim from operating the trim motor.

    • How dare you bring facts into the situation, 737Fixer? Didn’t you get the memo that today is the day (well, everyday, for some) to bash Boeing and demand the type certificate for the 737 and every Boeing jet yanked with immediate effect?

      In all seriousness, I wonder why Boeing and EVERY OTHER CIVIL AVIATION AUTHORITY ON THE PLANET (YES, including the vaunted Europeans) didn’t seem to mind this omission……

      • How can you incriminate the EASA about a missing information in Boeing’s documentation ? If it’s not written anywhere, how the EASA can know that the feature exists ? Please make us know how you can prove that EASA pilots have more information than airlines pilots ?

      • Guess which FAA branch does the certifying ?

        That would be the one at 2200 S 216th St
        Des Moines, WA. Which is located just South of Seattle Tacoma Airport. It couldnt be more in Boeings pocket if it was just across the road from Boeing HQ at Oakesdale Ave Tukwilla
        Generally international agencies follow the lead of someone like FAA and rely on their approvals

        • There must be Failure mode effect and cause analysis done also by EASA to check off each box in their compliance sheets.
          There must be at least one page full of check boxes per sensor and how the system reacts in each mode at every altitude/speed/c.g. combination/bank/climb/dive/Tamb. Then redo it for a combination of faults and double check with certifiation test reports. Still test pilots are used to faulty systems and shut off automation quickly as soon as it behaves unexpected, that can be different from normal airline pilots that are used that systems works pretty normal year after year unless they fly old soviet planes.

      • And try doing that with another issue in the system as it appears there was.

        And no training that it will repeat every 5 seconds.

    • Are you sure? Just like the engine pitch up moment at high AOA is part of the MAX, the compensation of it could also be baked into the fcs logic, independent of trim.

    • That may be in your airlines QRH – Quick Reference handbook but thats at odds to what is said here-
      “Pilots flying Boeing’s 737 MAX for American Airlines and Southwest Airlines were not informed during training about a key change to an automatic system that’s been linked to the fatal crash of a Lion Air jet last month, according to pilot representatives at both airlines.”

      Its all very well having something buried in a QRH, but if you are totally unaware of the new systems existence, what use would those instructions be … and in the middle of a crisis.
      Not thats not easy peasy. That approach is what car dealers do when handing over a new car.

      • This deliberate secrecy regarding a system that can – and will as now proven in a very practical case – interfere with the pilots’ ability to control the aircraft is so far beyond the pale it beggars the imagination that Boeing and its lawyers could conceive of it.

        If – as some of the comments above seem to indicate – it was done to preserve the old type certificate for the MAX it is simply greed allowed to prevail criminally over safe operations.

        What – if any – heads are going to roll at Boeing? So far no indication of such and not any expression of contrition either. Perhaps they feel they can tough it out and plow through with business as usual? Interesting to see what airlines customers are going to say and do.

        Was the FAA aware – or complicit in this omission?
        If unaware they were not doing their job.
        If aware and coopted by their Boeing neighbors across the street, as suggested above, heads should roll there too.

        The NTSB report should make interesting reading when it does eventually come out.

        • You assume a conspiracy when pole are fully capable of and continue to prove creating a complete balls up without any help from said conspirators.

          • Being charitable we can posit a combination of stupidity and pride on the part of some Boeing “decider” . Chance are there will be fingerprints all over this as I would bet good money a few actual pilots in the shop advocated for transparency and were overruled – in writing!

    • Below is the “Runaway Stabilizer” checklist from a Delta Airlines 737 NG QRH with revision date 6-9-2oo8. As far as I can see, this is identical to the 737 MAX checklist with revision date 7-2017 posted above by 737fixer, except for no mention of autothrottles and the addition of a note about RVSM restrictions. Is it then the case that what is new with the MAX is not what the recommended response to a runaway trim situation is, but that the MCAS system adds new and unfamiliar failure modes that could cause undesired and inappropriate trimming? Or is it the case that some airlines did not previously include runaway stabilizer checklist’s in their 737 QRH’s, or that I am missing some important difference between the NG and MAX checklists??


      Condition: Continuing rotation of the stabilizer trim wheel in a manner not appropriate for flight conditions.

      Control column . . . . . . . . . . . . . . . . . . . . . . . Hold firmly
      AUTOPILOT (if engaged) . . . . . . . . . . . . . . Disengage
      Do not re-engage the autopilot.
      Control airplane pitch attitude manually with control
      column and main electric trim as required.

      Note: Flight may not be permitted in RVSM airspace.
      Contact ATC. Refer to the Airway Manual,Navigation
      section, for RVSM requirements.

      If runaway continues:
      Stabilizer trim CUTOUT
      switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . CUTOUT

      If runaway continues:
      Stabilizer trim wheel . . . . . . . . . . . . . Grasp & Hold
      Stabilizer . . . . . . . . . . . . . . . .. . . . . . . Trim manually

      Anticipate trim requirements.
      Complete the normal DESCENT, APPROACH and
      LANDING checklists.

      Establish proper airspeed and in-trim condition early on final.”

      • The Delta 737 NG checklist with revision date 6-9-2008 that I referenced above may be found by searching for “Aviation for All 737QRH”. See page 9.12 of the QRH. For some reason, the Leeham website keeps rejecting any post in which I include the direct web address to this document.

  15. If it happened to Lion Air and not an U.S. airline it is simply that Lion Air should have repaired!

    Indeed it is useless to let the pilots know when an air carrier is serious.

    Lion Air is your answer

    • No, sadly, its a combination of events that usualy leads to these.

      If Lion Air did not know about it, then its an unexpected event.

      It differs from runaway trim in that it keeps repeating.

      I think I am a poster child for that kind of event. In a spin, the controls via the yoke (in my case) that are normal simply quit working.

      You might want to try that in a simulator, its like the Sun rose in the West, shocked is not quite it. Your whole world goes si wash for a second, or two or three.

      Ask the guys on the E-190 that looks to have had the left/right controls reversed how easy its to handle.

      If Lion did not know it could not train its pilots (and there is more than that going wrong) .

      It then gets into a throw of the dice as to knowledge, how you react etc. if you can save it.

      Pilots are like people, some poor, most in between and a few really good ones. Your odds are you are flying with an in between pilot.

      Like Boeing auto throttle in the FLCH that turns off as part of another mode change, you can created a trap – the idea behind automation is to make it easier, not have to known bad design that then has to be over come with knowing the drill while you have a lot of other stuff to understand.

  16. Boeing screwed up but isn’t the FAA certified the aircraft, it’s manuals, everything. Why isn’t more scrutiny being placed on the FAA. It was up to them to say “Hey Boeing, before we certify this jet, you need to update your manuals and do some training on the MCAS.”

    They didn’t.

    Also, since the same jet had issues the flight before, why didn’t Lion Air bring in Boeing and ground that jet? Seems totally irresponsible to have a new major flight control issue, and not ground that jet until they were 100% they understood what happened. They supposedly replaced the AOA sensor, but that obviously didn’t fix the issue and the next crew appears to have been unaware of the previous crew’s issues.

    Anyway, the FAA should be getting the same or more scrutiny than Boeing since they certified the whole thing.

    • I do agree the FAA has a part, I would be interested in knowing if they review the manual.

      Boeing clearly should have, FAA manual review may not have caught that the tech group approved it and an update was needed. All depends on the credibility of the cross check process.

      Keep in mind its the same FAA that agreed a good test of an Li Ion battery was to drive a nail in it! (on Boeings word, the RTC set standards when the wheel came off that wagon)

  17. Assuming the root of this problem is an AOA sensor fail, the MCAS just worked as programmed, how are pilots programmed for an AOA fail in the NG? Have the AOA sensors failed very often in the NG? Some alarms go off but the pilots realize the AOA is fine by visual reference? Any AOA sensors failing on the NG at night?

    • All things fail. How often?

      But, as Bjorn has said several times, there looks to be more to the failure than just that.

      Another factor may be the root and the MCAS (what a mouth full) made it worse to assess.

      AOA tends to be more oriented to military training (they fly in that zone a lot)

      I can see previous 737NG and prior pilots, ho hum, AOA is gone again.

      More like a light burned out (though that was the core cause of the L1011 crash into the Florida Everglades, trying to trouble shoot a stupid light problem.

    • That question might be covered by this part of the story…
      “It’s unique to the MAX because the 737 MAX no longer has the docile pitch characteristics of the 737NG at high Angles Of Attack (AOA).”

      • I guess my next question would be…
        How docile or unstable are the NG, MAX, A320ceo, NEO, 787, A350 at high AOA on a quantifiable scale, and what numerical ranges are known as docile or unstable?

        • Pointless comparing modern full FBW aircraft that are ‘naturally unstable in pitch’ with the older aircraft that dont have this feature like the 737, 767, and 747.
          As Bjorn says in the article -“The 737 is a classical flight control aircraft. It relies on a naturally stable base aircraft for its flight control design, augmented in selected areas. ”
          The 737 didnt even have an auto throttle and flight management computer till the end of the -200Adv and the start of the Classic series in 1984.

          • All modern FBW aircraft are ‘naturally unstable in pitch’. I did not know that, plus the subject is all new to me. Can we compare the FBW aircraft and their history of auto respond to bad inputs to the MAX and the MCAS?

          • not naturally unstable, reduced stability margins. huge difference.

          • SW reports a couple of AOA failure recently.

            But it not only has to fail, it has to fail with bad data saying its stalled to invoked the MCAS (and flaps up and flying by hand if I have that right)

            So odds of it doing all the wrong stuff at the wrong time??????????????

      • It sounds like a borderline situation that is not that critical, more a technicality of FAA deciding it needed a fix and Boeing doing so, but will stay tuned.

        Keep in mind this does not look to be the whole story.

  18. While the fact, that an apparently critical new system was not included in the documentation is highly worrying, I find the Boeing statement from a few days ago extremely troubling. At least morally this is a real shame.

    Instead of admitting that there was information withheld, Boeing tried to create the impression it is a proven system and by apparently not following existing known procedures (read simple pilot error) the crash happened.

    That’s a real shame. But since when do big companies act ethical?

    • I would put it well past a shame. 189 people dead?

      Much like the FLCH trap that the NTSB ruled should not be allowed (which has been disregarded by the FAA and Boeing)

      Its not one item, its when they compound that the issues begin and Bjorn feels that it was compounded by another issue in air speed system, computer or??????

      That leaves pilots trying to sort through multiple issues that they should not have to.

      Horribly implemented in all regards with single point of failure, no documentation and no training to alert of that change vs what you know and that the first thing you do regardless is disable it, so you can deal with the other compounding issue.

      I don’t think criminal is too strong a word.

    • Boeing has been trying to parse their words carefully. It won’t be long before the first ambulance chasers start moving in. Critical stuff.

    • You understand companies like BA have dedicated staff to prepare for such events. Think about the Toyota/GM/etc faulty parts (if any) of recent memory.
      Companies like that have a duty to their shareholders not to admit guilt. No matter what. Their are manuals pun intended on how to do such circus mangement.

      Let’s see what the facts bring up. Personally I would not admit guilt until I knew what really happened.

      Critical will be also the voice recorder. Did they find it?

      • Duty to shareholders?

        Is that written into Law someplace?

        They have additional duties the supersede that.

        One is not to put a flawed product into service.

        Reminds me of the Catholic Church when they started siting Church Law. Hmm, really, you think your internal operation MO trumps the Law of the Land?

        So you did not think you had to report it because you have internal OPS that say you don’t?

        Getting beyond absurd.

        Boeing is also mandated to meet the regulation as well as the actual laws.

        While I think this is a balls up and I doubt it was deliberate in a conspiracy way, someone made some very specific decisions not to comply with the regulations. Arrogance and or ego and who knows.

        Those decisions were not caught.

        Legally the Boeing Corporation put a product into service that does not begin to meet a miner change that does not affect ops.

        It will only cost them money. Oddly, as far as I know (unless the Supreme rule otherwise) Corporations still are not allow to kill people.

        Technically this is somewhere between person slaughter and 2nd degree probably with a bias to person slaughter.

        It is a very significant change and by itself would have caused problems.

  19. The event is somewhat similar to the SK751 MD80 accident where Douglas had an “ATR” Automatic Thrust Restoration system logic installed that the pilots and Airlines where unaware of.
    Here is another well intentioned safety system that airlines and pilots were unaware of and did not perform simultor training on in combination of other failed sensors/systems.

    • Thats a good point about the DC9 -ATR
      The inquiry results were:
      “However, the newly installed ATR prevented the pilots from successfully performing the normal remedial measure to halt compressor stall, i.e., throttling back the engines, as the ATR system – designed to prevent pilots using less than normal thrust when climbing out after take-off for noise abatement reasons – restored engine take-off power throttle settings contrary to the pilots’ reduced throttle commands. This damaged the engines, until eventually, they failed completely.”

      While the ATR system was described, if you read the manufacturers documents carefully, SAS never included them in the manuals for its pilots.

  20. The quality of the report is very good for a neophyte like me.

    The 737 seems to have been somewhat rejuvenated 3 times at least in the past. What strikes me the most is the picture showing how the engines fan ‘encroaches’ on the wing. Instinctively this seems more unstable. But as said many times no aircraft is anymore inherently stable for performance reasons.

    I can only relate having built million lines level software systems all my life. These are also inherently patched over (read: rejuvenated) as it is too costly to rebuilt from the ground up. They last 2-3 decades for sure. And we tell our customers they will work. Convinced as we are engineers that we get it right. We write self correcting code to correct runtime faults etc. after a while we lose control anyhow. And many many (code) simulator runs convince us we have seen everything.

    Maybe entropy is also catching up on the 737 platform.

    But remember that humans can’t built perfect systems. We learn as we go. See the car reference in a comment above. Some behavior (may) be criminal but most organizations realty try to do the right thing.

    The question is how many oversight layer systems have been added on top of the existing ones to handle a perhaps larger inherent in stability flight envelop in the MAX?
    Should BA or anyone inform folks on all of them? Tricky plquestion. Yet sure they may have been way too optimistic.

    • The counterpoint that usually does not get brought up in 737 discussions is the Second System Effect, defined in _The Mythical Man Month_. As summarized by Wikipedia:
      “The second-system effect is the tendency of small, elegant, and successful systems, to be succeeded by over-engineered, bloated systems, due to inflated expectations and overconfidence.”
      Designing a new system ab inito with the latest and greatest thinking in modern design does not necessarily result in a “better” outcome, for some/many values of better.

      • Ivory:

        While that is good sense, also keep in mind that pilots are trained to expect things to work the way they should.

        When something is NOT working the way it should, then there is confusions. You can’t explain it.

        Throw in another issue and the fog of confusion sets in. How are they related. Why is it doing X and Y. Whats the link (when in fact x and y may be two different failures)

        Something like that stall system should never be a result of a single bad input, computer or even a bad logic path.

        Code in aircraft is supposed to be sorted, not like sloppy programs you get from Microsoft. More like the old CPM programs that were paired down to the bare basics as you did not have processor to run excess code (and unknown results)

        I have run into cases in my world where they had a problem and rather than solve it they threw more code at it.

        Aircraft are not like that.

        As a former Pilot, I am astonished/stunned Boeing would make that kind of change without notification as it is core relevant to aircraft ops.

        You design that stuff so it can’t happen by a single point of failure and you let people know its there so they can deal with it if it does fail.

        Equally at the heart of this is how Boeing got there and how the FAA approved it.

  21. Let’s see, have I got this right. Boeing didn’t see the need to inform the pilots about this new system because the ultimate soloution was the same as the old system, turn the damm thing off and do it yourself.
    We are speculating that the pilots should have known about it because they were working through their training and the book and wasted a lot of time and mental energy wondering why they couldn’t stop the runaway by pulling against the yoke as they had been trained to do as the first measure .Is that right?How much time did they have to sort this out before they lost control?

    • yes, the step that would have solved it was step 6 on the checklist (see the above comment with the procedure.

      event onset was at 5000 feet at ~250 kts TAS, in the final dive, they went from 5000 ft to zero in about 11 seconds.

      the automated system kicks in on 5 or 10 second intervals.

      it seems likely that they got to step 5, the problem appeared to be resolved or at least stabilized, then the 5 second interval hit, trimmed them into another dive and they didn’t have time/mental resource to take the next step on the checklist.

      • Thanks Bilbo.
        Ofcouse a big mound of cheese slices had already been munched through by the failure to get on top of the technical problems and possibly a failure to appreciate a previous near miss, that might only have been saved by luck or above average piloting.

      • Didn’t the plane fly for about 13 minutes after the problem was first reported to the local ATC?

  22. How about just terminating all the automatic, gee whiz crap and flying the airplane.

    • I think that as they were apparently flying in manual mode, they were probably thinking that they had turned it all off. Boeing didn’t tell them that this wasn’t so…

      • Harry:

        As a pilot and a technician, the first thing that flashes through your mind when its not working the way you understood and were trained for?

        Will I make it worse?

        Keep in mind, this is your car going out of control, you are turning into the skid and the skid gets tighter not stops.

        One of my vehicles has auto steer and counter steer is wrong.

        The other one does not.

        So what happens if you get into your vehicle and it suddenly has counter steer? At the same time its doing other things you have to sort out (the brakes down’t work)

        Confusion sets in.

  23. I think that the solution will require more than just increased training. Boeing will have to change the system to make it more failsafe to bad sensor information.

    • Ted: That is solidly true.

      In the controls world (mine not aviation) we call it cross linked.

      A clear example is a Halon System ( yes I know we have no new halon system but a lot of legacy and it applies to the replacement)


      I had one in a bank vault that was 100 feet through passage to get out of. When the tech set the system up, it was cross linked to two sensors. I also trained the vault personal on what to do and how to inhibit it until all were out of the vault.

      Critical aircraft system should have multiples of that.

      Both AOA should say the same before action other than a input disagreement, still chewing on adding more into it.

      It is horribly thought out and stunning it was released to the MAX without modifications by review group (and any engineer that proposes a single point of failure like that should be fired and probably hung just to ensure he doens’t go do it to someone else)

  24. The following post by 737Fixer is a curve ball for all the statements so far. See the date of the QRH update. July 2017.
    1. So can the claims that Boeing hid the system details completely from Pilots, true?
    2. When the MAX pilots were trained (or conversion from NG) no one bothered to ask what is this system that trims my Stab?
    3. QRH steps are fully rehearsed (Some memorized) in the SIM. Yes or No?
    I am not a B737 Pilot. So just curious.

    November 14, 2018
    Here is the procedure for Runaway trim from my companies MAX QRH. The revision Date is July 2017.

    1 Control column. . . . . . . . . . . . . . . . . Hold firmly
    2 Autopilot (if engaged) . . . . . . . . . . . . .Disengage
    Do not re-engage the autopilot.
    Control aircraft pitch attitude manually with
    control column and main electric trim as
    3 Autothrottle (if engaged). . . . . . . . . . .Disengage
    Do not re-engage the autothrottle.
    4 If the runaway stops after the autopilot is
    ■ ■ ■ ■
    5 If the runaway continues after the autopilot is
    switches (both) . . . . . . . . . . . . . . . . CUTOUT
    If the runaway continues:
    trim wheel . . . . . . . . . . Grasp and hold
    6 Stabilizer . . . . . . . . . . . . . . . . . . . Trim manually
    7 Anticipate trim requirements.
    – – – – – – – – – – – – – –

    That procedure WILL stop MCAS or any trim from operating the trim motor.

    • Missing is recognize it as a out of control trim issue because its not acing like one.

      Add in the missing element of what else was happening at the same time.

      • Hello TransWorld,

        Regarding: “Missing is recognize it as a out of control trim issue because its not acing like one.”

        I don’t know what trigger condition is stated for the runaway stabilizer checklist for the 737 MAX QRH quoted by 737fixer; however, here is the trigger condition stated for the runaway stabilizer checklist in the Delta Airlines 737 NG QRH that I reference in posts elsewhere in this thread.

        “Condition: Continuing rotation of the stabilizer trim wheel in a
        manner not appropriate for flight conditions.”

        If the MCAS on the MAX does not cause the trim wheels to rotate when it kicks in, I think that this be a much bigger curveball for 737 pilots used to having autoflight systems move the airplane controls along with autoflight control inputs, than anything else that has been mentioned in this thread.

        • AP:

          Again, this is not the only issue the pilots faced, they also had another one going (or maybe more)

          In this case, there will be instant confusion as the system is also calling out stall and it is taking action that is not what you expect, let alone why you would be stalled when you know you are not.

          So the first instinct is to pull back on the yoke to stop it (which it should). Then it does it again which is against all previous system knowledge.

          What else did the pilot have to look at that was compounding this as not the only emergency going on?

          If it was the pitot static system then you don’t have your altitude or VSI (on the backup instruments maybe – I believe that is a completely separate feed)

          You also have a co pilot who may or may not be in sync with you as things are happening so fast that even communicating is not possible – he may be seeing different information than you are and confused by the stall warnings.

          Its not that you can’t sort it out, its you have to sort it out and determine what action to take.

          And when things are going totally wonky, how much faith do you have left in even turning the whole automation system off?

          Its easy to be sitting at a key board saying how they should, its a lot different being on the sharp point of the spear.

          It gets into background, training, capabilities.

          Some might recognize part of it right way and turn off the MCAS (trim) – but which do you do first and whats the most aware thing?

          System is screaming at you you are stalled and you don’t think so but you are also trained to believe the system.

          It takes time to disconnect and adjust and it looks like they ran out of time.

          I have had probably 4 of those ah ^%$# moments, I was lucky to survive them. Trust me, its not a well you want to visit once, let alone more than once.

          • Hello TransWorld,

            Regarding: “And when things are going totally wonky, how much faith do you have left in even turning the whole automation system off?”

            By my understanding of the following quote from the Forbes article at the link after the quote, “turning the whole automation system off” is exactly and precisely what United Airlines ALPA Chapter Chairman and 767 Captain Todd Insler would advocate doing if “things are going totally wonky”.

            “The addition of MCAS to the 737MAX is not specifically referred to in the United manual, but the procedure for recovery from automatic unwarranted deployment of similar systems is clearly spelled out and long has been, Insler said.

            A Boeing 767 captain who has flown the 727 and 747 but not the 737, Insler said that on the 727, “there was the known possibility of a runaway trim, and you could manually stop it. You could manually reset the trim.”

            The key, he said, is that “You have to manually take control—that is one of the early things they teach you when you fly jets. The procedure is there in our manual, and we practice this over and over again. The first time I see an adverse event, I want to see it in a simulator, not with 300 people behind me.

            “As a United pilot, I fly the airplane,” Insler said. “I don’t want the airplane flying me. I am always looking for things to go awry, and I am always prepared to take control if that happens. I wait for something to go wrong because then I can use all those years of training that I have.

            “The reason mainline United pilots are among the highest paid airline pilots is because United pilots are exceptionally well-trained,” he said. “What passengers pay for is to have well-trained pilots get them from point A to point B.”


          • AP:

            We don’t know ALL of what information the pilot was getting.

            We do know the AOA triggered a false stall condition.

            Your trim may be moving but your attention is pulled to the stall warning.

            The plane then pitches down. Have you caught the trim moving yet?

            So, now you are into cross checks.

            You don’t seem to get issues with the main Pitot system can also be feeding you false info.

            Have you recognized that its an out of control situation yet?

            What is Indonesians training in general?

            I doubt it (or anyone’s) at the first pass is to simply turn the automation off. I don’t care what the United Pilot says.

            In the meantime the aircraft is doing something its not supposed to.

            So where do you focus, on a stall that is a known killer?

            Sure post input, most pilots would dump the trim and then assess.

            But this is the first time anyone in the world other than Boeing test pilots have seen it.

            As a pilot you are trained to go through the drill. But you are also taught that the aircraft is not actively trying to kill you.

            As I noted, I was there once, I did get it sorted out before I died (fortunately only me) but it was a really close thing. Half a second more and ……..

            This is not like a car skid. You have a know reaction to that.

            Some puts auto steering in and its wrong.

            Fog of war.

            Given enough time, maybe they would have got there. Sometimes you run out of time and altitude.

            Runaway trim would normally be obvious, sudden the plane pitches up or down, the wheel is spinning, OFF.

            But it does not start off with a stall screaming at you with all the associated stick shaker doing the same.

    • Hello Tech-guru,

      Regarding:”QRH steps are fully rehearsed (Some memorized) in the SIM. Yes or No?
      I am not a B737 Pilot. So just curious.”

      The QRH consists of all checklists, both emergency and non-emergency, for a particular aircraft. It includes only, or almost only, the checklists, additional training or explanatory material such as system diagrams or design philosophy, that may be found in the full aircraft manuals are stripped out. It is typically kept in a special compartment within arms reach of the pilots.

      Memory items are a small subset of the contents of the QRH. Only those emergency checklists items that it is judged must be completed immediately before there is time to flip to the appropriate page of the QRH, or its electronic equivalent, are memory items. Recurrent training will typically include all memory items, but not every checklist in the QRH will be practiced in every training session. A QRH for an airliner is hundreds of pages long, memorizing the whole thing would be beyond the memorization capabilities of most people.

      The excerpt below is from a Delta Airlines 737 NG QRH with revision date 6-9-2008. “Non-normal checklist” pretty much means an emergency checklist vs. a “normal checklist” such as a pre-takeoff or landing checklist to be used when nothing is broken or on fire.

      “Checklists can have both recall and reference items. Recall items are critical steps that must be done from memory and are placed within a box. Each crew member is required to know all recall items. Bullets, notes and bracketed items within the recall box support action steps and are not considered recall items. Reference items are actions to be done while reading the checklist. In the Table of Contents for each non-normal checklist section, the titles of checklists containing memory items are printed in bold type.”

      This QRH contain a “runaway stabilizer”non-normal checklist that is highly similar to the MAX checklist posted above by 737fixer. This checklist contained no memory items.

      • The Delta 737 NG QRH with revision date 6-9-2008 that I referenced above may be found by searching for “Aviation for All 737QRH”. See page CI.2.1 of the QRH for the description of recall and reference items that I quoted above. For some reason, the Leeham website keeps rejecting any post in which I include the direct web address to this document.

        • This QRH is 334 pages in length. Much more than I would want to have to memorize.

      • Hello Tech Guru,

        More regarding: ”QRH steps are fully rehearsed (Some memorized) in the SIM. Yes or No?”

        See below for a video of some student pilots practicing a runaway stabilizer emergency in a 737 classic simulator. The QRH checklist they reference at about 5 minutes and 10 seconds into the video sounds essentially the same as the July 2017 737 MAX procedure that 737fixer posted, and the Delta Airlines June 2008 737 NG procedure that I posted. Most importantly, the classic, NG, and MAX procedures all call for turning the stabilizer trim motor off if disengaging the autopilot does not stop the runaway. Whether you are in a 737 classic, NG, or MAX, or any other aircraft with mechanical control connections and motorized trim, if the trim goes wild and you don’t want to crash, you obviously need to turn the trim motor off and crank by hand. I don’t see what the difficulty or subtlety is with this, or where the statements that there was no procedure in the MAX manual for dealing with runaway trim is coming from, when for every version of the 737 back to the original, the QRH says turn off the trim motor if the trim runs away and disengaging the autopilot doesn’t stop the runaway.

        • The 737 runaway stabilizer simulator training session video that I posted a link to above, was posted to YouTube on 7-2-2015.

        • If the MCAS trim actions don’t cause the trim wheels to spin, then I would see where the subtlety and difficulty is, since 737 pilots are accustomed to autoflight control actions causing the physical controls to move as if a pilot were making the same control inputs.

          • According to the excerpts below from the 11-17-18 Seattle Times article at the link after the excerpts, I am apparently not the only person in the world who thinks that based on long established 737 emergency procedures, pilots should know to turn trim motors off if trim is running away or behaving erratically. Reading this article makes me inclined to fly United instead of Southwest or American when I have a choice. An airline whose Chief Pilot says his pilots are confident flying their aircraft manually with auto everything off, is an airline that I will prefer to fly on.

            “In an interview Thursday, Capt. Todd Insler, chairman of the United branch of ALPA, the Air Line Pilots Association union, broke ranks with his counterparts at American Airlines and Southwest Airlines who earlier this week publicly complained that this wasn’t disclosed to pilots during training or included in the 737 MAX pilot manuals.

            Insler said many systems on an airplane work in the background without the pilot’s knowledge. He compared it to watching television: “I don’t need to know how it works.”

            On Airbus jets, which unlike Boeing’s are designed to a philosophy that gives more autonomy to the automated flight-control systems and less to the pilots, there are dozens of systems that constantly work in the background without the pilot’s direct knowledge, he said.

            Insler said it’s premature to say anything about the cause of the Lion Air crash. “I don’t jump to conclusions,” he said.

            He added that while the 737 pilot manual doesn’t specifically describe the new system, it does include a standard procedure to shut down the flight-control behavior it induces — whether it’s the new system causing it or something else — and the Lion Air pilots should have been aware of it.

            “The story here is not why we didn’t know about (the new system), it’s why the pilots didn’t fly the plane,” said Insler.”

            “Tim Canoll, ALPA national president, sent a letter Thursday to the Federal Aviation Administration (FAA) and the National Transportation Safety Board (NTSB) saying, “We are concerned that a potential, significant aviation system safety deficiency exists.”

            “In expressing this concern, Canoll was merely following the leadership of the other unions at American and Southwest. But Insler at United, the only U.S. airline flying the MAX whose pilots are represented by ALPA, hadn’t been consulted and was furious at Canoll’s initiative.

            “We’re upset with the national leadership,” Insler said.

            Insler said one of his pilots flew test flights on the MAX and that all of United’s pilots are very capable of hand flying the plane if automated systems fail.

            “If the plane doesn’t do what I want it to do, I make it do so. If it’s not responding, I make it respond,” Insler said vehemently. “There is plenty of feedback as to how this airplane flies, more than enough inputs and opportunity to recover.”

            He dismissed as “speculation” the heavy discussion in the media — largely based on a safety-warning bulletin sent out to all airlines by Boeing and a follow-on airworthiness directive by the FAA — as to whether the MCAS system is implicated in the Lion Air accident. He said people should wait for the investigation to come up with a definitive account of what caused the crash.”


          • When MCAS operates the Stab, it uses one of the Stab Trim motors. On this aircraft the stab cutout switch names are different. What was Main Elec in NG is called PRI in MAX and the ‘Auto Pilot’ in NG is called B/U. Which ever motor moves the stab, the cockpit wheel has to move as it is back driven by cable. There is no other way to move the STAB. Visual cues are present for MCAS opn.

          • @AP Robert,I was once told by a BA pilot to fly Delta because they employ a lot of ex USN fighter pilots and they are the people (almost said guys!)who are best at coping with an emergency.

          • Hello Tech-guru,

            You seem to have a pretty detailed knowledge of the inner workings of the MAX. You state that you are not a pilot, I am curious how you then came across your knowledge of the MAX’s inner workings. Are you a mechanic, an engineer, or someone who doesn’t work in aviation but enjoys reading airliner technical manuals?

        • Kinda flies in the face of many statements and speculations made so far. Quite interesting.

  25. §25.1309 Equipment, systems, and installations.
    (a) The equipment, systems, and installations whose functioning is required by this subchapter, must be designed to ensure that they perform their intended functions under any foreseeable operating condition.

    (b) The airplane systems and associated components, considered separately and in relation to other systems, must be designed so that—

    (1) The occurrence of any failure condition which would prevent the continued safe flight and landing of the airplane is extremely improbable, and

    (2) The occurrence of any other failure conditions which would reduce the capability of the airplane or the ability of the crew to cope with adverse operating conditions is improbable.

    (c) Warning information must be provided to alert the crew to unsafe system operating conditions, and to enable them to take appropriate corrective action. Systems, controls, and associated monitoring and warning means must be designed to minimize crew errors which could create additional hazards.

    (d) Compliance with the requirements of paragraph (b) of this section must be shown by analysis, and where necessary, by appropriate ground, flight, or simulator tests. The analysis must consider—

    (1) Possible modes of failure, including malfunctions and damage from external sources.

    (2) The probability of multiple failures and undetected failures.

    (3) The resulting effects on the airplane and occupants, considering the stage of flight and operating conditions, and

    (4) The crew warning cues, corrective action required, and the capability of detecting faults.

    (e) In showing compliance with paragraphs (a) and (b) of this section with regard to the electrical system and equipment design and installation, critical environmental conditions must be considered. For electrical generation, distribution, and utilization equipment required by or used in complying with this chapter, except equipment covered by Technical Standard Orders containing environmental test procedures, the ability to provide continuous, safe service under foreseeable environmental conditions may be shown by environmental tests, design analysis, or reference to previous comparable service experience on other aircraft.

    (f) EWIS must be assessed in accordance with the requirements of §25.1709.

  26. “Graver, it was news to the Pilots flying the MAX since 18 months as well.”
    Don’t call me Graver, Shirley.

    • The backup flight instrument (IFSD) is in the middle and it appears to me to be small.

      If it was going to be fully good cross check, someplace centered in front of each pilot.

      Its the one independent from the main pitot static system system backup but it is not where I would want it.

      Assuming there is a Pitot system aspect to the situation, once quick cross check is what I call the AI (attitude indicator). Nose up, nose down, ok, we are level, cross check to the independent system, VSI steady (or in reason) also on the horizon (or in reason) not turn, airspeed good.

      I was trained to do a complete instrument scan steadily, including the backup ones.

      Interesting it has its own battery power so its stand alone from the rest that way as well. Just what you want other than awkward cross check location.

  27. There is a lot to keep track of. Still cross verify

    1. The MCAS kicks in if flown by hand (this may factor in if the pitot system is wonkers)

    2. Flaps have to be up (that would be normal above X feet).

    The backup instruments also has air speed as well as altimeter and VSI (assumed) from a complete separate stand alone pitot static system (two static and one Pitot).

  28. Wrong again. It isn’t about the Centre of Gravity, it’s about the Centre of Lift. For the record moving the CofG forward reduces sensitivity to pitching moment, it doesn’t increase it! The reason is that the static margin increases.

    The CofL has moved forward by an amount significantly greater than the forward movement of the CofG, causing a significant reduction in the safe AofA before stall.

    The reason is that the engine/wing mounting is so closely coupled that the mean cord of the wing has been extended forward because the upper engine cowlimg is now part of the wing. So yes the engine cowling is producing lift but at all AofA. That is very, very bad for it increases the likelihood of flow separation at high AofA and also reduces static margin. A reduced static margin increases sensitivity to pitching moment.

    That is why Boeing developed MCAS. Personally, I’d of just told pilots that the stall margin was crap.

    Scott, Bjorn, you won’t publish. But I want you to know I know.

    You should apologise to 190 dead people. Trashing me is one thing, trashing two dead pilots is another!

    • I don’t know what your problem is, Philip. Bjorn’s articles and my post do not trash two dead pilots. Bjorn has written that pilots should be able to fly through the circumstances, provided they knew about the new system–and it didn’t appear they did (which is what Lion Air says was missing in the manual). How is that trashing two dead pilots? My one column on this listed a dozen areas of investigation, including pilot error, as routine areas of investigation. How is that trashing two dead pilots? We have nothing to apologize for. You’re abusive language in your first post on this topic was out of line, which was published anyway, and your second to last line in the post above is out of line, as is the last line.

      If you want to see a story that takes on two dead pilots, see this one in which United Airlines pilots directly say it’s the Lion Air pilots’ fault.


      • Scott: I saw that and thought the same thing, sheer arrogance on his part.

        I saw comments that Sullenberg could have made it back to Newark as well. We are not trained to make it back, but to do the best you can ahead. Turn backs are so low a success rate as to be only if you are at 5000 feet directly over an airport.

        When confronted with an emergency, you have to assess the issue. Snap judgments are lethal.

        These pilots were confronted with what is still a fully unknown set of issues.

        The fact that the aircraft is screaming at you its stalled when everything else says its not, and taking action on its own is going to cause a major confusion.

        Knowing what happened post even is easy, turn off the trim, nice, would you have figured that out DURING the event?

        People continue to focus on just the MCAS, and while its a part of it, I go with Bjorn it was not all of it and while it created its own “Fog of Flying” they might well have figured it out (at least cut the trim off) if it was the only issue.

        • The absence of the Cockpit Voice Recorder is a critical missing piece. Without it, we don’t know what the pilots were saying to each other or thinking/wondering What is going on? We don’t know what audible alarms were going off (though I supposed the FDR would give this indication). Were so many audible alarms going off as to be distracting?

          Most importantly, were there a cascading set of issues that simply overwhelmed the pilots, which caused them to run out of time and altitude before they could figure out how to fly a plane with flight control issues? TransWorld refers to Sullenberg’s experience. Fortunately, he and Skiles didn’t have control issues to also contend with at 3,000 ft.

          Think of United 232 (Sioux City, 1989). Three pilots were faced with control issues that were beginning to overwhelm them. A fourth pilot joined from the cabin and as a coordinated four-man crew, they performed a miracle and made it to the airport. This event started at cruising altitude. Had it stated at 5,000 ft, they would have crashed.

          Think of Qantas 32. there were five pilots and four of them were engaged in dealing with the cascading systems failures. Fortunately, they never faced a control issue. This flight incident began on the extended climb out to cruise altitude after takeoff. Two pilots would likely have been overwhelmed.

          Contrary to Mason’s assertion, neither Bjorn nor LNC have claimed or concluded pilot error. On the contrary, my initial view is they may well have been confronted with a series of failures/control issues and that, starting the descent from 5,000 ft, didn’t give them enough time to understand what was happening to them. But it’s too soon to definitively conclude anything.

          • Scott:

            I have yet to hear a CVR that really clarified anything.

            The FDR is giving us what happened, we know what the aircraft system do (and now the MCAS).

            So yes there would have been stall, stick shaking and the increments of that. j

            What we really need is a video to see what they DID.

            We also need the whole FDR and the breakdown of what was going on at what point including all the other data inputs. There are hints of Pitot/static problems in the record but not confirmed (that would be with the full FDR.

            If so, the PFD sitting in front of the pilot could be lying on both speed and altitude situation (both what it is and the VSI.

            The Sioux city was a classic of the help.

            QR32 I still believe is still in the myth stage. They kept trying to sort through alarms when all they told you was something was totally FUBAR on the left wing and you better get it on the ground.

            The fact they kept trying to get the auto pilot to land the airplane says a lot to me.

            With that much damage you don’t know what the computer system is going to do.

            Sullenberg did two things, (actually three) he kept his head (not easy) he picked the Hudson (right move but a lot of dead pilots have not) and he started the APU that was not on the checklist (full control) – that kept the aircraft flying normally though engines kaput.

            I don’t often say it, but you have to be a pilot and have been on the pointy end of the airplane to get how fast things happen.

            And if its not doing what is normal (despite the emergency the laws of physics should not have the sun rising in the West) what that does to your thought process.

            And that is where the human bell curve comes in. Is this emergency where you are strong or weak?

            While my instructor never got me messed up on the unusual attitude instrument recovery, he also could not induce false information into the panel. He simply took away instruments with a cover.

            Easy to take out of the scan like that.

            How would I have done with say the speedo there but lying to me?

            All I know is that I could use VSI and the Artificial Horizon to determine what was going on and what to do about it.

            But that meant a check off, shift to the VSI and AH to see what was going on. Only a couple of seconds.

            In a spin (or a dive) a couple of seconds is two or three turns (or more) and ……..

    • Philip thanks for this insight. I concur with fog of the problem, conflicting and confusing warning signals, trim wheels winding, normal pilot inputs doing nothing and not much time to figure it all out. I believe that the fundamental problem may lie in statistics. How many transport category jets on revenue flights with flaps up have stalled in flight with no recovery? Perhaps 4 or 5 in say a billion cycles? Why are we addressing this now? Apparently normal flight training handled this event quite well. This unfortunately covert fix introduced some electronic and software complexities that did fail. From what we know of this air frame from the inbound log, the aoa had failed along with other significant input to the ADC introducing a rather exciting flight in the vertical mode for all aboard (flightracker24 trace). I believe I read, perhaps from Reuters, that there were even additional aoa an pitch problems experienced by this same air frame that had been logged before the inbound leg. Apparently aoa’s have a bit higher failure rate than the possibility of an unrecoverable flaps up stall.

      I believe that in this case, Boeing fitted this machine with a device designed to protect against something that has the probability similar to that of being hit by a meteor, with a device, the MCAS, which is dependent upon a subsystem, the aoa among others, with a probability of failure perhaps 1,000,000’s of times greater than the event it was designed to prevent.
      Here, the prevention statistically is much more lethal than the event it was designed to prevent! Previous commentators have expressed numerous ways aoa’s can fail and do. I suspect that nearly every pilot who flies something with an aoa aboard has seen them fail. The fix was usually immediate and effective, ignore it. In this case, the MCAS stall prevention system becomes a greater concern by a very large factor than the stall it is designed to prevent! Unfortunately, in this case it could not be ignored.

      Whatever happened to reducing power on these lethal forward and closer to the wing mounted engines? No software to mess up, no avionic sensor that decides to bail out and put your nose straight down.

      I think that in this case hindsight is a bit cruel. Leave a perceived problem alone if its is statistically irrelevant for your fix may become a very relevant and statistically significant problem. To have left the MCAS in a box and never have placed it on or near any airplane I believe would have prevented this horrific accident. My suggestion is not simply come up with an emergency AD but to figure out how to get these things out of every machine that has the misfortune to be so fitted before they create another tragedy.

      Keep the ball in the middle,

      • I made your very words clear through a series of e-mails initiated by Scott. I used the analogy of the three monkey’s, hear no evil, see no evil, touch no evil. The FCC deprived the pilots of hearing, sight and touch by displaying wrong flight data, issuing wrong audio data and producing wrong physical movements at the controls. Only leaves smell and taste left. The pilots had no chance.

        The 737 max has lousy safe AofA before stall caused by the engin/wing mounting. The engine/wing mounting has heavily compromised the aerodynamics.

        I always understood why the 737 NG/MAX was inferior in performance to the A320 by some way? The engine/wing mounting. It did not occur to me that it had significantly reduced the safe AofA before stall, until now. The MAX is worse than the NG for the engines are further forward and now glued to the wing.

        There’s a very good reason for this thing called a pylon!

        Boeing are in serious, serious trouble. NMA move over, time for NSA

        • This is an interesting point. There have been previous occasions B737s have rocketed into the sky followed by spearing into the ground. Its a big problem to analyse though,because these events are statistically tiny, the plane statistically ultra safe and the pilots have been found to be at fault and theoretically should have been able to overcome any fierce handling properties.

          • Clearly Boeing were of a different view, otherwise they would not of written MCAS. To turn it round. Boeing wrote MCAS because they took the view that pilots couldn’t handle the stall margin.

          • Philip:

            Your knowledge level is down around the bottom of the Mariannes Trench (negative number if you don’t gt it)

            I had an acquaintance who said never argue with an idiot, they will beat you to death with their experience.

          • @TransWorld: Watch it. you know you’re not supposed to get into this personalized name-calling.

          • Yes, but I parsed it like a Republican, I simply commented on poor knowledge level followed by a philosophical statement attached to no name.

            I suppose I am still guilty, sigh (segue in the usual histrionics)

          • @Philip,I meant the NG has an amazing safety record. The MAX currently has a statistically poor safety record.I am not in a position to judge the 737s handling characteristics,although I have read that its fierce when pulling up sharply ,but it’s an interesting question, is it alright to ignore a known problem if it very rarely ends in a disaster?

          • Thanks TransWorld, but not worried about by knowledge of the laws of physics. I spent 50 years studying the laws of physics.

            Thanks Grubbie. I didn’t know the 737 could be fierce in pitch. The issue of static margin is beginning to be more clear. That adds to the debate on MCAS.

            My view was the safe AofA before stall when flying through still air. The NG diminished it and the MAX deminished it more. Add a fierce response to pitch then we begin to know why MCAS was written.

          • “Yes, but I parsed it like a Republican”

            Yeah, Democrats don’t do this all the time as well…

          • But have you seen the news lately?

            Masters of the universe, I stand in awe.

            If it wasn’t winter I would be raking our Forrest!.

          • Philip:

            We do not know who initiated the drive to the MCAS.

            It could have been FAA or Boeing.

            It is not Boeing like.

            A320 and 737 all have very close to the same loss rate, and both are extremely low.

        • @Philip, Talking about fierce, I find you posts very interesting but we are all speculating about the cause of the crash.Only 737 test pilots can talk with any real authority at the moment, and possibly dead 737 pilots.

          • As I said to Scott through e-mail, the FAA was somewhat explicit. They kicked Boeing’s bulletin into touch and also kicked Boeing into touch with a boot the size of an elephant. It was a very ‘fierce’ emergency AD. To say the least, the FAA was not very happy with Boeing. Boeing have kept every quiet ever since. The FA have the data recorder. It tells all about the flight except what the pilots said to each other. They know where the blame lies. It is not the pilots.

            With regard to MCAS. There can only be one reason for it, safe AofA before stall. Safe AofA before stall is determined by longitudinal stability. This article doesn’t meet the pyhsics of longitudinal stability. I’ll leave it at that.

            Botttom line. The stall margin is lousy so they developed MCAS to keep the pilot under control when flying manually. But the word ‘manually’ is also a contradiction for the FCC/MCAS was in control even though the pilots were of the view they were flying the airplane. Imagine the confusion that would cause.

            I accept the FAA do not know why FCC/MCAS did what it did but they do know what it did. Hence the ‘fierce’ rebuke to Boeing.

            For the record, when you flick the switch in an Airbus to fly manually that is what you get. It’s then down to how good the pilot is. I remember the example of a pilot flying an A320 into a bunch of trees. The pilot forgot that it takes 6 seconds for the engines to go from idle to full power. Anybody else remember.

          • Grubbie, I will add to my comment because comment on test pilots is relevant.

            It’s about seeing, hearing and touching, the 3 monkeys. I think the pilots would have got home even in all visual data and all audio data was wrong. So it’s about touch.

            Specifically, when the pilots touched the controls the airplane didn’t respond as expected. So in a sense tge two pilots were elevated to the position of test pilots.

            But test pilots have reference data created through theoretical and emperical simulation, starting with computational fluid dynamics and wind tunnel tests leading into full blown simulation of flying characteristics. All of this reference data became invalid. Why: When the controls were touched the airplane didn’t respond as set out by the reference data. Instead it responded to something neither pilot knew existed, MCAS. MCAS was doing its own thing using unpublished reference data and unpublished control algorithms.

            Even though the airplane was being flown ‘manually’.

            As all pilots will tell you they need some valid reference point. There wasn’t one.

            If the airplane add responded to the pilots touching the controls they would have got it home. It was a clear day with a clear horizon.

          • What you are missing is the Stall and Stick shaker progression.

            That is where this immediately diverges from a runaway trim.

            Runaway trim is not LEAD by a stall and a stick shaker.

            It can be the consequence, but not the cause.

            When you have stall screaming at you and the stick shaking, that puts you into stall recovery mode, not runaway trim mode.

            What else may have been going on we don’t know.

          • “For the record, when you flick the switch in an Airbus to fly manually that is what you get. It’s then down to how good the pilot is. I remember the example of a pilot flying an A320 into a bunch of trees. The pilot forgot that it takes 6 seconds for the engines to go from idle to full power. Anybody else remember.”

            I remember Air France 447…

          • Transworld, I’ve never written about runaway trim. So I’m not clear what you are trying to tell everybody

            Yes, according to the FAA, there was stick shake, just to add to the confusion.

          • Transworld

            Think of traction control on a car. On my car there is a symbol on the dashboard showing traction control is on or off. When engaged the symbol flashes. Not hard. Why didn’t Boeing do it for MCAS.

            As I said it was a clear day with a clear horizon. In other words the pilots could have used the horizon as their reference point. In simple terms point the nose at the horizon and then have a think about what to do next.

            MCAS wouldn’t even let the pilots do that. Instead MCAS insisted on nose down whilst shaking the stick to indicate stall. In other words, the nose is below the horizon but the stick is shaking. Interesting! But then the pilots couldn’t trust anything because as the FAA said the FCC issued conflicting data warnings.

            As I said the pilots were elevated to test pilots. But they were flying the airplane without reference data. There one hope. The horizon. But MCAS wouldn’t let them control the airplane for the purpose of allowing them to use the horizon to get home

            The first law of flight control laws. If the pilots want to fly the airplane let them fly the airplane.

  29. When MCAS operates the Stab, it uses one of the Stab Trim motors. On this aircraft the stab cutout switch names are different. What was Main Elec in NG is called PRI in MAX and the ‘Auto Pilot’ in NG is called B/U. Which ever motor moves the stab, the cockpit wheel has to move as it is back driven by cable. There is no other way to move the STAB. Visual cues are present for MCAS opn.

    • I think there is one trim motor for each stabilizer.

      Ergo, two circuits.

      I do know on 767 you can cause one to go full up and full down (I asked a flight instructor on that as the Egyptian 767 crash made no sense as that was the result of the pilot pulling back and the co pilot pushing down committing suicide )

      Keeping in mind the stabilizer affect is huge vs the elevators, its going to cause an out of proportion force.

      • Transworld: Where did you get this?
        I think there is one trim motor for each stabilizer.
        Ergo, two circuits.
        I do know on 767 you can cause one to go full up and full down

        There is only one Stab actuator (Screwjack), and both stab move together. The screw jack can be driven by any of the two elect actuators in different functional modes.
        Yet to see anyone design something otherwise.

        • This is a quote and confirmed by a large commercial jet flight instructor I asked about it.

          Ergo the elevators can split on a FBW. Getting into the stabilize operation that used for trim but more affect due to size.

          “The NTSB investigation fairly quickly centered on the actions of the relief first officer, Gameel Al-Batouti, and this drew relatively minor criticism from the Egyptians.[19] The NTSB determined that the only way for the observed split elevator condition to occur was if the left seat pilot (the captain’s position) was commanding nose up while the right seat pilot (the first officer’s position) commanded nose down.”

          I don’t know if that can happen on the 737, its a older design.

          There are two trim motor and I don’t know how they are coordinated.

          So we are getting into the elevator and the stabilizer and how it all interacts.

          Two motors on one jack screw? Hmm, two motors and two separate jack screws?

          Need more info clearly.

          • Hello TransWorld,

            Regarding: “Two motors on one jack screw? Hmm, two motors and two separate jack screws?”

            One jack screw, connected to a single electric motor and both trim wheels. If the trim motor fails, either trim wheel can be manually turned to move the stabilizer through mechanical advantage. Firmly grasping either trim wheel will override the trim motor, which is why the runaway stabilizer checklist says -“Trim wheel , grasp and hold.” While pitch trim is via electrically driven stabilizer, non-trim pitch control is via control column movements which move the elevators, with hydraulic boost normally, or manually without boost if hydraulic boost fails.

            Here is how it works on the NG according to the slide show at the link below.

            From Slide 35: Elevator Control Column Override Mechanism In the event of a control column jam, an override mechanism allows the control columns to be physically separated. Applying force against the jam will breakout either the Captain’s or First Officer’s control column. Whichever column moves freely after the breakout can provide adequate elevator control. Although total available elevator travel is significantly reduced, there is sufficient elevator travel available for landing flare. Column forces are higher and exceed those experienced during manual reversion. If the jam exists during the landing phase, higher forces are required to generate sufficient elevator control to flare for landing. Stabilizer trim is available to counteract the sustained control column force.

            Slide 44: Stabilizer The horizontal stabilizer is positioned by a single electric trim motor controlled through either the stab trim switches on the control wheel or autopilot trim. The stabilizer may also be positioned by manually rotating the stabilizer trim wheel. Trim motor used by both Autopilot and Trim switches. Gear box Cable Drum turned by moving trim wheels and back drives trim wheels when trim moves electrically Screw jack turned by the motor or trim wheels

            Slide 47: The STAB TRIM MAIN ELECT cut out switch and the STAB TRIM AUTOPILOT cut out switch, located on the control stand, are provided to allow the autopilot or main electric trim inputs to be disconnected from the stabilizer trim motor.

            Slide 53: Manual stabilizer control is accomplished through cables which allow the pilot to position the stabilizer by rotating the stabilizer trim wheels. The stabilizer is held in position by two independent brake systems. Manual rotation of the trim wheels can be used to override autopilot or main electric trim. The effort required to manually rotate the stabilizer trim wheels may be higher under certain flight conditions. Grasping the stabilizer trim wheel will stop stabilizer motion.


          • Oops!, in my post above I should have written “737 stabilizer jackscrew in action” instead of “737 elevator jackscrew in action”.

            The 737 tail compartment tour video at the link below includes footage clearly showing the stabilizer jackscrew, the electric stabilizer trim motor, and the drum through which the cockpit trim wheels drive or are backdriven by the jackscrew.


          • All Boeing aircrfat from B707 thro 777 have two trim motors. Only on NG there is only one motor. Later aircraft 747 on wards the motor is Hydraulic. All have only one screw jack.

          • How can people moan about air travel?I can’t afford to fly very often, so I haven’t lost my sense of wonder.Look at that thing, basically a car jack operated by cables, designed 50 years ago. But for a small amount of money you can travel at speeds unimaginable 150years ago at a height where you should die of lack of oxygen and cold.And 3 hours away from an airfield and above the sea is absolutely normal.

  30. When mooring some boats the throttle control can sometimes reverse itself by trying to engage reverse from forwards too quickly,so this only happens when you are already under a lot of pressure.Everybody thinks they can beat the trap because they have been forewarned about this possibility and because it’s obvious that the boat is accelerating towards the quayside.The reality is that no one can and everybody piles on the revs and hits the wall.Just a few seconds more and you would probably manage to get it into neutral.
    The United chief pilot is making a reckless statement and tempting fate when he says that he makes the plane do what he wants.Apart from anything else all United pilots can’t all be of exactly the same standard.

    • No ones pilots are. They all undergo the same general training.

      My understanding is FedEx is a leader in the area as they recognized earlier that it was an issue and began to train to challenge the pilots in unusual not the rote.

      I think Ak Airlines teach unload, unload unload. I wonder if they got that from Boeing. Right thing to do in some situations, not in this case.

      Like Sullengerg, the nit pickers said he could have turned back and they did it in simulations. But that is not what you are or should be trained to do, its a crap shoot and a bit of wrong and you kill your whole plane and those on the ground.

      I think the DC-10 engine loss was the same. But you had to train for it and be ready. Fly another 5,000 hours and how ready would you be for something that should never occur?

      That too was a massive error as the slats should stay locked down not held down by hydraulic pressure (ie check valve)

      What I detest are the shoulds covering up the bad.

      The Asaina pilot in SFO 777 crash should not have got himself in that positions.

      But he shouldn’t have to remember that FLCH trap either. That is junk design for the Auto Throttle to go off entirety due to FLCH mode. NTSB agrees. Boeing sadly resists.

      But who pays when pilots get trapped by poor design choices?

      Then the should becomes a tragedy and the system should work to keeping those out of itself.

  31. One glaring issue is that the 737 is a LCC workhorse with many low hours first officers. A far greater workload for the PIC than a more established airline. When a LCC carrier PIC has to leave the cockpit, the aircraft should be at least be safe in the hands of an inexperienced FO. if only for a few minutes.

    • I’ve often wondered about that.Whenever there is an accident the press often comment on the pilots lack of hours. I propose that qualified but inexperienced pilots might actually be safer.If you think about it, they have the same training as more experienced pilots, but much less experience of the plane doing exactly what they expect to happen. Experience is only useful if you survive it.

  32. I’m so glad people are waiting for all the facts to come in and are not advocating prison time and are not saying the plane or code is flawed (warmed over death trap) and are waiting for the expert’s final conclusion. I’m so glad no one is rushing to judgement based on incomplete information or using this as an excuse to grind their personnel axes.

    I’m so glad this is what is happening!

  33. Reply to AP_Robert
    ” Hello Tech-guru,

    You seem to have a pretty detailed knowledge of the inner workings of the MAX. You state that you are not a pilot, I am curious how you then came across your knowledge of the MAX’s inner workings. Are you a mechanic, an engineer, …….”

    Yes I am an engineer. Started on B707 through 747 and 777, and all the Airbuses till A380. The only missing piece was B737 in my portfolio. Now retired (after 40yrs)and enjoying Collecting (from friends in the industry) and reading tech books about all aircraft. Also contributing my two pence worth in these columns.

  34. That is great.

    Any info on the trim motors and how that system works to be gleaned from those who know on the 737?

    I see two of them in the circuit and clearly the two shutoff (and or CB switch) for them up front.

    • Typically there are two geartrains, each with its own motor. They are both driving the a gear on the common jackscrew, in an active-standby logic, i.e. at any given time only one is actively driving the jackscrew, the standby one is backdriven due to the jackscrew motion. The cutouts have the effect of i) applying brakes on both motors and ii) cutting-off electrical power to the motors, in this order. Pretty much all stab unarrested runaway failure conditions may result in a CAT event. An excursion of ~ 2 degs of stab is huge in terms of control power (~ 5 x elevator’s effect).
      Not sure how it actually works on the 737MAX, but from leafing thru the posts it seams to be similar. Hope this clarifies things a bit.

    • Hello TransWorld,

      Regarding: “Any info on the trim motors and how that system works to be gleaned from those who know on the 737?

      I see two of them in the circuit …”

      According to the videos and 737NG ground school slides I posted links to above, there is only one stabilizer trim motor on the NG. The trim motor can be activated either by switches on each control wheel, the autopilot, the speed trim system (see slide 55), or the stall warning system (see slide 40).

      “The horizontal stabilizer is positioned by a single electric trim motor controlled through either the stab trim switches on the control wheel or autopilot trim. The stabilizer may also be positioned by manually rotating the stabilizer trim wheel. Trim motor used by both Autopilot and Trim switches. Gear box Cable Drum turned by moving trim wheels and back drives trim wheels when trim moves electrically Screw jack turned by the motor or trim wheels.”

    • I stand corrected about Stab trim motors. There is only one electric Trim motor on 737NG. Either control wheel trim switches or the auto pilot trim channel can move the stab through this motor. I was writing from memory from earlier Boeing aircraft. In fact all Boeing (From Boeing 707) aircraft have two trim motors for stab, and even on later aircraft (From B757 through 777 have Hyd motors).
      On B737 NG series, there is only one Elect motor shared by both Manual, STS and autopilot channels. MAX ,I am not sure.

      • Hello Tech-guru and anyone else trying to figure out how many trim motors 737 have,

        According to the following excerpts from a Continental Airlines 737 Flight Manual with revision date 11-15-02, the 737-300 and 500’s in Continental’s fleet at that time had two trim motors, one for the cockpit trim switches, and one for the autopilot, while the 737-700, 800 and 900’s in Continental’s fleet at that time had only one trim motor, which could be activated either by the cockpit trim switches or the autopilot. In Continental’s classics there were two cutout switches, one for reach of the two trim motors. In Continental’s NG’s, there were also two cutout switches, one for trim switch input to the single trim motor, and one for autopilot input to the single trim motor.

        “Stabilizer Trim
        737-300, 500:The horizontal stabilizer may be operated by either a main electric trim motor, an autopilot trim motor or by manual cable control.

        737-700, 800, 900: The horizontal stabilizer may be positioned by a single electric trim motor, controlled by either the autopilot trim or by stabilizer trim switches on the control wheel or by manual cable control.

        737-300, 500: The main electric trim has two speed modes: high speed with flaps extended and low speed with flaps retracted.

        737-700, 800, 900: Stabilizer trim switches on each control wheel actuate the electric trim motor through the main electric stabilizer trim circuit when the aircraft is flown manually. With the autopilot engaged, stabilizer trim is accomplished through the autopilot stabilizer trim circuit. The main electric and autopilot stabilizer trim have two speed modes: high speed with flaps extended and low
        speed with flaps retracted.

        If the autopilot is engaged, actuating either pair of stabilizer trim switches automatically disengages the autopilot.

        The trim wheels follow automatically when electric stabilizer trim is actuated and the stabilizer trim indicator shows the trim unit setting.”

        “Trim Cutout Switches
        737-300, 500: Main electric and autopilot trim motors may be disengaged by individual cutout switches located on the control stand.

        737-700, 800, 900: The stabilizer trim main electric cutout switch and the stabilizer trim autopilot cutout switch, located on the control stand, are provided to allow the autopilot or main electric trim inputs to be disconnected from the single stabilizer trim motor.”

  35. Apparently most comments are from pilots the following link will interest you. Well made video by a pilot about MAX.

  36. I’m still curious as to what the various pitch up forces or moments are on various modern aircraft, at high AOA. Does the MAX have the most reduced stability? The 787 engines seem to have a large area and be forward of the wing, same with the A330neo. How do these compare to the MAX?

    What does the pitch up force or rate compare on these aircraft? Is the MAX have more reduced stability, and to what degree more than the 787 or A330neo, 10% more, or 3 times more?

    What does reduced stability to pitch up mean in the context of modern aircraft with large fans?

    • Ted:

      Each aircraft has its own unique characteristics.

      As this is the first anyone public was ware of the pitch up issue on the 737MAX, we have to wait the details.

      Its not the pitch up I suspect, its the pitch up into past stall. So coming up on stall or into it it pitches up.

      Based on nothing other than my feel and take, I would put i close to 10% than anything.

      I flew small aircraft, they did not do that. What big jet Aircraft do is Bjorn’s area.

      Location and mounting of the engine as well as the shape all play a role. MAX is pushing it into that area due to the needs to get as large as they can on an old tube engine frame.

      My take on Boeing stubborn on this is they simply put it in the out of trim runaway correction.

      But runaway trim does not start with a stall, stick shaker and the squawking. Out of context even if the remedy is the same your cross checks are different because you have to take a stall warning as top priority until you confirm otherwise.

      Then it becomes a split decision as to fly the airplane and ignore it or figure out why in the world its telling you its stalled (when i never did that in any similar training)

      I teach fire response in buildings. The first thing you assume is it is a fire. To respond by turning pumps off is not allowed.

      You have to confirm there is no fire before you do.

      This truly gets into a issue as if the initial response is to turn it off and its right, then follow up actions are wrong.

      I don’t know how many times I have seen the report, well the alarm system was turned off because of all the false warnings.

      As time goes by we will hear how Airbus deals with it.

  37. What was the profile of the final dive? If the trim wasn’t or couldn’t be corrected, was the downward attitude of the aircraft constantly increasing, going past 90degrees inverted towards an outside loop?

  38. This is some more good information, he is a bit condescending in my view but the info is good

    I think it misses to a degree the issue if you are not aware of a system on an aircraft, then its behaviors when gone wrong makes no sense. Any alert that what it can do and its symptom triggers the required, turn it off – not because its a runaway trim but its a Runaway MCAS as your main AH (and backup) still tell you what degree of vertical the aircraft is in.

    Issues with the static pitot speeds adds a huge aspect and the need to shift to the backup combo display (in the center)

    Will follow up on the Brazilain authorities comment,

  39. This is also interesting. I liked the part at the end about what the hell else don’t I know about!

    Sums it up quite nicely.

  40. Seattle times has done an update

    One of the item is that the AOA on that flight and the previous one disagreed by 20 degrees on the ground.

    That should be a huge red flag. 20 degrees being stall.

    It appears the previous flight resolved their immediate issue with by turning off the trim systems (after 12 evoluations so they too were confounded – not as long unfortunately as the next6 crew)

    There is vebiage in regards to using both AOA which I Bjorn thinks you can’t do (AOA issue between a high and low side?)

    And add in it had to have been tested and test pilots did not wight in or were dismissed.

  41. The comments by an ex-Boeing flight control engineer in the excerpt below from the 11-27-18 Seattle Times article (probably the same one TransWorld referenced above) at the link after the excerpt, pretty much agree with what I have been thinking based on what has been reported so far about the Lion Air accident. I can understand how given only tens of seconds to react the pilots might not have thought of checking the pitch trim when unusual control forces were encountered, but it is baffling to me that given minutes to react, airline pilots would not closely examine the control (trim) that changes control forces and neutral position and turn off the pitch trim motor off if the trim wheel was spinning in the direction that would apply the control forces they were fighting.

    “Beside their seats a large wheel, called the stabilizer trim wheel, which rotates as the horizontal tail swivels, would have been spinning fast and noisily. Such an uncommanded movement, which could be triggered by other faults besides MCAS, is called a “runaway stabilizer” and pilots are trained to deal with it in a short, straightforward procedure that’s in the flight manual. Flicking two cutoff switches stops the movement completely.

    “Somehow, the pilots ignored the spinning stabilizer wheel, perhaps distracted by the shaking of the control column — called a “stick shaker” — and the warning lights on their display which would have indicated disagreement between the AOA sensors and consequent faults in the readings of airspeed and altitude.

    The NTSC preliminary report confirms that, shortly after takeoff, the pilots experienced issues with altitude and airspeed data.

    Still, their failure to shut off the automated tail movements is baffling.

    “No one would expect a pilot to sit there and play tag with the system 25 times” before the system won out, said Lemme. “This airplane should not have crashed. There are human factors involved.“

    “Lemme said the Lion Air crash will inevitably lead to a re-evaluation of the MCAS system design.

    In his view, it wasn’t a case of Boeing’s design engineers ignoring the consequences of a single sensor failure. “It’s a case of overvaluing the pilots’ response.”

    “I’m sure the systems designers that approved this assumed the pilot would hit the cutout switches and move on,” Lemme added.

    “With hindsight, he said, when a calm assessment is done by engineers, they’ll probably conclude that a single input shouldn’t be allowed to trigger the system.

    He said MCAS is designed to kick in only in extreme circumstances that an airliner should basically never face: something like a high-bank, high-stress turn, experiencing many times the ordinary force of gravity and approaching stall.

    It should only engage when the sensors are certain that’s the situation. “You need a second input to make that judgment,” Lemme said. Some logic could also be inserted to consider the reliability of the AOA readings when the plane is still on the ground.”

    • When I was taking flying lessons many years ago ( I quit before I got my license), I was certainly nowhere close to airline pilot caliber, to put it very kindly, but once when I was surprised by how hard I had to pull the yoke back to take off in a lowly 100 hp Cessna 150, it only took me a few seconds to think of checking the elevator trim wheel, at which time that I discovered that I had not set the elevator trim wheel to the takeoff mark. Control forces unusual = check your trim, is what I was taught.

      For those who are not pilots or ex wannabe pilots, when hand flying an aircraft most pilots are constantly making trim adjustments to set the control neutral point to the current aircraft configuration, rather than having to spend most of the flight pushing or pulling on the control wheel to maintain the desired speed, level flight, climb, or descent. Since the Cessna 150 trainers I flew had no autopilots, hand flying was the only option, there were no auto land, or auto climb, or auto anything buttons to use instead. Here is a trim cheat sheet for the lowly 50 to 120 mph Cessna 150 with requires much less trimming than a 150 to 550 mph airliner.

      “A Cessna 150 has nearly the same trim setting for level cruise flight as is needed at 1500 RPM, full flaps and 60 kts descent. Thus, the full flap short approach requires no change in trim unless power is off. This setting is constant for nearly every loading. The instructor will help the student determine this initial setting. If the C-150 has been landed with full flaps it will be near the correct setting for level cruise but not for takeoff climb. From this starting point of the trim wheel the following apply:

      1. For a takeoff climb at 65 kts, the C-150 trim wheel must be moved down one full finger tip turn from the full flap landing/level cruise position.
      2. To level off from this climb it must be moved up one full finger tip turn.
      3. Three full down finger tip turns from level will give descent at 60 kts at 1500RPM.
      4. Trim down four finger tip turns for a no flap glide at 60 kts with power off.
      5. Trim full down four finger tip turns for minimum controllable without flaps. About 2000 RPM no flaps.
      6. For full flap slow flight or minimum controllable trim up one finger tip turn. Full power.
      7. Most Cessnas have one full finger tip turn of the trim between level and climb settings.
      8. In each case fine trim movement may be required.

      Removal of the flaps during the go-around finds you trimmed for level cruise. One full finger tip trim down will give Vy climb at 65 knots. This same procedure can illustrate why, when making a short approach, reduction of power to 1500 and application of full flaps at the white arc will give you a hands-off approach speed of 60 knots.”

  42. What is the source for this article’s assertions that the 737 MAX is not “naturally stable” in pitch? And what is the source for the assertion that the source of this instability is increased lift generated by larger engine nacelles only at high angles of attack?

    If it is solely the author’s opinion, then it is highly suspect.

    When thrust is increased (such as during stall recovery), underwing-mounted engines create a well-understood nose-up pitching moment. The amount of this thrust-induced moment will obviously change based upon the position of the engines relative to the aircraft center of gravity. Placing engines (not nacelles) further forward increases the nose-up moment when thrust is increased. It is likely that this is the reason why Boeing introduced the MCAS control law into the 737 MAX’s flight control software.

    In the 1998 Boeing AERO Magazine article entitled “Aerodynamic Principles of Large-Airplane Upsets,” this dynamic is explained: “With underwing engines, reducing thrust creates a nose-down pitching moment; increasing thrust creates a nose-up pitching moment.” The article goes on to discuss recovery techniques in a variety of aircraft attitudes. The recurrent theme, of course, is the necessity of lowering the angle of attack, chiefly via “apply[ing] as much as full nose-down elevator.” But it also warns that “it may be necessary to reduce some thrust in order to prevent the angle of attack from continuing to increase.” [See

    If the author has a source for the contention that the CFM Leap 1B engine nacelles on the 737 MAX contribute more (if any) lift at any angle of attack as compared with the underwing engine thrust moment, then he should publish it. If not, he should retract his erroneous analysis and conclusions.

  43. Pingback: When you expect Max 8 pilots to be counter-intuitive during an emergency … – Ishok Yushoku

  44. This is an excellent article describing the issue, I learned a lot. Anyone else here in March 2019?

  45. Well, this is the most poorly informed article I’ve read on the subject since Trump’s tweet.

  46. Pulling up the yoke does not pull up the plane. What? What? This is like telling drivers that stepping on the brake will accelerate the car.

    That is plainly inviting trouble. People are not expected to be counter-intuitive during emergencies.

  47. This is criminal on the part of Boeing and FAA. Isn’t it precisely during emergencies that the pilots need to know what kicks in and what is different (esp. counter-intuitive like the yoke pulling with MCAS)? Those who took the decision to not inform pilots and operators of these changes should be brought to book for the manslaughter of over 300 people.

    I shudder to think of what will happen when our streets are full of self-driving cars. The legal precedent must be set now holding such decision makers, and the people who advise them, to account.

  48. I am pilot retired. I flew Airbus. Anyway, someone that explain me the following:
    I don´t know if trim cut out switches in the pedestal that the 737 Max have, are also installed in the NG. I understand that Boeing, may not find necessary to give training in runaway stabilizer in the MAX versión. That I wonder is how a crew, that going to fly this new versión of a plane, and already had: a ground school, a simulator training, a number of observer hours, a number of enroute check ride hours, for finally become active crew member of the plane, NEVER, asked to somebody, what for are those switches labeled STAB TRIM CUT OUT switches!!!! The event both planes have experienced is so dramatic and fast, that there is no time to read any QRH procedure. If may be, the pilots would got the INFORMATION that those switches were the chance to stop “a very seldom chance of a runaway stabalizer” lookig a this Wheel running extermely fast, may be they could remember the use of those switches. How may lives woul be saved!!!As I know up today, they never asked, and nobody tell them nothing, about those switches.

    • I too am a retired pilot. I flew all versions of the 737 except the max. All had a procedure for runaway stabilizer. It was a BOLDFACE emergency procedure to use the cutoff switches. In other words a procedure done from memory without use of a checklist

      • Terry, I can’t find a copy of the MAX runaway-trim memory item. Can you? Or anyone else reading here?

    • In all versions of Boeing starting from B707 through B777 and B787 the Trim cutout switches are located at the same or similar position near throttle levers idle position and have similar function in all models. But in my 42 years working in aviation, I have never seen even one report where a Boeing pilot had to use this switch for a runaway STAB condition. Except now with MAX.

  49. Retired engineer, 36 years, US Patents

    It is clear the MCAS was ‘included’ to counter the added uplift forward of the CG due to the new engines’ physical size and placement relative to the legacy 737 design. I highlighted the word ‘included’ because my core question is, at what point in the development process was the MCAS added? The answer will shed light on the nature of the whole mess. For example, if the designers saw the need for a compensating force during the earliest stages of dynamic modeling, then the MCAS was likely one of several possible remedies that were considered during design meetings. The notion of adding compensating surfaces aft of the CG may or may not have been suggested. I sent this suggestion to Boeing a few days ago. But I suspect the notion of adding compensating surfaces aft of the CG lost out to an easier software MCAS ‘fix’, since the former would entail added development time and cost, time being the main driver. But again, I highlighted the word ‘included’ earlier, because if this software patch (MCAS) was added only after the uplift issue was discovered during physical prototype flight tests, this would confirm that the MCAS was absolutely added solely as a patch rather than part of the initially modeled design. If the designers had seen the uplift issue early in the modeling phase they might have been more motivated to address the uplift by implementing counter force surfaces aft of the CG, either by adding fins to the fuselage sides, aft of the wing or possibly as fixed surface extensions aft of the non-control areas of the wings. Those added surfaces would not induce drag, or only minimal drag, when the aircraft was flying at normal cruising speed with its slight uptilt. So the added countering surfaces would not have detracted from the core objective of the Max design effort which was fuel efficiency optimization. It will be interesting to see the questions asked, “At what point in the development process did the increased uplift become apparent and once the need for a counter balancing force was seen, what alternative methods were suggested to address it, other than MCAS? What decision criteria drove the decision to implement MCAS to address the uplift issue rather than a purely aerodynamic approach such as the addition of compensating surfaces?”

  50. Ahhh , just to say pilots gotta know wut’s is
    going on especially when flight gets abnormal
    gotta switch -off the autopilot and rid the power to
    electric trim motor. ( electric motors are very strong)
    Now got to trim the damn air machinery to a correct
    pitch control. Such must be taught in simulator before
    strapping Yo’ ass in seat. Could save airplanes and
    lives. The future airplane ✈️ will have but only one
    Person in the cockpit. Automation will definitely reduce population on planet earth. I will not fly.
    Now retired with little over 24,750 hours as instructor and Flight
    Examiner ….

  51. Any unwanted trim input should trigger trim cutout action by the pilots.

  52. Keep hearing that MCAS was not in the manual. It’s in mine and bas been since at least early February. MCAS can be over ridden exactly the same as the pitch trim runaway is. Using a memory item (requiring memorization) to fix the problem. Read the Boeing manual, not your company’s.

    • If this Boeing employee means Feb 2019 it was too late for JT610.
      Requiring memory must be a joke. How about new pilots.
      Also doesn’t have each plane its own manual because of different variants with different specs and different configurations. Only its own special manual is valid.

      Most important ET302 tried the manual trim wheel and it was NOT working.
      Reg 25143: The plane must be SAFELY controllable and maneuverable without exceptional piloting skill or strength. For conventional wheel type controls, the maximum control forces permitted are 10 pounds.
      Since it’s not forbidden that a First Officer uses the lavatory, these 10 pounds can’t be devided among 2 pilots.

      Boeing’s new advice that both pilots together need to turn the manual trim wheel because of high forces doesn’t follow regulations. How can a plane be SAFELY controlled if both pilots need to turn the manual trim wheel with high forces and around 50 times for only one degree on the stab.
      Must be criminal if FAA certifies this, same as their stupid AD after JT610.

  53. This is the only ace I could find that explains why, even though the engines are moved more forward (at least suggesting more natural nose down), what actually happens at high AoA is nose op due to the LIFT created by the nacelles.

    The only article I could find on the web explaining this.How do you explain THAT?

    And thank you, by the way, Bjorn.

  54. Pingback: Overview of many failures by Boeing in designing the Boeing 737 MAX – Feit of fake

  55. The claim that MCAS was not disclosed is utter nonsense. The Boeing 737-7/-8 System Differences Training Manual on Flight Controls, Volume 1, dated January of 2017, clearly describes MCAS on page 748.


  57. It looks like – from various sources including Seattle Times – B is engaged in a TOTAL rewrite if the MAX software, to involve both flight computers, multiple inputs from instruments etc.
    If the report is accurate this implies a monumental task, and the review thereof is also going to be monumental, and very lengthy as regulators will have to discard everything they think they know about MAX and begin review ab initio.
    2020 or 2021 anyone?

    • The aircraft needs a major modification. New wings that provide adequate lift without all these electronic fixes.

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