Bjorn’s Corner: 737 MAX ungrounding, the technical background

By Bjorn Fehrm

November 20, 2020, ©. Leeham News: This week’s big news is the lifting of the grounding of Boeing’s 737 MAX.

I wrote about the changes made to the MAX Wednesday and why I believe it’s safe. Let’s use our Corner space to walk through what I wrote about, but with a more technical angle.

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

Airliner pitch stability

I ran a Corner series two years ago after the first 737 MAX crash of Lion Air JT610 on October 29, 2018, digging deeper into pitch stability and why airliners have helper systems.

The following is a bit of refresh of many themes discussed there (to read the original series, put “Pitch Stability” in our search box). Here we only use the necessary parts to explain what MCAS does for the 737 MAX, why it was necessary, and why the modifications are sufficient to make it safe again.

The airliner control problem

Airliners cover a vast range of speeds and heights when flying their daily sectors. From an aircraft design perspective, this can be summarized in two key problem areas:

  • A wide range of dynamic pressures. Dynamic pressure is the force on the airplane from the air molecules when we fly. At low speed, we have low dynamic pressure = small forces. At high speed, high dynamic pressure = high forces. The dynamic pressure working on the wing and stabilizers of the 737 MAX is typically 3kN/m2 or 0.5 PSI at takeoff and landing. At cruise at M0.78 and 35,000ft (FL350), it’s typically 10kN/m2 / 1.5PSI.
  • This 3:1 change in dynamic pressure creates challenges. The efficiency of wings and control surfaces vary a lot from takeoff to landing. It isn’t easy to design the aircraft to be consistent and controllable at every point between these extremes.
  • The change in forces also complicates the aircraft’s stability around its three axes; Pitch, Yaw, and Roll.
  • The most challenging axis is the Pitch axis, where the lift force is equal to the aircraft’s weight. We talk about a 500kN/110,000lb force working around the aircraft’s center of gravity that shall be balanced to equilibrium at all times by the horizontal stabilizer with its elevator.
  • The horizontal stabilizer shall balance these massive forces over the complete dynamic pressure range, so the aircraft has just the right stability (nose down tendency) at all times. Too much stability and it’s starting to be unsafe. Too little, the same problem.

We saw in the Pitch Stability Corner series this isn’t easy. A well-behaved aircraft has a straight Pitch Moment curve with a consistent negative slope (it will nose down if disturbed to a higher AoA, with the same response to a stick displacement (i.e. control force) in the whole AoA range).

I have recreated the 737 NG Pitch Moment curve as I understand it in Figure 2 (trimmed around 9°AoA, the maximum for the normal flight regime).

Figure 2. A representation of the 737 NG pitch moment curve. Source: Leeham Co.

It’s very close to the ideal curve with a bit less stick force per AoA in the stall, which is typical behavior. Observe that airliners don’t fly above 10° AoA unless they are in trouble.

Our example of contemporary aircraft was the Douglas DC-9, the main competitor to the Boeing 737 until the mid-1990s, Figure 3.

Figure 3. Pitch moment curve of the DC-9. Source: Stanford University.

The DC-9 has a troubled moment curve at high AoA, typical of T-tailed aircraft. These have difficult stall characteristics. This necessitates a flight control helper system called a ” Stick Pusher” that stops the pilot from flying into this region, as the positive curves post-stall mean you can get stuck there in a deep stall.

The 737 has no such vices. It’s straight forward to fly, including stall. This is part of its good historical safety record.

The MAX problem.

The larger engine nacelles of the 737 MAX (Figure 1) added nacelle lift ahead of the wing just before stall. Figure 3 shows the planform of the 737 NG on top of the 737 MAX.

Figure 3. Planform of the 737 NG on top of the MAX. Source: Leeham Co.

The larger 737 nacelles (compare in Figure 1) add additional lift ahead of the aircraft’s center of gravity at high AoA. This results in a Pitch Moment curve as in Figure 4 (green curve with the red segment at the end).

Figure 4. Pitch moment curve of 737 MAX. Source: Leeham Co.

We see that nose down moment per additional AoA reduces when flying above 12-13° AoA. While still fully controllable by a Pilot that is aware of this change, it’s not allowed by the FAA certification rules.

There are several ways how the curve can be bent back to the green desired curve. We look at the different methods in the next Corner and analyze why Boeing choose MCAS as the solution.

63 Comments on “Bjorn’s Corner: 737 MAX ungrounding, the technical background

  1. The US pilot unions have raised a number of checklist / memory items and how often certain items should be retrained ie MCAS. Have you had time to analyze tnis set of variables being debated ? Thanks and keep up the great work.

    • Hi Brian, no not yet. I will check it. But as a non-checked out 737 pilot, I think others can comment better.

  2. Don’t the stored or grounded MAX need an Annual or C check, depending on how long they have been stored, to be brought back into service?

    • I will have a special article about it next week. There is a well-established procedure to take aircraft out of this type of storage as airlines and lessors have stored aircraft since the beginning of air transport when the market is down.
      It doesn’t involve a base check like an Annual or C check. It’s an adapted procedure including de-conservation, running up and BITE testing all systems, followed by test flights.

  3. Björn, I remember you described in detail that human power won t be sufficient to pull back the trim wheel at higher speed. How did that get solved – or why do we not hear anything about that anymore, even in your article right now?

    • This is detailed in the FAA final AD preamble report, as it was raised by several commenters.

      The extensive testing that was done on the trim wheels, showed that for a pilot of average physical strength (using a composite of male and female capabilities), there was no issue in the controllability of the wheels, within the safe operating flight envelope. Which is consistent with the 50 years of experience with the trim wheels in the 737 family.

      The testing was done both with random male and female airline pilots in the simulator, and by Boeing, FAA, and other regulator pilots in the MAX aircraft during flight.

      To commenters who raised the issue of controllability outside the flight envelope, the FAA said that the purpose of the regulations was to encourage and support basic safety and airmanship, such that flight remains within the safe operating envelope, as considered and covered by the regulations.

      The FAA also said this issue had been considered extensively by the JOEB, based on random pilot testing in the simulator and the execution of non-normal checklists. This was part of the determination of the mandatory pilot training. Pilots will have the opportunity to practice and demonstrate proficiency with the trim wheels, under professional instruction, during all modes of flight. That was intended to give them practical experience that they might not encounter in service.

      • I’ve seen some comments about cyclically unloading the elevator with the yoke to milk the stabilizer trim with the handwheels. I don’t know the systems on 737, but it seems to me that this should give the electric system some authority despite high air loads….love to hear more from some left seaters

        • Funny MCAS is outside the normal flight envelope just like the manual trim lockup.

          For those confused, the only time(s) manual trim would be used is

          1. Trim motor is turned off due to MCAS dumping the nose (less ability to do so in MCAS 2.0) or Trim Motor Runway.

          2. Trim motor seize up and in that case you have to break out the clutch to get the gearing to move. I have not seen that address. I have worked with clutches and break out and its no fun.

          Notice how this is parsed out for Normal Envelope. Ego we can ignore pilot overload and they wind up with excess speed per Ethiopian.

          I would have to run the calcs but due to air density (or lack of it) Addis Ababa is around 7700 feet of altitude.

          They would be used to what would seem to be excess speed to other pilots on the filed for takeoff as well as landing but add in approach and departure altitudes and you would be outside the norm for most flight ops but common for them.

          In short, they would normally fly faster due to lower air density any time they were in and out of Addis Ababa .

          And then hit with something trying to kill you and yes, you can have excess speed though god, the FAA and Boeing has said thou shalt not.

          Cherry pick the parameters and you can justify anything.

          Note that Dickson claims EASA within days and its more like weeks. But then the spin is not new.

          • Perhaps even faster as higher speeds can be used to meet second-segment climb gradient requirements after thrust of one engine lost.

            I call that ‘overspeed takeoff’, brain fade on Boeing’s term. Aircraft must still be able to stop from decision speed V1, so in effect runway is sacrificed for climb performance. (Tire speed rating and brake energy limit may constrain. I’ve
            seen performance calculations for 737-200C that optimized takeoff weight such that all four factors were limiting.)

        • Jim, I think you are referring to the “roller coaster” technique that was listed in the classic series of the 737’s flight manuals.
          That can use up about 7000 feet of altitude to complete in some situations. With the reduced size of the trim wheel on the 737-NG’s and 737-MAX, I wouldn’t be surprised if it took even more altitude, time and effort. Also, the 737-NG & MAX version of the 737 has a larger stabilizer surface area. So the smaller trim wheel is operating against a larger stabilizer. On the classic the Stab area was 31.40 square meters, and on the NG/MAX it’s now 32.78 square meters. With the more powerful engines on the MAX, and the difference in engine placement, you’re asking the Pilots via a smaller trim wheel to do a lot more than before.

          • More powerfull engines or different placing don ot effect how hard it is to rotate the wheels. Only the aerodynamic load on the stab. =speed and trim position. As mentioned above, the roller coaster technice is well known by b737 pilots. And the “by heart” memory item to move c/o switches to cut Out if in doubt that there is a problem with pitch trim.
            AND not leave the thrust levers in full thrust as Ethiopa did….

      • “…there was no issue in the controllability of the wheels, within the safe operating flight envelope. ”

        Which the curbed MCAS and/or pilot procedures are intended to keep the aircraft within?

        (Recall illumination of Boeing’s design philosophy of a large stabilizer trim range.)

        As an aside, I see original MCAS as an example of engineers and pilots and even FAA going overboard. And Boeing people not paying attention to what the KC-46A designers did with a similar function that is quite useful to its pilots because of possible large CofG changes from transferring fuel within or off of the airplane – the limited authority of the feature. (I don’t know how the KC-46A fuel system works, obviously there are fuel stores forward and aft, with substantial flow off the airplane to the rear, I don’t know how they are balanced in real time. A whole nuther FMEA I expect, though named in a top level one.)

  4. Did the DC-9 have the same problem as the MAX?
    That being that it could not pass the two required stall tests (one in level flight, one in a banked turn), which specify a given stick force for a given deceleration all the way to stall.
    Did the stick force on the DC-9 fall below the given limits?
    Was a stick pusher an allowed solution, just as MCAS is now deemed an allowed solution? How failsafe was the stickpusher system?

    • Different problems and different solutions.

      The T-tail in the DC-9 caused a moment reversal at high alpha, as shown in Bjorn’s graph. You cannot correct for that, you can only avoid it. So for that case, the stick pusher was an appropriate solution as it prevents the pilot from encountering the behavior.

      The MAX has a change in moment slope at high alpha, but not a reversal. So the slope change can be corrected and doesn’t need to be avoided. That correction is what MCAS does, so it’s an appropriate solution for that case.

      In terms of the stick or column force, the slope of the moment curve is a rough indicator of the required force presented to the pilot. If the slope is constant (straight line), the force remains uniform across that segment. If the slope is lessened (the red line for the MAX), the force is lessened also.

      For the DC-9 moment curve, the slope not only lessens, it reverses sign as well. That would be experienced by the pilot as needing to push on the column instead of pull, to maintain the same position. Obviously that is extremely dangerous. so the stick-pusher stops the alpha advancement before that part of the curve is encountered.

      • So on the DC-9, the requirement to be flown to stall was exempted by the stick pusher as a definitive stall avoidance system? Would this be allowed today?

        • It’s allowed today with the appropriate level of safety (very low probability of failure, i.e. redundant systems supporting it) for the stick pushers operation. All T-tails have this problem and most business jets have T-tails, so they have this problem and thus solution.

        • Stick pushers generally have an override mechanism in case of erroneous activation. Some have a kill switch on the column, others have a force override if the pilot resists the pusher. So my guess is that in stall testing, the test pilots intentionally override the pusher protection.

          Here is an interesting post (about halfway down, Jerry Lundry entry) about the DC-9 development. It was in the flight testing phase when the first T-tail crashes occurred elsewhere. There was a “holy crap” moment as they quickly proved in the wind tunnel that they had a huge problem. So they devised a number of solutions, none of which were adequate, but together with the stick pusher they were enough enable safe recovery from normal stall, with avoidance of deep stall.

          Interesting also in the difficulty encountered with aerodynamic tweaking to tune the pitch moment curve. It sounds easy on paper but isn’t at all. The MAX was criticized for not using these measures instead of MCAS, but this link demonstrates why that might be. I’m sure Bjorn will discuss this more next week.

          • A recovery parachute may be used during flight testing.

            Was on the Canadair Challenger business jet, tragically on one flight it could not be jettisoned, all but Captain got out through overwing exits and parachuted to safety.

        • The discussion of stall testing and the DC-9 reminded of the video of a MD95/717 test flight at the link below.

          “In the video above, you can see that the pilots initiated a powered approach to stall in a climbing right bank. As the angle of attack increases, the jet appears to stall, then rapidly rolls left, and snaps inverted over a span of about 1 1/2 seconds.”

          Note that recovery is accomplished by skilled and calm pilots skillfully moving the controls with their hands and feet, not by a panicked computer technician, masquerading as a pilot, pushing an auto recovery button on a flight computer or autopilot.

          • Thanks AP, that video is incredible.

            The absolute calm and focus of the pilots and how they work together, with the copilot encouraging the pilot. Really difficult to sit there with controls available right in front of you, and yet rely totally on the other person to save your life.

            And as you said, key was their fundamental understanding of what was happening, the aircraft, and the aerodynamics involved.


            Probably not reasonable to expect this from line pilots, but it does show the value of manual flying skills.

            Avionics are evolving to blend the human-aircraft interface more fully. In the F-35, the pilot can enter a flat spin and fly out of it at will, with the help of avionics that assist him.

            But also if the pilot loses consciousness, the F-35 will take over and return to level flight. S0 there is not a substitution of skills so much as the avionics functioning as a skilled partner, as we see in this video.

            In countries where there is shortage of these skills, you can see that the pilot is somewhat disadvantaged if his partner is not functioning at the same level.

          • Wow, thanks for the video link. The MD95/B717 test pilots seemed surprised by the quickness of the event and genuinely relieved after their successful recovery. Any idea what altitude they were at and how much altitude they lost?

          • Reality is that standard manual flight training does not prepare you for something like that (or the film I saw of the F4 Phantom stall series)

            Upside down attitudes was not part of the flight training. Spin training was not part of it nor is still.

            Simulators cannot generate aerobatic (unless you are in an Air Force/Navy type).

            Knowing your craft is the first step in calm. Some have it and some do not.

            Statistically, Civil War era on through Korea, 10% of the line rifle men did the effective shooting. The other 90% did none to non aimed.

            It took an incredible amount of comportment to stand in a line, not only aim and shoot a muzzle loader, but then calmly go through the reload process and do it again for many hours at times.

            And it has nothing to do with character, it all has to do with physiology and what your brain does (panic or stay calm).

            The more in depth the training the more able the mind is to go through the steps in dealing with the situation.

            The better the training system is the better the outcome.

          • Test pilots!
            They are specially chosen and then given even higher level training in simulators and on ground to do all that.
            Its totally impossible to have that level of skill for line flying day in day out. Nor would the test pilots want to do every day routine either- maybe they do a bit of it to see what the everyday pilot experiences.
            The airlines want to have their pilots following the SOP to the letter and pushing the right buttons in the right sequence.
            The DC9/B717 is the old school anyway, has none of the FBW features on modern planes from the A320 onwards.

          • Duke, no one disputes any of that, or TW’s similar remarks. There is no expectation for line pilots to have that level of skill or experience in upset situations.

            The point was more to show what manual flying skills can accomplish. They are a major benefit and something that can’t be emphasized enough in training, because as with this video, you may need them at a moment’s notice.

            The manual flying skills issue is not just AP’s opinion, or mine, it’s been recognized around the world by every safety agency and aviation organization. Sully has written about it. Even the pilots are in favor of boosting their training, as we saw in the the recent JOEB comments.

          • The excerpt below is from the comments at the link below. If true, it was not the first time that either of the MD95 test pilots in the video that I posted a link to above, had been inverted in or spun a jet aircraft, in real life, not just in a simulator. It would also probably not have been their most difficult day of flying, since they didn’t have to worry about an undetected MIG or surface to air missile battery trying to blow their aircraft out of the sky, and could concentrate 100% on flying their aircraft, rather than having to split their concentration between flying and detecting and evading or engaging hostile aircraft or missile batteries. Practice makes perfect, as long as you survive the practice to live another day?

            “Doing a little research on this, it appears that this is a McD test pilot crew in the 1998-1999 time frame. Boeing had owned McD by the time they rolled out the first MD95/717, but remember that McD was still a subsidiary at that point with its existing lines of authority and organization. So these are McD guys in the cockpit, apparently ex-Navy Vietnam fighter pilot Randy Wyatt in the right seat, who went on to be a Boeing test pilot, including on the 747LCF, and Gary “Bear” Smith in the left seat. Bear was a Blue Angel and still active in the Naval Reserves, and was a McD test pilot.”


    • The DC-9 also added some aerodynamic hardware via vortex generators “vortilons” to help control pitch at high AOA.
      I believe one of the Boeing test pilots Ray Craig suggested looking into a hardware fix, such as this, when the initial high AOA problem was encountered during flight testing, that lead to the birth of MCAS.

      • Richard, if you read the link I posted above on deep stall, written by one of the DC-9 developers, it makes clear that none of the aerodynamic solutions they tried were adequate, so they had to combine them with a stick pusher.

        That highlights the difficulty of tuning the pitch moment curve aerodynamically. In some instance it can be done and some it can’t. I hope Bjorn will talk about this more next week in his further description of MCAS.

  5. Slightly Off Topic I am afraid – but relevant in a discussion concerning Federal oversight and regulation of the aviation industry

    For one: Re certification at FAA level can be seen to require corresponding measures at FDA level (or preferably a specific new Fed authority) to make sure it is safe health wise to fly the new Max, and of course any other airplane, otherwise re certification is stymied

    For two : One could argue that more engineers in Congress would enforce improvements in regulatory oversight of the engineering, as per this Max fiasco

    And that more (health) scientists in Congress would surely initiate and enforce much improved Federal Health measures, notably at airports, to permit airtravel uptake, as well as provide an healthy overall plan to diminish current freeplay of the virus

    ‘Follow the science ‘ I took for an empty slogan, but it turns out to have some meat on the bone

    Much like the CIA Democrats, who wear two hats, they are scientists who are also politicians, and who can be counted on, if anybody can, to not only follow the science but to make sure you do too

    The article is a fascinating insight into how the US has evolved into a loosely allied rabbit warren of confronting tribalisms and/or idpol & managerial subsets : in essence a caste system

    « « “This year 27 candidates—incumbents as well as new challengers—were endorsed by the science advocacy group 314 Action. The group recruits people with backgrounds in science, technology, engineering or medicine to run for office, endorses candidates and has a political action committee that contributes to their campaigns. In the House of Representatives, just two endorsed challengers out of eight won, though one race remains too close to call because mailed ballots are still being counted.” « «

    • Gerrard, I’m glad to see you are acknowledging that science has some value, and that greater scientific awareness and thinking in our government & leaders would be beneficial.

      An issue strongly related to that is term limits. As envisioned by our founding fathers, political service would be people leaving their livelihood for awhile to bring issues important to them to the legislature, and help craft the laws to address those issues. Thus they did not provide for large salaries, as it was deemed a public service. Only a stipend to tide you over until returning to your former occupation.

      That has evolved into the career politician system, where they are well paid and remain in political life as long as possible. Lost in that is the daily life experience and bringing to the forefront issues of concern to the common person.

      In place of that experience, the lobbying system has likewise evolved, such that industries bring to the forefront their concerns. While that is not wrong, there is a displacement and a shift toward those issues, as opposed to more common perspectives.

      Term limits would enforce the original concept of the government, and reduce the influence of lobbying as the representatives would be more closely tied to their roots, than special interests.

      Limits also get around the argument that paying politicians less attracts less qualified people. With term limits, the pay could actually reflect the person’s resume and ability, as occurs in the rest of industry. Within limits of course, we could not afford to pay Bill Gates his equivalent income. But my guess is those people would view it as public service, since they don’t need the money

      Another consequence is that as science (and any other knowledge or skillset) builds up in society, that would be reflected in the legislature, which goes to the point you made above.

      • Rob:

        Coming from you that is really a belly laugh.

        What comes out of Boeing Managements mouth or the FAA is not science , its spin.

        You then attempt to present it as factual when in fact it not only is not, it has no scientific or data support (saying something is not data nor is it science) . So, by your standards any talk is science and they are all right. Phew, my head hurts.

        Your definition of science is something that agrees with you despite the source being bogus as a $3 bill.

        Some of your information is in fact factual, most of it is not.

        • TW, like Bryce, you reflect onto others what is true about yourself. The things I’ve said, here and elsewhere, are true and are independently verifiable.

          They don’t support your views, and so you say they are not true, I am wrong, etc. You incorporate a healthy dose of ridicule in your comments, and like Bryce, that is an indicator of your true nature and intent. I’ve asked you for evidence of your criticisms dozens of times, but again like Bryce, it is never forthcoming.

          Finally like Bryce, you’ve been admonished by Scott for this behavior. But you don’t stop or change, you only retreat enough to avoid the consequences.

          So there is really nothing to say. As always these are your opinions, which are uniquely your own. You have the same right to post them here as anyone else.

      • Jefferson’s “yeoman farmer” concept was obsolete in the Atlantic nations at the time he advocated it for the United States, and of course he never lived that way himself. The experience of US states that have implemented term limits is that the always-new legislators have no experience with or knowledge of the problems they are supposed to legislate on, and they are uncertain where their next job will come from, so they turn to those with (a) long-term experience and (b) jobs on offer: lobbyists for very organized, very powerful, and very wealthy organizations. In principle everyone agrees 40+ years is too long for one person to spend in the legislature – yet who had the standing and institutional courage to handle civil rights issue that John Lewis did with 34+ years in the House?

        • sPh, the term limits need not be so restrictive as to eliminate the benefit of prior legislative experience. That would be taking things to an extreme.

          The goal would be to get people into the legislature who are there with expertise for a specific interest, rather that than having that expertise and interest defined externally by the lobbying industry, for uninformed and uninterested legislators. Also to get people who are not overwhelmingly from the legal professions, but rather a balance of professions.

          Another factor is that today, legislators have professional staff and an extensive professional bureaucracy to rely upon, and who are the ones that actually maintain institutional memory. That was not either true or needed in Jefferson’s day, when that memory and understanding of the government was concentrated in a relatively few people. Jefferson and his contemporaries served in many roles because there were few alternatives. That is less true today.

          Lastly although the executive already has term limits (for a different reason, the concentration of power), the value of the legislature as a training ground for the executive branch is undeniable. So one might envision that a skilled and experienced legislator might move to the executive branch after congressional term limits expire.

        • @sPh

          I agree with a lot of what you say

          There is a basic conundrum in all notions of democracy : how to balance in house experience and specialist and professional knowledge, the heavy pressure of corporate interests, against the requirement that the politician be judged and elected for the common qualities of representation observed or seen to be shared by a majority of the common people

          An electorate would find professional and administrative skills harder to judge ; in practice such skills, together with the ideology of their prime importance in essence and in application, must also be subservient to the uniformed majority

          The pure rule of the technocrats does not work : their class interests (or group think) quickly predominate and their decisions are for what they determine to be the good of the people rather than any expression of popular will, and on many occasions the direct contrary

    • Gerrard:

      I am the epidemy of a techno crat, I tend heavily to left brain (much to my wife’s annoyance ).

      What is reality is that there is a balance of science that can solve some things and the areas science does not work in (put it in the realm of human relation and leave it at that to avoid a political firestorm) .

      Many times I would present data and facts to management and have it ignored and even contradicted with a dismal or just the opposite.

      I then would be beat about the head and shoulders to agree. Sorry, I don’t agree, I will follow orders as best I can, but I don’t agree with them.

      A really balanced person then figures out how to present it in a non data manor that gets the job done (Politicians).

      I have yet to see a scientific formula to solve the issue of Poverty. We know things that can help. Just like we know how a board should be run. Sadly, greed overcomes sanity every time.

      Some areas lend themselves to science and some do not and there is a balanced involved in all that.

      We do not need all technocrats, its hugely helpful to have people who understand the difference between science and politics in presentation.

      I do not being to claim nor have any magic formula. You can sort out people of good faith from those of bad. You can’t trust the bad ones no matter what they site because they do so for an end and leave out anything that disagrees with that end.

      We had a case not too long ago where a scientist pursued his agenda with his morale compass in the toilet. So science in and of itself or even a scientific process used for evil only produces evil.

      Werner Von Braun fell under that area. He wanted to build rockets and did so at any cost to humanity and human beings. We gave him a home but we were structured around free people and paid and not slave labor.

      The one we have to watch the most are the ones who claim the mantel of science and reason and in fact use it when some sliver of information looks to support them when in fact its taken out of context or presented as fact when its not even close.

      The reality is that 70% of once group comes to believe a totally false narrative and that is what we are dealing with.

      • Without trying to start a dispute or argument, I’d like to present a more nuanced view of Werner von Braun.

        Many in Germany (and occupied territories in Europe) cooperated or collaborated with the Nazis, for various reasons, usually related to compulsion or personal consequences. There is moral ambiguity in times of war and authoritarian rule. While there are grounds for criticism, we shouldn’t paint with too wide a brush.

        Here is an excerpt from a balanced ethical treatise on von Braun:

        “Von Braun seems to have accepted his situation and the idea that he was powerless to effect real change, avoiding looking into matters too deeply. He simply continued his work, allowing his dreams of space flight to obscure any doubts that he may have had.

        At the same time, his actions do not seem to be those of a true Nazi believer. His protection of a French scientist prisoner, as well as resistance to the attempted SS takeover of the rocket program, show that his true feelings, though he allowed them to be suppressed for his work, were not in line with those of the upper Nazi echelon.

        In 1933, all faculty with leftist political views or Jewish ancestry were expelled from von Braun’s university. This was followed by significant pressure on all students to either join the Party or at least to join SA-affiliated organizations. At the same time, all rocketry work in Germany was militarized and declared secret.

        When the SA gave a temporary exception to sign up for a non-binding probationary period, von Braun joined the SS horseback riding school in western Berlin, as the least militaristic activity. As soon as this probationary period was over, he dropped out of the organization, and was not part of the SS again until he rejoined in 1940.

        This rejoining of the SS was allegedly again due to pressure from the Nazi establishment. According to von Braun, and backed up by other anecdotal accounts, he received an offer of SS membership as Untersturmführer, and it was stressed to him that it was a “very definite desire of Himmler” that he join.

        He initially resisted but consulted Walter Dornberger before acting one way or the other. Dornberger,
        according to von Braun, informed him that the SS had been attempting to gain control of the rocketry work, and that if von Braun wished to continue his work, he had no choice but to accept SS membership.

        The question “how much of a Nazi was he?” is central to much of the writing about von Braun, but his membership in the party by itself is not necessarily the complete endorsement of the Nazis that some have claimed. The picture was likely more nuanced, and the very real fear of ending up on the Nazi regime’s bad side was pervasive in much of this period. Many were in fear of being persecuted by the regime if they didn’t play along (or their families and associates).

        In addition, the work von Braun was involved in was impossible to do without Nazi membership, or outside of the military. With access to top secrets, he could not leave the country, and the alternative would be imprisonment. Given this context, and the evidence that von Braun did not participate first hand in the politics of the organization, his membership is perhaps understandable.

        After visiting the V2 slave work camp at Mittelwerk, von Braun reported that conditions for the laborers were “hellish. My spontaneous reaction was to talk to one of the SS guards, only to be told with unmistakable harshness that I should mind my own business, or find myself in the same striped fatigues”, continuing that he “realized that any attempt of reasoning with the SS on humane grounds would be utterly futile.”

        By most accounts, when approached by Himmler about the transfer of authority of the rocket program to the SS, von Braun did not play along, resulting in his imprisonment and interrogation by the
        Gestapo three weeks later. He was only released through the actions of Dornberger and Albert
        Speer, who took the issue directly to Adolf Hitler.

        His arrest followed a year of surveillance, during which he was overheard telling colleagues that he saw no possibility of victory in the war. In addition to this lack of faith in the war effort, it has been suggested that Himmler was looking for an excuse to get rid of von Braun after he had resisted Himmler’s attempts to gain control over the rocket program.

        Despite these shows of resistance, von Braun’s Nazi career speaks mostly of inaction and acceptance of authority. Ultimately, this inaction, whether it stemmed from a feeling of fear and helplessness or from a genuine lack of caring about the plight of others, or even a combination thereof, tarnished his later career and caused him to become for many the archetype of the inhuman scientist, willing to accept any human cost to further his work.”

        So this reputation may or may not be deserved, depending on the weight you give to various actions. He certainly was not a hero, and was a collaborator, but perhaps not a villain either.

        In the remainder of his life he made enormous contributions, and had no hint of Nazi ideology or support. He also was active in supporting civil rights within NASA during his administration there, even in the midst of the deep south.

      • @TW

        You know my antipathy to the notion that only scientists, or ‘experts’, can be allowed to assess and make decisions, supposedly on behalf of the masses, but in reality not – often these decisions are imposed on the pretext of ‘emergency’ (terrorism, etc)

        The virus too has given rise to a long line of supposedly expert or scientific measures, many arbitrary, many not well conceived, badly defined and poorly administered, yet all claiming to be following the ‘science’

        Responsibility for any failures these measures have encountered is denied : the common people are held entirely to be responsible and are accused of failing to obey and properly execute

        Lack of trust (two way) between the mass of people and such experts, and politicians and administrators in general, renders adequate governance unworkable

        Unless there is another class other than the technocrats that can communicate, persuade and unite the commonality

        • TW & Rob

          Try at least to get the mans name correct.

          Not Werner but Wernher von Braun.

          • Rudolf, I screwed up the “h” in your name as well. I apologize. Silent “h” always gets me. I write from memory rather than checking. Bad habit.

  6. If you follow facts you are irredeemably hampered in any public media driven contest against those that don’t bother and just spout what their potential voters want to hear.

    Same goes for constructive behavior against “winning by destruction”.
    Few of the public judging today are wise enough to see what Solomon saw in the case of the haggling mothers.
    Today quite often the decision would go to quartering the child.

    • Reply to Rob.

      Thanks. No need to apologize. I didn’t get offended. It happens a lot of times to me. I don’t know why you have to have two ways to spell the same name!

  7. Aircraft are designed around their centre of gravity. What Boeing did with the MAX update was failing to adhere to the 737’s COG. It’s that simple. They then relied on a computer to make up for the design flaw of the MAX, essentially bypassing the laws of physics and fluid dynamics. When this system failed, the new, structurally out of design CoG caused by the new engine size and placement, took over, creating an unstable aircraft. Bottom line, even with the new software fix, you still have an aircraft that structurally, is no longer designed to fly according to the laws of aerodynamics. Its CoG is not where it should be.

    • Romain, the CoG argument/theory circulated widely after the MAX accidents, with even some people from MIT weighing-in on it. I get their links from 2019 thrown at me quite a bit.

      But in all of the investigations and reports that have been done on the MAX, none of them point to that as an issue. So it was an example of early speculation in the absence of data. It might have been a semi-reasonable first guess as to the purpose of MCAS, but has since been debunked.

  8. B737 MAX is a perfect aerodynamic stable aircraft just like 737 JR, CL and NG. Otherwise Max would never being given it’s type certificate by FAA and EASA. MAX don’t need MCAS to fly.
    MCAS will most likley never be operating or activated during Max lifetime.
    The other pitch systems/software, Mach and Speedtrim installed in CL, NG and max is a different story. They operate at certain phases during all flights.
    Speedtrim=A/P Off.
    Machtrim=A/P On.
    When is MCAS needed/activated?
    When the pilots have put the Aircraft in an dangerous situation and is approaching a low speed stall with:
    Flaps Up.
    A/P Off.
    AOA more than a certain degree.

    Pilot reaction should be to disangage A/T and move throttles fully FWD and push Nose down on the yoke.
    When applying full thrust on a Max the pitch Up moment is higher than om CL and NG. To compensate the pitch Up, MCAS will apply some ND om the Stabilizer to help getting out of a potential stall situation.
    And. Why is MCAS really needed in the first place? It’s not needed to fly the aircraft. It’s money and the famous “Race to the bottom”.
    Passengers demand cheap airfares.
    Airlines demand cheap aircrafts that dont need expensive crew training.
    Less crewtraining means same Type Certificate. Max has the same Type Certificate as all the previous 737 so pilots don’t need a new type rating. Remember, you can only fly one type at a time.
    Max new powerfull engines made max a bit different to fly/feel than the other 737. Enough different so max would have to have it’s own type certificate/rating causing pilots to have two separate type ratings. Airlines didn’t accept that with Soth West and Ryanair shouting loudest.
    This is the short version of THE MCAS explaind for dummies.
    B737-2/3/4/5/6/7/8/9/Max engineer.

    • “”MAX don’t need MCAS to fly.
      This is the short version of THE MCAS explaind for dummies.””

      Do you mean Bjorn is a dummy?
      Because Bjorn wrote this: “While still fully controllable by a Pilot that is aware of this change, it’s not allowed by the FAA certification rules.”

      Some engineers are dummies.

    • “Pilot reaction should be to disangage A/T and move throttles fully FWD and push Nose down on the yoke.”

      Almost correct, except that both Boeing and Airbus have changed their procedures to do it the other way around – First unload( push nose down), _then_ apply power smoothly. The reason is the heavy pitch up tendency aircraft with underlung engines have when thrust is increased – which can aggrevate the stall.

  9. “”We see that nose down moment per additional AoA reduces when flying above 12-13° AoA.””

    Isn’t it a still kept secret when MCAS gets active in a real MAX-8, -9.
    It’s different at high speed and low speed.
    FAA didn’t flight test at low speed. FAA did sim testing for low speed, believing Boeing programmed the sim right, when Boeing failed at it before.
    FAA should have tested it during cert flights in 2017, but it seems FAA did nothing (undue pressure).
    JT610 report describes elavated AOA, not high AOA.
    How does LNA know that it’s 12-13 deg AOA?

    • FAA flight tested MCAS at high and low speed, both in the original certification and in the recertification. Also in the original certification, they flight tested both the original and modified MCAS. That’s in the IG report.

      Bjorn was estimating the slope transition for his constructed pitch moment curve for the 737. He wasn’t trying to give the MCAS trigger value. The exact value is not needed for the conceptual discussion, and may be variable as well.

      • Rob. MCAS is not an Anti-stall system.
        MCAS is only installed for one reason: So MAX can have the same Type Certificate as previous 737 models. It must handle and feel similar.
        MCAS do not have a “trigger point”!
        MCAS activates when AOA is more than a certain degree and:
        Flaps are Up.
        Autopilot is Off.
        By then you are most certain in the yellow band of the speedtape and will get warnings from the stall warning systems.
        The anti-stall warning system is a combined computer (SMYD) sharing stall warning and Yaw damper functions.

  10. B737 MAX is a perfect aerodynamic stable aircraft just like 737 JR, CL and NG. Otherwise Max would never being given it’s type certificate by FAA and EASA. MAX don’t need MCAS to fly.
    MCAS will most likley never be operating or activated during Max lifetime.
    The other pitch systems/software, Mach and Speedtrim installed in CL, NG and MAX is a different story. Mach and Speedtrim operates at certain phases during all flights.
    Speedtrim=A/P Off.
    Machtrim=A/P On.
    When is MCAS needed/activated?
    When the pilots have put the Aircraft in an dangerous situation and is approaching a low speed stall with:
    Flaps Up.
    A/P Off.
    AOA more than a certain degree.

    Pilot reaction should be to disangage A/T and move throttles fully FWD and push Nose down on the yoke.
    When applying full thrust on a Max the pitch Up moment is higher than om CL and NG. To compensate the pitch Up, MCAS will apply some ND om the Stabilizer to help getting out of a potential stall situation.
    And. Why is MCAS really needed in the first place? It’s not needed to fly the aircraft. It’s money and the famous “Race to the bottom”.
    Passengers demand cheap airfares.
    Airlines demand cheap aircrafts that dont need expensive crew training.
    Less crewtraining means same Type Certificate. Max has the same Type Certificate as all the previous 737 so pilots don’t need a new type rating. Remember, you can only fly one type at a time.
    Max new powerfull engines made max a bit different to fly/feel than the other 737. Enough different so max would have to have it’s own type certificate/rating causing pilots to have two separate type ratings. Airlines didn’t accept that with Soth West and Ryanair shouting loudest.
    This is the short version of THE MCAS explaind for dummies.
    B737-2/3/4/5/6/7/8/9/Max engineer.

    • Roald, thanks for pointing out that airlines have been complicit in the desire to avoid training. I suspect they know this full well, that’s why in the comments for the proposed recertification AD, the airlines did not protest against the now mandatory training.

      There were some voices wanting to reduce the simulator level from full-motion FFS to flight-deck FTD, to reduce costs and accelerate training. The FAA did not specifically address that, but did not change the ruling either.

      • A question for Rob: are you *paid* for your inevitably and indefatigably pro-Boeing comments; either by that company,
        or perhaps by another entity? You are, at minimum, the Energizer Bunny of pro-Boeing commenters..

        It’s always good to know who or what one is dealing with. Thanks.


        • You’ve made that allegation before and it’s been answered. I provide the facts that I know and have extensively researched, so as to balance the discussion. I am almost the only pro-Boeing commenter here, so there is a great deal of answering to do.

          There are many others here who equally and consistently post anti-Boeing comments, yet they are not singled out as biased. It’s like Sesame Street, which of these things isn’t the same as the others?

          Within virtually any Leeham article, within the span of the first few comments, the discussion invariably turns against Boeing. So I try to provide the balancing view when that happens. Readers are free to make up their own minds, all I do is provide information and another perspective.

        • Bill7,

          Rob is working for Leeham.
          Someone needs to keep the Boeing brand up after so many bad news.

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