Bjorn’s Corner: MCAS fix on the way

By Bjorn Fehrm

April 19, 2019, ©. Leeham News: Boeing’s CEO Dennis Muilenburg yesterday flew with the final version of the updated MCAS software on a 737 MAX. It will now enter certification flights, having completed 120 Boeing test flights.

Here my perspective on MCAS and the overall Boeing 737 safety record.

The 737 has a good safety record

The Boeing 737 is flying with more aircraft around the world than any other aircraft type except the Airbus A320 series. Both have around 7,500 aircraft in service. And both have good safety records.

For the 737, this has been the case over its 50 years of operational service. The type has no special issues, like deep stall or difficult handling or landing characteristics. It’s a vice-free aircraft compared with many other airliners which have operated the skies.

This shall be remembered when one judges whether the 737 MAX will be safe after the updated MCAS is certified and the MAX enters service again. If only the original MCAS implementation had got a 10th of the attention the now updated function has got. Then we wouldn’t have had two fatal crashes with 346 persons killed.

If the original work with MCAS would have done ONE of the following three things correctly, we wouldn’t have the MAX glued to the ground right now:

  • Implemented the function with the care and attention such functions shall have.
  • Made a proper Emergency checklist for the system.
  • Informed the Pilots of the function and trained them on its fault modes.
Revealing investigation

The many investigations into the MCAS debacle will reveal how all three of the above conditions could be ignored. If any of them had seen proper action,  the accidents wouldn’t have happened.

The introduction of the improved MCAS addresses all three of the conditions, and by it, should ensure we won’t have any more MCAS-related accidents. The 737 MAX can return to be a backbone of our air transportation system. The attention shall make MCAS a problem of the past.

One now ask what else could have fallen victim in the race against the Airbus A320neo? Was any other area of the 737 MAX glossed over like MCAS? Here the ongoing investigations and Boeing’s own soul searching shall make sure anything else which is not a 100% job will be addressed. Will this happen?

We tend to forget issues with our airliners are detected on a daily basis and get fixed by the established system. Our high level of air traffic safety comes from this daily work.

There is a stream of ADs (Airworthiness Directives) from the authorities and SBs (Service Bulletins) from the OEMs which correct and improve our aircraft.  The 737 included and this type has not had more issues than any other type. Its track record over the 50 years is good.

If the race against the A320neo caused any other non-perfect MAX solutions to be introduced, Boeing should focus on fixing them ASAP. Any more issues with the 737 MAX and the trust in the type will wear thin. The sound 737 base aircraft does not merit such a fate.

Note: Our partner Mentour Pilot has released a video showing the effect of a miss-trimmed elevator when manually trimming a 737, worth a look. It’s here.

235 Comments on “Bjorn’s Corner: MCAS fix on the way

  1. AFAIK the max airframe is longitudinally unstable due to the engine size and position well in front of the center of pressure. MCAS was required to ‘fix’ this by introducing active control on the elevator. Earlier 737 models didn’t have this instability. Why would their safely record be relevant?

    • If the 737MAX is aerodynamically unstable then my understanding is that it could not be certified as a civilian transport category aircraft. Can you provide some links to the analysis that shows that it is unstable within either the standard flight envelope or the larger envelope required for certification? Thanks.

    • I would say the question of the aerodynamic stability of the MAX remains unanswered by Boeing, the FAA, or other agencies. How much different is it than the NG, the A320neo? Specifically in the natural pitch down force when these aircraft are configured with maximum nose up stabilizer flying at high AOA. I have not seen any real data on this. How much does the righting moment of the -7 differ from the -10? I would these questions answered by the FAA or other agencies.

      • The question is unanswered by Boeing and the FAA, but on the other hand someone in Boeing saw fit to make MCAS repeatedly put in 2.5degree trim inputs.

        Those are very large trim inputs. That’s not a modest tweak of a flight characteristic, that’s shoving the aircraft firmly and repeatedly away from a corner of the flight envelope. The magnitude of the trim inputs suggests the denied area of the flight envelope is marked, “Danger, do not got there”.

    • no. that is 100% incorrect.

      it is dynamically stable. the forward engine position means that in certain, far off normal flight AoA situations (well into stall), the level of stick effort required to go further into stall is less than with the NG, and MCAS was a poorly implemented attempt to make the MAX handle just like the NG from the pilot’s perspective.

      once again _IT IS NOT_ dynamically unstable.

      • So then, MCAS could have been removed, but it would have flown differently than the NG, which would have required some training?
        I would like to see some data on how well MCAS actually works. A comparison of the graphs of the moment versus AOA curve on the NG, the MAX without MCAS, the MAX with MCAS. How does it do on making the curve look like the NG? Is it precise, or all over the map?

      • Is it not so that in cruise at high altitude, the higher the AoA, the stronger the tendancy of the MAX to getting sucked into even higher AoA, from an increasing ghost ANU aerodynamic pitch torque created by the nacelles’ positive lift times their long bending arm in the new forward/upward location on MAX’s pylons vs the NG, an unwarranted problem that called for adding the (hidden, hush-hush) original MCAS 1.0 in the first place ? I mean, let’s call the cat-in-the-sack by its name, oder ? If this mind-disturbing issue was what led Boeing’s system engineers into designing MCAS 1.0 the way we all have been given finally to know, PLEASE BOEING IDENTIFY WHAT HAS CHANGED WITH THE MAX THAT PRESENTLY ALLOWS YOUR NEW – DOWNGRADED – MCAS 2.0 to cope satisfactorily with the same aerodynamic issue ??

        • Is it not so that in cruise at high altitude, the higher the AoA, the stronger the tendancy of the MAX to getting sucked into even higher AoA, from an increasing ghost ANU aerodynamic pitch torque created by the nacelles’ positive lift times their long bending arm in the new forward/upward location on MAX’s pylons vs the NG, an unwarranted problem that called for adding the (hidden, hush-hush) original MCAS 1.0 in the first place ?

          MCAS was not needed at all for high altitude cruise. The regime where it is needed is high AoA at LOW speed and high load factor.

          • Are you an authorised Boeing spokesperson ? At LOW speed and high load factor you’d normally select minimum Flap 1 —> MCAS inoperative !?

          • The description of MCAS provided by Boeing states that the system is designed to activate only “during steep turns with elevated load factors and during flaps up flight at airspeeds approaching stall”.

            I should’ve said “LOW speed or high load factor”. Flaps up flight at airspeeds approaching stall would qualify as low speed to my knowledge, especially compared to cruise speeds, which is what you are talking about. Flaps-up steep turns would give high load factors but would probably normally occur at moderate speeds. I don’t think a pilot should often be making steep turns or flying close to stall while at cruise altitude.

          • @ Mike Bohnet re “The description of MCAS provided by Boeing states that the system is designed to activate (only … and) during flaps up flight at airspeeds approaching stall”.

            The second case hereabove referred to implies (in my take) that MCAS could be designed to intervene also in the event the aircraft is flown – imprudently or in unawareness – in the vecinity of the “coffin corner”, which was my point.

      • You got it bilbo.

        The only thing I would disagree with is: “… far off normal flight AoA situations (well into stall), the level of stick effort required to go further into stall is less than with the NG …”

        My understanding is the stick effort to cause further pitch-up, when in certain high AoA/low speed parts of the envelope, was indeed too small and needed to be augmented to satisfy certification requirements. The AoAs that required control augmentation were high, but PRE-STALL and up to stall.

        There has been a lot of talk in this forum recently that the MAX is aerodynamically unstable, and that Boeing needs to completely re-design it to make it stable. These notions are absurd and, as far as I can tell, based on faulty understanding aircraft stability and misinterpretation of the relatively few available facts.

        • To all:

          A Jones definition of pitch stability is correct. He even gave you accurate references. Why argue what can’t be argued!

          • I agree. Speaking mumbo jumbo is not science even if you use scientific language (see Intelligent Design so called Theory)

            Bjorn has said it does not have issues and that is good enough for me.

            Now that is a gold standard.

      • @Bilbo

        The non-constant / reversing stick force vs. AOA is the definition of an unstable aircraft. The FAA mentioned in the document released on Tuesday, that the 737 MAX is unstable in certain flight conditions without MCAS and “MCAS augments aircraft stability”. Here is the most comprehensive definitions of airplane stability I could find, if anyone is interested:

        A longitudinally stable airplane is defined by the FAR-25 to have to meet 3 conditions:
        “1-with the airplane trimmed at within envelope speeds, a PULL must be required to obtain AND maintain speeds below the trim speed. Conversely, a PUSH must be required to obtain AND maintain speed above the trim speeds.”
        “2-The speed must return to within some specified percentage of the trim speed if the the cockpit control is release from the push or pull condition implied by 1”
        “3-The stick-force vs speed gradient must not be less that that specified in the regulation”
        (J. Roskam APD Part 7, Ch. 3.1.3. referencing FARs §25.171, §25.173, §25.175, §25.253, and §25.255)

        A reversing stick force vs. trim curve (which MCAS is mitigating) violates the requirements of longitudinal stability in certain flight conditions, hence making the airplane unstable. Dynamic vs. static stability distinction is immaterial at this level.

        • Wow, an expert in aeronautics as well as the entire FAA test community (who test and do not make the laws that apply) has said otherwise.

          I guess the earth is flat and the sun rises in the West.

          • @Transword

            ‘Expert’ is a relative term, and when the reputation of the most profitable product of Boeing is at stake, accuracy of technical statements is not anyones top priority. Let’s not forget that we are talking about an engineering company that forgot/ignored a single point of failure on it’s highest volume product.

            Also – the FAA’s FSBR report (released 4/16) says clearly on Page 8: “Pitch stability augmentation is provided by the MCAS function of STS [Speed Trim System]…”

            The FAA is basically admitting that pitch stability (which is closely inter-related to stick force vs. AoA behavior as per my last comment) was lacking and in need of augmenting. An airplane can’t have (static) pitch stability issues and be dynamically stable; static stability is a required condition for dynamic stability.

          • A Jones:

            I am well versed in basic aerodynamics, its part of getting a pilots licence (and commercial goes deeper) and I have that.

            I can follow it, I can’t being to predict it despite the fact I am an expert (says so on my pilots license)

            That is because I don’t have to design an aircraft to fly it nor do I have to understand every stand of molecules in the air flow over the surfaces.

            I do have to know how to recover from a stall (dump the nose push in the throttle) as well as how to land, takeoff and navigate .

            For someone off the interest to say that Bjorn does not know what he is talking about on the MAX is saying the Einstein had E=MC2 wrong.

            There is a gray area in pilots and what they did, but any decent pilot would have been challenged by the situation.

            I would love to see if I could have managed it (without the real training needed) just like they had to. Knowing what I do, I give myself less than 40% possibility of doing so.

            So, your mission, should you decide to accept it, is you put in your application to the FAA, clearly you are more qualified than any of them and getting a position in a newly enhanced and hiring FAA will be no problem.

            You can then show the FAA and the rest of the world where they are wrong and make the world safe from the MAX.

            Me, I am going to trust people that actually work in the aircraft design Industry and know how to assess the data.

          • @TransWorld

            it is hard to admit defeat, is it?

          • Here is a quote from an MIT professor of aeronautics…

            As R. John Hansman, a professor of aeronautics at the Massachusetts Institute of Technology, told me in a March 28 interview,

            As I understand it, at high angles of attack the Nacelles — which are the tube shaped structures around the fans — create aerodynamic lift. Because the engines are further forward, the lift tends to push the nose up — causing the angle of attack to increase further. This reinforces itself and results in a pitch-up tendency which if not corrected can result in a stall. This is called an unstable or divergent condition. It should be noted that many high performance aircraft have this tendency but it is not acceptable in transport category aircraft [emphasis mine] where there is a requirement that the aircraft is stable and returns to a steady condition if no forces are applied to the controls.


          • Gundolf: Well when I have been proven wrong (and more than once no problem admitting it)

            Defeated? This is not a game, its real life. People died. To turn it into some bizarre aerodynamic conspiracy theory is to insult their loss and to ignore that that loss gives us. They paid the ultimate sacrifice for the rest of people to be safe. Its an ugly fact, but sometimes that is how we advance.

            What we are discussion is factual versus totally unsupported conjecture based on no science, no facts (saying CG this and CL and in turn that create X then and spinning it into something weird is not science is nothing more than pure fabrication).

            Show me an aerodynamic model or go test a 737 MAX and PROVE IT!!!!!!!!!!!!!!!!!

            I put considerable money into my learning to fly and my ratings. Included in that was aerodynamics and practical aspects and affects.

        • @A Jones it is not “reversing” it is different from the NG and required effort decreased as AoA increased beyond a certain point, but it never goes negative. this violates the principal that effort should be constant or increasing consistently as AoA increases, but is not “unstable”. the aircraft will not tumble ass over teakettle nor will forward stick be required to prevent AoA from increasing further.

          in fact, the dynamic stability margins of the A320 are lower as it was designed from scratch that way to take full advantage of FBW and reduce elevator downforce in cruise to reduce drag.

          • @bilbo: No public data is available on that curve, but if the pilot has to pull the yoke less to prevent the AOA from increasing at an ever increasing rate (even at a high AOA or envelope corner point), this is called a “reversing” stick force curve (i.e. the term “reversion” refers to the time gradient of the stick force curve d(dF/dα)/dt, not the direction of the stick force – qualitatively, it is exactly as you say). Remember that the stick force doesn’t have to go negative entirely for the platform to be unstable; the force gradient curve just has to change above a certain threshold for it to violate the regulations and be deemed “unstable”.

            No doubt it is different (worst) than the NG, but that doesn’t mean the implementation is acceptable or safe. Most robust way to compensate for this would have been a new or enlarged tail, which Boeing did not do for whatever reason.

            A FBW airplane with fully artificial feedback system can entirely mitigate the stick force – the stick force is what the computer demands, not what the aerodynamic forces cause. If sufficiently redundant (quadruple redundancy in case of A320) sacrificing static margin to have less drag is deemed acceptable. FBW airplanes developed post A320 all do that and haven’t had issues related to longitudinal stability and control.

          • If it is just the difference of force needed to pull on the yoke compared to the NG, why bother to move the stabilizers?

            Wouldn’t it be so much cheaper and easier to just artificially increase the forces on the yoke?

          • Or to simply do what Boeing did (badly) and put MCAS into it!

            The need for MCAS was clear to the FAA (to be consistent with the regs)

            The implementation sucked as did the final approval process and review.

            To then spin that into the sky is falling is insane.

        • Well it is not so severe as you are allowed to continue the flight with a disabled MCAS to your destination, hence no diversion to the nearest airport is required. I guess most CAA’s will require some simulator training with MCAS off and with other problems popping up at different speeds, c.g., altitudes and angles of attack.

          • And I would not require it either.

            As you are not supposed to stall, you have a stick shaker and alarms telling you that, its an easy correction, lower nose, power.

            Its worked for 100+ years.

      • How stupid. This is an unstable aircraft period. Why do you think Boeing came up with MCAS…for the heck of it?! No. MCAS was introduced to —acting independently in the background and without anybody knowing— solve a problem that did NOT exist in previous 737 variants. They did not even acknowledge it and nobody got trained on it, trying to preserve the illusion that the Max was just like any other 737. And it was badly executed software on top of it. The whole thing is a massive engineering and managerial FUBAR.

    • Unless I have completely misunderstood (I’m just a pilot, not an aerodynamics engineer…), an aerodynamically unstable aircraft is close to impossible to control without fly by wire controls – with a computer between the stick and the control surfaces. Like the F-16 (and probably other fighters as well).

  2. “Was any other area of the 737 MAX glossed over like MCAS?”

    I think that’s the big question. BA will undoubtedly be looking at everything before anyone else does, the problem is what if they find something fundamentally wrong that requires too much change ?

    The MAX, and the A320 are too big to fail, and I see that as a problem, I see the common type rating as a potential obstacle to safety.

    Why didn’t BA notify the airlines of the existence of MCAS before the Lion Air crash ? (Common type rating a factor ?).

    Why didn’t they add an AOA warning light to the PFD ? (Additional pilot training to affect common type rating ?).

    After the Lion Air crash BA, and the FAA work on MCAS 2.0 but it’s not general knowledge until just after ET302 ?

    I completely understand the position that BA is in, but if safety really is an airframers number one priority, a common type rating needs to be a lower consideration than safety.

    I think Marc Garneau is sending a message to the FAA regarding simulator training, lets see how this turns out, will he stand his ground, will EASA, and CAAC also decide simulator training is necessary ?

    I still don’t understand why the yoke back trim cut out switches were changed, especially in light of the fact that so much effort was made to not change anything that could affect the common type rating.

    I’m not clear if pilots were made aware of this change prior to the Lion Air crash.

    • Jak: How can you not be clear when the pilots had not a clue of those changes , existence of MCAS let alone no training in them?

      • @TW
        I wasn’t clear on what I wasn’t clear about.

        Specifically, prior to Lion Air were pilots made aware that the ‘yoke jerk’ would no longer halt trim as it used to on the NG.

        Was this change in the FCOM ?

        I do understand that pretty much everyone was in the dark about MCAS before the Lion Air crash.

        • As the Yoke change was inherent in the MCAS ops, I doubt it was listed either (in the tech manuals yes)

          I can’t prove it but being aware of one change then begs the question of why it does what it does now and that did not com out until the Lion 6109 crash.

    • It wasn’t intended, I think some spell checker didn’t like transportation. Fixed.

      • Another typo is Muhlenberg -> Muilenburg (the spellchecker may have changed this original Dutch name ;-))

      • Another automatic system that needs to be curbed, Microsoft Word keeps reverting to auto-correction when the locked-down default should be simply advise.

        A friend handling IT for an organization had a colleague come to him in a panic, as email software had changed the word Pentium (a computer chip of that day) to a different word beginning with the letters pen.

        Fortunately he could retrieve the email as it had not gone out of the organizations system.

        (One configuration of email software is that the mail is stored on the network not individual computers, so an admin can access messages, deleting it in that case. I’ve seen that done with Microsoft Outlook Exchange.)

        (Microsoft did change Word software to default to not saving changes to documents. Previously if the user used the quick save feature changes were kept in the file. So people could see the price you originally thought of asking, etc.

        And one day I was showing some people how to look for attributes like author of a file, conveniently using a file I had open at the moment, and lo! there was information showing the proposal document was modified from a proposal to a competitor.

  3. Björn,

    I just have a remark on the whole issue (i am NOT a pilot, only a Passenger):
    everyone concentrates on the MCAS addition, but isn’t the major ‘logical’ fault for the certification being the removal of the ability to switch all automated trim of the elevator?
    This was available for all the NG pilots (and possibly older models), possibly used in the memory procedures, and removed from availability without the related training required?

    For me, as long as the desk switching functions are not restated, this should enforce the requirement for quite a few hours of simulator.

  4. “One now ask what else could have fallen victim in the race against the Airbus A32oneo?”
    What else could have fallen victim in the race? What about the race against A350? Is there not always a race? So there is no excuse for a rushed work in this business.

  5. And now there’s a problem with premature coking of injection nozzles in the MAX’s CFM LEAP engines. Another potential certification headache for Boeing. Even if it’s not their fault, it is their problem.

    • Nigel:

      Its not a certification’s issue, its a repair issue and like any other engine related problem, they

      1. Come up with a replacement schedule that is safe
      1A: If in the very unlikely even they are unable to do so ground the aircraft then item 2. (see RR Trent 1000 and 10 isuses) RR Trent 800 issues, PW seal issues.

      2. Fix the issue

      3. Go on with life.

      • “In the case of the Southwest engine, the wear( hot spots from uneven burning ) led to a turbine blade failure”

        That’s a certification issue when the first sign of problems is contained failure of the engine.

        • No its not a certification issue unless there is no remedy.

          You clearly disregarding that Trend 1000 and 10s are flying that had serious and critical issues and in flight failures.

          If it can be assessed as good for a readoanble number of flgiht, then it is groudned. Its an engine certficion issue though not an aircraft even if you have to groudn the aircraft due to the engine.

          GE with the shedding turbines in a couple hours of running is an immediate grounding.

          As the 737 has a single engine its grounded.

          As we have seen , 787 can conti9ne to fly as could an A320 with the alternative engine.

          Indian Authoritative refused to let P&W fly on the A320NEO due to that issue, they just did not buy two suspect engines in the air at the same time was a sane idea. It to was such a short failure time there was no sane latitude to be given.

          Note that others did. I agree with the Indian AHJ.

          • Theres quite a list of other CFM Leap engines ADs from the FAA

            #[Leap] turbofan engines with a certain high-pressure turbine (HPT) stator case (HPT cases) installed. This AD requires removal of affected HPT cases from service and their replacement with a part eligible for installation. This AD was prompted by the discovery of a quality escape at a manufacturing facility involving unapproved welds on HPT cases.
            #This AD requires removal, inspection, rework, and re-identification of the high-pressure turbine (HPT) stage 2 disk, part number (P/N) 2466M52G03. This AD was prompted by a quality escape at the manufacturer that resulted in cracks appearing during forging of the HPT stage 2 disks.
            # This AD requires removing certain electronic engine control (EEC) system operation (OPS) and engine health monitoring (EHM) software and installing versions eligible for installation. This AD was prompted by six aborted takeoffs on the similarly designed CFM LEAP-1A model turbofan engine after those engines did not advance to the desired takeoff fan speed due to icing in the pressure sensor line.

          • And the point is?

            All engine have ADs. Some should have required repairs and not allowed to fly.

            Unless the coking is a flight safety issue they will come up with a fix and a time to correct it.

            Even if it is a flight safety issue (P&W seals) they may let it go.

            Some is right and some is not but the relevance is the certification of the MAX is not at issue its the performance of the engine and what needs to be done about it.

          • Previously you said with RR their ADs were a sign of poor design. Now it’s CFM that has design errors/production issues it’s just one of those things? Must be American exceptionalism at work again

  6. Unfortunately this incident has nothing to do with the overall 737 safety record from it’s past but with the current MAX alone. It was a hasty and desperate attempt to compete with the A3230NEO period. I have totally lost confidence not in Boeing products but with their senior management and their mindset. There is a very simple rule in life…Never think or act Cheap…It will always end up costing more in the long term when you have to correct it…

    • “It was a hasty and desperate attempt to compete with the A3230NEO period.”

      I tend to think that the executive-management driven failures of the 787 program affected Boeing’s ability to move forward with the NSA concept and led indirectly to the 737MAX. Although it is not as straightforward as that because it is not clear Boeing’s major customers would have accepted a new and more expensive NSA in preference to an updated 737 – there are reasons the airline fleet planners, chief pilots, and CFOs like the 737.

      However – although the final design of the MAX may have been a bit rushed Boeing had people working on “Plan B” – an update of the 737NG – for more than 10 years. Plenty of work had already been done and was sitting in the design library waiting to be fed into the final effort. To imply that Boeing started from scratch after the announcement of the A320neo is not correct.

      • One wonders why Boeing did not go ahead with the new single aisles plane then.

        My theory is that they got stuck at some major decisions. The hardest one might have been the question CFRP vs. aluminium. While make a full aluminum plane would would have given them something very much like a A320NEO, only a couple years later, any addition of CFRP would have increased the performance of the new plane, but at the same time would make it more expensive in production. Worse, the mass production of wings or even fuselages in CFRP was (and still is) really difficult, maybe impossible.

        The conclusion from a managers standpoint is simple: Upgrade the existing product so it can compete with the competitor and safe the new concept for later, when the important questions about CFRP mass produced wings (and fuselages) have been answered.

        I’m sure that quite a lot of people at Boeing knew that was the wrong strategy, but apparently they got over-rules and silenced.

        It’s often the most difficult thing to admit defeat, but usually leads to better decisions. In this case a A320NEO copy, rather late but at least with a slightly better performance, would have been the way foreward.

        • “I’m sure that quite a lot of people at Boeing knew that was the wrong strategy”

          That is an opinion often expressed in comments at this site, and it is a reasonable viewpoint. However it also has an unstated assumption: that the customers would have accepted an all-new Boeing NSA type with attendant higher cost and full training for pilots and maintenance staff. There are published reports that Boeing’s 737 customers – including Southwest and Raynair – were strongly opposed to the NSA path.

          • If I had always done what my customers asked of me, my company would never have prospered but probably long be bankrupt.

            You customers rarely develop a long term vision. usually they are just looking at their own short term advantage. That’s why I don’t even ask my customers directly. What we do is make a deep analysis of our customers future demands, our competitors stragegies and technological advances. Then we try to find a solution to combine all that. And if we get it right it’s usually a really big surprise to everybody. Think of the iPhone. Who asked for it? Or maybe the 747 or the A300 for that matter.

            The problem is that you need people at the helm that have a vision and that are more interest in long term success than short term profit. Which we apparently not have at Boeing for some time now.

          • It really does not matter how Boeing got here, they did and its how they went about it that is relevant .

            The rest is fictional alternative history .

            Should have, could have, would have…….

          • Even if Boeing wanted to make a new small aircraft they needed it to be approx 15% better than the A320neo. Without a new engine it is very hard to do with just structures and aero. The engine designers pulled most stops designing the LEAP and PW1100G and now need to mature them to stay on wing for its intended 20 000cycles between shop visits. Having them design something 15% better now will cost $15-35 bn each and will probably need an UDF with a custom designed fuelage and a bit slower cruising speeds.

  7. Will be interesting to see how the “shaving” worked in the past.

    Back ahead of the GFC all financial control instruments had been thinned down to minimal thickness … IN the US most everybody was certain that this still was a perfect system.

    The collapse shew that such a system does not just break in one place but avalanches through destruction for much wider damage.

    Can one “build” a similar scenario for the MAX ( or come to think about it Boeing products in general? )

  8. Boeing thought that the MAX MCAS action would never happen in real life and was just to satisfy FAA requirements in one corner of the flight envelope. The response was already in the checklist for stab run away so it was probably deemed a non issue. Then it should have been run thru the Failure mode cause and effect analysis and that is probably were the faulty work began as Boeings own rules of single probe failure causing system trigging, elevator could not override stabilizer in some cases and repeted MCAS activation was violated. Bjorn might be right as there might be hidden similar omissions in the FMCEA analysis? Probably it was redone by th top team and Boeing discovered some more that made it into the final software release for FAA cert.

    • The question of what else is lurking is the biggest danger to Boeing, and not just the MAX.

      The symptom is that a really terrible system implementation made it all the way through certification. The delay to the fix, reportedly down to something else that got noticed just recently, also highlights that something else got through into service.

      The issue is that these glaringly obvious problems made it past the initial certification process. Therefore the correctness of the certification process has to be questioned. And if you question that, then one also has to question the certification of all aircraft approved under that process. And that, AFAIK, is every Boeing design current in widespread commercial service.

      That is where the danger truly lies. That is the conclusion that Boeing really, really cannot risk the rest of the world reaching.

      Yet it’s a conclusion that will more likely be reached if the FAA / Boeing keep rolling out the “business as usual” PR line, behaving as if the FAA’s reputation is still good, and if there are persistent news headlines about debris / poor working practises / ignored whistle blower complaints.

      There’s also this proposed grand council of aviation agencies from across the world to join in with the FAA to re-approve the MAX. There are going to be differences of opinion. That’s inevitable when you get more than one person in a conversation. There’s also going to be a big mix of cultures too, and it will be very easy for differences of opinion to escalate into walkouts. Especially as the rest of the world’s Agencies are already wary of the FAA’s and Boeing’s attitudes.

      Seems to me to be a high risk strategy. If it goes wrong the FAA and Boeing are completely screwed. I think that a less hurried, more studied approach to restoring the MAX to flight would be a better idea.

  9. Lack of diversity in the narrowbody market is a mortal danger for a company as well as the poor travellers. Hopefully BA & AB have learned from this.Imagine the mess Airbus would be in now if they had gone for the GTF as the sole engine choice.
    The 737 has actually been in service for more than 50 years along with other incredible Boeing products, B 52 and Chinook.

    • Like George Washington’s axe, very little of the original 737 design remains.
      Some of those features caused problems, such as the 6 x seating wider fuselage was heavier structure than the competing 5x seating planes, Boeing’s answer was to use a ‘thinner skin’ to save weight. The original wing was also for a slower cruise speed which was ok for short distances but not when you are flying 3 hours plus.

        • I don’t think it’s a fault. Just pointing out significant changes since first model flew. Other planes have changes too but didn’t have the original compromises retained….like no FbW and especially the low undercarriage.
          A380 didn’t have any changes

          • The A380 went through a great number of unadvertised changes.

            One of the discussion centered on the Dr. Peter early builds as “undesirable” as they were not the latter production standard builds.

            And we can talk about wing join feet as well.

            The A300 underwent monstrous changes becoming the A330/340. Makes the 737 look like a piker frankly.

            Nothing to do with the 737 MAS has to do with its control system, it has to do with engine placements and what was done about it.

            If MCAS had been done right we would never have heard about it.

            Failure of the manual trim load on the stab issue dates back to the original and how and why that is allowed certainly is a fair question.

            As is the training and should there be a fix as you can’t alwyas unload in an emergency.

            Do I think the 737 should have gone past the NG? No.

            The low gear was not a compromise though, it was a design feature that made sense in the day it was build and where it was intended to operate.

            I agree it would be interesting to know if they envisioned larger engine as the future.

            KC 135Rs had no issues hanging the CFM under its wings.

            Would Boeing have opted differently anticipate r larger diameter engine or gone with the low gear for loading peop0le and baggage?

            Of course you have to be a bit older to remember the non Jetway days.

            Someone showed me they have Q400 and ATR Jetways now, really? Why?

  10. I think those in public prudent to their safety avoid the aircraft for 5 years if pilot training in sim not part of solution.

  11. Hi Bjorn,
    Regarding items 2 & 3 on the list above :
    I understand the checklist will now require the pilot to cut off MCAS in the event of this happening in future and not to re-engage for the remainder of the flight. In addition the pilot to be trained for this and other situations.

    I think this needs to be pushed further. If the pilot does switch off MCAS, the pilot should also have already shown they not only can do this in a simulator training session but further, demonstrate they can continue to safely fly and land the aircraft with MCAS disengaged. This should be a requirement before flying this aircraft, not just a rubber stamp to say we have fixed MCAS so back to business. Can a pilot trained to fly an NG safely fly a MAX without MCAS? (Particularly if required to apply high throttle setting at some stage of the remainder of the flight)

    • I second this suggestion. If we’re calling the 737-MAX a 737. Then any 737 NG pilot should be able to fly it in a simulator with MCAS off. Bjorn, if you took the flight test data, wind tunnel testing, computer simulation studies of the 737-Classic, 737-NG, 737-MAX, and a couple of other random aircraft tossed in the mix, and gave the data to a class of aerodynamic engineers, just with labels of A,B,C,D,E etc … Would that class consider A,B,& C to be the same aircraft? I guess if you blind folded pilots and put them in a simulator for a 737, 737-NG and 737-MAX would they notice the difference in flying characteristics?

      • Why install a MCAS if the aircraft can fly it with MCAS off ??

        • It is a bit like alternate mode. It works but not per all FAA requirements in all corners of the flight envelope but acceptable for one flight, no diversion required, so after landing you need to fix the snag and next flight is per spec and MCAS working.

        • I don’t think Claes reply is correct. If that would be true to auto trim and stick shaker should be all that is required.

          The MCAS had to be deployed because the Max is instable, as the center of lift moves forward with increasing angle of attack in a rather unprecedented fashion. This leads to potentially dangerous situation especially with higher load and hot/high airports and difficult weather, especially while turning and lower speeds with not slate/flaps extended.

          This is why the MCAS had such a “hard” characteristics. You really don’t want to stall near the ground.

          So not, it’s not for the pilots comfort. And that is why it’s absolutely required for the Max.

          Actually, some time ago, when all this was quite fresh I came to the same conclusion, proposing that the Max would need a full fly-by-wire-system to make it a safe plane. I’m back at that conclusion now. If you don’t want to change the hardware (which is unstable) you have to have such a system. The combination of constant automatic trimm plus MCAS is an inherently bad patched up replacement and doesn’t change the fundamentally “illegal” setup.

          • And where do we get the term “unprecedented fashion”?

            After all, its not a whole new science , obviously the regulation is there because it has happened. You don’t write regs on hypotheticals.

            Claes is spot on correct. Anything else is speculative fiction .

          • It depends on your definition on pitch unstable. The stick force per g’s is not linear in one corner of the envelope and this is a certification requirement lots of aircraft design has had problems to solve. It is not that the stick force changes sign just that the force to get more g’s in pitch get lighter hence the MCAS. Another solution to this problem was on the Saab 2000 where the massive Hercules engine selected and its stabiliser position in the prop wash made it very hard to get the stick forces required especeilly in one engine out conditions and finally Saab made a simple pitch FBW system to get certified.

  12. As Bjorn points out “There is a stream of ADs (Airworthiness Directives) from the authorities and SBs (Service Bulletins) from the OEMs which correct and improve our aircraft. ”

    Bjorn is there currently no better way to measure an aircraft’s AOA than the current sensors flapping around in the airflow vulnerable to damage, weather etc. Are their values not be checked against a value from a RLG ?

    • Exactly JakDak,
      Some posters here just think is a B737 Max issue no nowehere else. They keep repeating the “unstable” staff even when Bjorn is clearly stating that that is not the fact for this plane. As soon as a poster writes that, it tells readers basically the knowledge level they have of the filed. Aircraft computers rely on sensors to do the job and if the computer codes are not good, there will be problems with them. If the sensors send the wrong info, there will be problems as well. Boeing messed up with the codes and the implementation and they had owned up to that already.

  13. I entirely agree with history. Boeing was the gold standard, wouldn’t argue with it. But what Boeing is doing and has being doing for ten years and more is not the history of Boeing.

    Boeing need to look at what Rolls-Royce are doing. When the Trent 1000 issues began to appear the CEO (John Rose) was shown the door. Then 4000 managers were shown the door. What happened to engineers. Nothing. Indeed Rolls-Royce are recruiting engineers. Equally, the new CEO took a step back to give Rolls-Royce engineers the time they need to get the products right. Boeing need to do the same.

    Six months to fix the FCC. Never. A year minimum.

    For example, the FCC didn’t even understand that an AoA of 75° isn’t possible. Then we come to failure states. The FCC didn’t have failure states for the alpha vane. In other words, it didn’t know the alpha vane had failed. A $30,000 car does better. For example, low pressure tyres are signalled. Low oil is signalled. Brake wear is signalled. And so on. In other words, the computer in a $30,000 car does better than the computer in $50,000,000 737 MAX.

    I still think there is much more to the situation than the FCC.

    Why was it not known that the elevators become inoperable in certain parts of the elevator? Why was it not known that manual trim becomes inoperable in certain parts of the envelope? Why was standard trim changed from 0.6 to 2.5 to keep the nose down?

    But above all, why are we still being told that MCAS was written to make the 737 MAX handle like the 737 NG? We all know the 737 MAX wants to go nose up, which is why much more severe trim stabiliser is required.

    Boeing need to take a leaf out of the book of Rolls-Royce or there will be another tragedy.


    The article does give itself a get out of jail clause as noted by another commentator. Very, very sensible!

    • From my point of view it’s a little bit comparing apples with oranges. They shouldn’t count all aircraft variants from one type certificate data sheet over the past 50 years and say it’s all the same.
      To many technical advantages over the years only the the hull from outside looks the same

    • Philip:

      Boeing has never been a gold standard for aircraft. Early on they had many crashes due to not traoing pilot on jet ops vs prop ops (apanly based on their test pilots could fly it vs the propr bus drivers who were not used to high sink rates, slow spppol up time etc)

      When challenged by trhe 737 rudder issue they failed miseraly.

      When challenged by trhe 767 thrust reverse deploy issue they failed miserably

      When challenge on the 787 battery they failed misrerably .

      Have you ever trouble shot a car system?

      They will throw 20 fault codes, any of the top 5 is the usually suspect but not always. They are rife with single points of failure. Can you say TACATA?

      None of it is critical. On the other hand my (well those exploding airbags are) – and 10s of millions in recalls but whose counting?

      There is no question that Boeing hosed up the MCAS and the FAA approved it.

      Fortunately the 737 does want to go nose up.

      Otherwise it would run off the end of the runway during takeoff. That is usually a really bad thing.

  14. I’m still sceptical ,all the experts including Bjorn and Mentourpilot declared that everything was fine and that it could never happen again after the Lion air crash and even after the Ethiopian crash. If its so easy to fix, why was it done in the first place?I have always believed that the pilots position at the front of the plane and therefore first to arrive at the scene of any accident was my guarantee of safety, this faith is being eroded.

    • Ahh, I once had a line in a play, ” Foolish Boy, Foolish American. ”

      How many thrill seekers do you see kill themselves? Mountian climber byh the way are thrill seekerns and hoards of them die.
      Well I am good and experience and it can’t happen to ME! (ahh Joe, you see that curling snow from about a mile to our left to a mile to our right ? That wouildn’t be an avalanche would………………)

      I ran trucks on the AK Pipeline and I was sent places I was terrified. I saw men drive rigs that were unsafe . they needed the job and as there is no way to weigh the risk, you just hope it does not happen to you (some think it can’t)

      I don’t understand why you ask why was it not done in the first place.

      It all has to do with profit and risk and thinking your drive for profit won’t bite you, wishful thinking or not.

      Its done a million times a day. Being at the pointy end only means you die first. Note often they say how heroic the pilots were. Really, they died to.

      Heroic was the guy that went into the Potomac River in freezing ice filled water to get the stewardess. That man risked his life and all the experts would have not done that (both had about 99,9% of dying). It was not smart at all but he could not stand it, that is a hero.

  15. An Airbus 320 encountered two frozen AOA sensors causing a loss of 4000 ft, when the automatic protection system kicked in. This incident has resulted in a great deal of study. A very detailed paper on AOA sensor failures and software protection can be found here How does MCAS handle two frozen AOA sensors? What is the chance of two AOA sensors freezing during MCAS activation? How simple is it to have a work around for this situation? Can MCAS be manually switched off by the pilots? (there was a column mounted STAB-OVERRIDE switch mentioned in previous versions of the 737, is it still available on the MAX? Not the CUTOUT switches on the console, which also have been changed functionally, or was that just a name changed as
    indicated in the FAA panel report?)

    • RD:

      Airbus has 3 AOA as that is required for a FBW with Envelope Protection in a commercial aircraft.

      MAX NG etc have two.

      MCAS could care less if the AOA freezes up. It only goes if its at a high angle of attack (with some other things like flaps up)

      Stab Override is the trim switch. As prior to MCAS it had command, not an issue. If it kept going then you cut the stabs power.

      MCAS changed that.

  16. I’m not an expert by any means, just a person interested in aviation and a passenger. Possibly Boeing has disclosed the “fixed” new MCAS software to the public and I just haven’t read about the detailed improvements. I don’t find it very comforting that Boeing just says it’s fixed now. They said it works in the first place, and then…

    I would expect that Boeing openly discloses the whole and complete logic for true experts to verify and scrutinize. Then, after a few years of field testing I might consider flying with a MAX. Until then I will happily choose airlines that don’t have MAXes in their fleet, to avoid risking ending up in one.

    Given that basically all Aviation Authorities have failed to expose that very amateurish system, I don’t have that much confidence in them either. Some crowd verification and offering a premium to anyone who finds a flaw should help restore full confidence in Boeing.

    • Matth, being a former computer programmer, I’d really be interested in seeing the MCAS software code, at least in flowchart format or even the logic blcok diagram they used to program from. I’ve only seen a few sentences describe the decision tree for MCAS, and I hope there is a lot more to it then that. I do not like that MCAS software or any software for that matter is now almost considered part of the aerodynamics of the aircraft certification process. Software most likely will be changed in the future, with a new version released, and I hope they have all the regression testing automated to recertify the complex code. I’d much rather have the plane ‘fixed’ by a redesign of the engine mounting, landing gear height etc. rather than a software update.

      • “Software most likely will be changed in the future,..”

        and the same stringent checks for a “benign change” will be applied. as FBW is integral to the aero design.

        things appear to be different for Boeing. MCAS is no-nintegral, an add on.

        What I do wonder is if we will be able to see the various changes on ancillary systems to MAXification published or if Boeing will go for stealthy bug fixes in the shadows of the “MCAS final FIX” ( just like they did on the 787 ?

  17. It is interesting to me that in the course of reading many online discussions of the 737MAX accidents that several pilots with experience in both the A320 and the 737 have reported that while the 320 is easy to fly there are situations such as gusting crosswinds where the 737’s direct flight controls are preferable to the 320’s computer augmentation. As if on cue investigation into flight AA300 out of JFK is now in progress in which the affect of crosswind on an A320 takeoff appears to be a factor. It is not always so simple as “new = better” and one should be cautious about assuming digital and computerized is automatically better.

    • Has it been determined that this really was a crosswind issue? How frequently does AB update flight control software? Still an A320 update pending from the Virgin Perth incident in 2015 I believe but not necessarily related to flight control.

    • What I could garner is that this could be due to pilots “wrangling” the A320 like a 737. i.e. they work against the airplane. A pilot training and/or systems understanding failure. comparable “A300 with vert stab broken off by inappropriate pilot action”.

      • Ah, but envelope protection keeps you from all that! – doesn’t it? Well ahhhhhhhh

        So, what you are say (shudder) the A320 has handling characteristics a pilot needs to know about or it will kill you?

        Dang, where have I heard that before, I will have to MAX out my memory on that one.

  18. «One now ask what else could have fallen victim in the race against the Airbus A320neo?»

    That’s exactly the point, that got not enough attention so far. MCAS worked as designed. There was not by accident an error in the code of MCAS. MCAS did exactly, what it was supposed to do. Flawlessly. But the design of MCAS was absolutely inadequate.

    Boeing made the decision for such a bad MCAS design purposely. Because it was a fast and cheap way to implement it and it met a major design target: Do not trigger simulator trainings (for commercial reasons). To implement MACS this way seemed to be the best way to regarding high profits (and maybe bonuses).

    Such bad decisions regarding the security of an aircraft should be impossible. But we learned now: They are not. If such bad design decisions regarding the security of an aircraft model are made, then it’s not likely that such bad decisions were made only in one single case. It’s simply a question of company culture. It does not count anymore, that the B737 had a good safety record for 39 years. That’s worth nothing, when the current management has not safety as the number one priority anymore. They have to check everything again, that has been changed from the B737NG to the B737Max.

    And Muilenburg must go. He was the CEO when MCAS for the B737Max was implemented, tested and certified. Muilenburg has the responsibility for 346 dead passengers.

  19. So they added the MCAS system because the other solution, vortex generators, would have to be too big and would cause a lot of drag to deal with the bigger engines. They did not want to increase the power to move the elevators since this would have opened up a can of worms of cost and certification. They made the redundancy of the system optional. Every step was driven by profit over safety. The bean counters cost lives and the costs only show up on the spreadsheet when it is too late. Don’t grandfather in the 737 history since safety has to be proven with every change to the aircraft.

  20. “If only the original MCAS implementation had got a 10th of the attention the now updated function has got”
    Yes, for whatever reason, not enough time and thought was given to the design and checking of MCAS. Boeing can’t have a design system with holes in it or holes that line up to produce a design failure like this.

  21. The only thing needs fixing is pilot training worldwide.

    Regardless the aircraft, there will be accidents due to the current poor pilot training.

    • That is utterly wrong. You can’t fix a deadly plane with training. Or will you next just skip certification and train pilots to fly with one wing???

      • Sure you can, you can fix a dealy Norton with training.

        Desirable? No.

        But then what is a deadly aircraft?

        As there are historically as many A320 crashes as 737, that too is deadly.

        And we now know it can be (gasp) mishandled into a crash.

  22. Hi Bjorn,

    Totally agree with your 3 points regarding the work that was done on the original MCAS. I wonder if people on the program got lulled into losing the bubble by thinking that the MAX is just a derivative with so much of the safety already proved by previous versions.

    Regarding your second point, something that hasn’t been talked about at all is the fact that the trim wheel can be grasped to stop its rotation. Peter Lemme mentions this in his blog:
    The recent AD also mentions this:

    Runaway Stabilizer

    Disengage autopilot and control airplane pitch attitude with control column and main electric trim as required. If relaxing column causes trim to move, set stabilizer switches to CUTOUT. If runaway continues, hold the stabilizer trim wheel against rotation (my emphasis) and trim the airplane manually.

    Can the pilots really overpower electric trim by grasping the trim wheel? In systems with mechanical advantage, it is often easier to prevent rotation of a geared wheel under load than it is to overcome friction and enact motion by rotating the geared wheel. So, while this could be possible, I’m not really sure that it is.

    If it is indeed doable, then the pilots of ET302 could’ve used electric trim to give ANU inputs while grasping the wheel to retard or prevent AND inputs from MCAS. However, both the AD and the 737 FCOM present grasping the trim wheel to prevent rotation as only a last resort if runaway continues after CUTOUT. So, it’s not likely an emphasis in training and the pilots probably didn’t know to try it.

  23. Bjorn, re your point 3 of 3 (“Informed the Pilots of the function and trained them on its fault modes.”). For Ethiopian, this was the case, right? In which case, I’m guessing you are suggesting that particular crash was primarily down to pilot(s) error. Am I following correctly?

    • FAA and Boeing failed on point 2 and 3 re ET302. Have an adequate Emergency checklist and train people on it. The Trim runaway checklist was not adequate.

      • OK, thank you for clarifying Bjorn.

        One more thing. Re “Here the ongoing investigations and Boeing’s own soul searching shall make sure anything else which is not a 100% job will be addressed”, do you have a sense as to whether there is anyting else that has changed significantly and needs to be addressed or if all is now done and dusted?

  24. I’m just throwing out a thought. I haven’t come across any discussions (on the internet) that moving the new engines forward may have also been necessary for aeroelastic / flutter consideration(s), and that the MCAS issue may be linked to an aeroservoelastic (ASE) oversight. I rise this point as two readers have made comments about the 737MAX dynamic stability.

  25. The three points sound nice.

    But in regards to the third point, is not Boeing and its addendum the FAA again trying to get away with minimum training?

    • Yes they are.

      Will they get away with it?


      Why, shake you head and walk about muttering you damned fools.

  26. I have to say, I have never seen such a depth of talent opinion wise back up by no facts.

    I never thought I would say it but all too many posting make the current administration look like pikers.

    Or I suppose in some alternate universe those people would be brilliant aeronautical engineers.

    • Have you considered that there actually may be some posters here that indeed have a deeper understand of things than you? And not only that, but I have to say I do very much enjoy the many different views provided by the various background that we see here. That does include your views, minus your comments when you just try to negate posts that do not fit yours.

      • Yes I do consider posters.

        They break into several areas.

        The best are Bjorn class and understand and know aircraft and aerodynamics to a depth of degree that is awesome.

        Some are well informed (I put myself there)

        Some have come up with bizarre idea (they are not theories) that lend nothing to a discussion on aircraft safety. Those are the ones that make me shudder.

        I have been in something like 10 major career changes over the years.

        I found out that if you don’t know what you are talking about, learn from those who do, read, inform yourself, work at it before you offer a view.

        When you do, have it supported by facts not speculation.

        As time goes by, you gain wisdom, experience and respect. If you do really well, like Bjorn, you get to where people listen and assess before offering a view .

        You do that from the facts, not something like we threw the Maiden in the Volcano and it quit, therefore the way to deal with Volcanoes is to throw maidens into them.

        Part of humanity passed that stage a long time ago.

  27. I am sure the MCAS fix will be fine in isolation. From what we know of this system and previous issues with the 787 power management system, Boeing isn’t working to an effective design and test standard. From a systems engineering perspective, I thought Boeing was lucky to get through the 787 implementation without something horrible happening. It looks as if its luck ran out with the 737 Max

    • No, the luck that ran out was the 437 (pax + diver) that were killed.

      Boeings cash just went a bit less.

  28. There are still too many technical unknowns in this puzzle to reach the general conclusions that Bjorn does in this article (albeit with him holding his considerable remaining good faith in Boeing in escrow). Likewise, the reference to past 737 performance is exactly the wrong type of inference to make here. The PIC of ET302 had >1,000 hours flying the NG, can’t recall about the FO.

    For example, what are the “other system inputs” to MCAS that Boeing vaguely refers to?

    Was it indeed the AoA sensor itself that failed mechanically or was there a problem with the Air Data Reference unit as left by Simon Hradecky as an open question.

    What could possibly have been the rationale for the change in the tail cutout switch design from the NG to the Max?

    Where is the publicly available data that would put to rest arguments about the basic aerodynamic stability of the airframe rather than anonymous posts with apparent (i.e., zero) authority behind them?

    And, as many have noted, can the Max be flown with no MCAS?

    The way to approach this problem is to mentally dial back the process until pilots, engineers, regulators and maintenance crews can identify a juncture where it went wrong. Then pick up and continue forward to safe flight.

    • Peter Lemme conclusively proved that it was the AOA itself, not something nefarious in the circuity.

      You have to understand both the hardware the logic to realize that though.

      You can’t just speculate.

      • “Peter Lemme conclusively proved that it was the AOA itself, not something nefarious in the circuity.”

        I don’t know what real world experience you actually have, but you clearly know next to nothing about “proving something conclusively.”

        An accurate way to put this is that Peter Lemme has taken great care to present an interpretation of available evidence that seems to be a highly plausible explanation.

        However, when someone with the dedication to aviation safety such as Hradecky has maintained an alternative explanation that is not directly refuted, it’s still an open question.

        • Who the hell is Hradecky?

          What are his credentials?

          What Peter did as analyzed the system and the conclusions is 99.9999999999 to the 1 billion power likely correct. Sometimes known as irrefutable logic.

          That is good enough for me.

          • probably Simon Hradecky, the lead behind
            ( I’ve never seen an opinion piece from him though. ONLY collected factual information. )

          • I am very familiar with the Herald but had not read it on this one, did not know who was bheind it.


            It is an opinion piece and first pass is that sketches and written description for pilots are not wiring and logic. Certainly in this case with rush to supply and not parsed for accuracy and the blinding assumption they had it all in order.

            Worth looking at for sure.

            Highly annoying not to have links posted.

      • Well I am wrong, you can speculate and many are.

        Its much harder to get the facts and make assessments, to much work for some, way too much.

  29. Tem, please see Bjorn’s series on pitch stability, parts 9 & 1o. He explains the rational behind MCAS and shows the corner of the flight envelope it was intended to address, specifically as it pertains to the 737 MAX. Why that corner was a concern for the FAA, and why they felt MCAS was needed. Also how MCAS works and what its function is.

    There continues to be the perception that the 737 MAX is unstable without MCAS. That is not true, MCAS was required because of the high AoA, high thrust regime where control column authority might not be sufficient to prevent a stall. This regime is possible on the MAX because the engines are more powerful and mounted more forward on the wing. Not because the MAX is unbalanced or unstable in flight. It can be easily trimmed, just as every other 737 model. The regime of concern is a small corner of the flight envelope, where stall recovery would be a concern, and so should be avoided. Bjorn explained this well in his pitch articles.

    Everything we know about the accidents is consistent with what Bjorn has written. There may be more yet to learn, but the understanding presented is at a reasonable level of confidence. It can never be perfect, but it’s not misleading either. We know that the MCAS implementation was flawed, that is not in dispute. We know what the fixes are, as reported by Boeing and others who have seen them. Those fixes also must now undergo their own, separate certification by the FAA. We will see if they are approved, or if more is needed.

    I think if you read those articles and then ask any questions you have about them, we can help you to fill in any parts you believe are missing.

    • Fair enough, but here we are six months from October and a month from March, and nobody can produce a definitive statement from Boeing or the FAA that MCAS was required for certification.
      If something so cut and dry as that is still in dispute, it is no wonder MCAS was such a mess and why it wasn’t dealt with earlier. Part and parcel of a culture of confusion. Who’s in charge, Al Haig?

      • Ted, I believe the MCAS system helped to assure both Boeing and the FAA that the 737 MAX did not require a new type certification. The MAX handling was similar to other 737 models, except in the envelope corner that required MCAS.

        So to help keep 737 pilots out of a regime where they might unexpectedly find that they lacked control authority to avoid or recover from a stall, MCAS was considered a safeguard.

        This is where the argument originates, that MCAS was not a stall prevention feature, but rather a pilot assistance feature to maintain pilot familiarity with previous types.

        In reality, both of these perspectives are true. MCAS was meant to address both issues. Obviously Boeing had a lot riding on maintaining the 737 type certification. MCAS was not inherently a bad solution to this problem, it has been used safely for military tankers. But the 737 implementation was very poor. To understand factually why that happened, we have to wait for the investigation.

        • The strange thing is that the 737MAX should in normal cases behave just like the 737NG, but behind the software agumentation they are different and hence the failure mode analysis will be different in some key areas. One feels that Boeing might have red across major parts of the failure mode analysis from the 737NG and not redone it completely as one would expect or they did the analysis early on and the MCAS came later and it did not open the tick box for a renewed complete failure mode effect analysis.

          • Caes, I believe you are correct in this interpretation. Concerns arose during FAA certification and MCAS was Boeing’s answer to those concerns. But apparently the addition did not get the safety review that was needed.

            There may have been over-confidence based on prior knowledge with the NG and the KC-46 tanker. But based on my experience with how things like this get messed up, there likely was crossover of technology between programs, but not the full understanding that goes with it.

            So you have people in one program borrowing things from another and implementing it, but they don’t have the same understanding of how it might fail, from the original program.

            In the tanker program, MCAS safeguards were in place, that were missing in the MAX. So the safeguards apparently did not come across with MCAS, only the basic idea and mechanicals did. They are coming across now, in the software update.

            Essentially a crack opened up in Boeing’s quality control process, and MCAS fell into it. That is frequently the cause of design problems. It’s not intentional, it just happens unless you are constantly on the lookout for it.

            It’s a classic Second Law problem, things spontaneously de-generate and de-organize unless work, energy and effort are put into them. It’s the effort that maintains the organization and quality.

            Unfortunately the integration people who do this, are often viewed as middle managers and superfluous to production. But there is a value in that work, as we’ve learned the hard way here.

    • if you have the center of lift more forward than the center of gravity, then the plane would normally want to pitch up? That would be unstable? Bjorn had a good article on why MCAS was implemented, but, really didn’t say where the points of CoL vs CoG were on the 737-MAX from what I read, but, since the 737-MAX want’s to pitch up in certain area’s I’m assuming it must be unstable in this region?
      most here probably know a lot more than I on aerodynamics, but, for those that aren’t pilots or engineers ..a very simplistic example

      • As far as I understand planes, the center of lift is not fixed but changes with the angle of attack. But it should always be in a safe area behind the center of gravity. That does not seem to be the case with the MAX, which is why the MCAS has turned into such a bad mess and this could also be the case why Boeing doesn’t communicate openly. Apparently the lift moves fore not only because of the large engine, but because it is placed before the wing. At high AOA this can only result in a loss of lift, which increases the nose up moment. This effect is also most probably not linear, which is why the MCAS offers such a dramatic reaction.

        To fix that issue you have to lower the engine, but that is impossible without major changes to the whole plane.

        • The very sudden risk of stall and/or the risk of not recovering quickly, must be the reason they have MCAS take direct flight control action, rather than activate the stick shaker and allow the pilots to take action. I hope they put in a direct “OFF switch” for MCAS 2.0, rather than having to disable the electric trim system, entirely, just to deactivate MCAS. How often did MCAS 1.0 activate in the past? Very rarely, every 10th flight, or never, except from a broken AOA? I wonder if 737-MAX pilots know?

        • Gundolf

          Technically both the CoL and CoG move during the entire flight because of fuel usage.

          There are three stabilities, positive (CoG ahead of CoL), neutral (CoG and CoL coincide) and negative (CoG behind CoL).

          Negative stability and unstable are the same. Civilian airplanes cannot have negative stability, cannot be unstable. The authorities would never certify it.

          Civilian airplanes usually have significant positive stability to prevent passengers from throwing up because of the constant pitching movements that occur with small positive stability.

          More importantly, positive stability must be sufficient to prevent the wing stalling when a pitching movement is caused by external forces or people forces, a vertical gust of wind or the engines are powered up/down or people move in the cabin or fuel is burnt off or importantly the pilot move the yoke. This is the issue with the 737 MAX.

          The 737 MAX doesn’t have sufficient positivs stability with control surfaces at neutral. So it flies with the trim stabiliser permanently positioned with a AND deflection. This causes the CoL to move back, increasing positive stability.

          This then comes to MCAS. It’s triggered when external forces or people forces cause a pitching movement that may lead to a stall. It’s action is to increase the AND deflection of the trim stabiliser aggressively, so aggressively that the elevators and manual trim become inoperable.

          Trim stabiliser AND deflection – CoL moves back
          Trim stabiliser ANU deflection – CoL moves forward

    • Rob, thanks for alerting me to those articles.
      It is unclear to me where the data for the graph in part 10 that shows the kink come from.

      Bjorn’s article above makes perfect sense on the 3 points he mentions and so forth. He also makes pointed comments about processes at Boeing. His leaps of faith, however, are problematic (e.g., clearly there is so much pressure that they will now get it right). Furthermore, the more MCAS is precisely tailored to a small part of the flight envelope (and he doesn’t go into fully-loaded versus unloaded configurations) the worse Boeing’s failures on this will look. Just the comparison with the

      I’m actually inclined to believe pilots who say: tell me about that part of the flight envelope and I’ll fly the plane, no MCAS needed (and I do understand that the FAA probably required it). Peter Lemme recently posted an incredible story from the 70s of what a skilled pilot can do with a highly unstable (jammed elevator) in real life.

      Now a question: why is the answer to the red kink near stall issue not found solely in changing the feel system for the plane?

      • Tem, I cannot say why there was a preference for the MCAS system as opposed to pilot education or training. The only thing that seems to address that is the desire to maintain type certification for existing 737 pilots, so they would not require re-training. Or perhaps there were other advantages of MCAS that have not been discussed, that would favor its inclusion. People have mentioned aft center of gravity and light loading as other scenarios that could result in pitch-up.

        As an engineer, I can see where the thought process may have been “we’ve solved this problem before on tankers, let’s do something similar here”. Not reinventing the wheel, using existing technology, being efficient, etc. But if that was the process, unfortunately they botched it.

        Also I cannot say why the design choice was to use MCAS rather than alter the tail design to enhance the control surfaces. I don’t know what would be required, and I’m sure that kind of change would affect the entire airframe. It may be similar to the landing gear issue that triggered the forward engines, in that there was no practical way to do it. But that is pure speculation.

        It would be difficult to second-guess Boeing on design issues that define the entire airframe. None of us possess the knowledge to do that. It would probably take multiple teams at Boeing to even attempt it.

        With MCAS, it’s an isolated system with a very specific purpose, so a person with a basic understanding of physics and control systems could make a reasonable guess at most of the problems. Some are blatantly obvious.

        That’s what has caused the crisis in confidence in Boeing and the FAA, along with the initial downplaying of the problem. The second accident might have been avoided with a different response, and I think that is what weighs most heavily on everyone. Boeing and the FAA have a lot of exposure on that. It’s good and reasonable that other authorities in the world are making them toe the line

        The issue is also unfortunately muddied by the fact that some pilots handled MCAS activation successfully and some did not. That raises the issue of pilot experience and skill. As you mention in the jammed elevator scenario, a highly skilled pilot can make all the difference.

        I think on the whole, though, we should strive not to put pilots in that position, but also give them the best training possible in case it arises anyway. Those are really the key issues, not the relative merits of the pilots who died. We need to learn from their choices without using them to assign blame. They did not want to crash, any more than we would.

        • Rob, thank you for taking the time here. What you say makes good sense from a layperson’s perspective. I appreciate that you highlight areas of uncertainty as well. It would be in the interest of all if Boeing opened up on the parts that are opaque even to aeronautical engineers not at Boeing. Instead that information will be extracted by lawyers during discovery probably too late for the urgent efforts currently underway. At some point it would be excellent to have some serious debate outside of comments. For example, to have Bjorn respond to Gregory Travis’s article of April 18. I assume that you would strongly differ from Travis’s description of the inherent instability of the Max but might agree with some of his certificate type opinions.

          • Tem, you are correct on both counts. I would agree on Travis’s conclusions for MCAS, except for one, I don’t believe MCAS pushes the control column forward. MCAS controls the stabilizer which is connected to the trim system. Feedback for trim is provided to the pilot through the rotation of the trim wheels.

            If you checkout MentourPilot’s videos, he has demonstrated some of these behaviors in the simulator. You can clearly see the trim systems engaging and spinning the wheels, and also what is required to manually override them. He ran through the runaway trim checklist to show how things work.

            The control column commands the elevators. MCAS and other trim systems very pointedly do not control the elevators. That is kept separate for the pilot or autopilot. Elevator and stabilizer represent two distinct control authorities.

            Travis is probably correct that a large force was required to counteract MCAS, but that is due to aerodynamic forces, not something commanded by MCAS. The stabilizer area, comprised of the entire tail, is greater than the elevator area, which is more similar to a flap. So the stabilizer has a mechanical advantage over the elevator.

            I believe this is done to minimize drag. The stabilizer, which is continuously trimmed in flight, can have a large influence with a small angle of rotation.

            Bjorn and MentourPilot both mentioned that in the simulator, control with elevator and stabilizer in opposition was possible but difficult, and became impossible if speed became too great. That is what happened in Ethiopia. In Indonesia, after 2o cycles MCAS had used the full authority of the stabilizer, which would have required continuous full elevator to countermand, with control being marginal at that point. So possibly there was pilot fatigue at the end, and they just couldn’t hold it back.

            As far as stability, I think the dynamic instability Travis refers to, is possible beyond a specific point of pitch very near stall. I wouldn’t say it was easy or likely to get the aircraft into that condition. But if it happened due to some other failure, you wouldn’t want to be surprised when it was too late and control was no longer possible.

            He makes the point that the aircraft should be stable in all modes. I think in reality, all aircraft approach instability as they near the edge of the flight envelope. The MAX definitely will approach that point faster than previous models. But I don’t know that I would label it as inherently unstable. I think if that were true, pilots would absolutely notice the instability and have serious reservations about flying it. We haven’t really heard that, or of any instance where MCAS would have legitimately engaged.

            On the type rating, that is something the investigation will need to address. If there was pressure or influence to either marginalize MCAS or lower its risk classification, either for type certification or to meet deadlines, that would be a huge credibility problem for Boeing and the FAA.

          • Rob:

            Well written and a breath of fresh air.

  30. Bjorn, Every time you say ‘The 737 has….’ you need to substitute ‘had’. The Max is inherently unstable because if you add power, it pitches up. Enter MCAS, and this article now demolishes the argument that software can make an unstable aircraft stable.

    I’ll never, ever set foot on a MAX.


    • I don’t believe the fore or aft placement of the thrust matters. I believe it is the orthogonal distance from the thrust vector to the center of rotation. Engines pushing on the back, DC-9, or a single engine pulling on the nose should not affect pitch. High or low mounting, yes.

    • Me think Bjorn knows what he needs to do and knows what not to do.

      Now, its your opinion of which you are entitled, and I and others of course can discount it for the lack of basis of facts.

      A fact ignored is indeed the issue of manual trim under stabilizer loading, how to deal with it and if that is at all acceptable.

      So, the Ford Explorer tires were suspect in that they were very close to the load they bore (and worse in hot)

      Now, is that the fault of the tire or the the spec that allowed that close a rating to load of a tire to be on the Explore?

    • Julius, all aircraft with underwing engines pitch up on application of power. It’s a result of force and torque balances. If force is applied below the center of gravity, an object will pitch upwards. If applied above the center of gravity, it will pitch downwards. That is not an issue of stability. The aircraft has trim systems to compensate for this behavior.

      The flight envelope issue that arose on the 737 MAX, and the reason for MCAS, was due to the more powerful engines, their more forward position on the wing, and the extra lift that could be generated by the larger engine nacelle area, at high AoA. In a small corner of the envelope, these factors combined could be enough to overwhelm the elevators, and this behavior would be unexpected for pilots accustomed to earlier versions of the 737. So MCAS was added to push the nose down and stay out of that corner.

      Again this does not have to do with stability. Every aircraft has a unique safe flight envelope, with varying degrees of performance within it. Every aircraft can experience loss of control outside of that envelope. In fly-by-wire aircraft, the envelope is computer-controlled and the pilots cannot depart from it. With pilots in control, they can depart if they feel it necessary. The 737 would likely be in a manual flight mode to depart and get into the unsafe corner. So MCAS is only active during manual flight.

    • In theory a great idea except when travelling above a certain speed it is physically impossible for the pilot to move the manual trim wheel when the stabilizer is significantly out of trim due to the force exerted on the stabilizer. That appears to have been the problem with the Ethiopian flight (although pilots may have made a mistake by not taking manual control of the throttles).

    • That’s why the FAA issued an emergency AD after the Lion Air crash telling Boeing to put it in the manual. Boeing put it in the manual but it didn’t work.

    • Old news Dude.

      At the time of the Lion Air crash no information given to any pilots about MCAS worked. You cant work out whats happening just after take off by ‘looking up manual’. The second crash showed how Boeings implementation of MCAS was unsafe. End of story

  31. @Bjorn Fehrm

    I would like to bring to your attention a theory that says the stabilizer trim motor is very likely to have overheated prior to both crashes, and in the case of JT610 during the previous flight as well.

    I first heard of this possibility while watching a Radio-Canada interview of Gilles Primeau, an engineer who has worked with Bombardier, Mitsubishi, Gulfstream and Honda Aircraft, among others.

    Primeau says that in the case of Lion Air the motor was activated 48 times before the airplane crashed and he is therefore absolutely certain that the motor overheated and may actually have stopped working because it was not designed to be solicited that much over such a short period of time. He believes more or less the same thing might have happened on the Lion Air flight prior to the one that crashed, and also on the Ethiopian flight that went into the ground with smoke coming from the tail before impact.

    For those who can understand French here is the link for this very interesting interview. It’s really worth watching the video even if you don’t speak the language.

    I have myself extrapolated on this theory to take into account the stabilizer loading and I have explained it in writing on YuTube in response to a comment made by one Gordon Richardson whom had written that the stabilizer trim motor cannot possibly overheat. Here is the link to the video below which I responded, followed by a copy & paste of my post:

    @Gordon Richardson:

    Well, they obviously did overheat in at least two instances. First indication was during the Lion Air flight prior to the crash the next day. That aircraft was saved because of a third pilot in the jump seat. However a very strong burning smell filled the cabin during the ordeal. Unfortunately this is not often reported or discussed anywhere.

    The second likely instance was that Ethiopian flight we are discussing here. At least one supposedly unreliable eyewitness saw smoke coming from the tail just before it crashed and that’s where this motor happens to be located.

    You have to keep in mind that those motors were working repeatedly and almost continuously under extremely heavy aerodynamic loads and that is why I think they probably overheated to the point where the Ethiopian pilot was at one point unable to get the stabilizer moving (with the thumb switches) in the opposite direction because the [overheated] motor was unable at that time to fight against a loaded stab. But that same motor was able to move more easily in the other direction when activated by the MCAS because under that command the stab becomes unloaded again…

    • If the trim motors overheated, they should find evidence of that in the investigation. When motor windings overheat, they do so from the inside out, and that will be evident from damaged or burnt enamel deep inside the windings. That’s why electric motors should not be re-used after they overheat, you often cannot see the damage externally.

      If the windings are burned from the outside (as in a fire), the deep internal windings will not have damaged enamel. So that would be something to inspect.

      • Yo also need to be aware the motors are outside the pressure vessel (pressurized fuselage) .

        And who reported b burning? All died, the Voice Recorder does not.

        More wild spin

    • @Normand, that would make sense, and explain the smoke seen by eyewitnesses.

        • Interesting theory, but what powered the final MCAS intervention that dived Ethiopian into the ground if the motor was burned out?If only it had.

    • Howard, good stuff.

      I mentioned in previous commentary that the trim stabiliser doesn’t have wizz-bang servo-actuators. But then they are not necessary if the trim stabiliser is only used to trim the airplane. But it isn’t being used to just trim the airplane, it’s being used to manuever the airplane. Not a good idea.

      Moreover in previous commentary I made clear that Boeing haven’t tested the trim stabiliser AND deflections being used by MCAS, otherwise they would hsve known that the elevators and manual trim became inoperable.

      So I’m not at all surprised at the suggestion that the electric motor burnt out. It won’t have been designed to address huge dynamic forces. You need wizz-bang servo-actuators for that!

      • Philip:

        You might be interesting that fighter aircraft exclusively use the Stabilizer for maneuvering (goes back to the F-86)

        Boeing did not test the MCAS in the mode that was gotten into as it was not part of the issue.

        Time will tell if they tested it at all with a bad AOA.

        But they knew about it as well as all test pilots FAA and the 737 Characteristics of manual trim.

        Where they let the world down was leaving it all out of telling airlines and the training.

        You will also see simulator training on the manual trim and unloading the stabilizer for any reason of out of trim and high speed.

        Oddly, for 60 some years elecric motors work fine.

        How do servo actuators work?

        • Yes, I know and have always known that modern military airplanes use all moving stabilisers. I told you that months ago, when I pointed out that the Tristar is the only civilian airplane that uses an all moving stabiliser

      • Philip: I looked it up, wow, could you be more wrong?

        A Servo Actuator IS AN ELECTRIC MOTOR!!!!!!!

        In my world they are called Linear Motors.

        And as they are encased, they heat up fast and they fail if over-cycled.

        Ask me how I know, seen that, been there, got the T Shirt.

        Standard electric motor dissipates heat better.

        I would be the 737 is rated continues duty. Never saw a linear actuator that was though you might find and cool it and help it out.

        • I know that too. Need to address the wizz-bang bit. High precision/high speed, neither of which apply because the stabiliser moves 0.25 units per second.

          Trim stabilsers are not designed to be all moving stabilisers. If they wanted to use it as an all moving stabiliser they should have upgraded it to an all moving stabiliser. But that would mean the loss of grandfather status

          • Uhhh I hate to break this to you but there is zero difference between a A320 stab and a 737 Stab function wise.

            A320 moves the stab the same as the 737 and for the same reasons.

            The only difference is that the A320 has all FBW backup vs a mechanical linkage.

  32. Every general aviation aircraft I have flown (Cessna, Piper) pitched up when power was added. Conversely, when power was reduced the nose pitched down. We were taught this was normal and not a sign of instability.
    It is my understanding from another publication that the original MCAS system was to enhance longitudinal stability at light weights and full aft CG with flaps and slats retracted. Otherwise the aircraft had sufficient natural longitudinal stability in all other parts of the flight envelope without MCAS to meet the rules.

    • Steve, likely right, its been so long since I flew.

      Its the sort of think you know is coming and make slight control adjustment to accommodate to, its so normal as to be automatic.

      I had two cycles that had shaft drive, you had jacking of the drive shaft. It was normal and no issue, chain drive guys made them a bit nuts (and I did chain drive and was fine with it)

      Go into a skid, old stuff you counter steered no big deal.

  33. We’re told that with the new upgrade, the pilot needs to cut off MCAS in the event of “AOA disagree” and not to re-engage for the remainder of the flight.
    – Since the MCAS was required for the 737 MAX certification, why not force the pilot to land at the neared airport once MCAS is off?
    – If Boeing thinks the pilot can continue his flight safely with MCAS off, why have it there as a product in the first place?

    I still have hard time to close the loop on this with all these conflicting messages:
    – We need MCAS. We don’t need MCAS.
    – B737 MAX is safe. We are making it safer. (This reminds me this french commercial of one of their detergents: Your clothes will be whither than white).

    • Whiter than white was true! They added reflectants to the laundry powder which reflected light so making ordinary washing look dull in comparison.
      Boeing’s version of safer than safe means more automation….which is true of the 787 but a joke for the 737.

  34. FAA just announced start on 4/29 of a “joint technical review” involving EASA, China, Canada, Brazil, etc… to last 90 days.
    Assuming all these folks agree on all aspects of the case over that time (perhaps a very large assumption) it looks.i,e the earliest date for MAX recertification would be around beginning of August.
    As noted in many previous posts, the unknown is what else will be dragged into the open that Boeing may have swept under the rug, and what will be the required – perhaps differentiated – remedies in the various geographical areas.

    We are in for interesting times!

    • I think it’s highly unlikely that there will be immediate sign-off at the end of the review. At the minimum additional training will likely be mandated prior to recommencing operations. MAX simulators are rare on the ground, and I doubt any of them simulate MCAS behaviour today.

      I would say best-case scenario is six months from now, which would take us pretty close to the end of the year.

      • I think you are right. Savvy airlines will be attempting to book all the MAX simulator time they can get right now.

        • In the US it will be flying by June.

          Rest of the world might take a bit longer.

          The required parts you can trim in an NG (stab off and the hard to crank trim)

          It no longer has the authority it had and is easily stopped (and hard to get going with two AOA. )

          If they had done this like that in the first place a few minutes on an I pad would have been fine.

          The only issue is the related but different one of using the manual trim for any stab issue that has given too much down authority and that is both separate and inherent in the 737 as they showed in the video that is gone.

  35. Given the FAA announcement, my original guess of early next year now looks unlikely. This could drag on. As others hsve said, other regulators will demand pilot training, and I think a lot of it. It will take time to ungrade simulators to address MCAS and the huge difference between the pitch stability of the 737 MAX and previous versions of the 737.

    With regard to the word “unstable”, I’ve avoided it because Boeing are allowed to use permanent AND trim stabiliser deflections to maintain stability. This is what they are doing to maintain stability. It just means the 737 MAX is a poor airplane.

    MCAS 2.0 will reduce the amount of AND trim stabiliser deflections available because the elevators become inoperable at moderate speeds. Why MCAS 1.0 was allowed to use trim stabiliser deflections that made the elevators inoperable, I will never understand. Equally why the trim stabiliser was given the ability to use deflections that maked the elevators inoperable, I will never understand.

    This comes to manual trim. It is also inoperable at moderate speeds. Are we going to be told that it is not necessary when MCAS 2.0 replaces MCAS 1.0?

    Returning to the word “unstable”. I have used terms such as ‘wants to go nose up’ and ‘wants to stall’ and the term ‘natural instability’ as well as other similar terms. These terms do accurately describe the situation with the 737 MAX. But all of the terms do recognise that the trim stabiliser is being used to maintain stability. It’s allowed. Very poor solution, but it is allowed.

    The bottom line difference between MCAS 2.0 and MCAS 1.0 is that there will be less trim stabiliser available to maintain stability. Whether some readers like the bottom line or not is irrelevant.

    We are told Boeing have done ~100 flight tests. I wonder if any have been done in a force 7/8/9/10 storm/gale in the climb out phase; the climb out phase is where the nose does really want to go up!

    • The 737 MAX line of jets has taken a hit. It most likely will recover with the software fix, etc.,… but it might not recover fully. Possibly the MAX 7 will fall by the way. The MAX 10 probably has enough interest to have some success. Customers are probably thinking (from all I’ve read – and there is a lot out there) it is “close” to the time for Boeing to bite the bullet and do the NSA.

      • Realistically, the current MAX customers don’t have anywhere to go. They will have cancellation penalties (unlikely that the grounding would give many of them a get-out-of-jail-free card) and Airbus can’t ramp up its capacity quickly in any meaningful way. There will be some defections — maybe some airlines will pick up the production slots of the shakier A320 customers — but I really don’t expect to see many.

        The bigger (business) challenge for Boeing will be to manage the grounding, including its production workforce and supply chain, and the resulting impacts on cash flow and aircraft storage.

        What I do hope is that this changes how the FAA operates going forward. A joint international certification would be ideal, not only for US manufacturers, but for everyone else as well.

        • Cancellation are irrelevant, those can be broken and likely for cause as to what happened, failed delivery and all that.

          But realist its a safe aircraft and it cna’t be replaced now and they will take it and likely go on with life just fine.

          Comet flue and had a semi decent career after its initial debacle.

    • Is the MAX different from any other aircraft in regards to full stab down, elevators full up? Do they all have more elevator authority than the MAX. At high speeds is elevator blowdown not an issue?
      I would assume the MAX is not unique in this design, just the situation the design was put in by MCAS.

      Although I don’t subscribe to the theory that the MAX is any worse in thrust pitch up than any other aircraft, I do agree that the worst case test for pitch stability is high thrust, maximum aft limit center of gravity, stabilizer full nose up, and then how does the aircraft behave when elevators are used to maneuver with more pitch up to turn or ascend quickly?

      • My understanding is that the MAX stabiliser is no different to the NG stabiliser.

        So if there is no difference in pitch stability between the MAX and the NG, why are we witnessing what we are witnessing?

        I do subscribe to the theory that the MAX has an aggressive pitch up moment that gets worse with AoA. There cannot be any other reason for using the stabiliser so aggressively.

        LNA have introduced the term “average pilot”. I’ll introduce the term “average engineer”. Don’t like it, but I will for the sake of commentary.

        Perhaps Boeing have average engineers who didn’t know what they were doing. So it’s all one big mistake. That’s one theory.


        Perhaps Boeing have managers waving pink slips as they walkthrough engineering offices. In other words, do it or else. That’s another theory.

        Take your pick. Either way, it’s wrong.

        • If the stabilizer was deflected full nose down on the A320, or 777, would the elevators be able to override that force and keep the aircraft level? Maybe not, and in this way the MAX is no different.
          The MAX and NG have the same stab, but since the MAX engines are larger and more forward, they produce more lift forward and more pitch up moment is not in dispute.
          I would assume the same is true with the A320neo versus the ceo. Does the 737-600 pitch up more than the MAX 10? The MAX 10 has a much longer moment arm to the tail, so which is bigger, 10′ more arm times the area of the stab, or 1′ times the 8″ width of the new engines? I would imagine the -600 is more aerodynamically unstable than the MAX 10, which is why I ask the question, if the NG was certified today, would MCAS be required.

          • You’re living in a world I don’t understand.

            With regard to Airbus, yes bigger engines mean different dynamics. But Airbus addressed the dynamics, Boeing didn’t. What Boeing did was done on the cheap!


          • I will add. A trim stabiliser that can overpower the elevators is not a trim stabiliser. Instead, it’s an all moving stabiliser. If the stabiliser is now an all moving stabiliser then grandfather rights are revoked. Boeing didn’t want grandfather rights revoked.

            Read into the words as you wish.

            Airbus don’t contravene the words. So please don’t tar Aitbus with the brush of Boeing.

          • The world of high school physics, torque, moment, force times distance? Force equals pressure times area? Area under the engines, area under the horizontal stabilizer, distance to the area under the engines, distance to the horizontal stabilizer, direction of torque on the aircraft?

            If one can grasp the concept that engines a foot forward of the NG cause more pitch up, is it that large a leap of comprehension to grasp that a horizontal stabilizer 10 feet back would be much more pitch stable?

          • “If the stabiliser is now an all moving stabiliser then grandfather rights are revoked.”

            Good to know, I think that all commercial jets have these.

          • Ted

            Presumably, you are referring to your commentary about rotation because of the forward position of the engine. That could also be a factor for it would push the nose up.

            Sorry for missing it. But yes I can grasp the concept.

          • That is pretty funny as the engine move forward AND UP is the whole issue here.

            Its been the heart and soul of the discussion since the start.

            All commercial aircraft have Stabilizer that moves and is used for the FBW and its trim functions.

            Assumption was the elevators with more movement could overcome that larger size but less movement of the Stab. This seems to have been proven untrue and the issue Bjorn raised of blow down of the elevator in high speeds.

            As this is not unique to the 737 then its an interesting modern aircraft question as well as our old dog 737.

  36. If the delays are now into 2020 where would Boeing park the gliders if they keep up production at 42/month?
    Likewise the cash drain would become VERY significant, even for Boeing, with (horror!) consequences for share buy backs
    The alternative is to suspend production, with all the attendant supply chain and learning curve impacts. Not a pretty dilemna.

    • I doubt they will be able to continue share buybacks in the near future anyways. 52 airplanes a month at say $ 50 million translates into $2.6 bn cash not coming into the pockets of BA.

      I know there is advances during production and so on, but it will have an impact on how much airlines are paying for those steps too.

  37. Questions for the FAA:
    -If the NG was certified today, would it be required to have MCAS?
    -What angle of attack triggers the MCAS function on the MAX?

      • “-If the NG was certified today, would it be required to have MCAS?”

        “Well they just certificated it with MCAS Rev 2.0 so yes.”

        Good to know.

      • Not certified.
        Just before Easter
        “Experts from nine civil aviation authorities have confirmed they will participate in the Boeing 737 MAX Joint Authorities Technical Review (JATR) that the FAA established earlier this month. The JATR team will conduct a comprehensive review of the certification of the aircraft’s automated flight control system.”

        Review of certification sounds the opposite of approval to me. I think it’s important to sift out ‘reports’ to look at exactly what the FAA is saying on it’s own website.
        Fake news spreads easily when some are careless

        • Plus the fact that my question was about the aerodynamic stability of the 737 NG, not the MAX. So there’s that.

  38. Questions:
    With respect to the original MCAS what distinguishes the Boeing 737 Max 7, 8, 9? Are there airframe or seating differences?

    When testing, what is the standard load configuration for commercial airliners? Cargo? Simulated passengers? How does the load configuration affect the feel in the approach to stall for the Max?

    What are some common examples of edges/corners of flight envelopes with markedly non-linear behaviors for other models of airliners that pilots commonly cope with?

    Considering Peter Lemme’s call out of ET302’s takeoff configuration and difficulty on the initial climb out with flaps down (in theory no MCAS), was the actual danger of stall significantly less than flight testing would have predicted? And, if yes, would that configuration have exacerbated the action of the MCAS?

    • Tem,

      Here’s a brief look at the different -7 -8 -9 verions of the Boeing MAX family

      When in flight testing, they want to use the worst configuration possible to see where
      the limit’s are. Sometimes, on small aircraft they actually have quickly movable ballast to change the aircraft center of gravity while taking readings or finding out different flying modes.

      It appears that with flaps deployed, the stalling characteristics are similar to previous 737’s. I can only guess. So that would be why MCAS is not active when flaps are used. (see some very basic info on flaps vs stalling here)

      • Plus, flaps deployed move the center of lift aft. Where center of lift forward is the is the pitch up condition that is critical for MCAS.

      • Thanks RD, but I’m looking specifically for differences in MCAS among those submodels.

        Would the worst configuration in the 737 Max would be an aft-loaded plane?

        • Ted: Its only critical as you approach the stall. All other behaviors in the usual flight envelope is normal.

  39. Pretty damming article from the New York Times about the non-Seattle produced 787 quality.
    Wow — would make Transworld proud 🙂

    I am always careful around systemic issue judgements. A few things do seems to stack up… the Qatar ceo decision is quite interesting.

    (somehow i cant paste the link on my iphone — sorry.

    • Ivory: I don’t quite get the reference to it making me proud?

      I don’t get what is meant by that, not insulted but ?????

      I do agree you have to add up employees with a grip and does it add up, but as you noted, Quatar decision that Everett is definitely better has weight.

      The union aspect is hard to play as the KC-46 has failed twice and that is an Everett product excursively by union.

      I would love for Boeing to do well, they sure are balanced wrong from what I can tell right now.

      You would have to have grown up in the era I did, Boeing was a huge success story despite issues with dealing with training into the jet age.

      That odd arrogance while still making some amazing products is baffling. 737 Rudder, 767 Thrust Reverse deployment.

      Airbus in their trial did vastly better on AF447. I don’t agree with their lack of logic on the Enveloper Protection and when it degrades, but their hounding down and definitively nailing what happened as a huge plus for them and a massive benefit to the industry as it revealed nutty pilot reactions (A or B) that while occurring had not gotten the attention needed to change the training approach.

      Reading the book “To Engineer is Human” and we only learn when someone dies and gets our attention is well worth getting it.

      • TW, my comment was only in reference to union vs. non-union.
        Your past comments are clearly pro-union. The NYT article was clearly pro-union. Hence the ‘make you proud’ comment.

        History tells us unions have a positive influence. There are counter examples but by and large that’s correct. But of course union activism should not be a carte blanche for falling to adapt or being blind to underlying trends.

    • You buys your ticket and you takes your chances

      But as well expressed in “To Engineer is Human”, our failures can lead to an assessment and changes.

      We look to be on the cusp of this getting addressed though the heavy lifting still needs to be done.

        • It so happens that I finished reading that book exactly one year ago today: 20th of April 2018. I wrote a review on Amazon Canada and Amazon UK (Amazon US would not let me):

          This essay is a collection of a dozen or so articles that have appeared before in Technology Review. Most of them date back to the early 80s. I remember having read some of them back then and that’s how I got to know Petrosky. But they show their age and many of these articles now appear terribly outdated.

          The writing style is outdated as well, for it lacks pace and conciseness. The first few chapters were indeed extremely boring to read. But I kept reading and found the subsequent chapters somewhat more interesting. But overall I was very disappointed because I expected this book to be a lot more technical than it is. Basically it can be viewed as a book about the engineering profession explained to the non-engineer.

          Like a boring person who cannot stop talking the author seems to take delight in writing long articles that in the end say very little with way too many words. I would not recommend this book except for beginners or slide-rule apprentices.

          • Thats a shame.

            The one at the Hilton where they changed the faster positions on the all thread was quite interesting.

          • @TW: “The one at the Hilton where they changed the fastener positions on the all thread was quite interesting.”

            I read that chapter when it first appeared in Technology Review some 30 years ago and indeed I had find it very interesting at the time. I read it again in book form and had the same impression as I had forgotten some details of this fascinating story that are very well explained here.

            Unfortunately there are very few chapters in the book that are as interesting as this one and that makes it a very uneven book.

            We have a mocking expression in French for people who seem to listen to themselves with admiration while they are talking to others. While reading this book I often had the impression that the author was talking to himself in a very narcissistic way.

    • Isn’t KC-46 built in Everett? It’s not obvious that the quality control is any better there. Or maybe the message is that, as bad as Everett is, Charleston is even worse.

      “They’re trying to shorten the time of manufacturing,” said Mr. Mester, the former mechanic. “But are you willing to sacrifice the safety of our product to maximize profit?”

      Well, I think we all know the answer to that question.

      • No disagreement there.

        Where the FOD comes from as its built in Everett but flown to Boeing Field South of Seattle for tree completion/install of all the system for the USAF.

  40. @TransWorld: “And who reported burning? All died, the Voice Recorder does not.”

    You did not read my comment properly. I said that the burning smell was reported on the Lion Air flight prior to the crash, the one where the pilot in the jump seat saved the show. It was the same aircraft and the same Flight JT610, but the day before and with a different crew.

    When several weeks ago I first heard this engineer mentioning that smell I remembered reading about it myself a few days before but I did not know what to make of it at the time. Now it made sense. We also have to keep in mind that if the motor overheated the wiring insulation may have started to burn at the same time.

    Gilles Primeau is no armchair engineer for he has worked all his career on flight control systems. And I am quite sure that the FAA is already hard at work studying his hypotheses because he knows those people very well, having worked with them for many years.

    On thing is for sure though: that motor was not designed to operate 48 times, over a period of six minutes, under heavy loads, like it did on Flight JT610. Especially after having gone over more or less the same scenario the day before on the very same aircraft.

    • I will look at GP,

      You also missed the fact the motor is not inside the pressurized portion of the fuselage. You can’t smell the burning even if it was and here say and let alone people making things up is standard in aviation crashes.

      How many peoples saw MH337?

      And motors come in continuous duty and that would include max amps at the higher possible load.

      Unless you have a link that the motor is not capable of FLA and continuous duty its speculation.

      • The assumption is that the airframe WAS wired per diagram.
        There is also the possibility that there was smoke odour, the wire bundle most likely runs through the fuselage, and improperly installed and chaffed.

        I have seen both assumptions fail.

    • Also helps if you post below the comment and not way on down, have to scroll through the whole thing to see where it was.

  41. In some statements about MCAS 2.0 (the new, fixed MCAS) .. they mention that if activated, it will only cycle once. Not every 5 minutes, as in the past. But, they don’t say for how long or what parameters would stop the cycle. Being a former programmer, I cringe at these vague descriptions. I could never begin programming with a partially filled out logic diagram. Does MCAS 2.0 alert the pilot in any other manner than the trim wheel turning? If the pilot doesn’t notice the steep AOA and MCAS stops, is the next event a stick shaker warning? (if it’s truly pitched that far up, I would think a pilot would notice). How likely is it, or how often do 737’s approach this region of the flight envelope? Can a sudden micro burst, or even a brief, strong wind gust trigger MCAS?

    • RD:

      It cycled in seconds not minutes. I believe a 5 second off period after 10 seconds of run only if interrupted.

      So, one shot and reset, also two AOA inputs.

      And if there is an AOA disagree it is locked out

      Other changes maybe as well with the column switch and counter trim.

  42. One of the issues in Aviation Herald is that he has stepped out and put in an opinion, not that specifically .

    But computer safety logic and control mandates if you are going to have a safety cutout, then its a power wire cutout.

    In short, the STABs are not inputs into the computer (doesn’t mean there is not a separate input contacts to the computer as well just like the AOA has two separate circuits into two different computers)

    So, no I don’t accept that the Stab power was not off.

    You need the wiring diagram and you have to be skeptical of written logic as well as that can be crossed up.

    The aircraft is wired to the diagram.

    • any “speculation” as to why the stab cutout switch design was changed from the NG? It seems to have baffled Lemme up until now.

      • And I have to amend my comment.

        I was able to pull up the flow diagrams in AV Harold and it does appear that the power circuit interruption at least is alluded to as a relay release off the stab switches.

        That is not a normal practice in my world but AV World?

        Its an interesting bit of logic. You would not use a contactor (big relay) for that function if it was on off as part of a control circuit, there is the issue of welding contacts (rare in contractors – I have never seen it, but possible – I have seen it in the small control relays)

        That said, as its passive and not a hot close conducting contactor , theoretically it would have no reason not to open up if its released.

        You could also have 3 independent contractors (one per phase) and as long as 2 our of the 3 release you would have no power that works, and even one out of 3 would current imbalance the circuit and protection would trip a CB or an overload or both.

        I can see the raised eyebrows.

    • I wonder how MCAS gets it’s ‘flaps are up’ reading? (one of the rules for MCAS to be activated) A physical micro switch on the flap handle? A simple toggle switch, in series with the micro switch, would ‘cutout’ MCAS without cutting out the electric trim system. I’d rather not have a byzantine series of switches but, if Boeing is determined to have the MCAS automated system in place, I want the pilots to have the ability to rip it out of the equation. Tripping the CUTOUT switches for the entire electric trim system seems nutty to me, if I only want the MCAS overridden. I can turn off the Auto Pilot, the Auto Throttle, the Flight director, but, NOT MCAS? The only way to turn off MCAS currently is to disable the electric trim system. That’s just nuts.

      • Yes, you put your finger on one of the named “other system inputs” to MCAS. So is this just because MCAS is an extension of Speed Trim?

        • In the ET 610 accident, if they had this toggle switch, maybe they could have regained control of the aircraft, without risking another errant MCAS nose down command. In the future, i’m hoping this will be the case (being able to isolate the shutdown of MCAS, without having to resort to manual trim if not necessary.) Actually, I”m hoping they reconfigure the aircraft with taller landing gear, so they can put the engine back where it should be and rip out MCAS completely. Maybe that will happen if they weigh the entire, long term, true cost of staying with MCAS.

  43. What are some common examples of edges/corners of flight envelopes with markedly non-linear behaviors for other models of airliners that pilots commonly cope with? Or more specifically, non-linear behaviors in approach to stall?

    • Tem, here is an article that somewhat relates to your question.

      It notes that there are too many modes of abnormal flight to address every one, but it classifies the basic parameters that typically go outside the safe flight envelope. They may occur together as well. It’s a good aerodynamic reference for envelope excursion and recovery..

      1. Pitch up too great
      2. Pitch down too great
      3. Bank/roll angle too great
      4. Speed inappropriate for conditions

      There is also the so-called “coffin corner”, where the difference between maximum stress speed and minimum stall speed, becomes progressively smaller as altitude increases, until eventually they meet and safe flight is no longer possible. For efficiency, airliners operate near this corner in cruise, but with a safety margin. All pilots will be familiar with the possibility of excursion in this mode, and all jet airliners have this characteristic.

      • Thank you, Rob. Another good reference and I appreciate the summary.

  44. TW: It was a Hyatt Regency, not a Hilton, but in any case they were just the operators of the building, not the owners or developers. As we learn more, the development and implementation of the MCAS in the 737 Max does seem to be approaching the level of incompetence/inattention/ball dropping/corner cutting in that famous, devastating and yet exceeding simple case.

  45. Up to now the MAX grounding has been a tactical issue for airlines. They are canceling flights and that will cost them money. But Boeing will make up at least some of that in compensation. So probably no long term impacts so far.

    When does this become a strategic issue for airlines? For example if it goes on till December SouthWest and United will have lost 9 months of fleet renewal. 9 months during which Delta is bringing on new aircraft.

    Or if Simulator training is mandated, that will mess with the SW model of any pilot can fly any aircraft. They may not even be setup for that kind of crew scheduling.

  46. @ TransWorld : of the 213 posts so far in the above thread, 56 were posted by yourself or an impressive 26.3 %. Obviously it must be a foregone expectation on your part that most or all us remaining AvGeeks who enjoy this forum each and every time we enter a new post cannot wait from eagerness to be acknowledged by TransWorld’s sanction thereof ? Or what else motivates your intense activity ? Tell us please just so that we may situate you better : are you busy in this forum as a kind of (appointed ?/self-appointed ?/free-lancing ?) Master of Ceremony, the intent of whom is to keep things going smoothly here @ LNA ? Please clarify where you fit in, I am convinced that many of us forumists here are interested in your profile ?! And please don’t get me wrong : I’m not taxing you as prolixe or grandiloquent or anything of that kind, just unusually voluble …

    • @FF: This is a humorous take down and I smiled while reading it.

      That said, people, don’t do this. Treat all posters with respect.


      • Scott: I don’t disagree with your last part but this I took as great and good humor.

        I needed a laugh for the day and it was a good one.

        Thank you FT. If you can’t laugh at yourself you are sunked (just to be sure my other part of errors is included) .

        • And all this chit chat for safe cheep flights check this song out about Ryan Air Cheep flights Fascinating Aida best airline song ever.

        • I hear bit coin farmers in Wenatchee and TransWorld posts are taxing Washington’s electric grid to the limit.

  47. @anyone

    Has anyone been able to find out what the second software problem that the FAA wanted fixed is about ?

    The Washington Post said “That additional problem pertains to software affecting flaps and other flight-control hardware and is therefore classified as critical to flight safety, said two officials with knowledge of the investigation.”
    “In a statement, Boeing called the additional problem “relatively minor” but did not offer details of how it affects the plane’s flight-control system. “We are taking steps to thoroughly address this relatively minor issue and already have the solution in work to do that,” it said.”

    If it’s critical to flight safety, then why is it a relatively minor issue, and why not be open about it ?

  48. Boeing self-reported the issue and the FAA ordered them to fix it. That correspondence is not public under the FAA rules.

    I think that is to incentivize self-reporting without fear of immediate legal repercussions. We have similar systems in place for other professions that are lawsuit-prone, such as doctors and hospitals.

    Without that, the issue might not be reported to avoid liability, and might not be fixed. Or if Boeing was caught fixing without reporting, that would be another legal quagmire, as they are required to report. Or if they knew the problem existed and did nothing.

    Agreed that greater transparency would be better, but we live in a litigious society. So a balance must be struck. I don’t claim to know where that balance is or should be, it’s a complex issue.

    If the system works, then the FAA is watching over this and should be making good decisions. That apparently did not happen wih MCAS on the MAX, and that’s something that will be investigated. It represents another balance, between regulation and business. We have to get the balance right.

  49. So there is “something”, self reported, which is “significant” but undisclosed… until nine other regulators or so get to see the now clean but previously dirty underwear and determine how white it is.
    I predict all gory details will soon be in plain view.

    More seriously, if this MAX crate is to get cleared to fly passengers again, there must be a full and thorough understanding of ALL the fixes, gizmos and thinggummies which have been somehow incorporated there in under the FAA’s benign oversight.

Leave a Reply

Your email address will not be published. Required fields are marked *