The Boeing 737 MAX Might Need 2 Computers To Iron Out Flaws

As the 737 MAX groundings continue into the summer, Boeing and international regulators are working tirelessly to resolve the issues facing the jets. As reported in the Seattle Times, Boeing and the Federal Aviation Administration may be redesigning the 737s flight controls. Here we explore the 737’s flight control architecture and the changes which are said to be coming.

A WestJet Boeing 737 MAX in flight
With the introduction of the new software fixes, the MAX might be closer to taking off again. Photo: Acefitt/Wikimedia

The 737’s traditional flight controls

The 737 is, at its core, an old plane. Originally designed in the late 1960s, and reiterated in the 80s and 90s, the aircraft architecture places importance on pilot input.

According to former Boeing engineer Peter Lemme’s blog, the Next Generation model of aircraft utilizes two independent CPUs. At any one time, however, only one of these two CPUs can provide a valid command.

Turkish Airlines 737MAX
Turkish Airlines has 50+ MAXs on order. Photo: Anna Zvereva / Wikimedia Commons

In autopilot, both CPUs are engaged to ensure no processing errors. Should any mixed signals occur, any one of the two CPUs can disengage the autopilot.

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Although unconfirmed, Lemme indicates that secondary CPU may not stop the primary CPU’s command for the Mach trim, Speed trim, and possibly the MCAS. He adds that if the secondary CPU uses the same sensor data as the primary CPU, both CPUs may make calculations based on incorrect data.

Unlike other Boeing aircraft, however, the 737 may also use the flight computer to augment pitch axis during manual flight. This means that, should both CPUs calculate on false data, flying manually would still make use of some of the computerized flight controls.

The two-computer solution

According to the AP, the use of two computers is aimed at fixing an issue brought up by the FAA earlier in the summer. This was when regulators found that human pilots were unable to satisfactorily maintain control of the aircraft in the event of a computer malfunction.

The malfunction in question occurred when the microprocessors randomly flip 1s and 0s due to high levels of cosmic rays.

LOT MAX
Lot has 15 MAXs on order. Photo: Jakub Hałun / Wikimedia Commons

Under the new proposed system, the two flight computers would be used to activate automated flight controls instead of just one of the computers. Moreover, each computer would use data inputs from an independent set of sensors.

Lemme told the Seattle Times that the new system would create a “fail-safe” two-channel system, adding that “this is a really good solution”.

Based on the schematics of the previous generation of 737, the NG, the new solution could rectify a possible issue with the old architecture. Essentially, this would ensure that the computers operate independently and continuously check one another, as well as the data inputs feeding them.

The time-frame

Boeing told the AP that it expects to present the software changes to the FAA by September and hopes to have the MAX back in the sky by October. The software fix is, however, only one the necessary fixes to the troubled MAX, the other being the MCAS system.

737 MAX grounded
Grounded MAXs near Boeing Field. Photo: SounderBruce / Wikimedia Commons

According to the AP, Boeing may have finished fixing the latter issue by limiting the system’s ability to push the nose down. As well as this, the manufacturer is mandating the use of both angle of attack sensors, instead of relying on just one.

With airlines canceling MAX flights all the way into January 2020, one can only ponder when the aircraft will take back to the skies. What is clear, however, is that both Boeing and the FAA are working hard to fix both the aircraft in question and their respective reputations.

What do you think of the latest MAX development? When do you think we will see the MAX in the sky? Let us know in the comments.

Simple Flying reached out to Boeing for a comment on the computer fix but, did not receive a response by the time of publication.

51 comments
    1. Exactly. I wouldn’t hesitate to fly the MAX (having flown on some of the most dodgy aircraft ever produced – IL18, Tu134, etc.!

      As far as I am concerned, if the pilot is satisfied that it’s safe and respects his own life, that’s good enough for me.

      Boeing and the FAA will never allow this plane into the air unless they are 100% sure of its safety. The consequences otherwise don’t bear thinking about.

      1. Sam, you and I may understand the safety fixes being incorporated into the MAX, however the non aviation public will have reservations in flying in the MAX. How many of the flying and general public will read articles like this one, to be reassured that the MAX is NOW ready for safe flights. It may take years of the MAX being in service to convince the safety of the MAX.

        1. I think you’ll find that the majority of the “non aviation public” couldn’t care less what plane they fly on. During a recent survey one member of the public was asked if they would avoid airlines such as Southwest because they operate the MAX. The response was….”We’ll, I do like their two bag policy.”
          Give it a few months after re-entry to service and the public will board them regardless. If the price is right, most people will take the flight.
          Those of us who do understand will know that the process to gain re-certification will have been thorough.

          1. Is that how low Boeing have sunk…hoping that passengers don’t notice that they’re boarding the Flying Coffin?
            It used to be “If it’s not Boeing, I’m not going”…now you’re hoping it will be “Well, I’m not sure it’s a Boeing, so I might end up going”.

          2. I wouldn’t say that Boeing were hoping nobody notices. It’s simply fact that most people don’t care. 99% of the travelling public are neither in the industry or stand at airports spotting flying tin cans. They wouldn’t be able to tell you one plane from another.

  1. This version of the 737 needs to be scraped for good. For once people’s lives before profits. Far too much pressure on the engineers to sign off on a sub standard airplane that has cost so many lives.

  2. Boeing may fix the Max and the FAA may try to certify it – but the rest of the world’s governing bodies (especially China, hello Donald Trump) will not be so quick to get it back into service. Methinks the political side of things have taken on a life of their own and will not be solved with some new lines of code.

    90% of the Max’s order book is outside the US. For those of you insisting “Foreign pilots…” & “Foreign airlines…” – those are the people who will buy and fly the aircraft. Beat ’em up at Boeing’s financial peril…

    1. Agreed, in the past when the FAA said a model was airworthy, then the rest of the world agreed.
      Until this recent issue came up with the lack of FAA oversight, many nations whose own civil air rules may now start questioning the FAA. These other nations may not be so quick to approve airworthiness just because the FAA said so. Plus with all the political, trade restrictions, and civilian pressures it seems inevitable that Boeing has a larger job of regaining confidence in this model.

    2. Excellent thought. Along with other foreign players, skeptical of both the Max 8 and the USA Government now, China may think otherwise about purchasing since they and the USA are playing an escalating game of “Gotcha”. Who knows where it goes?
      Interesting how government/industry “incest”, complex software, aeronautics, pilot skills, the airline industry, human air travel, MAX 8 groundings, economies of nations, politics, jealousy, and perhaps even toxic masculinity are now all being mixed in a roaring pot of confusion by the souls of 346 innocents. It seems a higher power is at work and just might be the only solution to the brew. The ride will be interesting, as well as the solution.

    3. Frank, obviously you have not investigated the training facilities and the rigorous training in India. You may comment on China et al, but please do not include India in your comment “Foreign Pilots & Foreign Airlines” and this includes Pilots and Airlines in the UAE.

    1. Hey NIGEL — shouldn’t you be coming up with the next excuse why that A321 from BA had to be evacuated — poor maintenance or was this “all in the passsenger’s head” too? Of notice, heard that little flight instability issue with the A321 might also being affecting the A320neo’s — maybe we should ground em here in the USA and wait for Boeing to clear em like the Airbus’s lackies in the EASA

      1. Say KP, i have two questions
        1. How many casualties in that BA A321 incident that you mention?
        2. how many casualties and hull losses that A321 flight instability that you mention causes?

        1. So if the instability causes no worries injuries, deaths or hulled it’s ok? This is just an accident waiting to happen. And remember Airbus jet flight controls are all software controlled.

          1. Well, to be more precise the instability in the MAXes isn’t what causes it to crash but the MCAS that patched to activate by just a single AOA sensor, meanwhile airbus has 3 AOA sensor working in parallel. All airbus planes are indeed sofware controlled but they are patched to work only if 2 or more of its AOA sensors agree. But yeah, lets just wait and see how things are going.

      2. Hey KP – this is NOT an Airbus issue – yes certification is going to have a profound upgrade out of this for all and that’s good. There will be more leaks from Boeing showing what was really going on with 737 Max development. It’s an old plane, old frame, wings too low to the ground, landing gear they didn’t want to rework, engineers don’t change it too much, with old processors, new BIG engines that don’t fit, so surprise surprise, let’s create a software fix to solve the poor aerodynamics!
        The flight control computers run on a 286 processor – most reading this won’t know what that is, but your latest smart phone has more computing grunt that this! 1960’s design, 1990’s tech with fixes to make it fly like the old one.

    2. I’ve supported Dennis at Boeing HQ and I can tell you he is extremely smart, hard working, personable, a great leader and visionary, a great businessman and an engineer that really knows the company and aerospace industry. Extremely quick on the update and is a good strategist, and has helped build a financially resilient company with revenues of over $1 billion. He also cycles about 40 miles a day on the weekends he is not traveling for business. He wouldn’t, nor would any Boeing employee, take a shortcut on safety just to save money. He’s been placed In an untenable situation, which started before his time, and the company is limited in what it can say about the accidents by NTSB. And your qualifications?

      1. Well said Paul Proctor. Besides the terrible loss of life, it is not in any manufacturers interest to take shortcuts as, from a business perspective, the reputational and financial damage as can be seen happening now is huge. As an employee myself, I know how much the company puts into us getting it right from a quality, safety and ethical point of view. Day after day the negative news keeps coming and it is painful to read. There is genuine regret for the loss of lives within the company and I feel for those who work hard on the 737 program with pride. We know that no amount of apologies will bring back those who perished and it is probably of little comfort to their families, but it is important that Boeing and the industry as a whole learn from these events and put measures in place to prevent it happening again as with any aviation accident.

        1. No shortcut? Then why not just reengine the 737 max 8 and 9 just like what u did to max 10 so u don’t have to put the MCAS on?

          1. If you re-engine it, you lose the larger turbofan and a huge chunk of the efficiency gains.

          2. Well, what i mean is to lengthen the landing gear to gain more clearance to the ground and eliminating the needs of moving the engine forward and upward to fit the new engines which probably eliminate the needs to install MCAS as well. But well, whatever.

      2. With all the interest in the media about the problem, I have not heard anyone ask either the regulators or Boeing if the MCAS went through a Failure Mode Effects Analysis (FMEA). Why? Did Boeing conduct one on the MCAS? If it did would Boeing be willing to publish the details of how the designers and (hopefully) pilots rated every failure mode?

        BBC’s Panorama programme on the subject suggested that the engineers had too much pressure put on them and were not given enough resources. The mantra of the vast majority of today’s business leaders seemed to have kicked in: maximise shareholder value!

        The people here may be too young to remember the Ford Pinto back in the 60s and 70s. Ford’s then President, Lee Iaccoca had set a target of 2000 lbs and $2000 for the Pinto. The fuel tank was located behind the rear axle and was prone to burst open if the car was hit in the rear. The pressure to get the car to market was so great that Ford did studies of costs of redesign v/s costs of potential injuries. According to their calculations, it was cheaper keep the flawed design. Ford was hit with the largest fine in history (~ $128 million). As a result, Ford first and then the rest of the automotive industry adopted the FMEA as part of their design process.

  3. How can you “fix” a bad design problem with a software fix? It is due to the engines being too large to place under the wings that has caused this problem in the first place. Boeings solution was to move the engines forward so that they had some ground clearance. If they made the landing gear longer on the max 10 ( to raise it up) to place the engines in the correct place under the wings then Boeing obviously knew there was a problem. I and anyone I know will not be flying on a Max 8 any time soon and I expect most of the flying public feel the same way.

    1. I agree Michael – why are the certifying the “fix” vs the design? Is Boeing really getting away with a 52 year design platform where the engines simply don’t fit under the wing? Let’s move the new GenX9 engines on the 777X forward and up on the wing and see how the 777x performs! Symptom vs Cause get it right regulators and if the FAA won’t call it, let’s hope some from around the world do go for a recall/redesign (whoops new design). Boeing engineers knew this was not a good idea! It would be awesome to ask Muilenburg a simple question… knowing what you know now, would you make the same decisions or press the go button on a brand new single isle design back in 2011?
      There’s a wonderful saying that Boeing’s board needs to embrace… No matter how far you’ve gone down the wrong road, it’s never too late to turn back!

      1. I’m not so sure the age of the design has all that much to do with it. The Airbus A321 and A320Neos seem to have a pitch control issue in certain flight regimes exactly as does the Max. I think what we are seeing is an industry wide effect of hanging ever larger engines under wings that are attached to a tube! The Airbus operators have been given specific conditions in which to load the aircraft until such a time that Airbus can roll out (and you guessed it)….. a software fix. I think that having control surfaces adjust automatically to maintain stability is perfectly acceptable. Yes there is an issue with the Max and the way the software reacted and lacked redundancy but done properly there is no reason why it can’t be perfectly safe and reliable. This is the norm across the industry with all manufacturers and will be for quite some time. More than 12 million people fly commercially safely every day on all aircraft types and we have to remember it is only because of the good work done by all manufacturers that we can do so. We all want to fly to more destinations and pay less whilst doing it, so as customers we are what drive the development of the planes in the way they are.
        As for certification of the MAX, there are representatives from many certification bodies sat in with the FAA to ensure their own standards are being met whilst the work is done.
        Michael Wheeler mentioned about the lengthening of the landing gear on the MAX 10. This was not done to fit the engines under the wing, it was done because the longer fuselage of the -10 would make it prone to tail strike had the gear not been lengthened. Yes Boeing did know there was an issue hence MCAS, which as I said, executed correctly is a perfectly suitable solution. It is important to remember that the MAX aircraft physically pitching up was never as issue. I think people are putting too much on something that will only occur right on the edge of the flight envelope. It was the data fed to MCAS that caused the response and because that data was extreme MCAS had been afforded too much power the issues occurred. The redundancy and power of MCAS are what is being addressed.
        When the MAX is certified again to fly, I will happily take a ride as I doubt there will have been no other airliner in the sky that will have been under tighter scrutiny.

        1. If that the case then just reengine the MAXes to avoid installing tha MCAS before selling them. Second, boeing only inform pilots about the MCAS after the first lion air crash and even worse boeing only give a 2 hours ipad course to pilots that doesn’t give any specific information on MCAS when introducing the MAXes and also i don’t know if this true or not but i once read an article that put it simply, the MCAS that FAA approved have less authority then the ones currently on the MAXes sold to airlines. Boeing decided to change and give more authority to MCAS after FAA approve them and don’t inform FAA about the changes and thus please give me some explanation.

  4. I’ve been watching this develop. initially when you couldn’t can’t get worse … Surprise! It takes a life time to build a reputation and very little to destroy it. With the issues over the past 10 years (777 delays and batteries, military order debacle and now the 737 MAX) I am wondering if this “hangs” (metaphorically speaking) over Boeing for an entire generation.

    I am now starting to objectively wonder if financially speaking the plane is worth it. Without an extremely high and rigorous standard of training world wide (ie Quantas quality of training) Inevitably another incident or accident will occur. Realistically are people going to fly on the plane?

    1. How do 2 computers vote to determine which one is correct if they detect a difference.? Usually an odd number of 3 or more devices are required. If one of the AOA devices is determined to be defective and one of the computers is determined to be defective, how do you switch the “good” AOA to the:Good” computer?

      Why aren’t the inertial platform and GPS systems used?

      1. “How do 2 computers vote to determine which one is correct if they detect a difference.? Usually an odd number of 3 or more devices are required”.
        Exactly the same question occurred to me when I read about this on Reuters a few days ago.
        Every undergraduate in computer science would grasp the point you just raised.

        1. Well i don’t know about computer programming but this bring me to question something, why would the 2 CPUs disagree with each other in the first place? Yeah i don’t know anything about computer programming so sorry about that and thus please give me some enlightenments.

          1. Then maybe just make a backup inputs like airbus 3 AOA sensors so that the CPUs could tell which one is incorrect input and which one is correct and make the 2 CPUs support each other to avoid overload but might as well to install the 3 CPU. Well not sure if this will work though.

          2. Passerby, your reasoning is sound. But it seems that Boeing just want a quick, cheap, halfass patch…

  5. Intrinsically there is nothing wrong with an aerodynamically unstable aircraft. E.g. the SAAG Gripen fighterplane was so designed to enhance manouvrability in close-in dogfights. Computers keep it safely in the air. Only one hull-loss in the development phase, none since. The MAX can easily be made airworthy in the same manner. Boeing’s very unfortunate and tragic mistake was to keep this feature hidden from its pilots, and to rely on one sensor only.
    BTW, Paul Proctor’s assessment of Dennis Muilenberg is spot-on, and the atmosphere in Boeing plants worldwide is one of resigned sadness with a resolute work ethic and fervent desire to overcome this tragic state of affairs. I have a close acqaintance with Boeing engineers and they WILL overcome. Once re-certified I’d be happy to fly MAX anywhere, anytime. It’s now in the hands of the computer geeks – with Boeing engineers questioning their every decision. NOT a “quick, cheap, half-ass” approach, Nigel. I know for a fact.

    1. 1. “Not a Quick”
      Boeing didn’t reengine the MAXes because that would take longer time and thus decided to move forward and upward the engines instead of reengine it which cause the MAXes to have some flight instability.

      2. “Not a Cheap”
      Boeing went and outsource the supplier of components including the sofware to companies in third world country to cut costs as much as possible even went as far as making the AOA disagree alert which should be vital for MCAS as an option.

      3. “Not a Half-ass”
      MCAS is patched to a single AOA sensor with more authority then what the FAA approved and didn’t even inform the FAA about the changes to MCAS and also boeing only give pilots 2 hours of ipad course that didn’t even mention the MCAS.

    2. And of course “the atmosphere in Boeing plants worldwide is one of resigned sadness”, because:
      – The share price has dropped;
      – Engineers realize the company is being run by greed-driven airheads;
      – Some managers are probably going to end up behind bars.
      Logical.

      1. Throwing invective around is most unbecoming, particularly as so many good people at Boeing are doing their utmost. Doesn’t help the discussion, and reflects poorly on you, Nigel.

          1. Let’s take your line of reasoning to its logical conclusion, Nigel. Some men beat their wives, therefore it”s OK for you to be a wife-beater, too…..
            I think we have all conceded that Boeing made a number of grievously incorrect decisions in developong the MAX, but here in this forum right now, we are talking about what it is doing to make amends. I wonder what you really know about the current workings inside Boeing, or about aviation generally for that matter. Then again, no point wasting my breath anymore as, like so many blogs and discussion fora, this one has more than its fair share of ill-informed stone throwers, none of which makes for a mature discussion. Goodbye mate, enjoy your stone-throwing.

  6. When the Space Shuttle was developed they used 5 computer systems with the software implemented by 5 different teams in isolation. The 5 computers used a technique of rendezvous periodically to compare the results of calculations. One of the issues they were addressing was the interpretation of the specifications. Even if the hardware was operational, maybe one team of developers interpreted the spec differently and produced a different result from the others. They spent years correcting the errors at the rendezvous points before they got it mostly right.

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