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737 Max

Boeing 737 MAX Needs New Computer Systems to Meet Airworthiness Requirements

Boeing 737 MAX Needs New Computer Systems to Meet Airworthiness Requirements
Joe Cortez

The troubled Boeing 737 MAX is one step closer to flying, but will require a complete overhaul on computer systems. The Federal Aviation Administration has submitted a proposed airworthiness directive, which would require new flight control computer software, MAX display system software, and other physical changes.

The Federal Aviation Administration is proposing a number of changes before the Boeing 737 MAX can fly once again, with most taking place in a cockpit. In a proposed airworthiness directive sent to the Office of the Federal Register, the agency is asking Boeing to completely change in-flight computer systems before the aircraft carries commercial passengers once again.

Airworthiness Directive Revolves Around Flight Control Computer and MAX Display System

The new airworthiness directive hinges on the improvement of two computer systems. After investigating the fatal crashes of Lion Air Flight 610 and Ethiopian Airlines Flight 302 and completing test flights with Boeing, the agency is requesting changes to both the flight control computer and the MAX display system.

The updates would change when the maneuvering characteristics augmentation system (MCAS) can force the aircraft to pitch nose-down. Instead of taking input from a single angle-of-attack sensor (AOA), the flight control computer system would be updated to take readings from two AOA sensors. If it is not fixed, the FAA determined MCAS “could cause the flightcrew to have difficulty controlling the airplane, and lead to excessive nose-down attitude, significant altitude loss, and impact with terrain.”

”These revised flight control laws would use inputs from both AOA sensors to activate MCAS,” the proposed airworthiness directive reads. “This is in contrast to the original MCAS design, which relied on data from only one sensor at a time, and allowed repeated MCAS activation as a result of input from a single AOA sensor.”

The Lion Air 737 MAX-8, registration number PK-LQP, sits at Soekarno-Hatta International Airport (CGK). This aircraft would operate Lion Air Flight 610, which would ultimately crash, killing all 189 souls on board. Photo courtesy: Wikimedia Commons

In addition, the flight control computer update would require systems to alert pilots if there is a disagreement between the two AOA sensors. Investigations into the aircraft discovered some 737 MAX aircraft did not have this feature, which was not included erroneously. The disagreement alert would inform the pilots of potential calibration issues, or even a sensor failure.

“While the lack of an AOA DISAGREE alert is not an unsafe condition itself, the FAA is proposing to mandate this software update to restore compliance with 14 CFR 25.1301 and because 11 the flightcrew procedures mandated by this AD now rely on this alert to guide flightcrew action,” the proposal states. “As a result of the changes proposed in this AD, differences between the two AOA sensors greater than a certain threshold would cause an AOA DISAGREE alert on the primary flight displays.”

Finally, airlines would be forced to change the routing of the horizontal stabilizer trim wires in the aircraft. While it is not necessarily related to the computer overhaul, the change would bring the airframes in compliance with FAA wire separation safety standards.

Changes Could Cost Over $14,000 per 737 MAX

If all the changes in the proposed airworthiness directive are approved, the bill to airlines would cost an estimated $14,160 per aircraft. For Southwest Airlines, holds the largest domestic fleet of 737 MAX-8 airframes, the cost of compliance could come to a total of over $481,000.

None the less, Southwest is optimistic that they will fly the aircraft again before the end of the year. In multiple statements, the airline has committed to working with Boeing and the FAA to get the aircraft back in the operational fleet before 2021.

Once the notice of proposed rulemaking is published in the Federal Register, the public will have 45 days to comment on the recommended changes. While the FAA produced the document early in the spirit of full transparency, the full dockets and comments will be available at

Feature image courtesy: The Boeing Company

View Comments (15)


  1. glob99

    August 3, 2020 at 6:36 pm

    What about EASA requirements?

  2. Pete Zahut744

    August 4, 2020 at 5:08 am

    Your title isn’t quite accurate. The flight control computer (FCC) is already capable of handling two AOA inputs. It was the code that was written that could not handle two inputs because it was felt it was not needed and adding a second AOA system would be an additional expense. There will also an option made to now be standard and that is an AOA indicator on the PFD (Primary Flight Display) which will give the pilots a graphic representation of the AOA on each side respectively. If there is only one AOA system working the MCAS will be disabled automatically.

    Just to also clarify, the cost is not being paid by the airlines, it is being paid for by Boeing along with a mod to the wiring to comply with a 2017 standard which was not in the MAX design.

  3. janderss

    August 4, 2020 at 5:53 am

    Dear Joe Cortez,

    There is a significant difference between needing new computer (FMC) software and needing a new computer system. The heading is sensationalist and inaccurate.


  4. blondietink

    August 4, 2020 at 6:16 am

    Why should the airlines have to pay for the fix? I think it is Boeing’s problem and responsibility to fix.

  5. Global321

    August 4, 2020 at 6:18 am

    “If all the changes in the proposed airworthiness directive are approved, the bill to airlines would cost an estimated $14,160 per aircraft. For Southwest Airlines, holds the largest domestic fleet of 737 MAX-8 airframes, the cost of compliance could come to a total of over $481,000.”

    Zero chance the airlines pay any of this. I believe Boeing pays 100% and re-training and probably more in compensation.

  6. kc1174

    August 4, 2020 at 6:24 am

    “Needs New Computer Systems”.
    It’s a software update.
    Also, the horizontal stabiliser trim wire routing is “not necessarily related to the computer overhaul” because it’s totally unrelated.
    It is not a new computer system or a computer overhaul when it costs $14,160. That’s the cost of 7 good MacBooks.

  7. KRSW

    August 4, 2020 at 7:15 am

    Um… the AD says the Max needs software, not a new computer:

    “This proposed AD would require installing new flight control computer (FCC) software”

    “installing new MAX display system (MDS) software,”

  8. vroberts

    August 4, 2020 at 7:41 am

    The headline for this article is incorrect. A software upgrade is NOT a “new computer system.” It is equivalent to installing a new version of Windows or iOS on your existing computer. No change in the hardware is indicated in your story.

  9. scfw0x0f

    August 4, 2020 at 8:03 am

    Click-bait headline. “New computer systems” makes it sound like the computer hardware needs to be changed; the story and cost per aircraft makes it clear that it’s a software change only. Bad on FlyerTalk for going there.

  10. DeltaFlyer123

    August 4, 2020 at 9:11 am

    My first thought after reading about these accidents over a year ago was that taking inputs from more than one AOA sensor would be the obvious principal solution. That was without knowing anything else about the accidents, other than they had a faulty AOA sensor. Similar to the A330 Air France crash over the Atlantic off Brazil with the faulty pitot tube reading. Everything else, besides training, is window-dressing. One can always look at a design after the fact and say that it can be improved, that’s how our industry moves forward.

  11. zarkov505

    August 4, 2020 at 11:39 am

    And they are STILL not looking into the REAL question: How the BLEEP did the hot steaming pile that was the original implementation of MCAS get past Boeing’s internal review processes in the FIRST place? Boeing design philosophy has ALWAYS been “Trust the pilot and tell him what is going on”, and NEVER “Take the airplane away from the pilot without warning or explanation”. MCAS was a major departure from that philosophy. HOW DID IT HAPPEN???

  12. BC Shelby

    August 4, 2020 at 11:53 am

    …the best solution, dump MCAS altogether and have the Max designated as a “new type” and require aircrews to be properly trained to handle the aircraft without it. I wouldn’t trust the system unless it had at least triple redundancy because you’re still looking at a 50-50 situation.

  13. redtail

    August 4, 2020 at 5:22 pm

    This should be considered a defect in the plane and should be covered by the manufacturer/OEM suppliers and not the airlines.

  14. Cedar Jet

    August 9, 2020 at 10:51 pm

    Who in their right mind will fly in a death trap 737max created by a criminal company?

  15. Bowen74

    August 17, 2020 at 3:16 pm

    One AOA sensor per aircraft is insane to me when you consider C-17 has 3-4 of them… there should be an AD for that.

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