Make the fix on Boeing 737-9 door plug fail-safe

By the Leeham News Team


Four missing bolts were the reason the emergency exit door plug separated from a Boeing 737-9. The inspections-and-repair edict from the FAA may not be enough for a fail-safe fix. Credit: NTSB.

Feb. 20, 2024, © Leeham News: Four missing bolts on an emergency exit door plug leg to the in-flight decompression of Alaska Airlines Flight 1282 on Jan. 5 of this year.

It’s not yet clear why the four locking bolts were not installed in the incident aircraft, a Boeing 737-9.

Information revealed to date by the National Transportation Safety Board (NTSB) discovered that Boeing removed the door plug in an unplanned process when some defects were discovered with some rivets. When Boeing line workers reinstalled the plug, for reasons as yet unknown, the four retaining bolts were not reinstalled. The bolts became separated from the plug during the removal. So far as is known, the four bolts never have been found in the factory. The NTSB’s investigation continues.

The Federal Aviation Administration (FAA) grounded the MAX 9s for three weeks while inspection and repair procedures were prepared, approved, and implemented. Inspections were expanded to the MAX 9’s predecessor, the 737-900ER, which had the same door plug. No grounding was required of the -900ER.

Although the processes solved the concerns over all MAX 9s produced to date, the question arises whether the procedures are sufficiently fail-safe going forward.

The inspection of the fleet to verify the correct installation of the lock bolts appears to leave a gap for future production, unplanned plug removals, and reinstallation.

Fail-safe fix

There is a small design change that could provide a fail-safe fix going forward that the NTSB, the FAA, Boeing, and Spirit AeroSystems might consider. (Spirit builds the 737 fuselage and installs the door plug before shipping to Boeing.)

The regulators and the manufacturers should consider using a wire lanyard to permanently attach the bolts to the doors. All that is required to do this is to use drilled head bolts instead of undrilled bolts, attach four lanyard mounts to the doors using eight rivets, connecting a thin wire lanyard between the bolts and the lanyard mount. At most, this adds three ounces to the total plug door assembly weight. This attachment method is already used throughout the industry.

The safety gains seem to outweigh any disadvantages.  There isn’t a mechanic in the world who would ignore four bolts hanging on lanyards near four open holes without questioning why they were there.  The permanent attachment of the bolts in this manner becomes a physical reminder that something needs to be done with them.

If the bolts were not there, a mechanic not familiar with the installation process is far more likely to miss them. Using lanyards virtually eliminates the chance of missing these safety bolts placing future aircraft at risk by relying on the status quo to do so.

This kind of corrective action reduces future risk. Inspections alone won’t get us to that better place. Lanyard installations, a very low-cost visual indicator, move closer to that future reduced risk place.

143 Comments on “Make the fix on Boeing 737-9 door plug fail-safe

  1. “There isn’t a mechanic in the world who would ignore four bolts hanging on lanyards near four open holes without questioning why they were there. ”

    Given everything we know, this seems a bold statement.

    • Agreed. It would be rare but then the alignment of 3 huge blocks of separate Swiss Cheese that lead to this is the same.

    • the fails to take into account that every time you idiot proof something, god invents a better idiot.

    • If it’s fail proof then you won’t need mechanics but then nobody would notice the error. Then it isn’t fail proof…

    • That is a bold statement and I am a certified A & P mechanic.
      But that is an excellent way to get your attention as lanyards are used in other critical airframe areas, one notably being the nose landing gear assembly link pin.

  2. One could argue that quick repairs done by the mechanics “on the fly” since WWII should be replaced with production engineering instructions and “mini jobcards” reflecting the quick repair and its documentation with engineering decided quality checks.

    • Claes
      This is exactly what went wrong. The RISR form for unplanned removals has a qa buyoff inspecting correct reassembly. That process failed us. A hardware solution adding visual cues makes sense here. Remember that during the fleet inspection, other missing and loose bolts were reported as being found. The inspection solution alone has shown that it is inadequate by itself. Belt and suspenders so to speak seem to be a reasonable choice moving forward.

      • Seems the new standard of step by step engineering instructions and document each task as you work is needed for all deviations even though it adds time and cost that many feel was not needed in 1900’s with experienced and pretty well paid mechanics

        • You touch it and you auto generate a complete process , mechanic to the bolt, confirm the work and then the inspector sign on.

          Computerize it as needed but like a vote, paper backup.

  3. This would definitely help, but I’m not sure if the last person to see that the bolts were missing would have refitted them anyway.My impression is, that it’s a systems problem,you have to know that whoever was doing the job has finished and that it’s your job to refit the bolts.Maybe the bolts got mislaid and that’s why they were not refitted at the appropriate time?That would explain the giant eyeball drawn on the window, but for that to work people have to know exactly which problem it refers to.

    • Same here.

      A better solution would be a design that absolutely forces fastening in order to fit the plug rather than a design that simply forces the fitter to think about fastening. At minimal extra weight, BOM cost and procedural cost. Maybe add some sort of tag to the lanyard that must be removed and processed by the fitter in order to sign off, yet that cannot be removed until all of the 4 bolts are fitted.

      But, if the lanyard method as described above is standard industry practice and has proved extremely reliable…

      • increase strength of the lifting springs.
        Door is lifted off the retainers if not bolted down?

        But that then is only one coping instance.
        What you need is better qualified and _motivated_ people on the job.
        “Jobsworth” individuals don’t fit.

        • ‘What you need is better qualified and _motivated_ people on the job.’

          How about managers & supervisors who don’t push staff to sidestep regs and get aircraft delivered?

          Culture starts at the top.

          (BTW – mgmt got rid of those ‘qualified and motivated’ people who knew what they were doing, when they offered buyouts and laid off 30,000 of them, along with ~1,000 quality inspectors. Those experienced airplane guys and gals cost way too much)

          • From Seattle times
            Boeing ousts 737 MAX chief in shakeup as blowout fallout mounts

          • Leaky Blimp.
            You can stay afloat as long as you have ballast available for dumping.

      • Often quality just look at one incident and demands fool proofing so they can close that single remark. You might have 10 000 different fasteners and other installations that are not fool proofed and you need a better system not assuming what worked before is still working 100% with the people you have in all workshops on all shifts. Boeing Renton is not Lockheed skunk works.

        • I am unfamiliar with this dialect. Do such authors ever read their [attempted] comments?

          “often quality just look at one incident..”

          oh. That clears things right up..

          • Stop nagging and put some energy into understanding what the poster wanted to say. ( Ok with some it is moot, but here .. )

          • The meaning is that a single fault sent to quality can be a forced a “belt and suspenders” solution for just that single fault when similar designs prone to the same error are “everywhere”. In Toyota language 7 more similar locations and times 7 more chances of same error. The logic is then that 49 problems needs a solutions for every reported error.

          • Toyota: 49 issues.

            Abstraction is everything.
            What is the common denominator!

            Yet you find quite often that
            a “49 individual bandaids” solution is forced.

            IMU the major issue with “vertical educated” “cubicle mind” staff.

        • More pronounced over the years due to reflexive acting:

          myopically fix some single case issue while setting up a dozen new traps as fall out.

          As a society we have lost to grasp the wider picture.

          Politics create new rules and laws much faster than the dissection of the causal incident takes.
          ( and invariably effect “something” that is later shown to be not the cause )

        • Absolutely.

          But not all of those 10,000 fasteners are as consequential as those maintaining aperture integrity, holding an engine on, ensuring control surfaces are in control etc. And many are likely, in effect, singular rather than to be considered as a package.

          So, horses for courses. I’m of the mind that those that are more consequential require more thorough procedural certainty and reduncdancy. Designed in a way that it also does not decrease, rather preferably increase, fitters’ diligence.

          • You can’t use an excess of safety designated as margin
            to dumb down your production.
            Margin used up in production
            reduces margin available for in use contingency.
            ( the reason why it was designed in! )

  4. There are several issues here. One is that the information flow used to control the assembly of the plane is not congruent with the assembly process. There is a virtual organization and they systems ignore that and have needless boundaries based on the corporate participants. There are multiple systems. On top of the information systems not being aligned with the virtual organization that builds the product, here is an incentive to avoid entering data where it belongs by those who are authorized. Management inserts itself into the process when they shouldn’t. They should be facilitators only, with kanban style information flows at the task performance level, and not going up into a management layer or two with the hope that they will come back down where appropriate. There is a kick the can down the road approach to issues instead of one that addresses them as they are identified. They pay more attention to rates than quality, so rework is rampant, which also means they actually don’t have a production rate, since it’s impossible to actually measure how long it takes to build a squak-free plane, they don’t build any – not even one per year. It goes on and on and on. It’s leadership incompetence in spades.

    The workforce should repeat the 1949 Toyota experience and throw the bums out. After all, not a single assembly or fabrication task can be done without them. They have all of the power. All they have to do is realize that and exercise it.

    • I agree – while the point of the article is valid, it’s just a sticking-plaster to patch this single problem rather than fix the actual root cause – the disjointed reporting/responsibility/quality systems and management culture working against them.

      You can’t go around attaching lanyards to every single item which needs to be in place before flight – especially when they are rarely removed like these bolts – as then you’d end up with an aircraft which is half-lanyard.

      What you need is a joined-up safety culture and QA systems where proper checks are built in to the hand over of a completed item of work to the next person responsible.

      • @someone in Toulouse

        Totally agree. I don’t know who wrote this article but it’s obvious he/she hasn’t worked as an aircraft mechanic, and I’m not talking about Boeing assembly line workers.

        Right …. Keep adding requirements instead of doing the job right in the first place!

        Hire better drug free production workers, the woke idiots they hired caused all of these problems in the first place.

        There I said it. Now the hurtful will slam me.

        • ‘Hire better drug free production workers, the woke idiots they hired caused all of these problems in the first place.

          There I said it. Now the hurtful will slam me.’

          After slamming workers (and the author of the article) with absolutely no proof whatsoever of who did what. One might even postulate that money grubbing managers pushed staff to perform the task and sidestep regs to ‘Just ship it’.

          But that wouldn’t fit your narrative.

          “Don’t criticize me for the baseless political accusations I am making, trying to hurt a segment of the population. That’s hurtful.”

          Projection at it finest.

          You ever look in the mirror?

        • BTW – Airdoc;

          When BA laid off ~1,000 inspectors, or the 30,000 employees a few years ago, did mgmt get rid of those ‘woke’ employees or people who ’caused all these problems in the first place’?

    • Which “bums” should be thrown out- and *how exactly might the workforce* do so?

      “do more good stuff, and less bad stuff” is not really a solution of significance.

  5. Thinking about this problem,it is usually dealt with in my much less safety conscious industry by putting the bolts in a plastic bag and tying it to the fitting .This is not foolproof,sometimes you get comments such as “I wondered what they were for”,but actually better than what Boeing was doing

    • Plastic box with the bolts in it,attached in such a manner that the door won’t close until it’s removed?

  6. ” One is that the information flow used to control the assembly of the plane is not congruent with the assembly process.”

    747 “documentation” vs “as manufactured” shew that this is not a new issue for Boeing.
    But now aggravated by dumbing down the workforce and supervisory management.

  7. This missing 4 bolt incident seems to be a ‘one off’ situation. A break in the usual routine (they had some rivets to to be fixed), requiring the door to be pulled and then put back on. Any non-normal situation needs additional inspection. And what of the ‘one off’ 737-MAX rudder loose bolts? What’s the fix for that?
    Again, any break in the routine needs additional inspection. People get on automatic pilot when doing routine jobs. They don’t have to think, it’s a repetitive process. Once a break in the routine happens, people are forced to think. Their automatic pilot goes away. They have to fly the plane manually. I’ve seen a lot of accidents happen with very high time pilots, when they only have a few hours in a new type of aircraft. You know exactly what the cause of the accident is most of the time. They reacted routinely as they had for 1000’s of hours in their old airplane, but, the new airplane needed some other reaction. When you have a break in the routine, you need additional inspection. I’m sure it’s the same for mechanics.

  8. Not an engineer, there may be a very basic answer to this question. My understanding is cabin and emergency exit doors are held in place by several solutions, including the fact that the doors are larger than the openings. Because of this, the pressure differential actually holds the doors in place, you could not open them at altitude if you wanted. Why are the plugs not similarly designed? Based on comments here, my guess the answer to this question is weight

    • ” Why are the plugs not similarly designed? Based on comments here, my guess the answer to this question is weight”
      Partly correct- the answer is COST-RATE- weight dto accomodate that traditional “Ten percent ” non standard configuration request by ‘minimal ‘ effects on the other 90 percent customers.- Thus we ” lose money” on every unit but make it up by volume’ as taught in McKinsey and MBA beancounter classes.

      Even so the lanyard method is probably the most reasonable fix and can be incorporated in all planes during C or D checks without removal of ‘ plug “

    • It is true that differential pressure pushes an aircraft door outward and practically speaking holds the door place, however, typically the door itself is outward opening and there are plungers or other mechanisms that bear on internal structure.

      In the case of the 737-9 door plug, there are 12 stop fittings on the door that bear on 12 stop pads attached to the structure.

      There are many reasons why an outward opening door is preferable to an inward opening one (not sure there is a weight savings as suggested by Bubba2 since the mechanism may have to be more complex and robust).

      A couple of reasons come to mind immediately:

      (1) an outward opening door frees up valuable space in the vicinity of the exit during emergency egress (if the door were inward opening, the cabin layout would have to accommodate the door);

      (2) in the case of Type III overwing emergency exit on newer aircraft like the 737 MAX, the door plug does not have to be handled by an occupant because it is hinged & spring loaded so it and opens outward & upward; and

      (3) most business & regional jets incorporate a stair into the door.

      So while differential pressure makes it impossible to open one of these doors in flight (it would not be humanly possible to unseat the door from its stops), the door itself is not larger than the opening.

      • You see door designs that open outward but require
        that the door be moved inward away from an interference fit, canted slightly and then moved outward.
        ( A320?, any Airbus? haven’t looked )
        Then you have the “garage door design” inward, upward into the overhead unused space. ( 767?)

        • Good points; I guess it would have been a lot better to say “common” rather than “typical”.

  9. The lanyard concept is good and has existed for a long time. It is an obvious solution that will likely be implemented and I see no reason it would not.

    That being said, I would not call this a “fail-safe” design for nothing failed except the process at Boeing. And the only broken thing they found was Boeing’s safety culture.

    Rather I would call it a fool-proof design for there seems to be many of those around Boeing today, starting at the very top of the company.

  10. The author is correct – lanyards would fix the door plug issue.

    The likelihood of any mechanic now forgetting to miss checking for the bolts installed, is very remote.

    – No airline ever used the fork lift to remove engines on a DC-10 from the pylon, after that accident. Correct procedures were followed.

    – Every pilot now knows that if you’re in a Max and you get an uncommanded pitch down, you hit the stab off switch and do the roller coaster (or whatever the proper procedure is).

    – After those two joy-riding idiot pilots from Pinnacle flew up to 41k and core locked the engines on their RJ, everyone said “OK, we’re not doing that”

    Every time there’s an accident, the cause gets a ton of attention and everyone becomes really careful about that particular thing.

    This doesn’t solve the Boeing issue about production quality, managements push to deliver as many aircraft as possible and the alleged circumventing of regulations.

    Any worker now asked to get it done quickly should ask “You want it done quickly or you want it done right? If you want it done quickly, please provide me with documented directions, in writing, to that effect. Until then, I’m following the rules. “

    • Frank P:

      Those are well listed incidents and in theory, once they occur never again.

      But if you watch Mentour (as well as follow aviation as you clearly do) then what you see is it does happen again, usually at a different airline.

      Just saw a E195 use less runway than allowed and from what I can tell, they got used to using the next access up and decided to use a lower one or got lost but still a mid field takeoff and any of these is good.

      You can lower the levels of stupidity or happenings of it but they do repeat elsewhere at maybe lower levels.

      And then the one in Indonesia I believe where they added a new ramp area and flooded the new fuel system with sea water.

      Something about the filters don’t do salt. So you got salty fuel and ……. you can do a one off fix for that

      Fuel system Extension was never flushed right.

  11. The reaction by Leeham Team is one I expect from far less well informed sources and I am disappointed.

    As a mechanic I can tell you things dangling in your face in your work area are an annoyance, yea, some would cut them off.

    It should also be noted, there were reference to LOOSE bolts/hardware but its not been listed as to what that meant. Were they in place and not snug but the washer, nut and cotter key in place?

    Putting a landyard on a fastener is not going to solve that, and oh, how about the washer nut and cotter key?

    Well we have this release type ty wrap (known generally as a Zip Tie) and …..

    How many items on an aircraft are the same as a door plug where the fasteners being missing or loose cause a loss of an important piece/assembly? Weaken one.

    Flipping this around a bit, a training flight of an A319 (I believe) where they had a computer fault and the Captain/trainer just reset the fault into computer insanity. Last in line is pure mechanical control.

    Bjorn has noted you really cannot land an A320 series (or any Airbus FBW aircraft) with mechanical control.

    Does that mean you heave ho Airbus FBW computer system? Yea they tweaked it but could not reproduce the failure.

    The answer is don’t do things like keep resetting into a fault, that was in no procedure.

    Go to the backup and then put the thing on the ground. You got a bunch of computers behind you still in the backup computer part even if you wind up in degraded mode.

    Do we wire the fasteners that hold the tail on to the airframe?

    Securing fasteners to the airframe is a feel good thing but its not the answer to what the true issue is that is well understood per above comments. Its the messed (there is a better word but we are not supposed to use it) system.

    The Road to Hell is paved with good intentions comes to mind.

    I just totally disagree with a one off patch when the issue is understood and been allowed to fail by all parties.

  12. To accommodate an optional (for sardine can seating) exit door, a hole in the fuselage was designed. An emergency exit door (EED) was designed to fit the hole. The EED system was designed to “eject” the door in an emergency deployment so as to avoid it interfering with aircraft evacuation. Makes sense so far.
    To save money on planes not outfitted with sardine can seating, a door plug panel (DPP) was devised to fit the EED hole. Not needing to function as a door, and not needing to deploy in an emergency many systems needed on the EED could be eliminated on aircraft fitted with the DPP. Still makes sense, and the bean counters are happy.
    Now we start to go off the rails- Why is the DPP still equipped with the ejector system needed for the EED? (To keep it from rattling is the only reason I came up with)
    There is also the question of where/when does the final sealing of the hole, whether EED or DPP equipped, take place? From what I’ve read it takes place after paint and livery… NOT ON THE ASSEMBLY LINE. I am not sure but it seems the hole is un-sealed as part of the paint process or to mask around the seal or for some other necessary, but un-sung, step in the process. Any assurance that the hole is properly sealed before this final un-sealing / re-sealing is essentially meaningless.
    Perhaps the closure panel could be locked in place with a single pin, attached by lanyard to an oversize package containing the actual final assembly hardware. The package would keep the interior trim from being installed until the package is removed and the single pin replaced with the included set of real lock bolts, nuts, and cotter pins.

    • Mike:

      The reason for the track and springs is to allow that exit blank to move up and out so it and the surrounding area can be inspected and or worked on.

      When it moves up and out then a set of brackets holds it onto the fuselage, aka the nonspecific position.

      That in turn means it can be removed.

      But, how do you remove a item like that unless its accessibly and suspended already?

      The ability to order an aircraft with an exit plug is somewhat questionable. It should be solid or have a door.

      But if you are going to do what they did , then the system they use makes sense and has worked for a long time correctly.

      You can just as easily have someone come behind the last inspection and remove the bolts (sabotage).

      And what do you do about suicidal pilots? Or the poor depressed pilot whose good friends introduced him to magic mushrooms and he was hallucinating? (while in a jump seat and pulled engine stops)

      • Thanks Transworld! One of my specific questions that I hope you can help with is :
        Are the panels (either one) ALWAYS unsealed at paint and livery?

        One account I read implied this is true, but always vs. almost always makes a difference.

        If it is true, it should be made obvious that NO panel is actually “closed” before paint, and ALL are sealed after paint. My suggested method is a take-off from a truck assembly line where a steering wheel is temporarily mounted (to steer the truck on the assembly line) before an instrumented “super wheel” is SOMETIMES added later. A nut was spun on to retain the temporary wheel but in at least one case the horn button was installed over an un-torqued nut. You can see where this is headed…
        The solution? A “special tool” to retain the steering wheels on the line: Weld a big washer edgewise onto the temp nut so the horn button can’t be installed over it. The steering wheel install process ALWAYS starts with “Remove the temp nut…”
        I’m not sure but the steps of “Torque the nut to xx Nm” and “Install the horn button” may have been moved TOGETHER to a subsequent station.

      • “The ability to order an aircraft with an exit plug is somewhat questionable. It should be solid or have a door.”

        Designing and building two different airframes rather than a single one to which either closure panel can be installed? That would call for knowing which fuselage was going to be ordered with sardine can seating before it was built (And locking it in all the way back to Spirit Aerosystems). Is this standard practice?
        I think that a door plug design that didn’t incorporate the exit door ejector springs (making it significantly more permanent as you suggest) would be preferred.
        But two different fuselages would allow the non-sardine seating aircraft to pass through paint and livery a bit faster.

        • Trans. wrote
          “The ability to order an aircraft with an exit plug is somewhat questionable. It should be solid or have a door.”

          The door plug is a good solution for building the Max-9. It provides a lessor or the initial customer for that matter the ability to configure the aircraft for less than the max legal exit capacity if he so desires. If the ownership re configures the door plug into an exit door at a later time in the aircraft’s life, minimal changes are required to remove the plug and install an exit door. Building a single configuration for the Max-9 fuselage is so much simpler to do logistically as you do not have to create 2 different skin panel assys with different window opening counts. If you wanted to add an exit door to the airplane in an aircraft previously built without the door provisions, its a ton of work to cut the openings and install the door surround, and this would adversely affect the residual values of non Edoor birds. This isn’t the way leasing companies want to do things. Also, as fuel critical as these things can be, saving a few hundred pounds of non-revenue weight on every flight really adds up and the door plug aircraft are lighter and get better economics. The problem here isn’t one of design, the design is solid and has been flying a long time. The problem here was Boeing losing the handle on their unplanned removal process that calls for a RISR to be issued for the opening of the door. The RISR form captures all the disassembly steps and logs them. It also requires that the reassembly process reverse the disassembly process and adds a QAINSP point to verify that the product was reassembled correctly. As far as the authors comments on lanyard use, they are on point as it would virtually eliminate the omission of the bolts and its hard to say that positive corrective action is doing the status quo and bolstering inspections, when we see that failed.

          • I understand virtually all of your response. Thanks. But what I’m really seeking an answer for is: Why isn’t the door plug panel (DPP) installed “more permanently” than the emergency exit door (EED)?
            With all the EED stuff (sensors, instrumentation, solenoid locks, escape slides, etc) that is deleted from the bill of material (BOM) when the DPP is optioned why keep the springs? (I’d also question how often an owner actually adds this stuff back after delivery. Kind of like “adding” mechanical fuel injection to a car sold with a carburetor) Why not bolt the DPP in place through the 2 lower sets of stop pads?
            The other key question is: Are both the DPP and the EED panels ALWAYS unsealed (Let’s avoid the confusion of “opened” vs “removed”) at paint and livery? This to mask (the seal?) or paint the edge of the panel(?)

            Thanks again!

          • Mike.
            You keep the springs so the door can be opened for servicing. Its a part common the escape door package. The Edoor does get retrofitted into a good many birds when they change hands into LCCs

          • It looks like this might wind up out of order but I’ll give it a shot anyway.

            So the DPP IS sort of frequently replaced with an EED. Good to know. If the new owner is adding a whole bunch of different seats, they’ll order the EED and all the trimmings.

            But that doesn’t answer why the springs aren’t part of ONLY the EED option package. The springs are there to EJECT the EED in an emergency. If the DPP needs to be unsealed, opened, removed or whatever why not just push it out, lift it off and separate it from the aircraft? Why not two different processes to R and R (remove and replace) the two different closure panels?

            Is the DPP is unsealed for inspection at the same intervals as the EED?

            But still, why not have different processes for the unsealing, opening, removal of the two different closures?
            And there’s still the question of unsealing either closure panel at paint and livery. Does P&L come before the interior trim is installed or after?
            And thanks!

  13. It’s a good point that if this approach were to be implemented ,almost everything would have to have a lanyard and as long as nobody believes it to be their job to replace the bolts ,then there is no reason to be believe that it would make much difference.
    Perhaps a better approach would be to do whatever the professionals do.Maintenance organisations remove these panels for access and heavy maintenance,how do they avoid losing the bolts and remember to replace them?

    • Grubbie:

      Because they have a process and they have paperwork to back it up.

      This happened for a lot of reasons, not just a single one.

      Boeing is hosed up all the way down to its floor managers because they set the system up that way. You don’t want people who thrive in that chaos, those are the worst of all.

      FAA is not doing its job for X reasons (we still need to see where it failed but with all the quality failures on the Doors/Blanks and fuselages that this did not get attention a long time ago means they have a hole you can run a carrier through and not be seen)

      Spirit: Ditto the Boeing failures and issues.

      • “Push down on the plug to open it” That does in fact make sense if they are talking about pushing it down just enough to take the spring load off the bolts so they can be slid out.

        At this point I’ll say the system could be designed with one specific bolt location that holds the plug a bit further down against the springs than all the others. As it stands (I think) one bolt in four bears most of the load but it’s a crap shoot as to which of the four. And designing them as if they will all bear at once is most likely to distribute the load after the panel “settles in”.
        Still I’d be curious to see if 3 of the 4 can be spun by hand while the 4th is pinched in shear (lower) or in bending and shear (upper).

        I confess, I never noticed the Zip Tie in Fig 16. But it doesn’t look like it’s restraining much spring force across that set of stops or it would be stretched. Just how strong are those springs?

        At present an opinion from an expert could cost somebody millions so they have good reason to stick to facts.

  14. There is another term for fail safe known as idiot-proof. There is also a common knowledge quip that when you do that the universe simply makes a better idiot. The lanyards aren’t a bad idea but the meat is in the paperwork. The bolts need to be an RII (required inspection item) however on a handwritten non-routine task it is difficult to insure that it will always be documented as such. The cold hard facts are that this isn’t something that is going to be happening on a regular basis. It may just be a one-off that is unlikely to ever happen again but there is no sure fire way to guarantee that no matter what you do.

    • “.. The cold hard facts are that this isn’t something that is going to be happening on a regular basis..”

      Why so, given the MAX’s and that company’s history?

    • “There is another term for fail safe known as idiot-proof.”

      Actually two different things.

      “fail safe” is single failure leads into a safe state (stopped, like railway)
      or single failure is compensated for in the design (must stay in the air, aircraft).

      Another item is “fault exposure”. Faults that are not exposed by design are a trap.

      “idiot proof” is another domain. ( and more difficult to achieve )
      Though it shares the wish for “fault exposure”.

      Best solution is “keep idiots away”, shoot on sight.

      On “Keep away”:
      Funny thing we found out: you can not have smokers in clean rooms, they exhale dirty contaminants all the time even with a mask.

  15. Fig Leaf: Something to cover up that you are actually naked.

    1. Moon Shot
    2. Cowering Workers
    3. Share Buy Back
    4. We are sorry and will do better (for the 10th time)
    5. Mandatory QC meetings and beatings will continue until you fix what we have hosed up (right)
    6. Safety is our first priority
    7. Driving a nail into it proves its good

    Calhoun looks at the landward thing and its, THAT IS THE PROBLEM.

    I never saw a high temp safety wired to a boiler. Many boilers have blown up and killed people. None that I know of was a design defect, all I know of were people bypassing safeties.

  16. At Bombardier we had a BOI (break of inspection) form we had to fill when we removed parts previously installed. Then we we would log the BOI in the aircraft paperwork also indicating where the parts were stored. The only way to close a BOI is to reinstall the parts to drawing and have it inspected.

      • This is basically the same process Boeing uses with the RISR, removal inspection ships record. The reason there isnt one on thr As incident airplane seems to be a matter of semantics between the words open and removal. Thats a aymptom of the cultural rot in Boeing where time is money, and money is number 1 ahead of building consistently sage products

  17. Individuals here are missing the point:

    The article is not about fixing BA culture.
    It is not about devising a new inspection scheme to catch all errors.
    It’s not about all the root causes that put Boeing in this mess.

    It’s solely an efficient, inexpensive and effective method to make sure that in the future, those Max 9’s go out with all the bolts installed in the door plug.

    1 problem. 1 solution.

    • The Boeing Aircraft culture is the root cause of this single door plug failure and a slew of other costly and deadly failures.

      • I think you’re right- and I also think that the [deeply financialized] BA culture will not be changing any time

        Let me know when a real C-Suite bigwig is disappeared- *without* a platinum parachute- or
        when the BoD changes significantly and with some prejudice. Articles get written; hands get wrung;
        but some how the trajectory downward for Boing never changes.

        odd- unless there is perhaps a larger realignment in play.

  18. God help us with media descriptions- or in new terms click bait as in today tues febc 20 ” Wing destroyed on flight from sf to boston . . .” when vido shows LE slat inboard of engine partly shredded ( its ‘ fibereglass basically ) probably due to bird strike – so ememgrency land in denver. MY point is the headline ‘ wing destroyed ‘ and passenger were glad to safely land, yada yada. –

    The biggest effectd would be flow-lift distorsion on wing requiring a relativey minor change in keeping wings level when landing, etc. photos show a minor dent in aluminum leading edge- so no real damage and wing NOT about to come off. All critical stuff is behind rear spar anyhow.
    Of course it was a Boeing – which nowdays gives rise to plug door etc.

    • LOCAL
      ‘Wing was destroyed’: Boston flight diverted after plane damage discovered mid-air

      By Kelly Sullivan, Boston 25 News
      February 20, 2024 at 11:02 am EST

      ‘Wing was destroyed’: Boston-bound flight diverted after plane damage discovered mid-air

      BOSTON — Passengers on a Boston-bound flight were happy to be on the ground Tuesday morning after the wing of their plane started “coming apart” in mid-air.

      Meanwhile back at the ranch

  19. I was wondering if this systems problem isn’t wider than just Boeing. Hadn’t this Alaskan airplane had several (3) pressurization warnings before the mid-air blowout? Where these warnings just ignored?

    • My understanding is that system warnings are quickly investigated and are almost always sensor or related component issues NOT THINGS LIKE PANELS COMING LOOSE. They are investigated, (but admittedly the interior trim was not removed in the investigation) it was as a result of the system warnings that the plane was restricted to routes with alternate airports available. There was no indication other than the sensors that the plug was leaking.

      • Mike.
        It seems that the plug was not leaking. The noise from an air leak of that size is unmistakeable. The pressurization warnings were an annoying but unrelated issue..

        • That was my impression as well. I suppose the plug might have been leaking slightly but a leak large enough to trigger the warnings would have been obvious to those investigating the warnings, correct? It is worth noting that false indications do tend to result in less attention to warnings in general. See “Boy who cried wolf”

          • removing fail indications by way of switching systems is a NoGo. ( though popular 🙂 switching from an indicated fault over to error indication is broken and fault thus not shown is possible! )

            NTSB report seems to show nothing about the pressurization failures ?

            If the plug was the culprit it must have already been lifted halfway out of the retaining lugs. ( is this visible from outside ) pressure cycling could then re-seat the plug?

          • To have 3 pressurization warnings with an aircraft that shows the plug was moving is getting into what we called “the coincidence” factor.

            Our corollary was there are no coincidences .

            Longer term when AK gets the jet back and it goes back into service and there are more alarms or no alarms that will sort out that aspect (we may never hear about it though)

  20. My wife and grandson flew to Alaska last week. On an Alaska Airlines 737 MAX. No parts fell off, no damage to the aircraft. Ho Hum

    • Rather a small sample size, no? “Relax- the MAX is safe to fly: my wife told me so.”


      • It was actually “Statistically we are still FAR more likely to die in a collision on the way to the airport than to experience an aircraft mishap”. We still drove to the airport.

        • If a Boeing MAX is safe enough for you, it’s safe enough for you.

          The last three all-fatalities airliner
          crashes have been Boeing 737s, and that’s not a pleasant trend. I will not mention the latest Alaska Boeing 737-9 door plug blowout.


    • There you go! All this fuss because one “door” fell off one plane. Unbelievable.

      • I sure do hope the above comment is satire, given the Boeing 737MAX™’s ill-fated history.

        “only 346 lives lost- so far! and nobody died- this particular time!”

        • I wonder how much of the content on this here [utterly opaque] darpaNet is worthy of trust.

          just a thought.

  21. Uwe said:

    > Stop nagging and put some energy into understanding what the poster wanted to say. ( Ok with some it is moot, but here .. ) <

    How might the reader "understand what the poster wanted to say", if not through these glowing icons on the page? Through clairvoyance, perhaps?

    I'm one of those odd ducks who thinks clarity in language is important- especially in such a distanced medium; one utterly lacking provided context. Given the curious evidence of your efforts you appear to not agree.

  22. Why worry about a better way to plug a hole in the fuselage? I mean, why not design the fuselage so that it has no hole which requires a plug? Wouldn’t that be easier…and cheaper?

    • Jimmy.
      Your question is good and I made a lenfthly reply to it. Here is the start of it….. look it up and ot will make sense to you……

    • No. One fuselage that can have the hole(s) filled by either plugs or doors is cheaper. And can be done safely, but not so quickly. The devil is in the details.

  23. The lanyard is a good idea. In addition, what about these additional measures?:

    FIRST: Eliminate the lifting springs. In an inoperable door that is designed to never be opened what purpose do the lifting springs serve? With four bolts missing wasn’t it the force of the lifting springs that moved the stop fitting off of the stop pad allowing the door to be ejected? I just don’t understand what purpose the springs serve and there would be a weight saving getting rid of them.

    SECOND: Design a fitting that would go over the stop fitting and stop pad making it impossible for them to become misaligned to the point that they fail to act together as a plug.

    • I’ve been thinking about those springs since the first pictures of the missing plug in the days following the incident. I was astounded that an airplane exit size opening, that needs to stay closed under all but a rare (on the ground) situation, was designed to fail to the open position if anything in the locking mechanism fails. Example-A bank vault door is designed so that tampering disconnects the lock from the spring loaded lugs holding it closed. If lock tampering caused vault doors to pop open the crooks would have all the money!

      Professional engineers would understand this, but they might get overruled by management, operations, maintenance, sales, accounting, or combinations thereof. Therein lies the source of all the discussion about corporate culture! I have opinions, but this is not the time or place for that.

      I do wonder what the preliminary design suggestions were for those lift springs? Your mention of eliminating them is one possibility but there might be others. With gravity in charge one could still forget to install the 4 locking bolts. Maybe an engineer would suggest springs as we have them, but strong enough to force the plug up & off the stops & upper guides so it pops open? Forgetting lock bolts in that situation means an open plug (unless someone puts a zip tie around a stop to hold it closed). A crew sent to install interior panels would NOT do so if plug was hanging open 2 feet, would they? Certainly, the plane wouldn’t fly. Maybe the current spring design is considered a passive safety device because it forces one to close & install lock bolts just to keep it closed? (Unless a safety device is bypassed) QUESTION- What is the policy? And what are the consequences of bypassing safety devices on airplanes?

      Bank vault engineering might put the spring ABOVE the sliding part of the lower hinges so they push down & hold that upper guide & pin closed? Bolts or no bolts. Of course on an airplane you would always have locking bolts for redundancy. And the plug would need to be pried up (after lock bolts are removed) against gravity & the springs to be opened. A little inconvenient in the rare case it might need opening, but certainly preferable to accidentally opening in flight, yes?

      Many have asked, and I think the question still needs answering, how did this plane make 250 flights with no locking bolts?

      • The purpose of the lifting springs is purely to reduce the effective weight of the door plug while it’s being maneuvered into the closed or open position. The weight of the door is sufficient to fully compress the springs when the plug is closed.

        Ignoring the irrelevant bank vault analogy, Boeing and the certifying authorities have clearly decided that the design, when correctly implemented, works. We have millions of flights with 737 door plugs staying closed as designed.

        I enjoy a good Boeing-bash as much as the next person, but before the flight in question, the design and operation of the door plug had, as far as I’m aware, raised zero concerns. I have no doubt that this was a one-off failure of process by Boeing. That’s not to suggest that Boeing’s processes do not need to be tightened up, they clearly do.

        • I’ve never worked on an airplane. Do you have experience opening an identical one? When you say the “weight of the door will fully compress the springs”, is that from experience or what?

          I think vault lock design IS relevant, but a simpler example of failsafe design might be suicide doors on cars and why they no longer exist. They were convenient and they were safe, as long as the latch was working. Errors, omissions, or unforeseen incidents affecting the latch cause the default door position to be OPEN vs CLOSED. The concept applies everywhere. Spring loaded farm animal gates to molten salt nuclear reactors.

          • As designed, the lifting springs (as their name suggests) are applying upwards force on the plug. They are there only to effectively reduce the upwards force that needs to be applied to the plug by a human when opening (or removing) the plug.

            The springs are not strong enough to lift the door on their own. If they were that strong, then significant downwards pressure would need to be applied in order to close the plug.

            The design is fine, it’s been certified and has operated safely on millions of flights. This whole episode is down to a process failure within Boeing’s production system. Is any design perfect? Possibly not, but it’s certainly good enough as long as it’s built as designed.

        • I worked on rolling steel and fabric doors for 35 years.

          The Springs inside (or visible on your garage door) do NOT open the door.

          They relieve the weight of the door (neutralize) it so that either you or the electric operator can open it.

          The is absolutely nothing wrong with the design. If you are going to make it a mix or match system (which goes back to the 737-900 ER, then it needs to be able to move so you can inspect it or replace a seal or even repair it.

          One bolt installed would have kept it from ejecting. It might have moved a bit. Two bolts would have stopped any movement.

          If your auto mfg leaves a bolt out in your suspension (or loose), you are going to have a failure.

          I have seen 3 bolts like that coming out of suspensions. Failure of quality control.

      • Bitterrootbackroads, Your second sentence is spot on. I’ve been commenting since on the same point but all I’ve seen so far is detailed discussion on the various elements of the plug and how they are supposed to operate.
        The vital aspect of this near-disaster is how the decision to use a fail-open design was adopted in the first place, not so much about how the detailed design evolved. It was a failure of process by way of, I suspect, the marketing/sales department overruling the Chief Engineer.

    • The purpose of the lifting springs, as their name implies, is to reduce the lifting forces required for a human to open the door plug (however rarely that might be required). The weight of the door plug is enough to fully compress the springs, enabling it to be fixed in place by the retaining bolts (when fitted!)

      I don’t think the NTSB has said anything about how it was possible (while pressurised), for the plug to transition upwards far enough for it to be blown out. It’s not impossible to imagine that a heavy landing or significant turbulence might be able to ‘jiggle’ the unbolted plug loose.

      • The new VP of Commercial should be a floor walker. I bet the procedure set up before the plug came out was just fine. But someone ignored it. I mean how many 737-900er’s were built…

      • My understanding is the “lifting springs” are designed to eject the emergency exit door (EED) that is sometimes installed to fill that hole in the fuselage. In fact, there wouldn’t be a hole there except that in the sardine can seating configuration an extra exit (one on each side) is needed to meet the evacuation requirements (Like everybody out through half the doors in 90 seconds.. Something like that). So the springs are designed to eject the EED out of the way WHEN IT IS A DOOR THAT IS INSTALLED! My question is, When the door is not needed, and is replaced with a lighter, less complicated, more permanent, door plug panel (DPP), why are the springs still used? The DPP never needs to be ejected. The emergency exit door does. Either one can fill the hole. If the EED is specified there is a lot of other stuff that goes with it: 1) It has a big lever on the inside that retracts pins (in the place of the bolts) allowing the EED to eject. 2) There are electric locks that are engaged in flight to keep the lever from moving/the pins in place. The door can’t be opened in flight because the locks are locked at takeoff. 3) There are sensors to light an indicator in the cockpit if the EED and the pins are not fully seated in position. These are separate from the depressurization warnings reported by Alaska Airlines. 4) There is an escape slide that goes with the EED. So an EED is heavy and expensive. If the customer doesn’t need it (for the sardine can seating configuration) they sure don’t want it. They want a semi-permanent DPP.
        On this particular plane the DPP was unsealed to allow access to repair faulty rivets. Again, my understanding, is unsealing the DPP wasn’t counted as opening the DPP and the reverse operation orders to re-seal it weren’t generated. Somebody was just expected to do it. Well it seems that (I get a bit snarky here) Mr. Somebody was laid off a while back and wasn’t there…
        The questions I still haven’t found answers for are: Why include the “ejector springs” in the DPP option? Why not semi-permanently bolt the DPP in place? and… It seems the closure panel (either the DPP or the EED) is unsealed for paint and livery on the outside of the plane. If true for EVERY PLANE, would that be the final, certifiable, inspected sealing of the closure panel ON EVERY PLANE?
        (Note this the conglomeration of answers from a lot of contributors here. If I got something wrong PLEASE offer a correction.)

        • Its not an exit wing type, its a door type .

          Full type door so that you can put a slide and people jump out per the front and rear doors.

          You can’t do that with exit plugs over wings so its a different system.

    • My understanding is that the lifting springs EJECT an emergency exit door (EED) when it is optioned to fill the hole. I have the same question: Why not option the springs ONLY when the EED is optioned? Don’t include springs under the door plug panel (DPP).
      I think (Hey, anybody actually know?) the DPP is semi-permanent. But it is sometimes replaced with an actual EED (and all the trimmings) should a plane’s owner decide to change to the sardine can seating configuration requiring the added exits. But it (the DPP) may actually be unsealed for inspection as often as the EED is. (Anybody actually know?)

      And I agree with your second recommendation wholeheartedly. Twelve huge zip-ties?

      My understanding is that the bolts (for the DPP) are replaced with a complex configuration of pins linked to the operating lever on the inside of the EED. Operate the lever and it pulls all 4 pins simultaneously. Bump EED outward and it goes flying, clearing the way for passengers to exit down the attached slide.

      • The springs are, by design, not strong enough to “eject the door”, they simply make it easier for a human to operate the door by effectively reducing the lifting effort.

      • Mike.
        The mid cabin exit door ia not ejected from the aircraft when deployed. It remains anchored to the airplane and pivots on the lower pins allowing the door to move up, rotate out and basically rotate 180 degrees anchoring the door slide pack to the fuselage as the slide pack deploys from the interior door bolster. Actuating the door retracts the upper door pins allowing these actions to occur. Im not sure why you think the door
        leaves the aircraft, but it doesnt…..

        • It was a piece in The Seattle Times that indicated the door plug was ejected. Hope this isn’t paywalled.

          Someone else also mentioned that the design of the exit door system called for it to be “ejected out of the way” of the slide and passengers exiting the aircraft. Still, hanging on below the opening would qualify as “out of the way”.

          I would though, find it easy to accept that the article gives an incorrect impression of actual deployment. And that those following the news would thus be misled.

          Can you tell me the sizes of the ID of lower door bushings and the OD of the washers atop the spring plungers? (i.e. do the washers retain the closure panel to the airframe when unsealed at inspection? Or do the washers need to be removed to actually separate the closure panel from the aircraft?

          It was someone who had some obvious Boeing knowledge who indicated FOUR pins are retracted when the exit DOOR lever is operated, but maybe I just read that into what was written.

          Many thanks to any and all with actual knowledge of the system!!!

          • Mike.
            The Edoor has 4 pins. When you pull the deployment lever, the decompression panel opens, the pins retract, the lift springs move the door up, the door falls out of the door opening and is held to the fuselage by 2 lower hinges. As the door approaches the lower limit of its opening travel, The slide deploys out of the door bolster and the passengers un-ass the airplane. Oh yes, in the attached video of a door deployment, if you watch it carefully, around 20 seconds, you will see the lift springs move the door up in the door opening. This is the action where you seem to be having the “ejecting” misconception.


  24. Here’s another thing
    Apparently it’s extremely expensive to convert the door plug arrangement into an emergency exit, if it’s likely to happen a deactivated door is recommended. So why not just keep the necessary structure and rivet the thing in place?It would save weight ,cost and complexity at the expense of a bit more work in the event of the hole ever being needed

    • Can you explain exactly what a “Deactivated door” is? It sounds like it’s a door that closes and seals but has no solenoid locks for the retractable pins and no sensors for a “door ajar” situation. And this deactivated door could be LEGALLY added when sardine can seating is retrofitted by an owner?? Good lord. Who recommends this?

  25. Thank You!
    Great reference that! A problem I’ve had with him/it is the description of the roller pins “going up into the guides”… Wait a sec! The roller guides (on the closure panels) get pushed down over the (stationary on the door frame) roller pins, don’t they? So as good as the guy and his channel are there is a bit of confusion there.
    Many of my questions have been answered but here’s one that endures: When sealing either closure (engaging the roller tracks on to the roller pins and compressing the lift springs) the closure goes through a single degree-of-freedom motion (It goes in and down along a unique, specific path determined by linear motion of the mounts at the bottom and the track of the guides over the rollers at the top). Here’s the key question: What determines the stop (end) position at full engagement? The tracks appear to “bottom” on the rollers, yes, but it appears the design (or at least this specific plane/plug combination) has some sort of equilibrium configuration when “closed” that allows it to sit stationary, with springs compressed, but without any bolts keeping it at the “closed” end of its travel. (It’s analogous to two foot-long pieces of 2 x 4 set end-to-end being used as a jack stand under a car. Don’t tap them at the midpoint.)
    Unless there’s still a gap in my understanding, I’d call this equilibrium point a design flaw. It allows the closure to appear secure when it is only critically balanced (like the car on the 2 x 4s). The corresponding design challenge is how to keep the shear forces across the pins (door) or bolts (plug) low enough for them to be pulled out with reasonable force.
    The system can be left “messy” without being unsafe IF $UFFICIENT VERIFICATION $TEP$ are included in the assembly process…

  26. You really need to watch the door videos on 727 technical channel. So many things u worry about are based on your misunderstanding of the system…..go study the tapes and then we can have a chat on reality items

    • > You really need to watch the door videos on 727 technical channel. So many things u worry about are based on your misunderstanding of the system..<

      727, eh? Are you the same commenter who claimed here that "MCAS was not hidden!", BTW?

      • Get on point and quit being a useless [Edited] stirrer. This isnt am MCAS discuussion so I wont take my time to show you how to pull your head out…

        Oh yeah my typo was in a constructive çomment showing him where to find answers. [Edited as violation of Reader Comment Rules]

        • So- your facts are consistently, demonstrably wrong, like in previously claiming “MCAS was not hidden!”, and now in “you really need to watch the door videos in the 727 [sic] technical channel.”

          Try to get your facts in order *once in a while* before posting, friend.

        • Some people think a typo negates the knowledge displayed.

          Its a sad thing.

  27. Come on boys, we’re trying to share correct information and at the same time suppress incorrect information (which I have unfortunately added to myself).
    Neither closure panel normally ejects from the aircraft. I finally have that straight. This particular door plug panel was torn off by 400-500 mph air rushing past the plane. Both panels are intended to remain attached at the lower hinge fitting posts until the double nuts and washers are removed from the tops of the posts.
    The 737 Technical Channel includes the error of indicating (diagrams and voice-over) that the roller pin is pushed up into the roller pin guide. In fact the roller pin guide (on the closure panels) is slid down over the roller pin (on the door frame). This may seem a small point until you are somebody who never handled one of these plugs and are trying to visualize the guts from a point of view on the tarmac.
    I still have some very specific questions that aren’t being answered (and the argument doesn’t help):
    1) About the lift springs: Do they lift the weight of the door without additional force being applied?
    2) About the upward path of the closure panels: Is there a small equilibrium spot at the “closed” end of the travel where the closures sit on compressed springs until they are “bumped” outward?
    3) About closure panel sealing: Are all closure panels un-sealed for paint and livery (P&L)?
    4) About the order-of-operations: Is P&L is ALWAYS completed before interior trim installation, and closure panel sealing, is completed? (Consider it is possible to un-seal and re-seal an exit door with its trim in place but impossible to un-seal a door plug with its trim in place…)
    5) Maintenance checks: Does a heavy inspection (D Check?) which I assume involves operating the exit door involve unsealing a door plug (if so configured)?

    I could probably come up with a couple more (Like does anyone have a horizontal cross section through a closure panel, the seal, the door frame/fuselage, and two sets of stop pins/pads?) but I’m tired.

    • Mike,
      I’m with you 100% on your questions #1 & #2. The first 737 tech channel video on this incident came out just a few days after it happened. If you read through the comments many there were pointing out things that didn’t make sense, myself included. The experts initially rejected those suggestions by quoting from the Boeing manual that says to push down on the plug to open it. Eventually even the experts realized something was backwards and admitted the manual was wrong. The plug moves UP to open. 737 Tech did an updated video, noting the incorrect manual, also better pics & animations, that cleared up that mystery.

      There was some agreement that the manual, as written, was actually suggesting a small downward push was needed to relieve the lift spring shear force on the lower lock bolts to allow for their easy removal before the plug opens upward. I think the answer to your 2 questions is right there. There IS considerable spring pressure against the plug that gets restrained by the lock bolts. There is no “equilibrium” point I think. There is a closeup photo in those videos of an intact lower hinge assembly, with lock bolt removed, that shows the spring pushing the green part to the very top of slide where it gets restrained by the nut & washer. That photo offers no context so maybe it’s taken when the plug is opened to a horizontal , or beyond, position? If so, the 63 pound plug is weightless in that position. In any case, your question #1 needs answering!

      737 Tech & Blancolirio both have videos in response to the recent NTSB preliminary report, that says the bolts were never there. As proof, NTSB shows a Boeing photo taken in September during the rivet rework next to door. The photo (figure 16) shows the plug in closed position with no bolts holding it there. So that makes a case that the lift springs are being held down by the weight of plug only. HOWEVER, Again the youtube keyboard engineers looking close at that picture pointed out a zip tie around one of the stop fittings, possibly holding the plug down in closed position against the upward pressure of the lift springs? I’m sure NTSB is looking at that zip tie now, but there was no mention of it in their report.

      Many have asked, myself included,- how did the plane fly for 2 months with a loose plug? The stealth 66 guy a few comments up insists, several times, that the springs are held down by the weight of the plug, but he offers no credentials or evidence. He says just “blind luck” the plug blew out when it did. Others are suggesting the zip tie finally broke, the springs pushed the plug up, and away it went! Without knowing the strength of those springs I guess either scenario is possible.

      I think it’s interesting that none of the aviation experts making the videos will reply to comments, or offer any opinions, on what that zip tie in figure 16 is doing there. I guess we wait 2 years for the NTSB to figure it out?

      • No, the springs are simply there to neutralize the weight of the exit blank.

        You can argue all day long if it should be there or not, but its been there for a long time and it works perfectly fine.

        There are bolts that hold the wings on as well.

        Getting into nit noid details does nothing unless you want to be an aircraft mechanic working on Exit Blanks and then its all answered in your training.

        • Trans.
          Please look at thw -900 deployment video. Clearly the spring pushes the Edoor up about 3 inches in the deployment sequence, a fine point yes but it matters in the accident sequence.
          The FAA reporting I believe shows a tie wrap used to hold the door down. This means the plug door had a lift force far in excess of a balance force by 150 pounds. So àbsent the bolts, when the tie wraps failed, the door exited the airplane.

        • I can’t help myself! I’ll go out on a limb again.
          I bet a nickel that the two thin lock nuts tightened against each other at the top of the spring posts are so a door fitter can adjust the fully-lifted-by-the-springs position of either closure so the opening shelf of its guide tracks line up with the rollers on the frame. And I bet another nickel there’s a spec for the clearance between the roller pin and the guide track shelf.
          (It would be virtually impossible to hit both targets, on both edges of the closure, by just building every component in the stack precisely. And if you tried, you would find it extremely costly.)
          If the above assertions are true, then I’d further assert that the springs do push the (somebody said) 63 pound closure up till it touches both washers, and does so even in the full vertical position. It also would not surprise me at all if the entrance ramps of the roller track fittings are not straight/flat but short arcs, with a large radius matching their distance from the hinge pivot points…
          So I am imagining taking a brand new closure assembly, which includes the springs and hinges, and bolting it into its brackets at the bottom of the door opening. The hinges have holes while the brackets are slotted allowing the pivot bolts to move about a half-inch inboard/outboard. I’ll pivot it up towards its installed position and suspend it with the straps. It is not clear if the “serrated brackets” are tight or loose at this time.
          1) Pull the closure to the plane
          2) Adjust the spring post locknuts to set the guide track clearances to the pins. Lock the nuts.
          3) Bump the hinge brackets forward and aft to fit the door skin into the fuselage skin. Measure the skin gaps (gap spec?) outside. Tighten (torque spec?) the brackets to the floor.
          4) With the guide tracks engaging the rollers, lever the closure down against the springs until a bolt can be fitted through one of the guide tracks below the roller (Another nickel says there’s a prybar tool for this at AeroSystems). Check that a bolt fits through at the other 3 bolt locations. Go outside and check gaps and flush around the panel.
          5) Adjust the clearance at each of the stop pins/pads. A match book will probably do (Just kidding!) and wire in place.

          At this point it might be a good idea to call it done for shipping. One bolt or pin (perhaps with a flag on it) will be sufficient to hold the panel for shipping. The final sealing of the panel will take place after Paint & Livery where EVERY panel will be recorded as unsealed (one bolt) and resealed (4 bolts). Any check or inspection before that is virtually meaningless expense.

          That’s my guess. Anybody from AeroSystems?

          • Mike.
            I cant help but remind us that we are talking about out of sequence work and the use or non use, of a removal process. This sort of makes all the previous work sequencing somewhat irrelavent.

            Your thoughts about paint timing depende on who the customer is, and where the topcoat color and graphics planning happens. Leasing companys are notorious for shuffling their deliverys among their customers very late in the build sequence. This means that the door jambs topcoated early in the sequence in wichita may be the wrong color by the time the airplane gets to everett and a lot of out of sequence happens. You may consider the fact that Boeing does not operate an assembly line in the common understanding. They build unit
            Production with a lot count of 1, exceptionally fast. You can order it any way you want. Any length, any avionics, any interior, any lav locations. No 2 consequitive airplanes are the same. Becauze oc tbis you might think your questions a bit

          • Mike,
            The more I think about those double lock nuts on the spring posts the more sense your idea makes. “Stackup of tolerances” is a very real engineering problem and a common solution is often something like “if you can’t make it exact-make it adjustable”. Double nuts to fix or limit travel or location is such a commonly known solution it appears on horse drawn implements 100+ years ago. When you see double nuts like that they are serving an adjustable function, and in this case as you say, they adjust the side to side clearance at the top the door and of course the door has to be pushed to it’s upper travel limit for them to have that function.

            The only good pic I’ve seen of an intact lower hinge assembly with lock bolt removed shows the spring pushing the sliding part up against the washer, but the photo gives no hint on orientation. It’s possible it was taken with door in the fully open / horizontal position? If so, it’s meaningless.

            Many keep saying those springs are only there as a cushion to take the weight of door when in the closed position. Everything I can see suggests the overall open / close function works better with springs that lift it to the upper limits, which is set with those double lock nuts.

            Since the first of the popular Youtube videos explaining the door/plug opening & closing function there were quotes from Boeing manuals on the procedure. I find it curious there are no updates.

        • “No, the springs are simply there to neutralize the weight of the exit blank.”

          Did Boeing ever shave weight from the exit blank?
          ( that actually is a “funny” : here a combined traffic railway Bascule bridgeb was fitted with heavy iron girders so that nobody could hide behind structure of the movable part. this ruined the hydraulic cylinders because nobody thought about compensating on the counter weight for the added mass.)

    • “The [737MAX™] airplane is by far the most scrutinized airplane in the world, in the history of aviation. It’s the safest airplane that can be out there today,” said Dave Schulte, Boeing’s commercial marketing managing director for Asia-Pacific.


  28. How about reverting to good design practice, instead of relenting to airline demands to not use a regular exit door in that location just so they can include another row of seats. If Boeing had said ‘no, you not getting that; any door we give you will be fail-safe and sealed by pressure, similar to the 1A boarding door’, this mess would not have come about.
    Please, Boeing shareholders, put engineers back running the company and put the accountants where they belong.

    • John.
      You dont stay in business long trying to sell a 60 million dollar vehicle without giving the customer exactly what they want. Alaska wanted the long fuselage, 179 passenger capacity and that meant the Edoor was not needed to meet the exit door requirements. The economics of flying with 300 extra pounds of weight each flight is literally hundreds of thousands of dollars over the life of the vehicle.

      • Scott- How exact is your 300 pound difference between the E-door package and the Door plug package? Is that per side or both sides? Also can you confirm the weight of either (or both!) the E-door or Door plug as they rest on the lift springs? Somebody mentioned 63 pounds but it was not clear which they were referring to.

        • Mike
          Its its very conservative on a per shipset basis as it doesnt include the slidepack, just the door delta itself. The slidepack exists within a different program item number in a different branch of the drawing tree

          • Thanks again! Would it be reasonable to guess that an emergency exit door would weigh at least 150 pounds more than a door plug? I’ll take your best guess.
            Now here’s one for you: Are the lift springs under the two different closures the same part? In another post I bet a nickel that the springs hold either panel all the way up tight against the washers, where the panel is adjusted (I noticed those two skinny lock nuts) to mate roller guides with roller pins. I am wondering if lighter springs go with the door plug and heavier ones with the heavier emergency exit door (+slidepack, unless it is removed when un-sealing the EED). I’m considering it might be tough to compress exit door springs with only the weight of a door plug helping. One solution would be weaker springs for the plug.
            I’m also curios as to where you had to spend time to attain this level of knowledge. (I’m retired from 25 years of supporting closure panel design AND ASSEMBLY PROCESS for 2 of the big 3 and a major truck maker. That plus a year in aircraft interiors- hence the detailed questions)

      • Well, the decision Boeing made re: this door design was one step on the road to stop being in business. There has to be some kind of restraint placed on customers who make accountancy-driven demands and Boeing engineers, being the experts, must be that. I sense there’s a subtle pressure within the company that devalues conservative design in favour of increased risk, which I suspect is the result of poor leadership.

    • To what has already been said I’d add it was not a failure of product engineering /design. It was a failure of process.

      • Mike, I agree; I have no doubt the plug was designed well and up to expectations. The fatal flaw was deciding to use it in the first place – a process failure, possibly rooted in the marketing/sales activities. This examination of events we are all commenting upon needs to get out of the weeds (i.e. hinge design, bolt placement etc) and revert to the primary causal processes.

        • John- I disagree. The door plug, installed using the process that was developed for the installation, is every bit as safe, or even safer than the door. It’s when they screw around, unseal and reseal it, and don’t keep track of who did what when that the problems arise. Still a Boeing problem, but it’s the process that needs discipline, not the plug that needs changes.

  29. John.
    You dont recognise good design. The door jamb is basic and stable construction for all fuselages of this length. It was carryover structure from the -900. The door is variable structure, you either install a plug or an exit door. Plugs are only removable on the ground, depressurized, after removal of the row of seats, the cabin sifewall and the 4 locking bolts. It does not rely on pressire to hold it in place, the stop pas function works irrespective of that.
    Thè exit door mounts to an identical door jamb basic steucture, adds the rerractable.lock pins, solenoids, sensors and other variable structire as well as the Edoor. The Edoor does not rely on pressurization for retention, it relys on the identical stop pads that function irrespective of cabin altitude. It only moves in an unpressurized state and has a decompression panel to make it so.

    Your suggestion that this is some.form of schlock engineering flys in the face of reality where Boeing builds what the customer requests.

    Remember, Boeing isnt operating an assembly line per se, they are assembking exceprionally variable products in lot quantitys of 1, really fast. The change on change impacts of all the customer differences one line number to the next are staggering, and not considered by most of those not shuffling the build sequences

    • I just don’t like the idea that internal pressure can blow a door off. It isn’t fail-safe. In the Alaska case, the holes in the Swiss cheese lined up.

Leave a Reply

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