NTSB Says Bolts Likely Missing When MAX Door Plug Blew Off


An NTSB preliminary report has confirmed earlier media reports that four key bolts securing a mid emergency exit door (MED) plug on an Alaska Airlines flight last month were likely missing when the door flew off in flight over Oregon. It also suggests the plane was delivered to Alaska without the bolts. “Overall, the observed damage patterns and absence of contact damage or deformation around holes associated with the vertical movement arrestor bolts and upper guide track bolts in the upper guide fittings, hinge fittings, and recovered aft lower hinge guide fitting indicate that the four bolts that prevent upward movement of the MED plug were missing before the MED plug moved upward off the stop pads,” the report says. It also says the damage to the door plug “was consistent with the MED plug translating upward, outboard, and aft during the separation.”

Investigators also went through manufacturing records that showed the plug was removed at the Boeing factory in Renton, Washington, to allow technicians from Wichita-based Spirit Aerosystems to repair five damaged rivets in the door frame. Those four bolts had to be removed for the plug to be removed. The report also includes photos taken to accompany the repair work that showed the plug back in place but without at least three of the four bolts not in place. One of the bolt locations was obscured by insulation. The report also noted that the door plug was made by Spirit’s Malaysian factory and that the incident “adversely affected [the airplane’s] structural strength” so the damage was “substantial.”

The report says the NTSB’s search of the manufacturing records showed no evidence that the door plug was removed at any time after the rivet repair at the Renton factory. That debunks a theory that circulated for a time that a crew installing Wi-Fi equipment in the aircraft had removed the door for access to the location of their gear. The techs who install the Wi-Fi equipment showed investigators how they do it and said they never take the door plug out. More interviews are planned with workers at Spirit and Boeing as the investigation continues. The full report follows:

Russ Niles
Russ Niles is Editor-in-Chief of AVweb. He has been a pilot for 30 years and joined AVweb 22 years ago. He and his wife Marni live in southern British Columbia where they also operate a small winery.


  1. Am I the only one to wonder at the “rivet repair” part — in an airplane still being built?
    Were they put in wrong, and no-one bothered until spotted later?
    Or did something large and hard smash into the door frame and deform the rivets?
    Cars used to get all sorts of weird welds before robots took over. Maybe time for Boeing to do the same with its rivets.

  2. Where was the inspector that would normally check the work before covering up? Feds approved the model to fly again, but if work is not being inspected during the manufacturing process, what other areas are substandard?

    • As I understand it, the “rivet repair” was done in conjunction with an edge seal repair aimed at fixing a pressurization issue (aka a “leak”). Possibly (and I don’t really know) the edge seal is riveted in place rather than an adhesive being used? Who knows. Either way, two quality control programs…the one used by Spirit, the other by Boeing…had a miscommunication. The edge seal/rivet repair was done to address the leak. The bolts were not reinstalled by Spirit’s people. But Boeing’s quality control program saw the repair was finished without the smarts to know that fixing those rivets required Spirit employees to remove the door. Only that a repair was done. It’s very clear Boeing did not go back and reexamine the door for proper installation after the work order was complete. Spirit made the first error. But the responsibility was entirely Boeing’s to own. That’s on them.

      • The rivet rework was done by Spirit in Boeing’s Renton facility. This was done while the plane still being built, long before any pressurisation issues.

        The report has pre-rework photos of the rivets as well as the door seal, which is pulled away from the jamb. I couldn’t see any sign of rivet holes, but the five rivets in question do go through the jamb in close proximity to the seal.

  3. so my question is, where did the 4 bolt that were removed go?

    does having extra parts lying around not spark anyones interest? gee where were these supposed to be?

  4. If facial recognition from photographs and video is possible, then it should be possible to check bolt installations from a photograph/video of the finished assembly. Another method would be to have the actual wrench used record bolts, bolt torques and position on the assembly. In 2024, an aircraft should leave the factory with high confidence it’s fastened together.

    • The bolts used in that application do not always require a torque wrench for the installation. Generally a castelatted nut is tightened to a snugged point, then backed off to the first slot that allows the cotter pin to be installed. In some cases, over tightening can cause failures in cast fittings. Wiithout seeing the specific installation instructions for these bolts, (retaining pins) you (we) can only guess at this point. No reason to assume there is anything faulty about the finished assembly if done correctly. It’s pretty obvious that the fact they weren’t installed is evidence enough and should not require a Rube Goldberg type of analysis. Google Rube Goldberg if you need to. 🙂

  5. From what I’ve read in multiple sources, Spirit (and to some extent, Boeing) has been motivated primarily by hitting production and Wall Street targets; there’s little reward for accuracy.

    The result is a “ship now, fix later” mentality, with many Spirit employees working full-time at Boeing in Washington to fix these many expected defects.

    The door plug fiasco was further exacerbated by cost-cutting. From what I understand, “Removing” a door plug is a known, defined procedure, but “opening” a plug is not. Never mind that the work involved is almost the same, including removing and reinstalling the four bolts in question. The result is an incentive to use the ‘simpler’ and less documentation onerous (therefore quicker) “opening” procedure to gain access to the rivets.

    This may partly explain why Boeing still hasn’t provided the NTSB with documentation about the work performed on the door plug. It’s because “opening” is not as well documented as “removing“.

    PS – all the usual disclaimers apply – this is based upon internet posts, which can be as trusted or accurate as any comments… such as the ones found here on AvWeb. 🙂

  6. I guess this will end (or at least slow) the speculation that a third party removed the door plug (in order to install additional equipment) after the airplane was delivered and failed to re-install it properly.

    • (R100RS) The door had to be removed because repairs/replacement of bad rivits done at the Spirit plant prior to delivery. It was discovered by Boeing employees and those repairs were done by Spirit employees at the Boeing plant. So yes, it does end speculation as it was a Spirit issue that led to the incident. (It’s one of those chain links that leads to accidents thing)

      The question might be is how Boeing ordered the work. (I) would assume they, Boeing, would expect the work to be completed in accordance with the original specifications. Which then could safely be assumes they (Boeing) would expect the Spirit workers to replace the door when the repairs are completed.

      But in the end, it is a Boeing product and they are responsible. And at least at this time they are not denying that. The problem between the two companies is one of trust at this point. It will more than likely at some point cause Boeing to bring this work back in house. The issue with that is Boeing isn’t Spirits only customer. Spirits second biggest customer just happens to be Airbus Industries. Apparenly Spirit does better work for Airbus.

  7. I’ve just read the NTSB report, so my point of view isn’t based on internet posts. I’m not trying to make myself look like an aviation expert but it was pretty obvious right from the get go those bolts were never installed. Anybody with any airframe experience would know this.

    A point that is made in the NTSB report clearly explains the installation and type of Fastners used in this application. Drilled bolts with castle nuts secured with cotter pins. Just as I suggested on day one. This type of fastener is used in a pin configuration and not intended to be “Torqued” or tightened in any significant way. The cotter pin is the retaining mechanism. It is and has been used in many applications throughout aircraft construction.

    All of those claims of loose bolts by airline employees should have never been reported if they applied to this application. And certainly, a publication such as this should do a little research before jumping onto the hype bandwagon. It’s what one would expect to read on Facebook.

    Blaming management has become a favorite pastime in this country for any issue that arises. These bolts were left out by line mechanics and crew inspectors. Not the CEO of Boeing. These are the same folks now demanding a 40% wage increase as a reward for their shoddy workmanship. As a manager most of my life I witnessed endless suggestions to delegate authority down the line. It’s pretty apparent that in this case that wasn’t a good idea.

    Had the employees of Spirit done their job in a professional and quality manner, this plug would not have to be removed in the first place. It was removed to repair faulty work discovered by Boeing employees and repaired by Spirit employees at the Boeing plant. Again, all of this is floor level issues, not upper management. In the end, I’m sure the root cause will be the lack of an inspector not checking the installation prior to installing the side panels. It is likely because of some delay in the process such as work breaks or shift changes.

    If you want to point to a culture issue at Boeing, I can say from experience that nothing destroys the culture of an organization quicker than a union, and IAM is certainly one of the most proficient at doing so. Yes, this was a nasty experience for all involved. Does it rise to the level of destroying our largest manufacturer? In the end, it was four bolts that were not installed by somebody. Make sure it never happens again and move on.

    • How about all the airplanes flying around out there with possible similar defects? Where were the inspectors? It is a management function to make certain there are enough inspectors.

    • You are ABSOLUTELY correct! Unfortunately our “never hold anyone responsible for their actions, it’s always someone else’s fault” culture has permeated our Society. When that happens, this is where we end up.

    • “I can say from experience that nothing destroys the culture of an organization quicker than a union…”
      To JetJoe: I can say from experience that you sound just like the McDonnell Douglas trained managers I had to work with in Engineering.

    • The CEO and executives are always responsible. A leader can delegate authority, but never responsibility. They set the priorities within the company. They ought to have made sure that no airplane left the factory in a substandard condition. Instead, they fostered a culture of cutting corners and pushing out shoddy work.
      If any line workers or inspectors falsified paperwork, they should be held to account, but so should the executives in charge.

  8. When I worked at Lockheed, if we even moved a wire, we had paperwork documenting it, we stamped with our PQC stamp, then an inspector would add their stamp. We alway knew who did what. So, I have to think Boeing has something similar in place. They know who did what. Now it’s just a matter of training. Possibly firing. Nah, the union won’t allow that.
    Former IAM&AW Local 509.

    • Yep! Always training. Just who trains the trainers? Do you train the mechanic how to install a bolt? Or train an inpector to look at the bolt and document it? Do you train the mechanic who covers the area with the sidewall to give it one last look prior to doing so? That would seem like something that should already be in place but retraining might be called for.

      Its human error at the lowest level. None of us are perfect but sometimes a mental lapse can lead to nasty issues like a door flying off.

      By the way, over my working life I’ve worked both sides of the union fence. The early years as an IAM local VP and was sent to what was then referred to as the “School for Scoundrals. Later years managing IAM airline mechanics. You’re correct. The union will blame management and fight to the death to save the culprits job everytime.

  9. Pretty much exactly what everyone figured all along. All that was missing was the disclosure that that yes, the door was indeed removed & replaced after the fuselage was delivered to Boeing, and why. But hey, the constant slow dribble of facts gives us lots of time to speculate and blame this group & that.

  10. Oh yes, people should be fired on this, definitely. You can say, “It was a mistake,” “People make mistakes,” and Let’s “Move on.” No, there have to be consequences! Unions are supposed to fight for members, who have no leverage against management. But it has to be based on the facts of the case, not blind loyalty to an idea or to a membership. Where the facts show gross negligence, or egregious carelessness or rule-breaking, some or or all of these: the answer is clear – wrong-doers must face the music. Union Member and lawyer, in that order.

  11. I wonder if the NTSB will be smart enough to ask Boeing and the FAA who authorized and approved a design change to the exit door. There is a lot of mechanism missing on this door compared to -900 doors.