Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

In this Discussion

Here's a statement of the obvious: The opinions expressed here are those of the participants, not those of the Mutual Fund Observer. We cannot vouch for the accuracy or appropriateness of any of it, though we do encourage civility and good humor.

    Support MFO

  • Donate through PayPal

Boeing 737 Max 9: A closer look at the much-discussed "missing bolts" -

edited January 10 in Off-Topic
1/8: From PBS: Diagram of Boeing "Door Plug" and associated hardware fittings


1/9: From The New York Times: Partial Diagram of Boeing "Door Plug" and associated hardware fittings


Note that the NY Times diagram identifies two fittings as "Location of Upper Bolts". However, on the earlier PBS diagram that same hardware is described as "Upper Guide Roller, (2 locations). Neither diagram is detailed enough to clarify this contradiction. One possible explanation is that there may be bolts, not shown, which are used to fasten the upper guide rollers. That, however, is only speculation on my part.

Now let's take a look at this interesting graphic- I found it on the internet, but without any easily traceable source other than a few words in a foreign language:


3:30 Pm PST:
New Information: From The Wall Street Journal, here's a good diagram of the so-called "bolt" assembly:



  • @Old_Joe Interesting, very interesting !!
  • edited January 10
    OK, finally this morning's Wall Street Journal (print edition) had a decent diagram and explanation regarding the so-called "bolts" that lock the door plug into position. But I can't find that anywhere in the WSJ on-line version, so I can't reproduce it here.

    EDIT: I finally found the WSJ diagram- see above for latest info.

    BUT... Take a look at the pic right above this post- two areas are circled in red. Disregard those, and focus right above the top of the lower red circle. There we can see a sort of round dark piece of hardware, and if we look very closely there also appears something short and dark extending over to the left from the round piece.

    OK, finally! That dark round piece is the actual retaining "bolt" for the door plug. The small extension over to the left is a cotter pin (or something similar) which is placed through the "bolt" to insure that it cannot move. Those bolt assemblies, one at each side of the top of the door plug, are all that keeps that door plug from coming loose due to vibration and shaking from landings and so forth.

    I say "all that keeps", but that is not a criticism of the design: that type of locking setup will be perfectly adequate and strong enoung to keep the door plug firmly in place. IF... IF the bolt and its very important locking pin are in fact correctly installed.

    A VERY important "IF".

  • Hey, @Old_Joe.
    I cannot see any cotter pin. I do see a spot where a tiny sliver of a silver-colored piece is visible. Might that indicate that the attached piece was not tightly snug? In other words, should we be seeing that tiny silver-colored sliver of a thing?
  • Yes, it's sort of a dark silver colored piece- very short. The actual bolt has a small hole drilled through the end, and the locking (cotter?) pin is then pushed through that hole and typically bent a little to prevent it's sliding out again. It's shown as correctly installed in that picture, which as I mentioned is of unknown origin. The diagram of the bolt and pin in the WSJ was much clearer.
  • edited January 10
    I finally found the Wall Street Journal graphic-


    @Derf, @hank, @Crash
  • edited January 10
    I’ve always been amazed at the important roles cotter-pins play in the assembly of all types of heavy equipment. On my ‘05 Silverado one holds the heavy duty trailer hitch in place. If you haven’t seen one, they’re somewhat stronger and more rigid than a big paper clip. While they bear little weight themselves, their importance cannot be minimized.

    A Little Neglect May Breed Great Mischief!

    “For want of a nail, the shoe was lost.
    For want of a shoe, the horse was lost.
    For want of a horse, the rider was lost.
    For want of a rider, the battle was lost.
    For want of a battle, the kingdom was lost,

    And all for the want of a horseshoe nail.”

    (Ancient proverb revised / published by Ben Franklin in Poor Richard’s Almanac. )

    Yikes @Old_Joe / What an impressive animated diagram! Thanks for all the heavy lifting here!
  • Well yes... perhaps the most impressive part is how they get the "bolt" through the hole since the bolt "head" is bigger than the bolt hole. (Picky, picky... it really is a decent graphic.)
  • @Old_Joe, thank you for the detailed diagrams and explanations. Cotter-pins I am familiar with on Honda and Toyota cars are self-locking that prevent sliding out from vibration. It takes some effort to open the pin, slides over several notches before the pin comes off. Surprise that there is not more failure redundancy build-in in door design.
  • @Sven- Hello therre- I am using the term "cotter pin" very loosely, as many people are familiar with that term. The actual bolt/pin setup on the 737 appears to be a part designed specifically for that application.
  • Possibly a roll pin is pictured ? At least as that picture shows. Maybe the wrong size pin was used ? From my limited experience with roll pins they need to be physically beaten out. Who supplied the roll pins ? I'm guessing they have more than one grade.
  • A perfect setup for Colbert:
  • @Derf - Doesn't look like a roll pin to me- looks like the so-called "bolt" is simply a short piece of round bar stock with a head which is a larger diameter than the bar itself. The bar stock would have a small hole drilled through it near the end, allowing the insertion of a pin-type lock.

    From the WSJ diagram the "pin-type lock" in this case appears to be a specially machined large "washer" with a pin that is inserted through it and the bar.

    From that diagram it would seem that the bar stock bolt would be pushed through the "guide track" from the rear, and then be fastened in place by pushing the large "washer" over the bolt end, aligning it's hole with the hole in the bolt, and then inserting some sort of locking pin.

    As @hank points out, that locking pin itself does not have to be very big, although if it were made of substandard metal I suppose that it might shear if enough force was applied by the door plug. Kind of like a shear pin on outboard motor propellers which are made of soft brass and are designed to shear if the prop hits a rock or some such.
  • edited January 11
    AndyJ said:

    A perfect setup for Colbert

    Yes. I was thinking that since there were no casualties the comics would have a field-day. Thanks for the link. Cobert’s acting ability shines through here. And a poignant look at U.S. political scene. Maybe bury this one in a time-capsule for future generations?
  • That Colbert clip was just great.
  • Loved it!
  • @Old_Joe The updated photo doesn't show the print that was include with WSJ photo on page A2 Wed. This told how the door was installed. I hope this is of some help. If you have posted photo with verbal explanation , I haven't found it.
    Ta Ta, Derf
  • Chris easy has great new report on
    737 Technical Aspects of AS1282 FAQs Video

  • So my son was scheduled to fly back from Maui to California yesterday on Max 9. Really cheap fare early Jan - $275 RT. Alaska switched plane to 737-900 and kept same flight. When I went to check status on Google I see a diverted message on Flight Aware. It said plane landed in Honolulu. My son said some technical issue and they just parked near gate and did some checks, refueled and took after after an hour. Flight was only 1.5 late, so all good. Now I can quote from comment on one video-
    BYOB- bring your own bolts.
    BYOW- bring your wrench.
  • edited January 11
    +1 Glad it worked out. Great news.

    On a recent flight a few days ago United “unfueled” our plane. Had been fueled for a longer flight when they swapped it for our shorter flight. So we waited onboard while they took fuel off. Aside from economy issues (more fuel onboard adds to weight & fuel burn) sometimes having too much onboard leaves the plane above the safe limit for landing (depending on the airport)

    I’ll say United was working very hard to resolve issues, but had just been slapped with the grounding of their Max 9 fleet hours earlier. They are one of the largest users of that craft. Under the circumstances i thought they did an admirable job.
  • Hank,

    We were both fortunate. Saw a report where someone was trying to rebook cancelled flight on Alaska and message said hold time was 7 overs. My son was on hold for 1.5 hrs and I think it just disconnected. Luckily they just changed aircraft and kept same departure time.
  • Some years ago we were all boarded on United and ready to leave Frankfurt for Sf. The pilots noticed that a small piece of metal on the wing appeared to be loose, and we all sat there while the local United mechanical guys did their best to temporarily patch it.

    After the repair pictures of the repaired section were internetted to United at SFO, who didn't like what they saw and turned thumbs down. United off-loaded us, bussed us to a really nice hotel room, dinner, and breakfast, which featured the very best bacon that I've ever had anywhere, before of since. The bacon highlight of my life.

    No complaints about our treatment whatsoever. They can do it when they want to.
  • edited January 12
    An unrelated horror story:
    Asiana. Competitor to Korean Air. Flight outbound on Christmas Day, 2018. JFK to ICN and onward to CEB. Not a hitch.

    Return? Not so much. Plane at last showed up, after waiting at the gate for 3.5 hours. Middle of the night. We boarded. Sat for 1.5 hours. NO communication. ZERO. ZILCH. Finally we were told somehow (or found out through the grapevine) there was a hydraulic leak. Un-fixable, after all. Flight canceled. By now, it's almost time for breakfast, the next day. Screaming babies with parents. I finally took the liberty to address one of the stewardesses: "How about you do a little THINKING, and take the families with small kids and put them at the front of the line?" (Because we all had to be officially re-admitted to the Philippines, by then. We'd all passed through Security already, to get to the Gate.)

    She took my suggestion. There was already a big event going on, so hotel rooms for us were hard to find. Four hours later, we were offered breakfast. Or was it lunch? Terrible food. I skipped it. Then back at the airport.

    A 10:00 p.m. departure the previous night finally took-off the next AFTERNOON. Staff was utterly untrained about what to do, and communication was non-existent. When we reached ICN, we were diverted to a Korean Airlines flight, back to JFK. Others were rerouted via Singapore Air, and a couple of others. Suck-holes. Asiana? Never again.
  • @Equalizer - I almost overlooked complimenting you on BYOB / Bring Your Own Bolts. My wife and I could hardly stop laughing at that one. At dinner last night for some reason it replayed in my mind and I started laughing all over again. The wife says "what are you laughing about?" I say "Bolts" and she starts laughing again too.

    Well done sir.
  • edited January 13
    Just a blurb from today’s FT. Gotta feel for United under the circumstances. What a mess.

    United Airlines, which flies more Max 9s than any carrier, said on Friday it was cancelling flights on the plane through to Tuesday, giving it more time to manoeuvre as it braced for winter storms across much of the US. "By cancelling this far in advance, we're trying to create more certainty for our customers and more flexibility for our frontline teams to do their work," the airline said.
  • Smart move. Rather than have hoards of passengers upset by last minute cancellations they give customers time to make alternate arrangements if possible and then gradually revise the UAL schedules as things get sorted out.
  • truth.
Sign In or Register to comment.