Back to Squawk list
  • 53

How the Max 9 door plugs are secured

Nice video presentation on how the door plugs at Alaskan Max 9 row 26 are supposed to be kept closed by 4 bolts. The links skips to a that part of a longer presentation. ( More...

Sort type: [Top] [Newest]

Richard Sucher 18
Seems like there is a very limited number of potential failure modes for NTSB to consider. Not an overly complex mechanism.
Russell Thornton 10
Hearing more on other airlines finding loose plugs etc. Maybe require new design. Big headache.
rob strong 6
US carriers still have MAX9s in the lineup, all week. Wonder what they're doing. Southwest spared big time using 8s and an order for 7s.
Marty Martino 5
Max 8’s only. Max 7 still not certified and, likely, won’t be getting certification anytime soon.
mbrews 5
Disagree. Still an open question of WHY the pressure controller failure lights came on. And open question of just how high the cabin differential pressure reached BEFORE the door plug let loose

Meaning - wait until readout of flight data recorders. If cabin pressure spiked wildly high, there could have been an extreme driving force to blow out the plug door.
Billy Koskie 5
There were actually 3 pressure controller failure write-ups on the aircraft since being put in service late October. Alaska must have assumed the controllers were the problem rather than a pressure leak - such as the door plug.
rebomar 9
The door has to be "raised" about 1 1/2 inches to clear the 12 plates that normally hold it against the cabin pressure. The springs on the hinges at the bottom of the door help raise the door when it is opened for maintenance. It is prevented from raising with 4 bolts. My take is these bolts were missing. AAR worked on the aircraft to add Wi-Fi. The 3 pressurization problems started after they worked on the aircraft. When I have a problem I go back to the last thing I did.
Ah. I was thinking that the upper guides were on the fuselage and the pins were on the door, but it's actually the reverse. So that makes it a little more understable that it could take a while for the door to work its way *upward* until clearing the pins and stop fittings.
Peter Fuller 14
The same-size airplane from the 737NG generation, the 737-900, appears to have an exit door or a door plug in the same location as the 737-9MAX. Does the MAX use the same design as the NG, or a new design? Either way poor MAX fuselage manufacturing process and quality control at Spirit AeroSystems seems likely, as does inspection quality at Boeing when they receive the fuselages.
I’m curious why the NG aircraft with door plugs are not also being inspected.
Larry Toler 6
I was wondering the same. The only reason I can think of at the time of manufacture there were different people in the QC process and they checked out okay. They've already been through C checks, so any issues were probably caught and fixed. The reason this is a big deal is because it's the MAX.
Billy Koskie 2
I don't think any 737 NG aircraft have door plugs. They don't have the passenger volume/density to require the 2 additional emergency exit doors whereas the Max 9 can be configured with a high enough density to require them. The door plugs are for aircraft that do not have the high density passenger configuration requiring 10 total emergency exits.
Kerry Moore 2
The -900ERs delivered to Lion Air have the doors activated. The 900ERs have the plug. Read TCDS A16WE.
David Johnson 5
A very good video, thanks. One question I have is that even if all four bolts were missing, what force was exerted on the door to overcome the springs in the bottom hinge?
avionik99 9
After watching that video, unless the mounts tore off (which does not appear to have happened) the only other way possible it seems is if they never bolted the door at all. It was put in place then the guy went to lunch and some interior person installed the inner paneling over it. An incorrect installation would have been far too obvious from a simple outside visual inspection. The official report will be interesting for sure.
Steve Pearce 7
Why is this piece of the jigsaw puzzle called a plug? A plug would normally be wider than the aperture and go on the high pressure side, such that when pressurised it cannot - physically - move outwards. I.e. like the actual aircraft doors.

Or think of a sink, you put a plug wider than the outlet so that water cannot flow - if its narrower than the outlet it would just get sucked down (at the point that pressure above gets high enough to force it).

Maybe 'plug' is just used to say that it fills the gap - but all this really appears to be is a sticking plaster on the outside that is only stopped moving by the presence (or in this case seemingly the lack) of sufficiently tight bolts to hold it back.
Bill Conn 0
Why is THAT DOOR, so important that it cannot be removed from the body's construction? Obviously it's a, "just in case door for a specific customer", thus the" plug"! I mean really, a" plug", in a fuselage!!! That's just insanity!!!
SkyAware123 3
When the customer decides to use higher density setup, the extra emergency exit door can be easily added. Why is this so hard to understand by people ?
wingbolt 2
Maybe a better plan would have been to make it a little harder to retrofit and no so easy for it come open. That is the part that is hard for people to understand.
SkyAware123 2
Well, you asked the question.
As far as easy to come open.... That's boeing quality for you..........
wingbolt 1
There is no doubt Boeing screwed up. But to make it so easy to retrofit for the very few customers that would retrofit after delivery is the part that has so many people confused. It should have been riveted in for the standard configuration with designed easy access for the customers that want to jam more people in later.

Truth be known this is taking the 737 beyond its original intent. It’s time for a clean sheet design.
Samuel Bixler 2
If I understand correctly, it is not a question of retrofitting after delivery-- the fuselages are ordered from Spirit with either plugs or emergency exits, depending on the customer's intended seating density. I assume, though, that retrofits would be possible in the secondary market, but it's a bit early in the type's lifespan to be seeing that yet.
SkyAware123 1
I don't see how this has anything to do with 'beyond intent' Any replacement this size , even clean sheet, will still need an emergency exit in high density setup and a plug in lower density. They'd probably use the same plug.
rob strong 12
gotta love that they recorded over the cockpit voice recorder. "In the chaos" noone thought to grab the data so it was overwritten. Nice.
Roger Harding 4
2 hours recording seems ridiculously short. These days digital recordings can be made that last forever all on a micro usb stick. I would have thought 12 hours minimum should be the standard or the maximum duration of a flight.
Our tax dollars at work, pure and simple.
Who does not think, that in ANY crash, grabbing that "Black Box" should be the first thing they would do.
Tobin Sparfeld 7
I dunno, I think the first thing they would do would be to rescue the passengers and provide medical care. Then maybe the second thing they should do would be to make sure the plane is safe for investigators to get onto the plane. So maybe grabbing the CVR would be the third thing.
My post is assuming the people are out, the fire is out, allowing entry to wherever the "boxes" are located in the aircraft.
btweston 1
So you don’t know how it works. Cool story.
Lance Neward 1
Thank you, ALPA
Steve Brown 3
Very excellent video Ichiro. Thanks.
Even if the upper and lower bolts were missing, how could the door move downward against the springs, AND against the lateral pressure (friction) of the 12 stop fittings and pads, in order to clear the upper guide fittings? Even without the locking bolts, wouldn't the force of the springs and stop fitting/pad friction keep the upper roller pins safely within the upper guide fittings? Or are the springs NOT strong enough to resist the entire weight of the door, but are there only to make opening the door easier during maintenance? In the second case, then yes, it would seem that all four bolts were somehow missing. But then why didn't the door fall out before, even when sitting on the ground? Did the door slide downward little by little over weeks (due to vibration?) until the stop fittings moved enough to the clear the stop pads? I wonder if the upper guides on the door are bent from taking the full force of the pressure differential.
mchutto 4
The plug moves upward to release. The guide pins are attached to the airframe and the guide fittings are attached to the plug. The helper springs at the bottom are not strong enough to lift the plug without additional pressure. Differential pressure between the cabin and outside air was apparently sufficient to launch the plug into the dark sky. The previous cabin pressure alarms indicate the plug had attempted to exit on earlier flights. The obvious conclusion is that the bolts were missing. Aircraft bolts are designed to resist shear pressure which is what the pressure would be in this instance. The probability that four bolts would shear is infinitesimally small.
May point to a process (Spirit) problem, i.e., plugs not installed correctly or missing and therefore quality control issue.
hal pushpak 6
According to Juan at the Blancolirio Channel, the doors are removed at Everett for seat, trim, interior config per customer. They are then reinstalled before delivery. However, when I see close-ups of the photos, it appears (to me at least) as if the bolts were never installed in the first place. There are no dents and scratches on the paint at the ears and they don't even look slightly bent from the force. Looks like it was a clean separation to me.
avionik99 3
it appears (to me at least) as if the bolts were never installed in the first place

Thats my take also.
mbrews 3
I didnt watch Juan's latest. But you said the doors are removed at Everett .. for configuration
(NOT final mounted at Spirits fuselage plant.)

Traditionally, all single aisle Boeings were built at Renton works. I have read that Boeing recently ? ADDED a 737 MAX production line at the wide-body Everett plant, in the unused 747 or 787 bay(s). Resulting with two Boeing plants that can assemble a 737 MAX

So, IMO that further adds to the concern : low-experience workforce & methods producing MAXes.

rob strong 5
Seems to me there should almost be thick metal bolts that would turn and go perpendicular against the seal so it would never be able to come undone. Especially if this is only opened for maintenance. Would be simple, pop off interior panel and turn the 6 to 8 handles to go parrallel with the seams. Again... $$$ Boeing no like.
hal pushpak 3
Yup, KI$$ instead of KISS..
mbrews 3
Most folks are overlooking the fact that this bird spent 10 days at OKC, late November to Early December. Still nothing said publicly who else worked on this a/c and what work was done ....
jeff creek 1
OK, what about all the others that have loose bolts . Did they also spend time at OKC also? Blaming Spirt is BS. Boeing is the one to insure parts are correct. Old slogan was "If its not a Boeing I am not going". It is now "If it is a Boeing, I am not going"
jmilleratp 2
How are they secured? Not well, apparently.
zuluzuluzulu 2
That was a very helpful video. Bottom line is the door is a panel and not a plug. I can pressurize my steam boilers at work, remove nuts and bolts from the man hole plugs and the boiler will remain pressurized and the plugs will be in place a year later.
David Apps 2
Airbus for me from now on
What does this mean, please? I'm not in aviation, I just like it. So I don't understand any of that, and God Forbid the media assign aviation-knowledgeable reporters to write these stories.

"The plug door is widely used for lower-density configurations that do not require an added emergency exit."

plug door - what is that?
lower-density configurations - what are those
do not require... - so some emergency exits are actually dummy emergency exits?
SkyAware123 3
lower density means less people in the plane than other configurations resulting in needed less emergency exists. As a result they plug the opening instead of having an emergency door there.
btweston 0
Holy cow. “The media” is not your mommy.
Jon Baugh 0
The most troubling part here is that the CVR was "recorded over" huh? GIANT can of worms there...
Peter Fuller 3
All crew and passengers survived and can be interviewed. The FDR was not damaged and can be read. ATC communications recordings are available. I don’t think an intact CVR recording is crucial to the investigation.

That said, in general longer-than-2-hour CVR time would be a good improvement.

The most troubling part here is that the door plug blew off!
SkyAware123 -3
Is this the final nail in the boeing coffin ? How many more screw ups/dead people do we need to see before it's clear boeing shouldn't be making planes anymore?
Frank Chaddock 1
Billy Koskie -1
Is it a coincidence that passengers were not sitting next to the door plug?
Ken Thompson 1
Of course. Those seats are extra cost and do not always get sold, though I did read one report that the pax assigned to those seats missed the flight.

Why do you ask? Itching to float another conspiracy theory?
harold smith 3
What? Window and middle seats cost extra? This wasn’t an exit row. It was configured for normal seating
John Louiso -1
I flew on a DAL 737 900 two days ago. Before boarding I saw what was definitely a plug a bit aft of the wing from the terminal.


Don't have an account? Register now (free) for customized features, flight alerts, and more!
Did you know that FlightAware flight tracking is supported by advertising?
You can help us keep FlightAware free by allowing ads from We work hard to keep our advertising relevant and unobtrusive to create a great experience. It's quick and easy to whitelist ads on FlightAware or please consider our premium accounts.