The door rests on the stops (on the inside) which transfer 100% of the pressurization load (from the inside out) into the fuselage. The stops look to be welded or part of the structure. There is no need to prevent movement inward because the force under pressurization is in the opposite direction! This door is apparently a 20 year old design, used on the legacy pre-MAX 737, it was not conceived by idiots.
The bolts don't carry this load at all. Their purpose is to keep the door from sliding upwards vertically up and over the stops.
The operation of the door for maintenance e.g. like opening a window for ventilation, the bolts are removed, the door is then lifted upwards with the help of springs, sliding past the stops and pops out. There looks to be a small strap to help keep it propped open.
Likely the presence of any one of the four bolts that restricts vertical movement would have prevented this, at least until it was discovered at a maintenance checkup.
It's possible the door was sitting on the stops with no bolts and enough landings happened inducing vertical loads to cause it to gradually slip out of place. Similar to how you can hold a mattress on top of your car with friction and your hand for a period of time, it just takes one gust of wind in the right direction and the rest is history.
No.
https://www.reddit.com/media?url=https%3A%2F%2Fi.redd.it%2Fq...
The drawing is from the inside of the plane. If it had been the other way around the door could have never gotten past the stops. And since it is from the inside that means that the stops themselves (which are stops, so they're not bolted into the door, just into the fuselage, the plug door is just resting against them) can't hold the door against the fuselage pressure any more than you can push on a rope. For that you need those bolts, they are the elements that provide the tensile strength counteracting the pressure in the cabin. That's also why the bolts coming loose led to pressurization warnings. If there had been no bolts the whole plug door would have come out immediately. The stops ensure that the door sits flush with the outside of the aircraft and it's the bolts that pull the plug door against the stops.
When you pull the door closed, the stops on the door are ABOVE and BEHIND the ones on the fuselage. The door then slides DOWN to lock it into place. So under pressure the tabs on the door push AGAINST the ones on the fuselage. The bolts prevent the vertical motion to unlatch the door and do not carry any pressurization load.
> they are the elements that provide the tensile strength counteracting the pressure in the cabin.
There are NO bolts here carrying tensile loads, shear loads only.
Source: https://www.youtube.com/watch?v=0jeO5fwRXLo
At 1m40s the chairwoman of the NTSB explains why you're wrong. I'll accept your retraction anytime. :)
The NTSB comment is just about the fitting guides not about the stops, and yes, they stop the door from moving upwards. There are no bolts through the stops and they do not mesh into any part of the door as far as I am aware, nor does the drawing show anything that they can slot into, it's just a bit of pressure. If it isn't the bolts providing the tension then it would have to be some other mechanism but none is apparent on the drawing. I'm sure the bolts will also stop the door from moving vertically, just as much as they stop if from moving laterally, the key bit is that if they do not engage that the door can slide up and outward and into the airstream on the side of the plane, which is a formidable force. After that it is just a matter of time before the door will escape.
The big question for me is whether all of the bolts had to come loose before the door escaped or whether it was enough for one or two of the four that were loose to come out to do start a feedback loop (door goes off a bit, more air, more vibration and so on). I also wonder if they'll be able to recover the bolts from inside the airframe or whether they've been lost.
> I'll accept your retraction anytime. :)
This is the sort of dumb comment that you may want to take elsewhere.
It is 100% possible that my reading of that construction drawing is wrong, but you haven't shown where or how it is wrong, just that the NTSB person said something that is either incompatible with the drawing or that there is a discrepancy between my understanding of the drawing and reality. If you want me to progress in my understanding you'll have to explain, not demand because nothing the NTSB officer said helps with that understanding other than to contradict, which is a good indication that I'm wrong but not how I am wrong. All she talks about is 'matching circles' but those run in a different direction than against pressure so I really don't see how that matches the drawing. It's possible the stops hook over the corresponding parts in the plug but that's not readily apparent from the drawing at all.
It's not a construction drawing, it's a cartoon showing the door in the open position and you are assuming (incorrectly) the operation of the door.
This will be my last comment on this topic because this argument is fruitless and you seem unable to see it any other way. That said:
This is a high res photo of an installed door plug:
https://nitter.privacydev.net/pic/orig/media%2FGDk50Aaa4AEsm...
You can clearly see the "stop fittings" on the door are on the INSIDE and rest on the ones connected to the airframe, preventing outward movement.
When the door opens, it slides up along those two black cylindrical things at the bottom, the stops move past the matching ones on the fuselage, and it hinges outward.
Fair enough.
> This will be my last comment on this topic because this argument is fruitless and you seem unable to see it any other way.
That's a wrong assumption on your end, it's just that I prefer to go by actual evidence rather than a bunch of unsourced claims no matter who makes them.
> This is a high res photo of an installed door plug:
So, finally something useful: the stops apparently hook over the brackets bolted to the airframe, that wasn't obvious from the drawing but I suspected it might be the case (see other comment). So pressurizing the aircraft will provide some holding force (the friction on the stops) even if all of the bolts would be missing or had come loose at any point after assembly.
Thank you for providing the picture.
Edit: I’m feeling charitable so here’s one, knock yourself out. https://www.youtube.com/watch?v=maLBGFYl9_o
Instead of arguing about it, maybe consider which way the pressure is pushing during various phases of operation and decide how you would design the thing if the highest forces push outward...
Indeed, picture provided by another poster above shows that is exactly how it works.
And I covered that eventuality in another comment:
> It's possible the stops hook over the corresponding parts in the plug but that's not readily apparent from the drawing at all.