Alaska Airlines 737-900 MAX loses a door in-flight out of PDX
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My understanding is that the springs are there because with a live door fitted (complete with slide, etc) it's too difficult to lift it over the stops with simple brute force on the actuation lever in an emergency.
When the door plug was developed, it was simpler just to keep the springs in situ, though of course they now offset a higher proportion of the door plug's weight (assuming the same degree of compression).
When the door plug was developed, it was simpler just to keep the springs in situ, though of course they now offset a higher proportion of the door plug's weight (assuming the same degree of compression).
Last edited by Old Ag; 11th Jan 2024 at 07:50.
It does not appear to me that the plug and the exit door share common hinges. The plug hinges only allow about 90 degrees of movement, while the exit door hinges allow more than than 180 degrees. The plug hinge assembly seems to be there to facilitate initial installation and adjustment of the plug as much as anything else, with the bonus of being able to partially open it after installation. So i doubt they share a common spring. But I could be wrong as I don't have schematics or part numbers for the two.
If the two installations have different hinge arrangements, there would have been even less reason to carry over the springs to the door plug installation, for something that two people can easily lift and which is only likely to be removed and refitted a few times during the lifetime of the aircraft, if at all.
Re the opening angle, the live door doesn't need to open to anything like 180° (and probably can't) - it only needs to open far enough to allow room for the slide to deploy at a safe angle.
I seem to recall seeing a video somewhere of the door/slide deployment - I'll try to dig it out.
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I'd put money on the hinges being the same for the live door and the plug,..
Re the opening angle, the live door doesn't need to open to anything like 180° (and probably can't) - it only needs to open far enough to allow room for the slide to deploy at a safe angle.
I seem to recall seeing a video somewhere of the door/slide deployment - I'll try to dig it out.
Re the opening angle, the live door doesn't need to open to anything like 180° (and probably can't) - it only needs to open far enough to allow room for the slide to deploy at a safe angle.
I seem to recall seeing a video somewhere of the door/slide deployment - I'll try to dig it out.
It opens more than the hinges of the plug would allow.
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Haven't found anything other than the plug being opened on the limiting cables. But if you look at the NTSB photos of the hinges protruding from the plane, they are both at about 90 degrees and appear to up against some sort of stop keeping them there. But again, I don't have schematics, so this is trivial speculation.
Initial thoughts on Renton pug-door removal; most of the cabin furnishings won't fit through the aperture. Even so, if I was performing a Check, I'd probably still want every possible door open for ingress/egress of personnel, tooling, pneumatic-air hoses, power cables and simply ventilation.
Subsequent thoughts. So the plug-door can't be fully opened without providing an external access platform to facilitate handling and removal. I then Googled images under "Boeing 737 production line". A million pictures of green fuselages in a factory, surrounded by equipment, cabin doors and emergency exits open, but I couldn't find any images of Row 26 doors open (of any type). Moreover, there's several images of a saddle-type access platform which is placed over the centre fuselage and provides a platform/guardrail outside the overwing exits; it doesn't appear to extend to Row 26, nor could I find a corresponding image of such a platform.
Purely subjective of course.
Subsequent thoughts. So the plug-door can't be fully opened without providing an external access platform to facilitate handling and removal. I then Googled images under "Boeing 737 production line". A million pictures of green fuselages in a factory, surrounded by equipment, cabin doors and emergency exits open, but I couldn't find any images of Row 26 doors open (of any type). Moreover, there's several images of a saddle-type access platform which is placed over the centre fuselage and provides a platform/guardrail outside the overwing exits; it doesn't appear to extend to Row 26, nor could I find a corresponding image of such a platform.
Purely subjective of course.
If the two installations have different hinge arrangements, there would have been even less reason to carry over the springs to the door plug installation, for something that two people can easily lift and which is only likely to be removed and refitted a few times during the lifetime of the aircraft, if at all.
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Thanks, I knew there had to be a sensible answer. I'm aware of the factors affecting curved structures carrying pressure under tension, but didn't consider the effects of the load path changes in the overall framed structure. I didn't know that certification came with such a high price tag!
I am aware that there are already 12 bolts in the plug side fittings and understand they serve for a different purpose.and do not protrude.
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When Gates makes assertions like that, he's typically passing on information from Boeing contacts. He's usually quite good at sifting and verifying, which is why he and his colleagues got that Pulitzer.
Yes, it would implicate Spirit, but it certainly wouldn't let Boeing off the hook.
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It is semantics. Semantics means "meaning."
Yup, sure is.
It will be surprising if they get the plug-equipped birds back in the air by then, so at least you won't have that to worry about. Fly safely.
It will be surprising if they get the plug-equipped birds back in the air by then, so at least you won't have that to worry about. Fly safely.
Too mean to buy a long personal title
I haven't seen this posted yet - apologies if duplicate. It seems to add some context to Tuesday's use of the word "mistake".
Yesterday (Wednesday), Calhoun told CNBC that a "quality escape" was in issue.
A Reuters report (Alaska, United cancel more flights as Boeing probes 'quality' issue) includes this:
Jon Ostrower has tweeted:
Sorry, I can't get the URLs to work.
Yesterday (Wednesday), Calhoun told CNBC that a "quality escape" was in issue.
A Reuters report (Alaska, United cancel more flights as Boeing probes 'quality' issue) includes this:
Boeing CEO Dave Calhoun told CNBC on Wednesday that a "quality escape" was at issue in the MAX 9 cabin blowout that left a gaping hole in the plane that had been in service for just eight weeks, but added key questions remained.
"What broke down in our gauntlet of inspections? What broke down in the original work that allowed for that escape to happen?" Calhoun said.
A quality escape was "a description of what people are finding in their inspections ... anything that could potentially contribute to an accident," he added.
"What broke down in our gauntlet of inspections? What broke down in the original work that allowed for that escape to happen?" Calhoun said.
A quality escape was "a description of what people are finding in their inspections ... anything that could potentially contribute to an accident," he added.
A quality escape is Boeing jargon for when something wasn't built or repaired correctly. The quality has "escaped" during the prescribed engineering or manufacturing process.
He's saying it was a manufacturing quality error that caused the AS accident.
He's saying it was a manufacturing quality error that caused the AS accident.
Just a thank you for all the explanations and theories. I haven’t had time to read everything so a couple of stupid questions from a retired driver:
Is the door plug just a stripped down normal exit door without a slide bustle?
Were the previously logged cabin pressure controller faults due to leakage induced bleed flow or something else?
And, if I may, supplemental irrelevant questions just for interest:
Does a 737 Max need a running (not just serviceable) APU for 180ETOPS?
Are Max main doors still dis/armed by kneeling and praying to the god of the girt bars, or have they been updated?
Is the door plug just a stripped down normal exit door without a slide bustle?
Were the previously logged cabin pressure controller faults due to leakage induced bleed flow or something else?
And, if I may, supplemental irrelevant questions just for interest:
Does a 737 Max need a running (not just serviceable) APU for 180ETOPS?
Are Max main doors still dis/armed by kneeling and praying to the god of the girt bars, or have they been updated?
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Just some clarification, the plug is held in place and immovable via tension against the 12 outward stop lugs that push the plug tight into the opening. There should never be loosening, to my knowledge, during any diff pressure changes. It has to remain sealed. The hinges and springs really only facilitate the operation of installing and opening the plug, and as designed, the ultimate locking of the plug acts THROUGH the guide system. Personally I think the design is flawed in the respect that the security of the system depends on the stop bolts acting on guide system and not a more direct fastening method. I feel that the tension against the 12 stops played a role in this detachment. Perhaps there was slop in that function. edit to add: But of course I expect the lock bolts were missing and allowed the motion out of lock position in the first place.
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CNN: Aviation experts raise questions about 737 Max ‘door plug’ design
BBC: US official says Boeing jets won't fly until safe
Couple of recent new stories - for what they are worth.
BBC: US official says Boeing jets won't fly until safe
Couple of recent new stories - for what they are worth.
Last edited by OpenCirrus619; 11th Jan 2024 at 13:15. Reason: Link text incorrect
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Just some clarification, the plug is held in place and immovable via tension against the 12 outward stop lugs that push the plug tight into the opening. There should never be loosening, to my knowledge, during any diff pressure changes. It has to remain sealed. The hinges and springs really only facilitate the operation of installing and opening the plug, and as designed, the ultimate locking of the plug acts THROUGH the guide system. Personally I think the design is flawed in the respect that the security of the system depends on the stop bolts acting on guide system and not a more direct fastening method. I feel that the tension against the 12 stops played a role in this detachment. Perhaps there was slop in that function. edit to add: But of course I expect the lock bolts were missing and allowed the motion out of lock position in the first place.
The fastening method is a feature: By giving it some wiggle room, it will adjust itself each time the hull is pressurized for minimum stress (besides the delta p).
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Indeed, compressive pressure against the lugs. The plug, I believe, is to be quite firmly pressed into the opening seal. I would bet if you gauged the proper movement of the skins in relation to each other in any phase of operation, you would get very near zero. Im not familiar with the specific procedure in the manual, but I would assume opening the plug begins with the loosening of the 12 lugs.
I doubt that, I don't think you would need to do anything with the lugs to open the plug or door. In a side view (looking along the airframe's longitudinal axis), the door or plug moves at a slight angle relative to the lugs so that it moves away from them (but against any pressure differential present in the fuselage) while moving up. That's why, when viewed from outside, there is room at the top for the plug/door to move up.
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It is doubtful that the springs are strong enough to lift the plug up and out of the closed position on their own. Otherwise the plug couldn't be closed and stop bolts installed without keeping downward pressure on the plug. That being the case, when the plug is closed the weight of it is carried by both the upper guides and lower springs, but essentially its located by the upper guides aligning the lower stop bolt holes perfectly for installation of the lower stop bolts. All of this is to say that the lower hinge slide fittings resist the springs upward force with the help of the weight of the plug. Therefore the lower stop bolts would have no shear force to resist unless an additional external upward force was applied to the plug. Same goes for the upper stop bolts.
My understanding is that the springs are there because with a live door fitted (complete with slide, etc) it's too difficult to lift it over the stops with simple brute force on the actuation lever in an emergency.
When the door plug was developed, it was simpler just to keep the springs in situ, though of course they now offset a higher proportion of the door plug's weight (assuming the same degree of compression).
When the door plug was developed, it was simpler just to keep the springs in situ, though of course they now offset a higher proportion of the door plug's weight (assuming the same degree of compression).
2) Therefore, the springs are strong enough that the door plug will not fall back behind the stops by gravity alone
3) This is consistent with a downward force being necessary to close the plug and install the bolts
4) However, one could imagine it may take additional upward force to overcome the static friction of the seals, "break the seals," in which case the springs would provide a "spring assist" to get the movement started
5) If the springs are strong enough to hold the door above the stops, by design, there is always an upward force on the retaining bolts
6) Therefore, in a sense, the design created a spring-loaded self-ejecting plug, only prevented from self-ejecting by the 4 bolts and static friction of the seals
7) This is the opposite of a "fail safe" design
8) Sometimes this happens when risk assessments for design changes are insufficient to assess new risks brought about by the changed design
9) One can assume the plug is a design change from the standard design of a Class II mid-cabin door. The upward spring force is a "fail safe" door design for emergency evacuation to keep the door open. The door has additional rods and cams and latches which are mitigations that prevent unintended upward movement of the door. The actual door, when the latch is closed, cannot translate upward without intentionally moving the latch.
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Just some clarification, the plug is held in place and immovable via tension against the 12 outward stop lugs that push the plug tight into the opening. There should never be loosening, to my knowledge, during any diff pressure changes. It has to remain sealed. The hinges and springs really only facilitate the operation of installing and opening the plug, and as designed, the ultimate locking of the plug acts THROUGH the guide system. Personally I think the design is flawed in the respect that the security of the system depends on the stop bolts acting on guide system and not a more direct fastening method. I feel that the tension against the 12 stops played a role in this detachment. Perhaps there was slop in that function. edit to add: But of course I expect the lock bolts were missing and allowed the motion out of lock position in the first place.
However, the properly adjusted stops should not cause static friction in the absence of pressure differential, otherwise it would prevent opening of the door! (Acknowledging the plug could stand to be adjusted in a way such that there is always static friction between the stops, but I am willing to bet the stops have the same adjustment specs whether a door or a plug is installed.)