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Re:United finds loose bolts on plug doors during 737 Max 9 i... by johnwalkr on Monday January 08, 2024 @11:13PM (#38922223)
Oh wow. I made another comment about how important tension in fasteners is, to provide a clamping load and therefore friction between two faces. I was thinking that there must have been a process failure. Fasteners often shear off if there is not enough tension and therefore friction. But in this case it looks like there is not any clamping load between parts for at least some of the fasteners, so those fasteners basically act only as pins. There are other "stop pad" parts that constrain movement of the plug but as far as I can tell they must be compliant/flexible parts. The video mentions "roller pins" which for a door would be used with a cam mechanism. I think that stop pads plus roller pins/door/cam mechanism holds the door securely, but stop pads plus plug/pins does not.

On paper all 6 degrees of freedom may be constrained with the plug but in principle compliant pads may allow shear forces and/or rattling on the fasteners and they eventually fail.

I will eat my hat if the eventual required solution doesn't involve some kind of mating cup/cone or wedge shaped parts to more positively constrain the plug.

Re:United finds loose bolts on plug doors during 737 Max 9 i... by dmix on Monday January 08, 2024 @11:44PM (#38922426)
The recurring question is that it was only 2 months old so likely had those bolts underneath the roller thing was not fastened properly or the whole concept is flawed and this one simply had some bad turbulence/rough landings which created the perfect pressure on them.