Originally Posted by
MechEngr
The fasteners would have been subject to shear loads rather than tension loads. This would have put the screws against the sides of the holes in the door. If they are replaceable element nut plates, the float of the nut plates would isolate the nutplate rivets from load. They may even have just turned with the rivet as the pivot to allow that contact.
I think I could make out on one of the NTSB field photos one of the aft post guide fitting bolts with the head pulled off. So I feel like the nutplates were actually strong enough in tension.
The issue with one-lug nutplates (and mickey mouse nutplates are even worse) is on installation. If the installer pushes too hard on the bolt while turning, they can put a lifting force on the nutplates and break the tiny rivets that way. Two-lug nutplates are less prone to that problem.
Probably not a factor in this incident, but something that jumped out at me about the design.