wanttaja
En-Route
Not sure. It could be a self-locking nut using a fiber insert, like the AN365, MS21044, or an all-metal lock nut like the AN363. The lock nuts would make sense from the manufacturing/cost point of view, as they would take less time to install and fewer tools. Used to be able to buy tons of all-metal stop nuts at Boeing Surplus.Clarify for this non A&P - For these six critical fasteners, it looks to me like they are each loaded in shear and retained by common low-profile shear nuts, which in turn are supposed to be cotter keyed. Shear nuts may have a torque spec (yes?) but the real problem is the lack of cotter keys.
Looking at the door design, access to the back side of the guide track is a bit restricted. Assuming the head of the bolt is on the cabin side, installing a cotter pin on the other side might be more difficult.
Looks like two roller pins at the top basically hold the thing in place, with bolts through the track to keep it from coming out, and two lower locking bolts at the bottom. But even if the door is shedding nuts, the bolts should stay in place (assuming the drawing is accurate, and the bolt head is on the inside so the bolt head is higher). Should be able to lose the upper locking nuts and not cause a problem, UNLESS BOTH THE LOWER BOLTS ARE GONE.
To me, it sounds more like all the bolts just plain weren't there. A potential scenario is someone deciding the plug had to come out for a short time (one story is that Boeing was installing the interior, the other is that it was necessary for rigging), and someone stuffed it back in place without securing it. As an ad-hoc shop activity, QC might not even have gotten installed.
Alternately, none of them had nuts, and the bolts worked themselves out.
Ron Wanttaja