[free2023]

Why are there bolts and machine screws in use in the first place?

The seating configurations for United and Alaska, the 2 major customers for this aircraft, don't require this plug-door feature. Structurally, for these large carriers, the plug door serves only as a fuselage weakness and failure point.

Why don't they just rivet it permanently to the fuselage and make it non-functional? Per the diagrams shown, it's a complex assembly that serves no purpose at all for these carriers.

(Apparently it was used as a cargo door to furnish the interiors, which seems like a trivial use case.)

[arrakeenrevived]

Aircraft are often sold between airlines, or reconfigured even with the same airline. If United ever wants to reconfigure their 737s to be higher density (which is pretty common), they might need to start using that door as a real emergency exit.

[free2023]

Yes I see, that makes good sense. Given the course of events, it's still a fair question from a design standpoint: Can this be engineered with a reversible option to switch it from functional to non-functional, depending on the seat configuration?

It just seems like a lot of complexity and moving parts, for a feature that's not in use.

[local_crmdgeon]

Saves Boeing money by manufacturing 1 frame

[free2023]

Yes, certainly. But the carriers could configure it to make it non-functional, since it serves no purpose for them. Or they could spec it as a rivet-it-shut option from Boeing. Just seems crazy to have this big failure point in the fuselage, adding to their maintenance costs, for a thing they don't even use.