OK Mike, we give up!

I have queried a (Cessna) engineering test pilot. Perhaps he has the answer ...

The answer is: some guy from Marketing thought it looked cool.

We are screwed. Mike's FlightAware shows that he was headed for KEMT.

Unfortunately, it is not possible to find KEMT.

Oh I'm sure it was a Service Bulletin that was handed off to Junior engineer. A whole bunch of operators then went out and complied with the bulletin only to find out Cessna cancelled it because it was designed improperly. Then they came out with revision 2 then 3 then 4. And operators are left to figure out if they get credit for doing an earlier revision.

The Cessna way...

I’m going with josh’s guess, page 1. Without the taper, the 4 windows couldn’t be symmetrical. Very unpleasant to the eye. No way i’d design a plane with 3 sym windows and one scootched down for the door. Implies lack fore thought. So they tapered?

From an engineering standpoint, stress increases with increasing unsupported spans. Windows are a weaker point so a shorter horizontal span with window has the same max pressure as a longer span with no window so perhaps the door is the limiting pressure component for cabin pressure? The vertical on the door is hoop stress.... better/stronger than horizontal so shortening the horizontal at the window makes some sense to me.

Great challenge.... I just need to Q the princess bride sicilian clip ....’truly a dizzying intellect’

What is the door hinge design on the early Citations? Wondering if the tapered shape has something to do with the hinge pivot axis and location vs door cutout and location.

I think an earlier supposition that they were constrained by the frames makes a lot of sense.

Max width at bottom for hinge
Taper at top to accommodate locking pins.

If that’s the answer I am not sure why it would have puzzled Mike C for so long and why he would have created the post. Has to be something more surprising no?

Would this apply to the "spacing" of windows?

I've been checking out photos of CJ3 doors: The door swings forward, the hinge is near the center span, forward of the door... so no hinge on the bottom. (except for the stairs which are inside the door and fold down) The locking pins are all around, so I don't think the taper is related to the pins. It looks like the door might extend closer to the top of the fuselage than the bottom. Maybe the taper is related to the geometry of the door closing and the asymmetry of the vertical position of the door.

Anyone know what the fuselage cross section shape is at the door station?

Reduces wind force on the hinge when open.

It is because of the deflection of the airframe tube between the wheels when loading and off loading. With concentrated loads of items and passengers at the door, the plane’s tube would compress inward at top. When flying the loading changes and deflection angles change. The tube flex’s up and down just like wings do. So more clearance is needed at top to account for this movement with out bending the door.