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One of the variants of the Metroliner, the SA227-AT Expediter, is a dedicated cargo aircraft with strengthened floors, an increased MTOW, and a windowless cabin.

However, despite being a cargo aircraft with absolutely no provision for the carriage of passengers, it appears, bizarrely, to still have been built with hatches for overwing exits!

what

(Image by YSSYguy at Wikipedia, via YSSYguy at Wikimedia Commons.)

Why are these hatches still included when there are no passengers to evacuate through them and cutting them into the aircraft's hull weakens its overall structure and requires extra time and labor during construction?

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    $\begingroup$ Might come in handy for the loading crew should a fire break out while on the ground. $\endgroup$
    – FreeMan
    Mar 21, 2023 at 17:24

2 Answers 2

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The window openings are still there, they are just filled with aluminum panels replacing the acrylic ones, and the joints are fine enough they don't show up in pictures unless the light is coming at low angle to the surface like in the shot below.

Nobody would ever build a cargo conversion of a passenger aircraft (as opposed to designing the fuselage of a special cargo variant of a passenger jet model from scratch) and go to the trouble of designing a completely new fuselage barrel to just to eliminate the window frames.

enter image description here

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    $\begingroup$ In this picture you can see some of the window frames on the exact aircraft from the question (VH-EEO). Does your last sentence also apply to big cargo jets? I always thought that purpose built freighters like the Boeing 777-200F do not have window frames (unless they are converted passenger planes). $\endgroup$
    – Bianfable
    Mar 20, 2023 at 14:25
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    $\begingroup$ My answer is about converted pax planes. It makes sense that they would eliminate windows, as well as building in a large cargo door, during design on a dedicated freighter model. $\endgroup$
    – John K
    Mar 20, 2023 at 17:22
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    $\begingroup$ This answer could use some clarity. When you say "build a cargo conversion" do you mean a new-build freighter from a passenger design (777-200F) or a conversion from an existing passenger airframe (P2F/777-200ERSF)? Planes like the 777-200F, A330-200F do not have plugged windows which contradicts your last statement. $\endgroup$
    – user71659
    Mar 20, 2023 at 20:02
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    $\begingroup$ I see the edits, but this answer is still not right. AFAIK, the plane cited was built new as a cargo plane, as the same class 777-200F. It is not a P2F conversion. Further, this answer doesn't address the exit doors. Doors are removed and reskinned in some situations (A321P2F). $\endgroup$
    – user71659
    Mar 21, 2023 at 18:28
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    $\begingroup$ If you zoom in on the pic of the one in the OP you can make out the window frames in spots. The Expediter was not built as a purpose built freighter with its own purpose built windowless fuselage. That's why the exit doors are still there. Because so are the window openings. $\endgroup$
    – John K
    Mar 22, 2023 at 4:58
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Adapting an airframe for a new mission requires a series of cost-benefit decisions. Removing the exits from the fuselage would require a complete set of structural testing to gain certification, which is a lot of time and money for little benefit when you can just paint the window. Plus, if you design out the exits you can't reconfigure the airplane back to passenger use.

The usual solution is to put blank plates in the place of the windows and emergency exits, which is the case here.

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    $\begingroup$ This variant already has the cabin windows designed out, though - so why not the overwing exits as well? $\endgroup$
    – Vikki
    Mar 20, 2023 at 11:35
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    $\begingroup$ They aren't designed out, the windows are still there, the seams are hard to see. $\endgroup$
    – GdD
    Mar 20, 2023 at 16:57
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    $\begingroup$ @DaveGremlin It's not that bad with metal fuselages, because it was one piece to begin with: they skip the step of cutting the windows out. The story may be different with carbon fiber. $\endgroup$
    – user71659
    Mar 20, 2023 at 20:05
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    $\begingroup$ You'd think that removing the windows would strengthen the hull (since adding windows weakens it). $\endgroup$
    – RonJohn
    Mar 21, 2023 at 0:35
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    $\begingroup$ @RonJohn No, because the structure was reinforced back to the same strength. When removing the window, they also remove the window frame and doubler, which where a lot of the mass savings are. Second, it changes the stress distribution of the fuselage, which needs to be re-analyzed. As real example, Southwest Flight 2294 blew a hole due to cracking because Southwest didn't cut a hole in the fuselage for an antenna. This caused the panel to have increased stiffness, which led to stress concentration at an adjacent panel. Boeing knew about this but underestimated the cycles needed to crack. $\endgroup$
    – user71659
    Mar 21, 2023 at 1:29

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