# How does the hinge mechanism of plug-type pressure doors work?

Many pressurized aircraft have the type of plug doors that open by first swinging inside, rotating about at least two axes, then moving through the opening and ending up outside parallel with the fuselage.

I'm intrigued by the mechanism that makes this possible, but I have never been able to really see how these intricate hinges work. As a passenger it's hard to even witness the actual opening or closing of the door. Some drawings are to be found on the web, but none that I know of give a clear understanding of its workings. Does anybody know of a video or an animation that gives some insight?

This video has a clear shot of how a classic plug door (in this case of a B737) works (or search for flight attendant training videos).

You can see the door pops in (tipping a bit downwards) and then rotates on a axis in the center of the opening and then moves outside sideways. This is possible because of how the geometry works out, moving sideways negates the boor being wider than the opening and tipping down lets it fit height-wise.

• Which means that the door is wider than the opening, but not higher. Aug 28 '14 at 9:38
• @JanHudec the door tipping inward lets it be slightly higher (though a separate flap is used for the bottom and top see youtu.be/BVxPBeu2PaI?t=2m14s) Aug 28 '14 at 9:41
• Why are manhole covers round? Because the holes are round. Actually, it's because a round cover can't fall through a round hole.
– rbp
Jan 30 '15 at 0:46
• @rbp That must be at least one of the reasons why aircraft doors are not round. Jan 31 '15 at 14:48

The door you mentioned is called a Plug Door.

On some aircraft the plug door opens partially inward, and through a complex hinge design can be tilted to fit through the fuselage opening, or the door may have locking hinged panels at the top and bottom edges that can make it smaller than the opening, so that it may be swung outward.

This video shows opening and closing of such door from both outside and inside.

• I know about those hinged panels, but afaik they are not used on all these plug doors. To me they seem to be a less effective solution, for the panels should open outward and consequently cannot (like the door itself) withstand cabin pressure without seperate latches. Aug 29 '14 at 9:25

A Google search of Plug Door Patents will yield many variants. The ones you want are:

I am going to build one of them as the entrance to my workshop - but I need to get the house built first.

• I also liked this one: google.com/patents/US4199120 I could not put more than two links in my previous posted answer. Jan 29 '15 at 21:17