Why can’t you open an airplane door mid-flight? You can’t open the door while an airplane is flying because of pressure, the design of the door, and because of safety mechanisms.
Large planes, such as the 747, have several doors on each side of their fuselage. Each door appears to be closed with only a lever, and you might think that if you wanted to, you would be able to open the door while the plane is mid-flight. You could try, and if you managed to get past the cabin attendants, you might be able to get your hands on the lever, but there would be no way you could open the door. In fact, most of the passengers on the plane pulling together would probably not be able to open the door.
We have evolved to live at sea level, where air pressure is measured at one atmosphere. That is the weight of all the air in a column stretching far above you. The weight of all of this air compresses the gases in the air down so that there are more oxygen molecules for each breath. As you get higher, the weight of the air above drops, and the air is less compressed, so the oxygen molecules spread out and there aren’t enough in each breath. If you get over about 10,000 meters, there won’t be enough breathable air to survive, and you will pass out and die. When you fly in a plane, you are frequently traveling above 10,000 meters, and to make sure you don’t pass out and die, the airplane pumps air into the cabin to keep the concentration of oxygen molecules at a level you can comfortably breathe. This has two advantages on a plane. The first is that you won’t die during the flight from hypoxia. The second is that you cannot open the door even if you try.
The higher pressure inside the air increases the weight of the air. Pressure is force spread over an area. All of that weight is pressing down on the door with a weight of 5.5 tons per square meter. Over the full area of a door, that is about the weight of a large truck. The only way you could open that door is if you could pull with a force of greater than a large truck, and the handle would break long before the door would open.
You can see the same effect if you are unfortunate enough to be trapped in a car underwater. The opposite happens here. The air in the car is still at one atmosphere, but the pressure of the water outside the car is far higher, which makes it much heavier and means you will not be able to open the door and escape until the car has filled with water and the pressure has equalized. That is why people carry a small hammer to shatter the window.
The second reason why you can’t open a plane door while the plane is flying is because of the design of the door. Aircraft use a door design called a plug door. The door is tapered so that it fits into the doorway just like a plug in a bathtub. To open the door, you have to pull it inwards first, to clear the lip of the frame, and then it swings outwards. This design means that the air pressure in the cabin pushes the door more firmly into the plug, sealing it in place.
The third reason you can’t open the door is that it is locked. They have multiple layers of safety built into them. The handle is mechanically linked to latches and locking pins, and there are safety catches intended to prevent accidental movement. Some aircraft also have electronic monitoring and, in certain designs, additional locking or inhibition features.
So, there is no way you can open a door while the plane is flying. However, you could open a door at lower altitudes if they are not locked. Not a good idea, though. The doors have been designed to be very strong. A weak point in any plane is the windows because they are holes that break up the structure of the fuselage. They are strong, but they are still weak points. And, because of all the pressure inside the fuselage, if a window breaks, there will be an explosive decompression. All of the air inside the plane will want to be outside the plane as fast as possible. People can get sucked out if this happens. One way of making windows stronger is to make them round. Square windows have stress points at every corner, and a lot of pressure can build up on these corners. Round windows distribute the forces more evenly. And this is what I learned today.
Sources
https://www.wired.com/story/physics-explains-why-you-cant-open-a-plane-door-mid-flight
https://matadornetwork.com/read/opening-airplane-door
https://en.wikipedia.org/wiki/Plug_door
https://simpleflying.com/can-plane-doors-be-opened
https://simpleflying.com/why-plane-windows-round
Photo by Magda Ehlers: https://www.pexels.com/photo/airplane-emergency-exit-view-during-flight-34723181/