Flying is stressful for a lot of reasons. From long queues at the airport to screaming children on the plane, flying pushes our buttons and makes us stressed. If this wasn’t enough, airplanes are a standard movie setting for when something goes wrong. Media coverage of aircraft incidents and terrorism have exacerbated people's fears of flying, and we often look at our fellow passengers like they might snap and try to unlock one of the doors, dooming us all.
So what would happen if you tried to open the door of a plane while the aircraft is in flight? Nothing. Well, you would be restrained by flight attendants and arrested as soon as the plane lands, but nothing would happen to the aircraft. Why? Because you wouldn't be able to open the door. The pressure would stop you from doing so.
“Think of an aircraft door as a drain plug, fixed in place by the interior pressure," pilot Patrick Smith blogged on the subject. "Almost all aircraft exits open inward. Some retract upward into the ceiling; others swing outward, but they open inward first, and not even the most musclebound human will overcome the force holding them shut."
The pressure inside the cabin is much greater than the outside. So you would need to be able to pull the doors with a superhuman amount of force. At cruising altitude, the inside of the cabin is at a pressure of about 0.7 or 0.8 atmospheres, which is equivalent to about 5-5.4 kilograms (11-12 pounds) of force per square inch. This is what you are trying to overcome!
Now, you might want to know what happens at lower altitudes. Again, this is the science so please don't take it as a challenge. Even a difference of 15 percent of standard atmospheric pressure would be too strong for humans to overcome. Doors can only be opened when near the ground. And that means very near. In case of an emergency during takeoff or landing, the doors should open easily and deploy the inflatable slides.
If you can open the door in the air, you have bigger problems.
It means that you have low pressure in the cabin. While it might not be cinematically intriguing, it can be as deadly as explosive depressurization, which happens when the cabin is damaged liked in the unfortunate case of the Southwest Airlines flight a few weeks ago. One of the engines of the aircraft exploded, smashing through a window and partially dragging a woman out of the cabin, who died due to the injuries from the debris.
The air rushed out of the cabin due to higher pressure, and oxygen masks were automatically deployed. At low atmospheric pressures, the human body can’t absorb enough oxygen and eventually succumbs to hypoxia. In the case of the Southwest Airlines flight, pilot Tammie Jo Shults was skilled enough to perform an emergency landing before any on board could be affected by the lack of oxygen. And a good thing too, since selfies from the plane showed that almost everyone was wearing the oxygen mask wrong. Cover your mouth and nose, people!
Even if you are at an altitude that would allow you to open the door, you wouldn't be able to – the cooper vanes would stop you. This mechanical device was invented in the 70s after D.B. Cooper escaped from an aircraft with a huge amount of cash, parachuting himself from the rear door of the aircraft. He opened it because he had the pilot depressurize the plane first.
You shouldn't fear fellow passengers trying to open the door because they truly cannot, and you shouldn't fear flying in general. In 2017, the safest year for commercial aviation, there were only 10 fatal airliner accidents out of 36.8 million flights.