Physics Explains Why You Can’t Open a Plane Door in the Air

It’s the nightmare of travelers sitting near the emergency exit and the inevitable fate of bad guys tussling on a plane with James Bond—the door erupting open mid-flight, sucking them into the cold blue and white.

This scenario was no doubt running through the minds of the passengers of a BA flight to Riyadh this week, when a man, reportedly in the grip of a panic attack, tried to pull open the aircraft door. He was restrained—by the brother of boxer of Dillian White, no less—and eventually calmed. The doors remained sealed.

Wired UK

This story originally appeared on WIRED UK.

This isn’t the first time passengers have attempted to exit a plane in midair. In 2015, a passenger gave it a go on a Hainan Airlines flight to Mongolia, this time as the plane was preparing to land. In June, Air Europa flight UX89 was forced to turn back after a passenger tried to pull open the emergency exit. And just last month, holidaymaker Chloe Haines appeared in court on charges of attacking two stewards who tried to stop her from doing the same. (The unifying detail of all of these stories is that the passengers were flagrantly drunk.)

While the prospect of being hurled into the troposphere due to the antics of a drunken passenger isn’t alluring, you’ll be pleased to hear that in all of these cases, the actual risk of the door being opened was nil.

There are two lines of defense at play here. The first is, as you might expect, that the doors are mechanically locked. These locks are controlled by the pilot. “You see that great big handle on the door—that’s actually locked shut,” says Steve Wright, an associate professor of aerospace engineering at the University of the West of England. ”When the plane touches down and is taxing to the gate, you’ll hear the pilot say ‘doors to manual.’ It’s only at that point where the pilot has handed off control, and where those doors are actually capable of being opened by someone standing near them.”

The reason the doors can be opened when you’re on the ground is simple, explains pilot Patrick Smith on his blog AskThePilot—it’s in case the plane needs to be evacuated. He points out that you may also hear the pilot relay the command “disarm doors,” which refers to the automatic deployment function of the slides. “Those slides can unfurl with enough force to kill a person, and you don’t want them billowing onto the jet bridge or into a catering truck,” he writes.

The bottom line of all this is that while you’re on the ground, it can be possible to open the door. In 2015, for instance, a video emerged of a man opening the door on the runway to “get some fresh air.”

During flight, however, it’s a different story, and it all has to do with air pressure. When we rise higher in the atmosphere, less pressure is exerted on oxygen molecules (known as Boyle’s Law). This means that less pressure is available to let these molecules diffuse into our vascular systems—basically, it gets harder to breathe.

Once you get up above 18,000 feet, we begin not to take in enough oxygen to supply the brain—you’ll pass out in about half an hour. Since airliners fly between 30,000 and 43,000 feet, air needs to be pumped into the airplane to keep the interior pressure at a survivable level. (At this altitude, you’ll grow delirious within seconds and pass out in less than a minute, which is why air masks drop down during depressurization events, and why you should attend to yourself before a baby.) We are in fact in a mild state of hypoxia all the time on a flight.

But what’s all this got to do with the plane’s doors? Simply put, the cabin pressure seals them shut. You need to think of the door like a giant bath plug, explains Wright—taking advantage of this plug hole effect is why almost all aircraft exits open inward. “As you step off the plane, have a look at the door, you’ll notice how it’s quite an interesting tapered shape,” says Wright. “And that’s because it’s actually plugged in—you’ll notice when the cabin crew opens it they have to do a special sort of Jimmy, or sideways shuffle, because effectively, the door is plugged into a hole.”

The math here is pretty simple, according to Michele Meo, a professor of materials at the University of Bath. “You cannot open it because the aircraft is pressurized, and the cabin pressure is higher than the outside air pressure,” he says. “The difference can be as much as 55,158.1 Newtons per square meter (or 5,500 kg applied to 1 square meter). Basically, the door is sealed against the aircraft frame.”

At lower altitude, the difference in pressure is smaller and it grows with altitude. According to Smith, this works out, at typical cruising altitude, at about 8 pounds of pressure pushing against every square inch of interior fuselage—1,100 pounds against each square foot of door. It doesn’t matter how strong the passenger who wants out happens to be; they aren’t opening that door.

For those of the morbid mindset, it’s actually the windows, not the doors, that are usually the plane’s weak spot, says Wright. And unfortunately, it isn’t a myth that in the event of a door blowing open, passengers would be sucked toward the opening. “In case of a decompression or door failure, the passengers will be sucked out because of the difference in pressure pushing the passengers outside, which is why it is always recommended to wear seat belts,” says Meo. “One famous accident was Aloha Airlines in the 1980s, caused by depressurization, but in that case there were existing cracks inside the airplane. The pressure acted from the inside and made the crack grow until the fuselage was ripped apart.”

This story originally appeared on WIRED UK.