When a plane loses pressure, the result is a noisy, terrifying scene in which passengers can be, and have been, sucked out of a plane.
After a 5-ft. hole opened up in the roof of a Southwest Airlines plane this past weekend, the FAA announced that it was requiring 175 aircraft to be inspected for cracks and fatigue so the frightening incident wouldn’t happen again. And Southwest said it was repairing five older planes and also canceling 650 flights.
Older aircraft with stress in their metal skin have faced decompression and serious accidents before, most dramatically in 1974, when a Turkish Airlines plane crashed, and again in 1985, when a Japan Airlines plane went down. A similar incident occurred in 1988 on an Aloha Airlines plane. It landed with one fatality.
(More on TIME.com: See the cracks in the Southwest Airlines planes.)
But what exactly happens when a plane decompresses?
To understand the process, you first have to know why planes are pressurized in the first place. As a plane reaches higher altitudes, oxygen levels get lower, which can cause serious psychological problems. So the FAA requires that the cabin altitude — the artificial altitude created inside the plane — doesn’t exceed 8,000 feet.
But a puncture or damage in the jet’s fuselage can cause depressurization, or decompression, and the scene can quickly turn dangerous.
“Depending on the size of the hole, explosive decompression can occur,” says Nihad Daidzic, a professor of aviation at Minnesota State University who has witnessed simulations of depressurization. “Within seconds you’ll get condensation. The pressure and the temperature will drop very quickly. Debris will be flying around, and people can get sucked out.”
Yes, that’s right: people can get sucked right out of a plane. That’s precisely what happened to a flight attendant who was blown out of the cabin in the Aloha Airlines incident. Thankfully, conditions in the cabin differed during the recent Southwest incident. While the hole may have been big enough for passengers or crew to get drawn into (many say it was at least 5 feet in length), it seems the tear in the roof wasn’t close enough to anyone to actually suck them through. Proximity, experts say, matters. Additionally, the hole seems to have gradually gotten bigger, giving passengers time to ensure that they were securely buckled in.
(More on TIME.com: See Southwest Airlines’ popular Twitter feed.)
The Discovery show Mythbusters took up this issue of depressurization a few years ago and disproved the myth (often seen in movies) that a hole in a window or the fuselage will automatically cause people to get sucked through. Again, it all comes down to size and immediacy: if the hole is big enough and people are close enough, anything can happen.
Yet even if passengers or crew members aren’t blown out of the cabin, the decompression experience can be a jarring ordeal. “The whole thing would be very noisy and very quick,” Daidzic tells NewsFeed, pointing to a physiological race against time. Within seconds, the lack of oxygen could cause issues like hypoxy, which clouds people’s judgment and is the reason that attendants tell passengers to put on their own oxygen mask before assisting others.
While rare, serious depressurization incidents do occur. But with the ordered FAA inspections of older 737 aircraft, hopefully the next time we see the roof blown off a plane will be in an action film.