Dear Cecil: If you're riding in an airplane and sitting in the seat next to the wing exit and the sign on the door says "Push lever to open in emergency," can you just push the lever to open at any old time around 30,000 feet up? If so, shouldn't they carefully screen the people they put next to the wing exits? We need to know. Byron, Greg, Janice & Paula, Chicago

Cecil replies:

Don’t panic, gang. If you’ll look closely next time you’re on a plane, you’ll notice that the emergency exits — they’re not so much doors as removable window plugs — open in, not out. When the plane is on the ground (which is when you’re supposed to use the exits), that doesn’t matter much, because the air pressure is equal on both sides. But when the plane is at cruising altitude, the inside (cabin) pressure is so much greater than the outside pressure that you’d have to have superhuman strength to pull the exit open. Let’s say the window plug measures 18 by 36 inches. The cabin pressure in a typical commercial aircraft is about seven pounds per square inch. At 35,000 feet atmospheric pressure outside is about three and a half pounds per square inch. This means that to get the exit open you’d have to overcome a net outward pressure of more than 2,200 pounds, or more than a ton. Fat chance. The same thing applies to the plane’s regular doors. In most commercial aircraft the doors open outward, but they’re designed in such a way that they have to be popped in a smidge before they can be swung out. As with the emergency exits, cabin pressure prevents the doors from being opened when the plane is at cruising altitude.

You may recall that in 1971 a hijacker named D.B. Cooper with $200,000 in his mitts parachuted out of the rear exit of a Boeing 727 flying over Washington state, never to be seen again. How’d he do it? Turns out the plane was flying at a low enough altitude — 7,000 to 10,000 feet — to enable D.B. to get the door open. Boeing says the exit has since been modified to prevent its being opened while the plane is in the air, no matter what the altitude. Just as well. When somebody pulls off one of the all-time great exits, you don’t want some copycat spoiling the effect.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.