Last Friday, while en route from Phoenix to Sacramento, a five-foot hole that appeared in the fuselage a Southwest Airlines-operated Boeing 737 jet forced the pilot to make an emergency landing. Since then, the Federal Aviation Administration ordered mandatory inspections of nearly two hundred 737s worldwide.
The plane whose fuselage ripped open was 15 years old and had taken nearly 40,000 flights. And the concern that other old models may have similar vulnerabilities proved warranted when Southwest found five other jets with fuselage cracks. Scary stuff really.
But much like the ongoing confusion and misinformation surrounding nuclear radiation risks, few people understand the actual risk of a mid-flight tear in a plane’s cabin. And when I say few people actually understand either of these things, I certainly include myself in that classification.
Fortunately, someone much smarter than I is here to explain.
Brain Palmer of Slate explains why no passengers were sucked off of Southwest Flight 812.
How risky might the latest incident have been for passengers? The pressure differential between the cabin and the outside was approximately 7.5 pounds per square inch, and the hole measured 720 square inches. That means the maximum force applied would have been around 5,400 pounds—more than enough to blow an unrestrained person out of the plane. But a passenger would only feel that much force if he were literally plugging the hole with his body.
Keep in mind that the hole was not right next to any passengers or beneath their legs. It was in the ceiling of the cabin, which would have been at least two to three feet away from the heads of anyone sitting inside. At that distance, the force of an explosive decompression would be greatly dissipated. Air-flow patterns are complicated, and it’s impossible to quantify this effect for any given passenger. But as a simple way to visualize the effect of distance, we might imagine the force spreading itself out across the surface of an expanding hemisphere centered on the hole. Using the formula for spherical surface area, we see that at a distance of three feet, the 5,400 pounds of force would be spread across an area of 8,143 square inches. Four feet from the hole, it would cover 14,476 square inches, and so on. As the force gets more and more stretched out, the proportion of it that would be working to push a body out of the plane diminishes. On top of that, the air would be free to flow around the passengers in their seats, which would make its impact still weaker. Since the hole was in the ceiling of the plane, any decompressive force would have had to act against the full body weight of any passengers, lifting them up and out of their seats before it could eject them in a gust of air.
Here’s an experiment that illustrates the principle: Plug your sink drain with a rubber stopper, fill the sink with water, and then slowly remove the stopper. You’ll notice that the stopper is much harder to budge when it’s close to the hole and perfectly aligned with it. But tilt the plug slightly, or pull it out a little bit, and the force becomes barely noticeable. That’s more or less analogous to what happens when a hole opens in a Boeing 737 at cruising altitude.
So I guess it turns out that you can’t believe everything you see in action movies. I really can’t believe Steven Seagal would be disingenuous with his art.
An interesting and highly scientific analogy. My description would have been much simpler. “It was only 18 minutes into the flight and the fasten seat belt sign was still lit”.
Myth Busters solved this one in one of their segments. Getting sucked out of the plane is not something I worry about anymore.
I was informed of this and saw it on the news! When I heard about what happened, I sent a concern email to Southwest Management in Dallas/Love Field. As a Southwest Airlines Captain myself, I am very serious about safety. Our safety record has been unbroken for more than 70 years and I am NOT going to let that happen.