When the “fasten seat belt” sign flashes on in airplanes, with its familiar accompanying ding, it’s often met with passengers’ equal parts annoyance and resignation, when it’s acknowledged at all. Like, “What? Again? Really? Do I have to …?”
The answer, of course, is yes. You really have to. As Mom would say, “it’s for your own good.”
A simple lap belt — or even other restraints, like shoulder harnesses — may not be enough to save a life if an airliner drops from the sky from 35,000 feet (10,668 meters), or undergoes a catastrophic mid-air failure. A seat belt wasn’t enough in the tragic death of Jennifer Riordan, who reportedly was wearing her seat belt when a part from a failed engine in a Southwest Airline 737 blew out the window next to her seat on April 17, 2018. She was nearly sucked out of the airplane when the air in the pressurized cabin rushed out of the window.
The rare accidents like that, though, or the more conventional plane-hits-ground type, are not the only reasons for seat belts on airplanes. They’re designed to protect you from the airplane during flight, too.
It’s simple physics, Newton’s first law of motion: A body at rest will remain at rest unless an outside force acts on it.
Think of it this way: If you’re not wearing a seat belt on an airplane that drops suddenly — which often happens with turbulence — you’re the one at rest. You’ll stay at rest as the plane, very literally, drops out from under you. If you’re strapped in, the seat belt serves as an outside force acting on you, taking you with the plane as it drops and saving you from bonking your head on that overhead bin above you.
A little reasoning might suggest that if a lap belt is good while flying, a shoulder harness — like those in cars and those in smaller so-called general aviation planes — would be even better. Indeed, shoulder belts or harnesses might help.
But they would be costly to install, and trickier to get to work correctly on bigger commercial planes, experts say. They’d probably be uncomfortable on longer flights. And wearing shoulder harnesses might meet a lot of resistance from the flying public, too.
Some wonder whether shoulder belts are needed on commercial airlines, considering lap belts — when they’re used — seem to do the trick. In smaller aircraft, though, shoulder harnesses — which are required for all seats in all small airplanes manufactured since Dec. 12, 1986 — work and work well. Used with lap belts, shoulder harnesses in smaller planes have been shown to reduce serious injuries from accidents by 88 percent and fatalities by 20 percent, according to the Federal Aviation Administration (FAA).
Ironically, the safety record of commercial airlines may be the overwhelming reason that shoulder harnesses have not been required of large passenger planes. In 2017, no one was killed in a commercial jet airliner incident anywhere in the world, making it the safest year ever for big passenger planes. In its Civil Aviation Safety Review for 2017, which examined accidents on large passenger aircraft, the Dutch aviation consulting firm To70 estimated that there were “0.08 fatal accidents per million flights [in 2017]. That is a rate of one fatal accident for every 12 million flights.”
With a safety record like that, it’s hard to argue that shoulder harnesses would lower the risk of flying enough to offset the costs, the effort and the resistance such a major change would generate.
Lap belts, though? They help. They help a lot. So when flying, it’s probably best to buckle up and stay that way. For your own good.
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