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Why don't seats on airliners have shoulder straps, like the seats in (European) coaches often do? Wouldn't a shoulder-strap be more effective than adopting the brace position, in the event of a crash-landing?

There's no definite answer in the other question. Speculation that the brace position may be safer than a restrained torso but unrestrained head. Speculation that seats may not be strong enough to usefully hold a shoulder strap.

I'd like to know whether the lap-strap is a "legacy" pre-dating automotive shoulder-strap inertia-lock mechanisms (retained for economic reasons?), or whether lap-straps are actually known to be a safer solution in an aircraft environment (without air-bags, with a seat in front).

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    $\begingroup$ Related: Why did my business class seat have a three point shoulder harness? $\endgroup$ – ymb1 Jul 17 '18 at 17:14
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    $\begingroup$ Perhaps it's because the main purpose of airplane seat belts is to keep passengers from bouncing around during turbulence, and a lap belt is sufficient for that? $\endgroup$ – jamesqf Jul 17 '18 at 17:44
  • $\begingroup$ Those European coaches only have shoulder straps on the first seat row. The rest has lap belts, just like airliners do. $\endgroup$ – Peter Kämpf Jul 17 '18 at 20:30
  • $\begingroup$ I think the duplicate question covers this one. But to re-iterate, it's because the purpose of the seat belt is not to protect the human body from sudden deceleration like in a car. Therefore it is neither pre-dating modern road car seat belts for economic reason, nor because lap belts are safer. It is a different solution engineered to solve a different problem: keep passengers in their seats during turbulence. The belts on airplanes keep passengers from going up while belts in cars keep passengers from going forward. $\endgroup$ – kevin Jul 18 '18 at 1:44
  • $\begingroup$ @kevin I don't think that's right. The lap belt decelerates your lower body in a lateral deceleration, while the seat back in front of you yields and supports your upper body. Note brace position, where you pre-position your head on the seat, as well as the fact that bulkhead rows or premium seats with legroom in front have airbags or shoulder belts. In a car, there is no close, yielding, flat surface in front of you. Rather, there's a steering wheel or windshield. $\endgroup$ – user71659 Jul 18 '18 at 3:28

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