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What's the point of the usual "please keep your seat belt fastened until the aircraft stops completely (at the gate)" in large passenger aircrafts? Since the plane is on the ground, it is not moving very quick. Even if it stopped abruptly, the seat belt won't prevent me from banging my head against the seat in front of me since it's a two-point seat belt.

The only reason I can think of is if two aircraft collided with each other, which could potentially generate enough force for the seat belt to be useful. Though, I could argue that when a plane is taxiing to the gate, it has to abide to a certain speed limit, which would render any kind of collision not serious enough to be prevented by two-point seat belts.

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    $\begingroup$ If not, people would stand up and move around. Chaos would ensue, not the least to say a sudden stop could cause people to fall and the frail and elderly to break limbs and so on. Do you undo your car seat belt whenever you move at slow speed? $\endgroup$ – Simon Jun 6 '16 at 11:15
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    $\begingroup$ example: avherald.com/h?article=432c535e&opt=1024 $\endgroup$ – Federico Jun 6 '16 at 11:17
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    $\begingroup$ @Simon That's a good point about keeping people seated. I was trying to think of an accident prevention use case but crowd control seems like a likely motivation for this rule. $\endgroup$ – mart1n Jun 6 '16 at 11:25
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    $\begingroup$ taxiing aircraft are moving at speeds similar to cars in city traffic (on high speed taxiways they can go pretty damn fast too by the way), braking hard (you don't need a collision) will cause anyone standing up to lose their footing. "Not moving very quick" is in many cases an optical illusion, you're high up on a huge taxiway, everything around you is big, and thus everything seems to be moving slowly. $\endgroup$ – falstro Jun 6 '16 at 11:26
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    $\begingroup$ "Why do I have to keep my seatbelt on in the car? Even at a stoplight?" Because you never know when something else might hit you. $\endgroup$ – abelenky Jun 6 '16 at 12:48
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Ground operations are just as dangerous as air operations. Strictly speaking the deadliest aviation incident actually happened on the ground (not saying seatbelt played a role or not however severe accidents do happen on the ground). The comments cover things well, (keeping people seated, keeping people from accessing over head compartments etc.) Planes are not safe simply because they are on the ground, they are only safe from flight related incidents and once on the ground they are susceptible to ground related incidents. By some estimates 27,000 ground incidents happen a year. The fact remains there are plenty of things to hit on the ground and plenty that can go wrong in taxi. These accidents are classified by ICAO under (RAMP) and (GCOL) codes (and potentially others). Boeing has a breakdown of accidents by flight category (taxi and ground ops make up about 10%).

Furthermore here in the US under the FAA FAR 91.107 as well as FAR 121.311 in the commercial case(basically the same wording) requires it

...(3) Except as provided in this paragraph, each person on board a U.S.-registered civil aircraft (except a free balloon that incorporates a basket or gondola or an airship type certificated before November 2, 1987) must occupy an approved seat or berth with a safety belt and, if installed, shoulder harness, properly secured about him or her during movement on the surface, takeoff, and landing. For seaplane and float equipped rotorcraft operations during movement on the surface, the person pushing off the seaplane or rotorcraft from the dock and the person mooring the seaplane or rotorcraft at the dock are excepted from the preceding seating and safety belt requirements....

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    $\begingroup$ Also possible that if passengers were allowed to stand up, they would remove their baggage from the racks. This could be a problem to have obstacles all over the floor (or in the hands of the passengers) if the cabin had to be evacuated due to hydraulic fluid leaking on the hot brake discs. $\endgroup$ – mins Jun 6 '16 at 18:07
  • $\begingroup$ @Dave I would add Mins comment to your answer. It's another excellent reason to keep people belted in. $\endgroup$ – Simon Jun 6 '16 at 18:49
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    $\begingroup$ Added and citied $\endgroup$ – Dave Jun 6 '16 at 18:51
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Twice, I've had vehicles (the tractors that tow the baggage carts) cut sharply in front of me as I've taxied toward the gate. The individual driving the tractor was either oblivious or reckless -- either way, foolish in the extreme -- but no matter what his issues are, I'll do everything I can to avert the risk of a collision. And that means using the wheel brakes that can stop the aircraft when it's moving nearly 200 mph... and using their full braking capability, right now. If anyone were standing, he'd have a face full of bulkhead or floor before he had an opportunity to react. If he were retrieving luggage from an overhead bin, the chance that he'd be able to control the bag are probably pretty slight, and now it's a projectile coming down on the back of somebody's head.

Even our Flight Attendants stay seated as we taxi in to the gate, simply because of the risk that the pilot may need to bring the aircraft to an immediate, even violent, stop with no warning. It's pretty rare, but when it happens, it happens hard. Taxiing out for takeoff, you've left the congested gate area behind, and this risk is lower, but after landing, you're heading to the most congested area with the greatest opportunity for something or someone to intrude into the path of the aircraft.

So, yes, by all means, please do follow the Flight Attendants' instruction, and example, and remain seated with your seatbelt fastened until we're parked at the gate. The face or other body parts you save, might be your own!

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  • $\begingroup$ The wheel brakes that can stop the aircraft from 200 mph don't actually have that impressive braking action. The limiting factor for stopping is not the deceleration rate (the runway needs to be long enough for take-off anyway) but the kinetic energy the brakes convert to heat. From 50 mph, any old bus can stop in a bit shorter distance than most aircraft (and people do stand in buses). $\endgroup$ – Jan Hudec Jun 8 '16 at 20:59
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    $\begingroup$ @JanHudec The deceleration rate of brakes is vastly important for an RTO, which is also the limiting factor for runway length. An emergency stop in a bus would throw people around too. Heck, regular stopping can knock people over which is why they ask you to hold on. $\endgroup$ – OSUZorba Jun 9 '16 at 3:54
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A plane that has just landed is actually in a new and vulnerable condition. The passengers may finally be relaxing because the wings didn't fall off and the Italian mathematician in has packed away his terrifying scribblings, but the aircraft has entered a new environment with new risks, and the crew are certainly not thinking "There, done that, work's over."

A stationary or slow-moving aircraft is at risk from a fuel, oil and even other fluid leaks in a way that one that's flying isn't.

A newly-landed aircraft has new, different stresses on its structure.

One that's just landed has hot engines, brakes and tyres. Tyres in particular, but also other components, can and do catch fire.

Unlike when it's in the air, an aircraft heading to the terminal is in close proximity to buildings and other obstacles, some of which also move around themselves.

For any number of reasons aircraft may need to be evacuated, or manoeuvred violently shortly after landing.

Those are not circumstances in which you want 200 people standing up, blocking each other's view of the cabin crew, talking loudly, pulling luggage out of overhead compartments, putting objects in the aisle.

The safe place for people to be is sitting quietly in their seats, until the doors are opened and they are invited to get up and leave.

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