Not a cc, however.......
go to disagree with you there, cockney steve, I've seen it happen a few times with strong braking during a landing...
In one case, a kid was lying across the mother's lap. we had a right time getting her to sit the child upright and put the armrest down (explaining that yes, it can move during landing and cause injury- not to mention that seatbelts don't work when they are loose and you are lying down)
Lo and behold we get the "crew prepare for landing" PA, I happen to look up and see the mother raise the armrest, and lay the kid back down. Despite telling her to correct it, she didn't and by this time it was semi-brace time so no more talking. (She had been warned)
We landed, quite a firm and fast one, and as soon as the guys hit reverse the armrest slammed down and clonked little Kevin on the head, eliciting a wail of pain and sent him crying for a good few minutes.
Not the last time I saw this happen either. I guess it depends on the aircraft make but I saw it more on older models. I guess the endless up/down of the armrests makes them easier to move. Newer aircraft you may notice have little pegs to stop them going backwards, but nothing for fowards, obviously.
In one case, a kid was lying across the mother's lap. we had a right time getting her to sit the child upright and put the armrest down (explaining that yes, it can move during landing and cause injury- not to mention that seatbelts don't work when they are loose and you are lying down)
Lo and behold we get the "crew prepare for landing" PA, I happen to look up and see the mother raise the armrest, and lay the kid back down. Despite telling her to correct it, she didn't and by this time it was semi-brace time so no more talking. (She had been warned)
We landed, quite a firm and fast one, and as soon as the guys hit reverse the armrest slammed down and clonked little Kevin on the head, eliciting a wail of pain and sent him crying for a good few minutes.
Not the last time I saw this happen either. I guess it depends on the aircraft make but I saw it more on older models. I guess the endless up/down of the armrests makes them easier to move. Newer aircraft you may notice have little pegs to stop them going backwards, but nothing for fowards, obviously.
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the armrest slammed down and clonked little Kevin on the head, eliciting a wail of pain and sent him crying for a good few minutes.
Funnily rnough, I nearly added to my original post, "unless madam suffering a broken fingernail counts"
tut tut, silly me.
You warned the pax that the self-evident would happen, IE piss-poor armrests with no friction pads in the swivel would slam down on rapid deceleration . they learned that you weren't telling porkies. but injury?...Nah!- unless you count their bruised ego.
I don't argue with the suggestion that they should be down, but all the dynamic mass in the overheads is more of a worry than a tap from a relatively lightweight armrest pivoting 90-100 degrees.
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The G though in a normal landing and deceleration is nothing compared to a crash.
And it doesn't take much to give a relatively light mass enough of a difference in velocity to give it a marked energy differential when it wacks something, square of the velocity and all that. If the plane declerates at 5G its on a pivot so will act as a lever which will turn it into a rotational system. It only takes 18 joules of energy to break an arm.
But I suspect we are getting over complicated and that the seats have only been analysed in the arm rest down position for the relevent codes. So they put in the manuals that they need to be down which then ticks a box for approval.
Engineering wise you don't want things moving within a system as relatively quickly there are huge forces occur with relatively small differences in velocitys. Which is why air bags are so effective stopping the travel of the persons body before there is to much difference between the relative velocity of the persons head and the dash board.
And it doesn't take much to give a relatively light mass enough of a difference in velocity to give it a marked energy differential when it wacks something, square of the velocity and all that. If the plane declerates at 5G its on a pivot so will act as a lever which will turn it into a rotational system. It only takes 18 joules of energy to break an arm.
But I suspect we are getting over complicated and that the seats have only been analysed in the arm rest down position for the relevent codes. So they put in the manuals that they need to be down which then ticks a box for approval.
Engineering wise you don't want things moving within a system as relatively quickly there are huge forces occur with relatively small differences in velocitys. Which is why air bags are so effective stopping the travel of the persons body before there is to much difference between the relative velocity of the persons head and the dash board.
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8900.1
Thanks...lj101,
I tried to give a simple answer without the JARGON
...you know...but your really put it right.
I tried to give a simple answer without the JARGON
...you know...but your really put it right.
Last edited by Cabin Safety; 29th Oct 2012 at 15:35.
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As somebody who has been in a pretty bad car crash, the forces applied to the body on impacts are something difficult to comprehend unless you've experienced it.
An armrest may serve to help the belt prevent lateral motion. Sure, a few bones may be broken but it's better that some of the energy is transferred to the rest rather than just the seatbelt absorbing the energy which I imagine could cause some further abdominal injuries (one of the drawbacks of not having 3/4 point harnesses.
An armrest may serve to help the belt prevent lateral motion. Sure, a few bones may be broken but it's better that some of the energy is transferred to the rest rather than just the seatbelt absorbing the energy which I imagine could cause some further abdominal injuries (one of the drawbacks of not having 3/4 point harnesses.
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^^^^^^ yup! that's what i've been trying to say all along....the "safety" aspect is an illusion...any "sudden decelleration" that causes an armrest to wag about forcefully, is going to "wag" the pax a f-in sight more.
I suspect they aren't primarilt designed as an energy absorber and as the last poster stated, they'll likely break a few ribs.
I, too have done the big motor-accident bit....internal organs don't like sudden stops, and as I pointed out, a waist-only belt can have dire consequences in high load situations. As no-one's produced any evidence that the whole pax-restraint matrix (rails/seats/belts) is designed to fail progressively before actually fatally injuring the occupants, one must assume the earlier poster hit the nail on the head, I.E. to hold the bodies in position and aid identification.
OK so I paraphrase but the gist is the same, IMHO, the pax restraints/crash-protection are largely illusiory in a situation where surviveability would be marginal.
Just suppose the armrests (remember them?
were longer and designed to ram into a socketin the seat in front....the seats could not tear out from the rails....the whole shebang would progressively collapse forward in a big bump.....now we have a 21st. century crumple-zone....add airbags in the seatbacks and redesign the aisle armrests or big sidewings on the aisle seats....
Pax may have an acceptance-problem , being held in what is effectively an individual booth (I prefer "Safety -Cell") but I'm damned sure that we could improve on the present system which is basically unchanged since the dawn of commercial aviation.
Dare I whisper "cost and what they can get away with"
I suspect they aren't primarilt designed as an energy absorber and as the last poster stated, they'll likely break a few ribs.
I, too have done the big motor-accident bit....internal organs don't like sudden stops, and as I pointed out, a waist-only belt can have dire consequences in high load situations. As no-one's produced any evidence that the whole pax-restraint matrix (rails/seats/belts) is designed to fail progressively before actually fatally injuring the occupants, one must assume the earlier poster hit the nail on the head, I.E. to hold the bodies in position and aid identification.
OK so I paraphrase but the gist is the same, IMHO, the pax restraints/crash-protection are largely illusiory in a situation where surviveability would be marginal.
Just suppose the armrests (remember them?
were longer and designed to ram into a socketin the seat in front....the seats could not tear out from the rails....the whole shebang would progressively collapse forward in a big bump.....now we have a 21st. century crumple-zone....add airbags in the seatbacks and redesign the aisle armrests or big sidewings on the aisle seats....Pax may have an acceptance-problem , being held in what is effectively an individual booth (I prefer "Safety -Cell") but I'm damned sure that we could improve on the present system which is basically unchanged since the dawn of commercial aviation.
Dare I whisper "cost and what they can get away with"
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That's right cockney, and something else you mentioned about the rest slamming down seems likely too, somebody dismissed your comment about that, but obviously a severe crash is going to create many tens of g's of force, possibly increasing the effective weight of the rest 40+x.
Imagine the if the armrest only weighed half a kilo. That's a potential of 20kgs+ of force which, if it hit you in the back (if your body happened to be moved laterally upon impact) it would smash into your spine. Just something else to consider, as cockney said. (I think the spine can absorb forces of about 20-25kgs before it gives way. (I watched on an anatomy programme).
Imagine the if the armrest only weighed half a kilo. That's a potential of 20kgs+ of force which, if it hit you in the back (if your body happened to be moved laterally upon impact) it would smash into your spine. Just something else to consider, as cockney said. (I think the spine can absorb forces of about 20-25kgs before it gives way. (I watched on an anatomy programme).
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Dare I whisper "cost and what they can get away with"
Some of you seem to be labouring under the illusion that industry safety criteria are knocked out in biro on the back of a beer mat by a few blokes in a pub in between wednesday night Karaoke numbers. Naturally, this means that armed with a few semi-digested facts, a DVD of Air Crash Investigation and enough time on your hands to marshall the resultant purée into something resembling coherence you believe that you can now make safety pronouncements with equal validity to the so-called experts.
This is a forum intended for use by people who are part of a team that take the safety of their customers very seriously indeed: They usually work for a company that shares that view, and work on-board aircraft that have been designed and tested over a long period of time by people who can prove that they are qualified to do so. If you feel that strongly about what is essentially T-Shirt sloganeering the path to safety, then why not start a Facebook cause and get your friends to "Like" if they agree: Meanwhile, the professionals can get on with what matters.
The original question has been answered, and yes, the OP had every right to pose such a question: PPRuNe at its best is when these questions are asked by customers, and then answered by people in the business who know - PPRuNe at its worst is when the answers are then ignored.
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Well, I waited 'till I cooled down a bit.
This is hardly the most dynamic sub-forum, yet when someone tries to stimulate a bit of intelligent discussion about SOPs that are blindly and unquestioningly followed, one gets patronised, scorned, belittled and shouted down. you want to stifle debate?
For what it's worth......
1- basic safety of Pax hasn't changed since the dawn of Commercial Aviation.....look at motor-car safety and then tell me it can't be done.
2 I stated that in a "sudden decelleration" SUFFICIENT TO MAKE THE ARMREST A REAL DANGER....the Pax would have a lot more serious injuries to worry about....well, they wouldn't , 'cos they'd be dead/unconcious)
3 Excuses about armrests swivelling backwards, is an excuse for piss-poor design and engineering. look at Cinemas/theatres/road transport....yup, they're regulated as well, "pax" have to escape from a bloody sight longer rows of seats than in a plane!- Granted, there ain't many Cinemas crashed recently
4 Blind faith in what your lords and masters decree, doesn't make it informed, honest , truthful and reasoned....even though you "take safety seriously"
5 a lap-belt gives some protection, a lap/diagonal is better, 5-point harness the best....they ALL work BY STRETCHING and slowing the body down in less than a foot, rather than stopping dead.....that's why airbags work so well....the smaller the amount of webbing, the higher the point-load on the body....victims die because organs slam around inside the body and get ruptured.
I never argued that "armrests down" was not good practise...of course it is.....so would removing overheads entirely and having reinforced stowage under the seat in front.....but it's unlikely to happen.
Why spend a rake of money on developing extra crash protection.....everyone accepts the current status-quo, so it's not cost -effective.......However, develop WINGLETS and even retro-fit them and the balance -sheet shows a goodly percentage fuel -saving every sector........
going to join the OP in Jet Blast.
This is hardly the most dynamic sub-forum, yet when someone tries to stimulate a bit of intelligent discussion about SOPs that are blindly and unquestioningly followed, one gets patronised, scorned, belittled and shouted down. you want to stifle debate?
For what it's worth......
1- basic safety of Pax hasn't changed since the dawn of Commercial Aviation.....look at motor-car safety and then tell me it can't be done.
2 I stated that in a "sudden decelleration" SUFFICIENT TO MAKE THE ARMREST A REAL DANGER....the Pax would have a lot more serious injuries to worry about....well, they wouldn't , 'cos they'd be dead/unconcious)
3 Excuses about armrests swivelling backwards, is an excuse for piss-poor design and engineering. look at Cinemas/theatres/road transport....yup, they're regulated as well, "pax" have to escape from a bloody sight longer rows of seats than in a plane!- Granted, there ain't many Cinemas crashed recently
4 Blind faith in what your lords and masters decree, doesn't make it informed, honest , truthful and reasoned....even though you "take safety seriously"
5 a lap-belt gives some protection, a lap/diagonal is better, 5-point harness the best....they ALL work BY STRETCHING and slowing the body down in less than a foot, rather than stopping dead.....that's why airbags work so well....the smaller the amount of webbing, the higher the point-load on the body....victims die because organs slam around inside the body and get ruptured.
I never argued that "armrests down" was not good practise...of course it is.....so would removing overheads entirely and having reinforced stowage under the seat in front.....but it's unlikely to happen.
Why spend a rake of money on developing extra crash protection.....everyone accepts the current status-quo, so it's not cost -effective.......However, develop WINGLETS and even retro-fit them and the balance -sheet shows a goodly percentage fuel -saving every sector........
going to join the OP in Jet Blast.
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...when someone tries to stimulate a bit of intelligent discussion about SOPs that are blindly and unquestioningly followed...
...going to join the OP in Jet Blast.
