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Exam Prep Question #3 - Seatbelts / infants AND (need a supplement loopbelt)

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t117tim created the topic: Exam Prep Question #3 - Seatbelts / infants AND (need a supplement loopbelt)

There is a question in the 3rd PPL prep exam about the 'carriage of infants in an aircraft' . . .

All the answers seem 'incorrect' in the context of Part 91 Div 20.03 ... given the infant actually needs a loop seatbelt attached to the adults seatbelt, they just can't be "held" in the arms of an adult as your answer suggests.

Yes the legislation does say they can be carried in the arms of the adult but the AND at the end of sentence means there are 'additional' considerations.

Is the answer out of date or what is it that I have missed ?

Thanks, Tim
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  • John.Heddles
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John.Heddles replied the topic: Exam Prep Question #3 - Seatbelts / infants AND (need a supplement loopbelt)

Seating has gone through many certification iterations over the years and infant restraint likewise.

Consider the physics of the problem -

(a) an infant may weigh in the order of, say, 5-15 kg

(b) survivable crash loads may vary considerably but, typically, in a range up to, say, 15g. Seats, for quite some time, now, have been designed on the basis of automotive standards where we are looking at higher loads which, in turn, vary with the type of aircraft intended for their use. As a sideline note, the highest loads are for helicopters which makes those seats super expensive.

(c) how would you fancy trying to hold an object (infant) whose apparent weight in a crash situation suddenly jumps to, say, 200-300 kg ? Holding an otherwise unrestrained child is somewhere between stupid and really stupid if the aim is to survive a crash. Mum or dad just are not up to the task, unfortunately.

(d) the majority of seat restraints are lap belt only. Have a look at this video (CAMI is the FAA's medical specialist facility for all sorts of stuff).

www.bing.com/videos/search?q=child+seat+...Bvideo%26FORM%3DVDRE

Current test requirements cover a range of considerations but, for the load, a fairly sudden 16g stop (for airline seats). Have a good look at what the test dummies do under the crash load. (The test facility is lit up like the MCG - you wouldn't believe the light intensity - due to the high frame speed and shooting exposure times. What you are watching is a VERY, VERY slowed down replay – in reality the whole thing is over in the blink of an eye.

Now, consider how you might try to hold the infant. Then consider, were you actually able to hold and restrain the infant, what would happen both to the infant and the adult as the adult collapses above and below the belt and crushes the infant. Just doesn’t work so those who hold to the idea of restraining an infant on the lap are way, way, away in la-la land.

So, what can we do ?

(a) just have the infant resting on the lap without any attempt to restrain ? Sure, but no good at all in a crash.

(b) have an auxiliary seat belt, or similar, stitched to the adult lap belt with the auxiliary belt restraining the child. OK, the child might not go sailing over the next seat but gets killed by the adult’s body loads. Not really an improvement. Then, again, it might not work anyway –



(c) have the infant in a separate standard seat. A bit better, maybe, but not much better. The size of an infant is incompatible with adult belt restraints so we would expect to see the infant ejected from the seat belt in a crash. Not really good vibes here.

(d) have the infant in a bassinet or child car seat restrained in a separate adult seat with appropriate restraints to the seat and vehicle structure. Works reasonably well as seen in auto sled tests for child auto seats.

www.aostechnologies.com/videos/automotiv...esting-of-baby-sled/

I couldn’t find a video of a bassinet test, although I am sure they exist. That would be a design nightmare and is one with which I have not been involved as an engineer.

I won’t comment, specifically, on the rule words as I am not a lawyer and I have long had the greatest reservations in respect of the rules for this problem. However, I think you might revisit your interpretation of the syntax.

However, we might consider the answer selection –

(a) the infant is unrestrained in this case from a point of physics so, no good.

(b) the child is not effectively restrained due to the geometry so, no good but, perhaps, a little better

(c) adult and child are restrained by a common belt. The child dies and, possibly, the adult as well.

(d) you’re got to be kidding me – an obvious distractor.

(a) is the old rule, traditional approach but, as discussed earlier, definitely not satisfactory and not kosher with regard to the current rules. The question is out of date and has some problems re the present rules.

About the only situation I see where the problem is addressed well is with privately owned light aircraft where the owner has had the aircraft modified to suit an infant auto restraint unit. In past years I have designed a number of these and they worked pretty well as well as being of modest cost to the owner-parent.

(Sidenote: in a previous life I was principal design and certification engineer for a major aircraft seating manufacturer).

Engineering specialist in aircraft performance and weight control.
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t117tim replied the topic: Exam Prep Question #3 - Seatbelts / infants AND (need a supplement loopbelt)

Thank you John for such a thorough, complete and "unrestrained" answer.

I'll take your experts opinion towards the end of the post to conclude the ANSWER suggested is indeed OUT OF DATE - per "(a) is the old rule, traditional approach but, as discussed earlier, definitely not satisfactory and not kosher with regard to the current rules. The question is out of date and has some problems re the present rules"

Any idea where can I claim my sparkling water for pointing out the exam question needs updating?

Cheers, Tim
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  • John.Heddles
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John.Heddles replied the topic: Exam Prep Question #3 - Seatbelts / infants AND (need a supplement loopbelt)

Any idea where can I claim my sparkling water for pointing out the exam question needs updating?

I'm sure both Bob and Stuart will spot your good deed when they get back from the holiday break.

Engineering specialist in aircraft performance and weight control.
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  • John.Heddles
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John.Heddles replied the topic: Exam Prep Question #3 - Seatbelts / infants AND (need a supplement loopbelt)

One should be familiar with the rules at Part 91 MOS Division 20.2.
www.legislation.gov.au/Details/F2022C00789

I overlooked including the follwoing link in the earlier posts - AC 91-18v1.1 Restraint of infants and children
www.casa.gov.au/search?keys=ac+91-18

Engineering specialist in aircraft performance and weight control.
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