- Hi, and welcome back.
So in the first part, we went over the new and novel seats,
what the FAA did to start addressing those,
and what test dummies we anticipated using in this research.
For part two, I want to go into the development
of the new injury criteria, some of the PMHS testing,
and that actually stands for post-mortem human surrogate,
the injury criteria that were developed,
the of the wrap-up of the projects,
and then I'll get into some of the policies
and the testing requirement.
Now you have the test dummies that we want to use
and we know what kind of structure
around the occupant we anticipate,
this is where we come up with new injury criteria.
And the way that we do that is we test a PMHS
and an ATD in the same situation, in the same circumstances,
at the same velocities and accelerations,
and we compare the loading and the injuries that we see
in the PMHS against the loading that we see
in the test dummy.
We used various restraints in both of these,
and we did a range of accelerations to figure out,
we know that there be an injury here,
but where does that injury start?
And that's why you'll see
that it's not always at the full certification pulse
that we run these tests.
We actually do it a little bit lower at times.
And we use the same configurations that we used
that were determined
during the CAMI testing in Oklahoma City.
So for the side-facing PMHS,
this is one of the tests that were run,
and each red mark, there are two slashes on the spine
and there's multiple red dots on the ribs
as well as a break in the clavicle.
And in the leg, we had a mid-femur,
a mid-shaft fracture,
and each one of those represents some type of bony injury
that occurred during the testing.
That was just one injury that we saw in one of the tests,
but for the side-facing, we broke it into two phases.
And in phase one where we were doing the full acceleration,
we saw very serious neck injuries.
In the common side-facing seat configurations under Part 25,
which is your transport category, Crash Pulse,
additional injuries that we expect
are rib fractures due to the belt and direct loading,
femur and hip fractures due to leg flail,
and carotid intimal tear due to the shoulder belt loading.
And that means that the belt
was loading so hard on the neck
that it actually did damage the carotid artery.
And some of the head angular acceleration levels
actually suggested up to an hour of unconsciousness,
which is not okay
because occupants need to be able to egress an aircraft
after a crash event.
Phase two used full body and isolated head-neck specimens.
What we found is the maximum lateral bending moment
produced in the PMHS was 651 inch-pounds,
and the corresponding ATD,
so ES-2 lateral bending recorded was 1,018 inch-pounds.
And at that level,
there were no detectable spinal injuries produced.
We're not just looking
for what type of injuries,
but we're looking at what level and what loading
do those injuries no longer appear,
and where's that threshold so we know
where to start protecting people at.
For the oblique PMHS results, here's another one.
This is actually three specimens
represented by these graphics.
We had several spinal injuries,
numerous rib injuries,
and that was at the 100% pulse.
So then when we ran it again at the 60%,
so 60% of the same energy
that goes into the certification pulse
is what we ran that one at,
there were no injuries detected.
That starts parsing down
where the onset of injuries might be.
Some of the injuries produced during the PMHS tests
are some of the same ones we anticipated
based on the initial tests at CAMI,
spine injuries, rib fractures.
And then we had a few other injuries that occurred
that weren't predicted.
MCW, the Medical College of Wisconsin,
conducted matched pair testing with the FAA Hybrid III.
And in particular, it was lumbar tension
that we saw that was an issue.
We had a spinal transection at the lumbar level
that we hadn't anticipated.
And the ATD test corresponding to the non-injury PMHS case
produced 5.2 kilonewtons
which is 1200 pounds approximately of tension in the spine.
And the testing done both at MCW and CAMI
showed that a poorly restrained occupant
in an obliquely oriented seat
is at fairly high risk of a fatal injury.
The test configurations we tested
are likely the extreme worst case.
There wasn't any structure in front of them
to absorb energy.
We didn't have any airbags involved.
So there's other cases that are gonna be less injurious.
The results indicated that our current policy
of really limiting flail
in both the side- and the oblique-facing seats is warranted.
Now that we know the type of injuries
and what our thresholds are,
we're going to use the ES-2re injury criteria
to help protect the occupants.
So first and foremost,
we're going to continue with a HIC limit of 1,000,
which is exactly what we have
in the forward-facing criteria.
We're going to use the upper torso strap load limit
of 1750 pounds,
which is also something that is used
in the forward-facing criteria.
But now we're going to have some upper neck limits.
So the amount of tension that's allowed
inside of the upper neck load is 405 pounds.
And in compression also has to be less than 405 pounds,
and the torque or the rotation in the neck
needs to be less than that 1,018 inch-pounds
that we saw as that onset of injury.
And the sheer in the neck
needs to remain below 186 pounds.
For the ribs,
we'll use the upper, middle, and lower rib deflection.
Each needs to be less than 1.73 inches.
The sum of the abdominal forces,
so it will separate them all out by front, middle, and rear.
You add them together,
and that needs to remain less than 562 pounds.
The pubic symphysis force is less than 1350 pounds.
We put in a lower leg flail limit of 35 degrees.
And I have a picture on the next slide
so that you can understand what I mean there.
And then the restraints need to remain on the ATD
throughout the event.
And that's just to make sure
that the restraints stay where they're supposed to
and they're not getting up into the abdomen
where they're not supposed to during the initial event.
And then the occupant support criteria,
that simply means that the pelvis
needs to be the load-bearing portion
at the bottom of the pelvis,
shall not translate beyond the edge
of the supporting structure.
The head and the neck shall not translate
beyond the plane of the seatback supporting structure,
and any lateral flexion of the torso
must not exceed 40 degrees
from the normal upright position during the impact.
And no occupant to occupant contact.
However, during rebound it's allowed.
The lower leg rotation, the criteria.
here is a picture.
There is a lack of biofidelity in the ES-2re hip,
and that means that even low energy
can still create a high rotation during rebound.
So we have a maximum femur rotation angle limit
of 35 degrees.
And you can see that one of the issues
is trying to capture that on video to quantify it.
In this instance,
we used TEMA Motion tracking software
to come up with 74 degrees
as the approximate rotation in that leg.
But you can also install an angular rate sensor
into the upper thigh bone and get that a bit more precise,
especially if part of the leg is obscured during the event.
And in this instance, the ARS gave us a value of 72 degrees.
During the rebound,
because of how the leg rebounds up,
that limit may not be quite as appropriate during that.
And that's true for both the full 16g test
and the threshold test.
The restraints have to stay on the occupant
during the impact and the rebound,
but some of the belt contact forces
are not likely to cause serious injuries
if the pelvic restraint slides off the pelvis
during the rebound phase of the impact.
Not the initial phase, the rebound,
if the tension in that strap remains less than 250 pounds.
Which means you're gonna have to make sure
that you capture the loads that you get in that belt.
Otherwise, you cannot prove
if that restraint tension stayed less than that
if the restraint ended up on the abdomen.
So here's a video of a side-facing test conducted at CAMI.
You can see that while the left leg
was captured by the structure,
the right leg was allowed to flail up
further than it should have.
And then there was a bit of rebound there
where the test dummy slid down just a little bit.
So we have this new criteria,
and the question is can existing cases
pass this new criteria?
So in the center there, that is a middle of the couch.
So there's no supporting structure next to the test dummy,
but with an inflatable bag
to then support the head and neck.
And you can see in this instance,
he passed all of the new criteria.
On the middle one there,
you have a test dummy up against a rigid wall.
So he's supported throughout the entire event.
Again, passing all of the criteria.
We didn't have to worry about rib deflection
or pubic symphysis forces
exceeding what they're supposed to.
Now, on that last one on the far right on your slide,
you can see we supported the head head and neck
and passed those criteria.
However, the leg, there was nothing to stop it.
And because of just the basic kinematics,
this one would have failed the leg injury criteria.
So in this instance,
it would need some type of a support
in order to protect the legs and then pass the leg criteria.
For the oblique seats, you must use the FAA Hybrid III.
We allow a HIC of 1,000.
Or if you have an airbag, you can do a HIC 15,
but it has to be less than 700.
We were able to use the neck, Nij,
so the neck injury criteria,
and you can see right below that bullet,
it's actually got the equation for it,
and it's a value of less than one.
And it's all based on whether or not
you're in compression and tension
and you use the appropriate numbers and values
to get your Nij.
The peak upper neck force
must be less than 937 foot-pounds in tension
and 899 pounds in compression.
No head rotation about the vertical axis past 105 degrees,
and no concentrated loading.
So this is another instance,
much like the lower leg flail in the side-facing,
you can use the video to try to estimate the neck twist,
but it's very difficult.
Especially in an oblique-facing seat
where you're now going to have to try to maintain
and figure out what the neck angle is
with respect to the upper torso.
So if you've got monuments or other things in place,
it's going make it very hard.
So in this case, on that picture at the top right,
we used TEMA again to try to do a video estimate,
and we got about 96 degrees.
But if you put an angular rate sensor in,
that's gonna give you a more precise number.
And then if your view is obscured
or you lose the ability to get that relative motion,
you can use the angular rate sensor information,
and we got an approximate value of 91 degrees
when we did that.
For the spine, we needed to maintain a lumbar tension,
so how much it's being pulled of less than 1200 pounds,
and no concentrated loading
between the pelvis and the shoulders during rebound.
So if during rebound, like in this picture,
your test dummy ends up being pulled backwards
just because of the nature of the structure,
usually if there's something behind
that may impact the spine, the test dummy may hit,
if there would be acceleration,
anything exceeding 20g must be less than three milliseconds
as measured by the thoracic instrumentation.
And that's because we want to make sure that on rebound,
we're not going to break the spine
because it impacts potentially the short shroud
around it.
So some type of structure or pod structure.
We want to make sure that that's protected.
and then no interaction with the armrest
or other seat components in any manner
that's different than would be expected
in a forward-facing seat installation.
Very similar to the side-facing,
any part of the load-bearing portion of the test dummy
must not translate beyond the edges
of the bottom seat cushion and supporting structure.
You have to support them through the entire event.
And then any leg axial rotation
must be limited to 35 degrees in either direction
from the nominal seated position.
And again, this is one
where because there's so much structure
around you potentially or around the test dummy,
it's easier to use instrumentation to get this angle
than to try to do it from photometric analysis.
So this was a test that we ran for the impact class in 2016.
And you can see that the airbag fired off to the left.
The test dummy impacted the structure in front of him,
and the head rotated as he rolled off
and then rebounded backwards.
So a whole bunch of things going on there
that you'd have to then assess.
Using this new tension criteria,
We took a look at with and without a shoulder belt
in all of our different configurations.
given that the tension limit is 1200 pounds,
you can see that if you had no shoulder belt,
you exceeded in every single situation.
So if you allowed the torso to flail forward,
you're going to fail the criteria.
But if we added a shoulder belt,
you see that there's actually a compression
that we see in the spine.
It makes sense.
As the test dummy rotates forward,
the shoulder belt keeps him from flailing,
and that load just goes into the lower spine.
But with our limit of 1500 pounds,
so that's our vertical injury criteria,
you're still well below that,
even with the compression loads generated.
So to kind of wrap it all up,
oblique- and side-facing seats are a novel design
not addressed rest in the current standards.
The current standards were written
for purely forward-facing seats.
And there's potential serious injuries,
injury risk due to neck tension, bending,
rib deflection, leg rotation.
And new policies apply the latest research findings
to ensure that we continue that equivalent level of safety.
And new procedures require
different injury evaluation methods
and a different test dummy.
You can't always use the standard forward-facing
if you're crashing sideways.
Current policies as of May 2021.
There is the technical criteria
for approving side-facing seats.
It was published in 2012.
The SAE has 8049/1B, and that's the performance standards
for side-facing passenger seats.
And that one is applicable to rotorcraft,
transport aircraft, and general aviation aircraft.
And that was from 2016.
Then we have for oblique,
a technical criteria for approving oblique seats,
and that's from 2018.
This is only for seats 18 to 45 degrees
with respect to aircraft center line.
So it does not apply past 45 degrees.
You would have to work with your certification office
if you wanted to install something
at let's say 60 degrees or something different.
And then the SAE has the performance standards
for oblique passenger seats,
but that one's limited for 18 degrees to 30 degrees
with respect to aircraft center line.
And the oblique research is still ongoing,
and as new data becomes available, the policies may change.
Testing requirements for these seats.
For the vertical test, there's no change.
You still have the same lumbar injury criteria.
You have the same structural criteria.
For the longitudinal structure,
you need to use the ES-2re,
the FAA Hybrid III or Hybrid II test dummies
to do your structural test.
And any supporting structures
need to be deformed with the floor.
When you do the injury assessment test,
you need to use the ES-2re for side-facing
and FAA Hybrid III for oblique testing.
And all of the references, all of the testing,
all of the reports that went into the research
that then the policies are based on
are on this slide as a part of the reference sources.
So you can go pull that up and read more in depth
if you're interested as to how we came up
with some of the criteria.
- All right, thank you, Amanda,
for a very engaging and informative presentation.
I hope everyone has enjoyed it as much as I have.
As I said, this is a lecture series that's a companion
to the dynamic impact test procedures training.
And so stay tuned for additional content and videos,
webinars in the near future.
Thank you and have a good day.