
Boeing 777X’s fuselage split dramatically during September stress test - exar0815
https://www.seattletimes.com/business/boeing-aerospace/boeing-777xs-fuselage-split-dramatically-during-september-stress-test/
======
tzs
> The relatively good news for Boeing is that because the test failed so
> explosively at just 1% shy of meeting federal requirements, it will almost
> certainly not have to do a retest. Regulators will likely allow it to prove
> by analysis that it’s enough to reinforce the fuselage in the localized area
> where it failed.

I don't understand this. So they did a test, and it failed at 99%. They
reinforce that one area where it failed, and show by analysis that the
reinforced area would have made it to at least 100%.

OK, but what about the rest of the fuselage? The rest was only tested to 99%.
Couldn't there be another place that fails at, say, 99.5%, which wasn't
detected in the first test because the place that fails at 99% stopped the
test?

Edit: I would guess that during this kind of test they have the plane heavily
instrumented with things like strain gauges so they can understand how it
reacts and see if it is behaving according to spec. So maybe it is the case
that the data from the rest of the fuselage showed that it would have made it
to 100% if the test had continued, and only the area that failed was in
trouble. That could explain why they aren't require to do another test.

That still leaves me unsatisfied, though. Presumably analysis of the design
_before_ the test said it would make it to 100%. If the failure was not due to
a manufacturing defect in that particular fuselage, then it suggests that they
analysis was not adequate. But then what assurance is there that their
analysis that shows that the reinforcement would hold is good?

~~~
lisper
The truth is that even the reinforcement they are going to do is more for PR
than for actual safety. This test was _intended_ to push the plane to its
limit. Not close to, but actually up to the limit, so it was actually
_expected_ to fail somewhere around this point. What they call 100% for this
test is actually 150% of what the plane is expected to experience in a worst-
case real-world situation. The difference between failing at 99% and failing
at 101% (which is what happened the last time they ran this test) is
negligible from a practical point of view. You'll almost certainly get more
variance than that in practice just from manufacturing non-uniformities,
random environmental factors, age, etc.

Boeing has committed a lot of sins recently, but this isn't one of them.

~~~
jodrellblank
> What they call 100% for this test is actually 150% of what the plane is
> expected to experience in a worst-case real-world situation. [..] The
> difference between failing at 99% and failing at 101%

So, what is it 100% of?

Not that I even care enough about Boeing clickbait to skimread the article,
but this discussion makes it seem like "percent" is a really poor fit for
whatever this is actually measuring and trying to communicate.

~~~
mlyle
So, first, airliners aren't really expected to experience more than 1.3G's of
loading in normal or even unusual operation.

They are expected to be able to survive 2.5G's (limit load) without structural
damage. The 777X satisfied this.

They are expected to be able to survive a few seconds of 1.5x this-- 3.75G--
without outright failure but possibly with (irreparable) structural damage.
Instead, it catastrophically failed at a loading corresponding to 3.70G's.

They are going to reinforce and fix the specific failure that happened at
3.7G's, and make an argument based on strain gauges and instrumentation that
another, distant failure was not likely before 3.75G's.

~~~
inferiorhuman
_So, first, airliners aren 't really expected to experience more than 1.3G's
of loading in normal or even unusual operation. _

This is 100% true. But the unexpected happens. China Airlines 006 saw 5G due
to pilot error. Everyone survived and the plane (Boeing 747-SP) saw another 25
years of service.

Additionally planes age. What's your failure point after 10-15 years of
service?

Another part that's worrisome is the original angle. Originally the failure
was reported as a cargo door blowing out. The pictures released show
otherwise. So the question remains: who got reporters to go with a cargo door
failure and why?

 _They are going to reinforce and fix the specific failure that happened at
3.7G 's, and make an argument based on strain gauges and instrumentation that
another, distant failure was not likely before 3.75G's. _

That depends on how much you trust Boeing's modeling and assembly skills. IMO
the pickle forks on the NG cast at least a little bit of shade on Boeing's
reputation.

~~~
mhandley
With regards to the cargo door story - a door did blow out, but it was a
passenger door, not a cargo door. Passenger doors are plug-fit (they're bigger
than the hole, and pressure holds them in place), so it's not really possible
for a passenger door to blow out. Cargo doors are not plug fit, so a latching
failure could cause a door to blow out. Everyone in the industry remembers the
DC10 cargo door failures.

I suspect the early rumours said a door had blown out, and as that's not
really a possible failure mode for a passenger door, it was assumed it must
have been a cargo door. Now, in this case a passenger door did blow out, but
it wasn't a door failure. The fuselage some distance below a door failed, and
split right up past the door. The partially unsupported door then blew out.
But the door was peripheral to the story. Boeing could definitely had handled
this much better, but it's not really surprising that in the absence of full
facts the rumour mill got this one wrong.

~~~
inferiorhuman
_Cargo doors are not plug fit, so a latching failure could cause a door to
blow out._

Right. A cargo door failure could be simply user error.

 _Everyone in the industry remembers the DC10 cargo door failures._

And the 747 ones too hopefully (user error and poor design).

 _The fuselage some distance below a door failed, and split right up past the
door. The partially unsupported door then blew out._

Right, the door failure was secondary.

 _Boeing could definitely had handled this much better, but it 's not really
surprising that in the absence of full facts the rumour mill got this one
wrong. _

Someone at Boeing obviously leaked part of the story (the door failed) and
Gates ran with what information he was provided. The question remains: why
only leak part of that story? Either failure will look bad to laypersons and
both would be dismissed fairly quickly by people more familiar with airliners.

Is the working theory that Boeing PR is simply that incompetent or short
sighted?

------
jvanderbot
This sounds fine. It's a catastrophic failure test. They push until it breaks,
then it broke, and they were very close to their designed target (within 1%).
If they had gone 1% past their designed target, they would have been upset, as
they could have made the plane lighter. They were 1% short of design limit,
they are upset because they'll have to add reinforcement.

Have you seen the wing failure test? I worked for the company that did these
tests (they did them before I worked there), and they still talk about how
upset the engineers were that it went over spec in strength.

[https://www.youtube.com/watch?v=Ai2HmvAXcU0](https://www.youtube.com/watch?v=Ai2HmvAXcU0)

~~~
awalton
The test on the Boeing 787 broke the load test machine - the composite wing
was so strong, they literally couldn't break it.

And let's just put this on record, so people can really shut up about this:
The Airbus A380 failed at 145% maximum wing load. That's a full 3.3% below the
safety margin. They did not retest, but did subsequently reenforce (just as
Boeing is here). The plane was put into service by the FAA.

~~~
neuronic
It's always the same on HN. Some post about any news at Boeing, be they good,
bad or whatever.

Someone has to chime in and drag Airbus through the dirt at least once. Let's
at least mention one issue regarding Airbus. Is this a sales platform?

Really makes you wonder. Maybe it's just some weirdo mix of patriotism and
capitalism.

~~~
awalton
This post didn't "drag Airbus through the dirt," it proved that there's no
issue with the testing process at hand. Airbus did nothing wrong, nor did
Boeing in this instance. Both "failed" to hit the target safety margin, took
remediation steps, and did not retest. This is the system working as intended.

The fact that you see this as somehow anti-Airbus is evidence of a personal
bias.

------
garaetjjte
>And the interior of the plane was pressurized beyond normal levels to about
10 pounds per square inch — not typically a requirement for this test, but
something Boeing chose to do.

Hmm. Does it lower structural integrity, or improves it?

~~~
sitkack
And is it likely to be a condition that a plane would experience during
conditions like the test? Seems like it should nullify the entire test.

~~~
v64
100% on the test is 150% beyond what would be expected from the absolute worst
case real life scenarios. It would require extraordinary circumstances beyond
what has been seen or modeled in reality to push an actual flight to these
limits.

------
starpilot
Very impressive. They strengthened the fuselage to meet requirements almost
exactly, and fell a tiny bit short. That's an incredible amount of
optimization, that means there's hardly any excess material (weight). This
keeps fuel costs low and airfares competitive.

~~~
michaelmrose
When I fly I know I'm always pleased to know that my flight didn't cost an
extra big Mac because the plane was excessively safe.

~~~
perl4ever
Excessively safe meaning safer than the regulated margin of safety. Nobody
really demands unlimited recursive safety margins.

------
jackalo
Duplicate of previous day's:
[https://news.ycombinator.com/item?id=21648826](https://news.ycombinator.com/item?id=21648826)

------
chiefalchemist
This was in the related articles at the bottom. I wonder how the decision is
related the test? I wonder how much say legal had. That is, if they end up in
court is human-made easier to defend than robot-made?

[https://www.seattletimes.com/business/boeing-
aerospace/boein...](https://www.seattletimes.com/business/boeing-
aerospace/boeing-abandons-its-failed-fuselage-robots-on-the-777x-handing-the-
job-back-to-machinists/)

------
esterly
Also a positive note, the carbon fiber wings bent 3x expected max

>bent the jet’s giant carbon composite wings upward more than 28 feet from
their resting position. That’s far beyond the expected maximum deflection in
normal flight of about 9 feet >All this simulated the loads in a flight
maneuver where a pilot would experience a force of 3.75 G, compared to the
maximum of 1.3 G in normal flight

>All this simulated the loads in a flight maneuver where a pilot would
experience a force of 3.75 G, compared to the maximum of 1.3 G in normal
flight

~~~
baybal2
Yep, and it is the fuse that broke, not the wing!

The reason fuse has an "expiration date" set by the amount of pressure cycles
is because aluminium breaks more due to microcracks and other metallurgical
fatigues, than due to ductile failure.

A composite lined fuse could've extended the life of an average airplane long
beyond its moral obsolescence, and for this reason airplane makers are afraid
adopting it.

~~~
perl4ever
What is "moral obsolescence"? If you mean "normal obsolescence", planes are
used for a long time, so what would draw the line between normal lifespan and
excessive?

~~~
baybal2
Think for yourself

------
kitd
Lol. Open the page, popup appears

"Sign up for breaking news!"

------
aidenn0
It seems to me that if nothing ever fails short of the 100% test its probably
overengineered, since the 100% already includes a significant safety margin.

Alternatively if nothing ever fails the test, then they could also just stop
doing these tests, since the analysis would already be shown to be sufficient.

------
techslave
click bait title. the plane basically passed. that is why a retest will not be
required.

------
basicplus2
What gets me is what is the point of a limit to test to if you are not going
to enforce it.

If 1% less is ok (Boeing) test to 1% less,

if 3% less is ok (Airbus) make the limit 3% less.

Not enforcing a limit smells bad and does not fill me with confidence.

Strengthening the failure area will change the failure modes to other areas
and may well make it fail at an even lower limit as other areas will be
bending more to make up for the reduced deflection of the area that is
strengthened.

Not re-testing it after a design change like this worries me.

------
neonate
[https://web.archive.org/web/20191128190035/https://www.seatt...](https://web.archive.org/web/20191128190035/https://www.seattletimes.com/business/boeing-
aerospace/boeing-777xs-fuselage-split-dramatically-during-september-stress-
test/)

------
jacobwilliamroy
Powerful destructive winds are only going to become more common over the next
decade. Boeing really should do another test to make sure.

~~~
jacquesm
Wind is never going to make an airplane experience this level of loading.
Think about it: an airliner going 900 kilometers per hour is flying into an
apparent headwind of 900 kilometers per hour, much faster than any windspeed
it is likely to encounter. The fastest winds that an airplane has to deal with
are the tradewinds.

The biggest risk to aircraft from high winds is during landing and when on the
ground. On the ground these forces are not going to cause a crash (for obvious
reasons) and during landing the bigger risk would be a wing strike or ending
up next to the runway. In neither case would the strength of the plane as
observed in these tests be a huge factor.

What _would_ cause such loading is a long dive or fall and subsequent
recovery:

[https://en.wikipedia.org/wiki/China_Airlines_Flight_006](https://en.wikipedia.org/wiki/China_Airlines_Flight_006)

~~~
jacobwilliamroy
Thanks for clarifying. I felt afraid when I first read this story, because of
the recent unpleasantness with Boeing. Now I see that it's unlikely for this
level of stress to occur.

------
zobzu
"we're not going to re-test. We failed the test but it was close enough"

Yeah that makes me feel safe Boeing, real safe. Specially given your history
now.

Planes used to pass these tests with flying colors and they've been pretty
safe. Have we forgotten already that planes used to break in half in the sky
when there's heavy turbulence? 3.5G sounds like much, but it is also not that
much. There's a reason why the test needs to be passed at a certain level, not
just below.

Heck otherwise, how about I pay 99% of my taxes, mortgage, pass 99% of my
exams, etc. What is this?

Note: before you read and trust the articles too much, airline planes have
been WELL above 3.5G already in the real world. The fact that they're not
supposed to go there does not mean they never do.

