[HN Gopher] Boeing looked for flaws in its Dreamliner and couldn...
___________________________________________________________________
Boeing looked for flaws in its Dreamliner and couldn't stop finding
them
Author : dangle1
Score : 128 points
Date : 2022-04-27 17:27 UTC (5 hours ago)
(HTM) web link (www.wsj.com)
(TXT) w3m dump (www.wsj.com)
| bombcar wrote:
| > The agency now has more power to choose which Boeing employees
| represent the FAA's interests, and there are new protections for
| them from undue pressure by company managers.
|
| This still smells strange, even if the Boeing employees are the
| most knowledgeable about the planes, having them be under FAA
| "control" but Boeing pay seems counter-productive.
|
| I wonder if after it's all said and done, whether the splitting
| up of parts manufacturing will really have saved that much money.
| I also wonder how much of this is caused by pushing materials as
| far as they can go to get to the fuel/efficiency targets they
| want to hit.
| rossdavidh wrote:
| 1) it is absolutely a problem, but... 2) to fix it, you'd have
| to pay federal FAA employeees as much as equally-skilled
| members of the private sector at Boeing, and that hasn't
| happened in a long time. My understanding is this system
| started because the FAA's best technical people kept leaving
| for Boeing and other private-sector employers.
| martin8412 wrote:
| Build it into the cost of certification. You absolutely want
| the brightest people working their hardest to uncover
| potentially fatal issues so they can be fixed before people
| die.
| bombcar wrote:
| There's problems on any side, if they're direct FAA
| employees they end up being paid way more than other
| similar FAA employees - though given that the _only_ major
| airplane manufacturer is Boeing you could just charge
| Boeing enough to pay _all_ FAA airplane examiners the
| requisite amount.
| macintux wrote:
| How often do you certify a new plane of this magnitude? I'd
| wager you would have to plan on contracting that out vs
| hiring a bunch of people to only work periodically, and how
| are you going to find contractors who know how to build
| these?
| phkahler wrote:
| >> even if the Boeing employees are the most knowledgeable
| about the planes, having them be under FAA "control" but Boeing
| pay seems counter-productive.
|
| Yeah but after I read this:
|
| >The FAA delegated an increasing number of tasks to a group of
| Boeing employees authorized to work on the agency's behalf.
|
| I first imagined a typical corporate group which might have
| turnover and I thought: What if the FAA delegated to
| _individual_ people, so if Boeing fired someone for raising too
| much concern the role would fall back to the FAA? But yeah, its
| still a conflict of interest no matter how you do it.
| black_13 wrote:
| nisten wrote:
| That's what happens when your executives vindictively outsource
| important software to the cheapest devshop they can find. You end
| up with a product being built by a team that by default has no
| sense of ownership.
|
| https://www.bloomberg.com/news/articles/2019-06-28/boeing-s-...
| https://www.industryweek.com/supply-chain/article/22027840/b...
| nonamechicken wrote:
| Common! This gets brought up all the time when the topic is
| Boeing. Max's issue had nothing to do with the outsourced
| software. Netflix has a documentary called 'Downfall' which
| talks about what all went wrong. AirBus also outsources, they
| haven't crashed right?
| amarka wrote:
| Not sure if the last sentence is in jest or not, but here's a
| list of crashes for just one of their plane models:
|
| https://en.wikipedia.org/wiki/List_of_accidents_and_incident.
| ..
| WalterBright wrote:
| There was nothing wrong with the software developed for the
| MAX. The flaw was in the specification of what the software was
| supposed to do. The delivered software adhered to the
| specification.
| [deleted]
| hemreldop wrote:
| justinjlynn wrote:
| > by default has no sense of ownership.
|
| Because they don't own anything. They're paid to enrich the
| requirements into software specifications and nothing else. It
| gains them absolutely nothing - so why would they ever feel any
| sense of ownership after the job is delivered and accepted?
|
| The business relationship is predicated on them being
| disposable contract workers. At a minimum, a sense of ongoing
| engineering ownership requires an ongoing relationship
| predicated on trust and support - which requires ongoing
| financial support after the software project is 'completed' -
| which Boeing, in hiring contract workers, explicitly did _not_
| want to provide.
|
| Given this, how can we seriously expect the engineers of an
| outsourced development shop, working under a piecework
| contract, to _ever_ feel any sense of ongoing ownership?
| dangle1 wrote:
| https://archive.ph/mby8X
| pseingatl wrote:
| South Carolina. Should have kept manufacturing in Washington.
| nickff wrote:
| The Washington manufacturing facilities seem to have issues as
| well.
|
| https://www.nytimes.com/2019/12/09/business/boeing-737-max-w...
|
| https://www.cnbc.com/2021/04/16/more-electrical-problems-fou...
| winslow wrote:
| Why is the South Carolina factory worse than Washington?
| dylan604 wrote:
| As soon as you figure that out, I'm sure Boeing would love to
| know as well
| zmgsabst wrote:
| They do know:
|
| - older, more mature organization
|
| - based near the engineering teams; frequent collaborations
|
| - unionized, highly skilled workforce
|
| The people who took over Boeing and moved the HQ out of SEA
| intentionally picked SC to union-bust their own workforce.
|
| MBAs just refuse to believe that workplace culture and
| experience matter -- so they treat high skilled workers
| like dumb, replaceable cogs and then their companies fail a
| decade later when the senior/principal staff are
| incompetent or non-existent.
|
| That same mentality is why their new planes have major
| issues:
|
| They don't have competent senior/principal engineers
| because they viewed mid-career engineers as "too expensive"
| -- and so didn't train any.
| kasey_junk wrote:
| Nit: The HQ was moved to Chicago, manufacturing was moved
| to SC.
| rob74 wrote:
| I guess you have to read "moved the HQ out of SEA" (to
| Chicago) and "intentionally picked SC [for 787 final
| assembly] to union-bust their own workforce" separately,
| then it makes more sense...
| tzayk wrote:
| Unless the answer is not politically expedient!
| michaelmrose wrote:
| nickff wrote:
| The trope is that the South Carolina facility is largely un-
| unionized (because it's in a freedom-to-work state), which
| has caused poor quality. I have not seen any clear evidence
| of this, as all Boeing facilities seem to have QC issues. On
| a related note, I'm not sure how Boeing's QC compares to
| Airbus, though both seem to have similar aircraft
| availability rates, which would indicate similar levels of
| QC.
| panick21_ wrote:
| SpaceX manufacturing facility in California is also un-
| unionized. The amount of difference between the two places
| is very large, to just conclude that it has to do with
| unions seems like a stretch to me.
|
| That one factory is the home factory close to where the
| designs are made and the other is so far away seems like a
| pretty important thing.
|
| This seems like the kind of argument people who really love
| unions would make.
| masklinn wrote:
| > The trope is that the South Carolina facility is largely
| un-unionized (because it's in a freedom-to-work state)
|
| FWIW "right to work" is the normal terminology.
| justinjlynn wrote:
| "Freedom to work" and "Right to work" are both Orwellian
| euphemistic terms, to be honest. Realistically, it's best
| described as "mutual right to terminate employment
| without cause" or just "right to terminate".
| masklinn wrote:
| > "Freedom to work" and "Right to work" are both
| Orwellian euphemistic terms, to be honest.
|
| The latter is essentially a term of art, the former is
| not. Using the former is imprecise and confusing.
|
| > Realistically, it's best described as "mutual right to
| terminate employment without cause" or just "right to
| terminate".
|
| That is a completely different concept called at-will
| employment. RTW is about union shops (not to be confused
| with closed shops, which have been illegal in the US
| since Taft-Hartley)
| rootusrootus wrote:
| Or perhaps "right to freeload"?
| masklinn wrote:
| ...
|
| What?
| rootusrootus wrote:
| That's the whole point of 'right to work.' Allow new
| employees to freeload on the union-negotiated rates for
| the shop without requiring them to actually join the
| union. Who would pay if they got the benefits anyway? So
| the union gets defunded.
| deltarholamda wrote:
| Interestingly, back when Jesse Jackson was in the news a
| lot, he did a lot of advocating for Right-to-Work
| legislation. The idea was that unions were racially
| discriminating against blacks, and RtW laws prevented
| this.
|
| Goes to show... something, I guess.
| blendergeek wrote:
| You are thinking of "at-will" employment [0]. That is a
| separate issue from "right-to-work" which has to do with
| labor unions [1].
|
| [0] https://en.wikipedia.org/wiki/At-will_employment
|
| [1] https://en.m.wikipedia.org/wiki/Right-to-work_law
| nickff wrote:
| They're euphemisms, but I am not sure they're Orwellian.
| How would you say they're Orwellian?
|
| It's better to just allow people to name their own
| movement, otherwise, you end up endlessly fighting about
| names (i.e. are people 'pro-life' or 'anti-choice' and
| 'pro-murder'/'anti-life' and 'pro-choice').
| kwertyoowiyop wrote:
| It does mean the opposite of what the phrase might
| normally imply.
| masklinn wrote:
| > They're euphemisms, but I am not sure they're
| Orwellian. How would you say they're Orwellian?
|
| Right to work laws do not in any way provide a right to
| work.
| djbebs wrote:
| They do though
| posguy wrote:
| South Carolina planes were getting flown to Washington before
| delivery to customers when I had a friend still working
| there. He was finding metal shavings in the fuselage of the
| plane, along with tools, nicked wires and such.
|
| None of this should have made it out of the factory floor.
| Every crew that works on a plane has to certify (literally
| sign off a form) that when they worked on the plane they left
| it in good shape (no obvious defects, like metal shavings,
| tools left inside, etc). If the next shift comes in and finds
| dangerous debris or damage the prior crew should have noted,
| then the prior crew is required by the FAA to have a formal
| report written against them, as they have created a dangerous
| plane.
|
| Management has applied heavy pressure to my friend repeatedly
| to not report these incidents, despite his legal obligation.
| Ultimately, he took a $25k hit paying back the Boeing
| relocation package and left after 10 months to work on
| repairing trains (which has been a significant improvement).
| lostlogin wrote:
| Completely alarming.
|
| Publishing his experience anonymously is likely impossible,
| but if not, I'd be really keen to read it.
| toomuchtodo wrote:
| Preferably as an open letter addressed and submitted to
| the FAA.
| quarterdime wrote:
| There are numerous reports on debris (metal shavings,
| tools, and even a whole ladder) being discovered in
| aircraft by customers after delivery. This requires not
| only that assembly signed off on the aircraft, but that the
| issues are not discovered in final inspection either.
|
| Some reporting suggests several major customers (airlines)
| were so fed up with this 'foreign object debris' (metal
| shavings etc) problem that they said they would only accept
| aircraft from Washington. From your story, I can't help but
| wonder if Boeing management got around this by flying near-
| complete aircraft from SC to WA to get around this.
|
| To give you a sense of how bad this debris issue is: the US
| Air Force refused delivery of new air tankers after finding
| debris (in fuel tanks if I remember correctly).
| rob74 wrote:
| The story about airlines only accepting 787 aircraft from
| Washington was from the time when it was still being
| assembled in two plants (Everett, WA and North
| Charleston, SC). Since March 2021 (according to
| https://en.wikipedia.org/wiki/Boeing_787_Dreamliner), the
| only plant assembling 787s is the SC plant, which is
| cheaper and non-unionized. I guess that's more important
| to Boeing than occasional quality issues...
| phkahler wrote:
| >> Management has applied heavy pressure to my friend
| repeatedly to not report these incidents, despite his legal
| obligation.
|
| Yeah, the idea is to have management put pressure on the
| people who left stuff in bad shape. Shooting the messenger
| isn't the right answer.
| posguy wrote:
| Shooting the messenger seems to be Boeing tradition of
| the last decade.
|
| When I was a kid, half the parents I knew worked at
| Boeing and were proud of the quality engineering or
| manufacturing they did, but over the past two decades
| Boeing has had this crew retire and has worked to shift
| to a blame the messenger culture.
| FabHK wrote:
| There's this documentary on Netflix that also notes the
| cultural shift, and largely blames it on the 1997
| acquisition of McDonnell-Douglas, and the subsequent
| shift, roughly speaking, from an engineering-dominated
| culture to an MBA-dominated culture.
|
| https://en.wikipedia.org/wiki/Downfall:_The_Case_Against_
| Boe...
| posguy wrote:
| Almost Live has a pretty good satirical take on the
| Boeing cultural shift:
| https://www.youtube.com/watch?v=tVUeZ2HLYlM
| panick21_ wrote:
| Wow, that reporter is Joel McHale.
| assttoasstmgr wrote:
| > In 2019, they detected gaps between sections of the
| Dreamliner's fuselage that were slightly wider than specified in
| the FAA-approved designs. The gaps, about the width of a piece of
| paper, were wider than the manufacturing tolerance of 0.005 of an
| inch allowed under the approved design.
|
| I feel like the article is really grasping at straws here, and
| I'd be willing to bet the author doesn't even comprehend how
| small this is. 0.005" is _small_. For the hardware-challenged:
| 0.005 " is a typical manufacturing tolerance for a standard-spec
| PCB. Some of the Chinese board-houses that deal in high volume
| are higher than that[1]. The fact that they even found a gap this
| size on something the size of an airplane is amazing to me.
|
| [1]
| https://www.pcbway.com/pcb_prototype/PCB_Manufacturing_toler...
| floxy wrote:
| I don't see enough information in the text to help us out here.
| The say it is out of the tolerance band of presumably +/-
| 0.005". But they don't tell us how far out of tolerance it was.
| Was it, say 0.0055", or 0.060"? What was engineering purpose
| was driving that tolerance? I could see that a +/-0.005"
| tolerance is from the title block (common default on mechanical
| engineering drawings), and that this was a reference dimension
| and not a critical dimension. But yes, 0.005" on something 20
| feet in diameter is pretty dang tight.
|
| And for reference a sheet of bog-standard copy paper is right
| around 0.004".
| jdavis703 wrote:
| I'm not expert enough to know if this is dangerous are not. But
| an aircraft is a combinatorial explosion of complexity. For
| example, innocuous sounding changes for the 737 Max caused
| several hundred deaths.
|
| If the tolerance was indeed too strict I would expect Boeing to
| go through a engineering review and seek approval from the FAA.
|
| People who work on assembly lines are really good at keeping
| the line moving. But I don't want someone who's perf bonus
| relies on pushing out aircraft determining on-the-fly if
| something that's outside of the spec is safe or not...
|
| And this isn't a knock on blue collar labor, almost no one at
| Boeing has the knowledge to work through all the potential side
| effects like this.
| bzxcvbn wrote:
| What do PCBs have to do with airplane fuselage design?
| dzdt wrote:
| 0.005 is 1/200. How thick is a 200 page book? About an inch
| seems right. Its not clear to me how much difference there is
| between 0.005" and the thickness of a sheet of paper.
| hathawsh wrote:
| The thickness of typical copy paper in the US is 0.1 mm. I
| measure it by measuring the height of a ream (500 sheets) and
| dividing by 500. This bit of trivia turns out to be rather
| helpful for 3D printing.
|
| Also, 0.005 inches = 0.127mm, so we're talking about slightly
| more tolerance than the thickness of copy paper.
| skybrian wrote:
| How do you use this in 3D printing?
| r2_pilot wrote:
| It's helpful to know how high above the print bed to
| print, so you can slide a piece of paper freely
| underneath the nozzle while only just feeling a tiny bit
| of drag from the nozzle. That way you have enough space
| to put your material down.
| [deleted]
| rootusrootus wrote:
| Indeed, 0.005 is thicker than many papers. 0.010 would qualify
| as card stock IIRC.
| [deleted]
| quarterdime wrote:
| 0.005 inch is indeed quite small, and a demanding tolerance
| indeed for carbon fiber composite construction. I trust that
| Boeing design engineers would have know full well that this
| tight tolerance would cost a lot of money, and would therefore
| specify it only if necessary. When the out of spec assemblies
| were discovered, Boeing could either use testing and analysis
| to show these gaps are OK or rework the aircraft to get them in
| spec. They chose the latter.
|
| In short, just because 0.005 inch is a small number does not
| mean the article is grasping at straws. I routinely design
| mechanical assemblies where the difference between 0.005 inch
| and 0.010 inch is the difference between a comfortable factor
| of safety and guaranteed failure under design loads.
| stevage wrote:
| Are you able to explain how a tiny gap causes a failure under
| load? I couldn't picture it.
| ew6082 wrote:
| Because gaps like this multiply out at the end of a beam.
| If for example the abutting structural member relies on
| that joint for support and is 12 feet long (144 inches) and
| lets say the flange is 6" across, .005/6 x 144 = .12" which
| is about 1/8 of an inch of wiggle at the end. If your gap
| were, say .010" instead, there is suddenly 1/4" of wiggle
| and when things can wiggle like that vibration gets much
| worse.
| munk-a wrote:
| There might be someone on HN who can legitimately answer
| you but I think this question isn't really helpful to
| discussion. Some experts have said y should be less than x,
| instead, y is greater than x... this is a problem. Someone
| may very well chime in with an explanation about how as
| long as y is less than 1.2 * x it's actually probably fine,
| but considering this is a highly technical field and
| considering the expense of making such a small gap I think
| it's a good idea to just assume there is some really good
| for y to be less than x.
|
| Edit: Actually there _are_ some highly technical replies
| and that 's awesome! But I still stand by my point - the
| time to evaluate whether a test is fair or not is generally
| not when you're failing the test.
| avs733 wrote:
| What matters isn't the size of the gap, what matters is the
| size of the gap relative to the size of the gap it was
| designed for.
|
| If I design a 10" Diam part to be assembled to another with
| a .001" gap, then a .010 gap is huge. If it's a 10' part
| that has the same tolerance, a 0.01" gap is still huge.
|
| Tolerances aren't arbitrary, they are analyzed and the
| issue is you generally don't k ow what happens accurately
| if those tolerance limits are violated.
|
| As for the mechanism, you need to worry not just about a
| single cycle load to failure, you need to also worry about
| shortened fatigue life (I,e, failure after many cycles -
| but many less cycles than predicted). Overall, load
| transfer is highly complicated in thin skin structures and
| that the gap is small doesn't mean that a change in that
| gap crosses a small change in load
| quarterdime wrote:
| This is a fair question but the answer can get complex.
| Honestly the design/manufacturing of this aircraft joint is
| way above my expertise and pay grade. I would hope that
| Boeing has some extremely specialized and talented people
| working on this. In short, the question of how a gap might
| affect this assembly is far outside my expertise. However
| if you want a simple example:
|
| Consider a geometrically perfect cylinder resting on a
| perfect plane. The contact is a line, with zero width.
| Therefore a contact area of zero. Pressure is force divided
| by area. So the nonzero weight of the pin, divided by area
| (zero) is... infinite? You run into the same problem with a
| pin in a slightly larger hole. How does this seemingly
| infinite pressure not lead to failures in wheels (think of
| train wheels on tracks), ball bearings (spherical balls in
| torroidal raceways with slight clearance), roller bearings,
| etc? We are surrounded by geometries that have seemingly
| zero area points of contact, but they support tremendous
| loads.
|
| Hertz (yeah, the same guy for whom the 1/s unit is named)
| figured out the math behind these contact stresses.
| Basically, for round (and round-ish) things in 2d and 3d,
| the contact stress has a lot to do with the deformation of
| the materials. To answer the riddle above (of the cylinder
| on plane infinite contact stress), you have to consider the
| deformation of the cylinder and the plane. The stiffness of
| the materials comes into play, as well as the geometry. You
| can read up on Herz (or Hertzian) contact stresses if you
| would like to know more. The math is not terribly
| difficult, especially for 2d geometries. For a 2d case of a
| pinned joint, you can often find that a change of a couple
| thousandths of an inch can mean the difference between a
| comfortable factor of safety and failure.
|
| I have given a hand-waving example of the importance of
| tight tolerances on clearances for a small class of
| problems. I hope it is close enough to the subject matter
| at hand to be of some use. My comment is from memory, so
| please forgive (and correct!) any mistakes I've made.
|
| edit: I am rereading my comment, and realize that I didn't
| make explicit the importance of tight fit for Hertzian
| contact stress. The smaller the gap between a pin and hole,
| the greater the contact area (with the same amount of
| deformation). Think of it this way--for a fixed amount of
| deformation (say strain at failure), you can carry way more
| load if the contact area is greater. How do you increase
| this contact area? By a smaller difference in diameters
| (smaller gap) of pin and hole. So all things equal
| (material properties, load), a smaller difference between
| pin and hole diameters will increase load the joint can
| carry.
|
| Another point: calculating these contact stresses is doable
| for most metals, but is far more complex for anisotropic
| materials (mechanical properties vary in different
| directions) materials like the carbon fiber composites.
| an1sotropy wrote:
| Thanks for these details.
|
| I think others might be forgetting (or not know) that the
| factors of safety* for the parts in airplanes (around 2,
| or less?) are very different than factors of safety for
| the structural parts of bridges (around 5?). Compared on
| those terms, planes are light and fragile, on purpose, so
| you can't f around with cheating tolerances.
|
| * https://en.wikipedia.org/wiki/Factor_of_safety
| krageon wrote:
| It causes a failure because it is not according to the
| design. Who knows what happens when you start doing things
| differently? You're not supposed to add or remove wings and
| the tolerances should be as described. You don't need to
| understand the math involved to understand that when an
| engineer tells you something is important, you should
| probably listen.
| MAGZine wrote:
| I'm not sure why you felt the need to explain to someone
| who was genuinely curious as to how something might fail,
| that they shouldn't ask questions.
| inkeddeveloper wrote:
| It doesn't matter. They didn't meet the standard. It was a
| standard for a reason and it failed.
| iancmceachern wrote:
| Exactly. If the spec was wrong, fix the spec. But we must
| meet the spec, and we must have specs that are meaningful
| and accurate.
| csours wrote:
| If you have multiple parts in an assembly, each with small
| deviations from the specification, those deviations add up.
| Now add some substantial load (like a whole airplane), and
| you can have a real bad time.
|
| Edit: in this case it looks like it was airplane skin
| panels, some (most?) of which may be stressed members -
| meaning that it's not a cosmetic piece, it's a load bearing
| piece. If you have multiple panels with tiny deviations,
| that changes the loading of the whole structure,
| potentially leading to warping, flexing, and premature
| failure.
| lazyier wrote:
| Why do you suppose there are gaps in the first place?
|
| Why don't they make it one solid piece? You can do that
| with composite construction. Just overlap layers and glue
| it all together.
|
| It could have something to do with how the fuselage change
| shapes and distorts under different conditions. The
| airplane goes through various different shapes depending on
| things like pressurization and thermal expansion. The body
| gets a bit bigger, the wings flap up and down, things get
| wider and shorter and harder, etc. etc.
|
| With composite construction things are glued into place,
| but they need to be designed to accommodate this movement.
| The glues and such things have a particular amount of
| elasticity and fatigue limits.
|
| Could be that a 0.005 amounts to 10% less gluing surface
| and thus the projected fatigue life of the glue is now much
| different because there is much less.
|
| Just speculating.
| assttoasstmgr wrote:
| > Why do you suppose there are gaps in the first place?
|
| > Why don't they make it one solid piece? You can do that
| with composite construction. Just overlap layers and glue
| it all together.
|
| Are you suggesting they build the entire fuselage as one
| piece and "glue it all together"? It's an airplane
| fuselage, not a MacBook chassis.
| throwaway0a5e wrote:
| >Are you suggesting they build the entire fuselage as one
| piece and "glue it all together"?
|
| That's basically how they build ships...
|
| It seems doable but QC would probably be a nightmare and
| it wouldn't be very repairable.
| monocasa wrote:
| They definitely stich sections of hull together to make
| all but the smallest ships.
| hedgehog wrote:
| IIRC a major rationale behind the 787 design is to allow
| sections to be manufactured complete with wiring harness
| etc in different locations and then shipped for final
| assembly. You can build really big parts (check out
| Janicki) but for this application probably not desirable.
| mjevans wrote:
| Not a mechanical Engineer, but I can imagine how.
|
| Both for pieces abutted against each other and for E.G.
| rivet holes, mechanical interfaces have extremely precise
| tolerances to support a range of possible stresses. Too
| wide a tolerance in one area can allow deformation and
| wiggle that applies unexpected forces on other areas. You
| should also remember that many aircraft are pressure
| vessels, since they operate at altitudes where the density
| of our atmosphere is substantially different.
| throwaway0a5e wrote:
| > I trust that Boeing design engineers would have know full
| well that this tight tolerance would cost a lot of money, and
| would therefore specify it only if necessary
|
| Hahahahahahahahahahahahahahahaha
|
| Source: worked in places that manufactured aerospace stuff.
| [deleted]
| emeraldd wrote:
| What really matters is where that 5 thousandths is ... If it's
| in the wrong place, that could compromise all kinds of things.
| Maybe not immediately, but definitely down the road. Watch a
| few May Day Air disaster episodes, some of the most innocuous
| sounding things can cause a crash a decade down the line ...
| TheCondor wrote:
| That and Boeing defined the specification, the FAA approved
| it and Boeing isn't meeting their own design specification.
| If it doesn't really matter, then why is it the
| specification?
|
| Sucks to be Boeing, I want them to be successful. Hell, I
| even liked that big goofy looking X-32 which was a JSF
| competitor. People die when their planes fail, it's nothing
| like a PCB as mentioned by the grandparent. They f-ed around
| with the 737Max and found out. Honestly though, if your loved
| ones died on a 737Max and then you found out that they
| weren't building planes to the specs that they defined, what
| would you think?
| thereisnospork wrote:
| >If it doesn't really matter, then why is it the
| specification?
|
| Sometimes you just need _a_ specification, because you have
| to tell your mfgr something[0]. Notably 5 thou is a pretty
| standard idgaf-tolerance, but in this specific case might
| be important.
|
| [0] e.g. a spec of 5" is meaningless, 5.00000 +/-.000001 is
| insane, and 5.000 +/- 0.005" is (generally) readily
| achievable and good enough.
| michaelt wrote:
| _> If it doesn 't really matter, then why is it the
| specification?_
|
| Bob: You've called for a 5mm hole here, but you don't have
| a precision specified?
|
| Alice: I really only need the sort of hole a 5mm drill bit
| would produce.
|
| Bob: Do you know what level of precision that is? Have you
| done any calculations to confirm that's the appropriate
| level of precision?
|
| Alice: Not really, in my judgement this doesn't rise to the
| level of needing such calculations.
|
| Bob: Well, our drawing quality standards require a
| precision to be specified. Would +-0.5mm be OK? If not, how
| precise does it need to be?
|
| Alice: How precise is the laser cutter we're cutting this
| out on?
|
| Bob: The spec sheet claims +-0.05mm
|
| Alice: The required precision is +-0.05mm
| [deleted]
| kurupt213 wrote:
| 5 thousandths is a pretty standard spec for precision parts
| jannyfer wrote:
| I don't think the _article_ is grasping at straws - it's Boeing
| who discovered this and it was reported in multiple news
| outlets at the time about it.
|
| This below site/article seems to give the most technical
| description, although I know nothing about aircraft
| engineering.
|
| https://www.key.aero/article/shims-thin-end-boeings-wedge
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