[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 ___________________________________________________________________ (page generated 2022-04-27 23:00 UTC)