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> 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

> 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_tolerances.html https://www.pcbway.com/pcb_prototype/PCB_Manufacturing_toler...

dzdt 4y ago
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 4y ago
  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 4y ago
    How do you use this in 3D printing?
    - r2_pilot 4y ago
      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 4y ago
      [deleted]
emeraldd 4y ago
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 4y ago
  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?
  - michaelt 4y ago
    > 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
    - bee_rider 4y ago
      This reads to me like Alice just isn't doing her job properly. If this results in specs that are really hard to fulfill, hopefully the process is accountable enough to trace it back to her.
rootusrootus 4y ago
Indeed, 0.005 is thicker than many papers. 0.010 would qualify as card stock IIRC.
quarterdime 4y ago
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 4y ago
  Are you able to explain how a tiny gap causes a failure under load? I couldn't picture it.
  - krageon 4y ago
    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 4y ago
      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.
      - krageon 4y ago
        The line of discussion started out with a frankly confrontational tone and had so far not yielded incredibly interesting results. I read this question in the same tone when I probably shouldn't have, that's fair.
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jannyfer 4y ago
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 https://www.key.aero/article/shims-thin-end-boeings-wedge
floxy 4y ago
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 4y ago
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.
kurupt213 4y ago
5 thousandths is a pretty standard spec for precision parts
bzxcvbn 4y ago
What do PCBs have to do with airplane fuselage design?
deleted 4y ago
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zardo 4y ago
Even if the deviation has no effect, the fact remains that the design was not updated. It's perfectly fine for manufacturing to say, "We can't meet this tolerance, are you sure it has to be this exact?" Then design engineering looks at it, decides it does not need to be that exact, and updates the tolerance. It's not okay to just ship passenger airplanes that don't meet the build specs.
- slavik81 4y ago
  Years ago, I worked in a manufacturing facility for heavy machinery and there was an engineer on staff who spent most of their time redoing calculations for expensive parts that were machined incorrectly (e.g. an extra notch cut into the part because the machinist measured from the wrong end the first time). The updated calculations were then filed along with a new revision of the drawings that specified the part as built. I have no idea what aircraft manufacturing is like, but the idea that a part might go out the door without matching its drawing is definitely concerning. The drawing and the associated calculations are supposed to be the proof that the matter was considered, and that an informed decision was made.

dzdt 4y ago

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 4y ago
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 4y ago
  How do you use this in 3D printing?
  - r2_pilot 4y ago
    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 4y ago
    [deleted]

emeraldd 4y ago

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 4y ago
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?
- michaelt 4y ago
  > 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
  - bee_rider 4y ago
    This reads to me like Alice just isn't doing her job properly. If this results in specs that are really hard to fulfill, hopefully the process is accountable enough to trace it back to her.

rootusrootus 4y ago

Indeed, 0.005 is thicker than many papers. 0.010 would qualify as card stock IIRC.

quarterdime 4y ago

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 4y ago
Are you able to explain how a tiny gap causes a failure under load? I couldn't picture it.
- krageon 4y ago
  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 4y ago
    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.
    - krageon 4y ago
      The line of discussion started out with a frankly confrontational tone and had so far not yielded incredibly interesting results. I read this question in the same tone when I probably shouldn't have, that's fair.

deleted 4y ago

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jannyfer 4y ago

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 https://www.key.aero/article/shims-thin-end-boeings-wedge

floxy 4y ago

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 4y ago

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.

kurupt213 4y ago

5 thousandths is a pretty standard spec for precision parts

bzxcvbn 4y ago

What do PCBs have to do with airplane fuselage design?

deleted 4y ago

[deleted]

zardo 4y ago

Even if the deviation has no effect, the fact remains that the design was not updated. It's perfectly fine for manufacturing to say, "We can't meet this tolerance, are you sure it has to be this exact?" Then design engineering looks at it, decides it does not need to be that exact, and updates the tolerance. It's not okay to just ship passenger airplanes that don't meet the build specs.

slavik81 4y ago
Years ago, I worked in a manufacturing facility for heavy machinery and there was an engineer on staff who spent most of their time redoing calculations for expensive parts that were machined incorrectly (e.g. an extra notch cut into the part because the machinist measured from the wrong end the first time). The updated calculations were then filed along with a new revision of the drawings that specified the part as built. I have no idea what aircraft manufacturing is like, but the idea that a part might go out the door without matching its drawing is definitely concerning. The drawing and the associated calculations are supposed to be the proof that the matter was considered, and that an informed decision was made.