Boeing discloses a new problem with the 787 Dreamliner(edition.cnn.com)
edition.cnn.com
Boeing discloses a new problem with the 787 Dreamliner
https://edition.cnn.com/2021/07/13/business/boeing-787-dreamliner-faa/index.html
45 comments
Let's put it another way.
Suppose you've got a gearbox, with a shaft in it, and a stack of parts on the shaft. The shaft with its parts must fit in the gearbox. The gearbox has a max and min size, and each part has a max and min size. The engineer divides up the tolerances so that if they are all at max size, and the gearbox housing is at min size, the parts will fit.
Now, if a gear comes back from the manufacturer larger than its max size, but enough of the other parts are not near their max size, the stack will still fit and it's ok. (But engineering still has to approve the fit.)
This is not in any way a crisis. It simply costs extra money because the out-of-spec part gets bounced to engineering for review.
Yes, I did these exact calculations on the 757 stab trim gearbox.
Suppose you've got a gearbox, with a shaft in it, and a stack of parts on the shaft. The shaft with its parts must fit in the gearbox. The gearbox has a max and min size, and each part has a max and min size. The engineer divides up the tolerances so that if they are all at max size, and the gearbox housing is at min size, the parts will fit.
Now, if a gear comes back from the manufacturer larger than its max size, but enough of the other parts are not near their max size, the stack will still fit and it's ok. (But engineering still has to approve the fit.)
This is not in any way a crisis. It simply costs extra money because the out-of-spec part gets bounced to engineering for review.
Yes, I did these exact calculations on the 757 stab trim gearbox.
TIL Walter Bright is actually an Aerospace Engineer.
I had always assumed that (as a compiler guru) you had a CS background. :)
I had always assumed that (as a compiler guru) you had a CS background. :)
> Bright is the son of the air force pilot Charles D. Bright.[4][5] Bright graduated from Caltech in 1979 with a Bachelor of Science in aerospace engineering.[6]
* https://en.wikipedia.org/wiki/Walter_Bright
* https://en.wikipedia.org/wiki/Walter_Bright
So often I come to HN and just read random comments from random people with out realizing that I'm listening to ACTUAL experts. It is rather humbling to know I get to talk to awesome people.
Here is Walter's wikipedia: https://en.m.wikipedia.org/wiki/Walter_Bright
He went to Caltech, studied Aerospace Engineering, wrote many books, has given lots of presentations
For my own notoriety, I am a large clam that has slaved away at data for 10 years in Financial Services. I'm about to quit my job for a TOTALLY AWESOME job somewhere else
Here is Walter's wikipedia: https://en.m.wikipedia.org/wiki/Walter_Bright
He went to Caltech, studied Aerospace Engineering, wrote many books, has given lots of presentations
For my own notoriety, I am a large clam that has slaved away at data for 10 years in Financial Services. I'm about to quit my job for a TOTALLY AWESOME job somewhere else
I'm guessing that the CS stuff is more intellectually challenging.
If you have friends in mechanical engineering, ask them to join you on a visit day at their workplace or any other place with engineering. That will change your mind.
The best thing about being an ME at Boeing is working with the old guys who knew what they were doing.
I don't know. Look at self-driving cars. The mechanics is trivial compared to the CS stuff.
Yeah, you need ME to do any useful things in the real world. Like try repeatedly making the same robot without any MEs on your team.
CS has interesting things going on but I doubt it's more intellectually challenging than designing airplanes and spaceships... The expression was never "this is like computer science" for a good reason.
Gears are usually slightly smaller than design size for clearance sake (and to make cutting the teeth easier). I imagine this tolerance disappears to almost zero in aerospace, though.
If the outer diameter of a gear tooth is too large, it can bind with the root of the matching gear, and this can cause rapid wear, and an unplanned disassembly at some point very early in the service life.
If the outer diameter of a gear tooth is too large, it can bind with the root of the matching gear, and this can cause rapid wear, and an unplanned disassembly at some point very early in the service life.
I can say that the aviation gears are far better cut and fitted than the ones you'll find in a car transmission! I once brought to work some gears from my car tranny, and the other engineers were horrified at them.
It seems like the manufacturers of these parts aren't producing in bulk, why aren't the tolerances exact and have a min/max? Are they not able to measure the parts out of the factory better? Is the measuring equipment on their end and the gearboxes company difference? Or are these like nanometer tolerances which we just can't manufacture consistently?
Here's an example for something as simple as a hobbyist using a metal lathe in their garage:
For a rough part, you can measure how much material you need to take off, do it in a few passes without stopping to remeasure, and you're within 5 thousandths of an inch or so.
For a shaft that is going to slide or rotate in a bore without too much force, you need to be within a thousandth or two, so for the last pass you will stop, measure carefully, and only take a little bit of material off at a time so that the cutting forces are low and there is less deflection in the tool to throw off the size of the part.
For a press fit (two parts are sized precisely enough that they can be pressed together with a hydraulic press and then never come apart), you need tolerances in the tenths of a thousandth of an inch. For this, you'll dust off your special expensive micrometer, and it's important to let the part cool before measuring, because the heat from machining can cause the part to expand and cause you to take off too much material, which would ruin the part.
So even for the same person on the same machine with the same material, the effort (and therefore cost, if you're doing this commercially) can vary quite a bit based on the tolerance needed.
I don't know aerospace, but I imagine the required tolerances require vary from "looks good from here" (seats in the cabin) to "must ride on a film of oil this many microns thick when spinning at 10,000 rpm." And the manufacturing processes can be anything from "intern with a saw" to "specialized metrology lab with most expensive machines in the world" depending on what engineering specifies.
For a rough part, you can measure how much material you need to take off, do it in a few passes without stopping to remeasure, and you're within 5 thousandths of an inch or so.
For a shaft that is going to slide or rotate in a bore without too much force, you need to be within a thousandth or two, so for the last pass you will stop, measure carefully, and only take a little bit of material off at a time so that the cutting forces are low and there is less deflection in the tool to throw off the size of the part.
For a press fit (two parts are sized precisely enough that they can be pressed together with a hydraulic press and then never come apart), you need tolerances in the tenths of a thousandth of an inch. For this, you'll dust off your special expensive micrometer, and it's important to let the part cool before measuring, because the heat from machining can cause the part to expand and cause you to take off too much material, which would ruin the part.
So even for the same person on the same machine with the same material, the effort (and therefore cost, if you're doing this commercially) can vary quite a bit based on the tolerance needed.
I don't know aerospace, but I imagine the required tolerances require vary from "looks good from here" (seats in the cabin) to "must ride on a film of oil this many microns thick when spinning at 10,000 rpm." And the manufacturing processes can be anything from "intern with a saw" to "specialized metrology lab with most expensive machines in the world" depending on what engineering specifies.
I forgot the details, but manufacturing costs go up by an order of magnitude with a halving of the tolerance, or something like that.
I don't know much about machining but this was a really cool explanation for the significant/difficulties of tolerances, thanks for explaining mrfredward
> why aren't the tolerances exact and have a min/max?
Because time and money are not infinite and +/-0.005 is a hell of a lot cheaper than +/-0.0005.
This is an assembly of stamped and sheared aluminum and composites. Machine shop level accuracy gets real expensive real quick with those construction methods and this isn't intentional defense industry pork so the cost does need to be kept under control.
Because time and money are not infinite and +/-0.005 is a hell of a lot cheaper than +/-0.0005.
This is an assembly of stamped and sheared aluminum and composites. Machine shop level accuracy gets real expensive real quick with those construction methods and this isn't intentional defense industry pork so the cost does need to be kept under control.
My understanding is that it's not about airflow, but about unplanned for localized stresses rather than having them distributed evenly. This means the joint does not meet limit load requirements. While it's not so bad it could immediately structurally fail under expected loads, over time the stress concentration could weaken the structure at those points, leading to premature failure or more likely, significantly shorter service life than expected.
The FAA said it wasn't a safety issue. Not meeting limit load requirements is a safety issue. Though I wouldn't be surprised if the CNN reporter got it all bollixed up. I wouldn't take anything seriously from CNN.
If it is the issues from last year, this article has a lot more detail: https://seekingalpha.com/article/4374235-boeing-dreamliner-m...
As I understood it, there are two issues, neither of which is a problem by itself, but if they occur simultaneously, it would not meet limit load requirements. But maybe CNN is reporting on another new issue - hard to tell.
It looks like this isn't exactly the issues from last year, but is a new related issue. This Seattle Times article has slightly more detail: https://www.seattletimes.com/business/boeing-aerospace/a-new...
Last year's issue related to joints around the rear pressure bulkhead. This article indicates the new issue is a similar problem related to the forward pressure bulkhead.
Last year's issue related to joints around the rear pressure bulkhead. This article indicates the new issue is a similar problem related to the forward pressure bulkhead.
I think this (the FAA involvement) stems from the previous rear fuselage issues, which was a safety issue, and the FAA is still directly overseeing that issue. It sounds like the FAA have not restored Boeing's delegated authority for final airworthiness sign-off on new 787s due to not having accepting a new inspection plan for that issue yet.
That would would explain why the FAA remains involved on an issue it does not consider to be a safety concern, especially as it implies there may be even more quality control issues than previously realized.
That would would explain why the FAA remains involved on an issue it does not consider to be a safety concern, especially as it implies there may be even more quality control issues than previously realized.
Perhaps “no immediate threat to flight safety” just means that no aircraft with the defect have been delivered or are in service?
The phrase "Boeing said 787 planes already in service do not need to be grounded" kind-of implies that there are aircraft with this defect in service, but it need not necessarily do so.
The phrase "Boeing said 787 planes already in service do not need to be grounded" kind-of implies that there are aircraft with this defect in service, but it need not necessarily do so.
> There are always going to be leaks.
As this seems to be something that's given quite a bit of thought, do you have an idea on what the maximum diameter hole through the fuselage to safely maintain sufficient cabin pressure during cruise flight at, say, PL390? More specifically, what's the maximum rate of pressurization that the cabin pressurization system is designed to support?
As this seems to be something that's given quite a bit of thought, do you have an idea on what the maximum diameter hole through the fuselage to safely maintain sufficient cabin pressure during cruise flight at, say, PL390? More specifically, what's the maximum rate of pressurization that the cabin pressurization system is designed to support?
I have no idea, as I didn't work with the tin benders (structures guys).
But I do know that there can be a hole the size of a quarter and nobody will notice a pressure drop. You're not going to knock an airliner down by punching holes in the fuselage, either (some people think a bullet hole will cause it to pop like a balloon, nothing of the sort will happen).
But I do know that there can be a hole the size of a quarter and nobody will notice a pressure drop. You're not going to knock an airliner down by punching holes in the fuselage, either (some people think a bullet hole will cause it to pop like a balloon, nothing of the sort will happen).
This article is terrible.
Are these problems specific to the problem-plagued 787-10 or 787s in general (all models of which have had issues)?
Is this specific to models built in South Carolina? I have read some Asian airlines are specifying Washington construction only.
Any business reporter (not specific to aviation) who has covered Boeing in the last few years would know that these two questions would explain if this is bad or terrible for Boeing.
Are these problems specific to the problem-plagued 787-10 or 787s in general (all models of which have had issues)?
Is this specific to models built in South Carolina? I have read some Asian airlines are specifying Washington construction only.
Any business reporter (not specific to aviation) who has covered Boeing in the last few years would know that these two questions would explain if this is bad or terrible for Boeing.
i remember listening to a lecture on this in my business class before all these issues, we watch a video on outsourcing and how this is the first of their planes that used an advanced supply management system to outsource. traditionally boeing did most of their major sourcing from mainly the united states, the united states has some of the strictest air safety laws in the world so previously it was nearly impossible to source overseas due to supply chain parts reliability. guess that is still the case then
Back on the 757, Boeing outsourced a lot of subassemblies to Japanese companies. We engineers liked them, as they produced very, very good parts.
Though personally I liked Saginaw Gear the best, as they did the forgings for the stab trim jackscrew, and made the best of the best.
Though personally I liked Saginaw Gear the best, as they did the forgings for the stab trim jackscrew, and made the best of the best.
Can you share what makes forged parts better than others? Wouldn’t it simply be better molds or finishing I suppose? I’m only familiar with forged gun parts and even the cheapest forged parts look and function as good as the expensive ones, but then again going bang is easier than keeping people in the air through crazy stresses and heat and cool cycles.
Forging orients the grain structure of the metal in a predictable manner. It also helps remove voids.
Generally, a forged part is going to be free of the voids and surface defects of a casting, and waste less material than cutting from an rolled or extruded piece of stock.
Generally, a forged part is going to be free of the voids and surface defects of a casting, and waste less material than cutting from an rolled or extruded piece of stock.
Forgings are 3x stronger than the equivalent casting. I'm not a materials science guy, so my knowledge of the details is a bit vague, but the grain of the metal follows the shape in a forging.
When I amped up the horsepower of my Dodge, I replaced the cast bell housing with a forged steel one, because I like my feet. (I've seen pictures of the flywheel coming through the side of a car.) All the spinning parts in the engine were replaced with forged ones, too.
When I amped up the horsepower of my Dodge, I replaced the cast bell housing with a forged steel one, because I like my feet. (I've seen pictures of the flywheel coming through the side of a car.) All the spinning parts in the engine were replaced with forged ones, too.
I understand what forging is, I was just asking what made their forging better than others is all.
Do you mean why Saginaw is the best? Because Boeing didn't have problems with defective parts coming from Saginaw. The Saginaw people knew what they were doing. Boeing didn't trust anyone else, as these are critical parts. I wish I could have taken one of the jackscrews home and mounted it over the fireplace like some people mount a sword :-)
Saginaw is Chinese owned and has a interesting history:
"GM in 1999 spun off its parts group as Delphi Automotive including Saginaw Steering. Saginaw Division was renamed Delphi Steering"
"With Delphi entering a lengthy bankruptcy proceeding, GM purchased Delphi Steering through their subsidiary, GM Global Steering Holdings LLC, in 2009 and renamed the company, Nexteer Automotive"
"Nexteer was acquired by Pacific Century Motors on November 29, 2010"
"Originally, Pacific Century was a subsidiary of E-town, the Beijing municipal government's investment company, and Tempo Group, a Chinese car component manufacturer."
"In March 2011, AVIC Automobile Industry Holding Co., a Chinese state-owned parts manufacturer, purchased a 51 percent interest in Pacific Century Motors."
"GM in 1999 spun off its parts group as Delphi Automotive including Saginaw Steering. Saginaw Division was renamed Delphi Steering"
"With Delphi entering a lengthy bankruptcy proceeding, GM purchased Delphi Steering through their subsidiary, GM Global Steering Holdings LLC, in 2009 and renamed the company, Nexteer Automotive"
"Nexteer was acquired by Pacific Century Motors on November 29, 2010"
"Originally, Pacific Century was a subsidiary of E-town, the Beijing municipal government's investment company, and Tempo Group, a Chinese car component manufacturer."
"In March 2011, AVIC Automobile Industry Holding Co., a Chinese state-owned parts manufacturer, purchased a 51 percent interest in Pacific Century Motors."
Can you extract one from one of the dead 757s in Arizona?
I think that video was not correct then or they talked about something else because Boeing has outsourced critical parts whenever necessary at least since the 80s. I think the parts came mainly from Germany and Japan but I'd have to look it up.
Is this a new issue, or just an update on the problem fastening the fuselage barrel sections together that was identified last year? This article has a lot more detail on that problem: https://theaircurrent.com/aviation-safety/boeing-pulls-eight...
So pre-Covid I would fly 160-200k KM per year. I loved the 787. The higher humility and cabin pressurization along with the larger windows makes the flight so much better.
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As far as I can tell, the problem is the gap between the bulkhead and the fuselage is larger than spec. This means that it'll take more airflow to pressurize the cabin.
There are always going to be leaks. The idea is that if all the joins are at the adverse end of the tolerance, meaning more air leaks, there must be enough pressurization air to keep it pressurized. But this is rarely the case, so one part being larger than spec should not cause a problem.
Parts get delivered out of spec sometimes, and they get bounced to engineering to evaluate if the design as a whole will still work.
I.e. it shouldn't actually be a problem unless the other joins are near the limits of their tolerances.
So, what's missing from CNN's reporting is why they are demanding a rework. The local newspaper, which should have a better handle on the situation, doesn't do any better at reporting this.