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Eight B787 pulled from service over structural issues

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Eight B787 pulled from service over structural issues

Old 6th Oct 2020, 20:18
  #61 (permalink)  
 
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That is correct.
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Old 6th Oct 2020, 21:32
  #62 (permalink)  
 
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Volume

Shims above a certain thickness cannot be used as there is a knock-down in joint static strength and fatigue strength. Above a certain thickness, capability falls off a cliff edge. You can also use wet shim up to a certain thickness. This appears to be a limitation of the manufacturing process (process variation). I expect that it was not a pop-up issue. Somebody would have authorised a design manual(s) for the product, and in that manual are a list of all the allowed tolerances for parts in design. The digital model is created as 'nominal' with appropriate spacing built in for positional tolerancing. Above and beyond that, tolerance studies are carried out for large scale assemblies to assess the assembly process. Some of those tolerances are well understood (i.e. machined aluminium), some of them come from new process data. All are as a result of some level of testing and measurement process. Then you get in to the production side of things. There are quality auditing processes on purpose, and some are more fit for purpose than others. That possibly a quality process was abandoned with no replacement or improvement, primarily in order to make rate is cause for concern over the whole assembly process within that particular function/building/company unit. I find it hard to believe that there wasn't a manufacturing engineering task to look in to this one way or another. This could have been because the process wasn't fit for purpose, or because the process would show parts to be out of spec, or because the part condition wouldn't allow the user to carry out the inspection. The worst case scenario is that these measurements were not taken and things that needed a concession carried out on them have not been found and checked. Usually these kinds of things show themselves as a fatigue issue rather than a static strength issue.

This is the problem with commercial aircraft sized composites - part tolerances are more like cheap car assembly or worse than what we're used to (and require for our strength data and analyses) with metallic aircraft, for joints anyway. To compound the issue, B and A want to build airliners like Toyota and Honda churn out cars. Of course they do - there are thousands of single aisle in the order list at A, for instance. Something has to give. You get to choose two of: On Time, On Cost & On Quality.
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Old 6th Oct 2020, 23:22
  #63 (permalink)  
 
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Originally Posted by unmanned_droid View Post
I find it hard to believe that there wasn't a manufacturing engineering task to look in to this one way or another.
I find it very easy to believe that Boeing cut corners. What is unbelievable to me was the fact that Boeing used the supposed automated control of the shim process as justification for reducing the number of QA personnel. The drip drip drip of examples of corporate malfeasance is truly scary.

Now if there is a crash of any newer Boing due to a significant design or manufacturing flaw, I have to think Boeing in its present iteration is finished.
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Old 15th Dec 2020, 15:36
  #64 (permalink)  
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It seems more defects in the same vein have surfaced. Quoting the Seatle Times
(Boeing officially states) “some areas of the 787 circumferential fuselage join may not meet specified skin flatness tolerances,”
flaw arose when software failed to flag that shims exceeding the maximum thickness per engineering specifications were being used.
“As a result, we delivered no 787s in November and expect the process will continue to slow deliveries in December,”
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Old 16th Dec 2020, 07:40
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Flight Global's report is here
https://www.flightglobal.com/airfram...141620.article

Seems like they now have a stockpile of 60 undelivered 787s,

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Old 16th Dec 2020, 10:08
  #66 (permalink)  
 
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That is a lot of inventory waiting for delivery and payment.
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Old 16th Dec 2020, 15:05
  #67 (permalink)  
 
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I’ve had the dubious “pleasure” of being a 787 pilot for several years now, starting with the unedifying experience of a manufacturer’s conversion course. None of this surprises me. I recall picking up an airframe from BSC. They are very nice people. However I did ask several probing technical questions that were met with absolutely blank stares - of the “what do you mean”, rather than the “that’s commercially confidential” variety. I didn’t leave with a feeling of increased confidence. If you’ve been in aviation a long time, and done enough factory/ engineering visits, spent your time in hangars, you know what an “aviation culture” feels like. It wasn’t there at all.

Hey ho, sooner I’m out of this mugs game the better.
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Old 16th Dec 2020, 17:55
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CAEBr

That has much more to do with the pandemic than any additional inspections (although the inspections aren't helping). Only 15 787s delivered since April (and only two passenger 777s).

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Old 16th Dec 2020, 19:30
  #69 (permalink)  

 
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Posts like Case One's (#67) really give me pause for thought. A while ago, I asked a 787 driver of my acquaintance what he thought about the batteries, and he said "We don't".

And now, the later, current, tales of Boeing incompetence just reinforce the impression of a once-great engineering company that has sold its soul to commercial success at all costs. How very depressing.

And is Boeing the only one?
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Old 17th Dec 2020, 05:22
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As a Li-Ion battery designer, this saddens me. From what I'd read about the mitigation installed, I'd happily fly on a 787 with a pre determined 100% chance of a battery fire. The risks are known, and the fix looked good from here in the cheap seats.

The rest of it though, yeah, no thanks. Never setting foot in most newer Boeings.

I've seen an erosion of rigor in engineering across industries in the last 10-15 years. My boss, the head of engineering, was fired a month ago for surfacing a few critical issues to upper management. Opposite of normal, which would be mobilization of a thorough containment effort. But shipments are still going out, so contracts are being met, payments being wired on time.

(looking for another job actually, could be criminal liability for some of the stuff I've seen leave production).
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Old 17th Dec 2020, 08:07
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And to top it off, there is FAA warning about software bug found in newly rolled Autothrottle uppdates. Affecting 787, 777 and 747. This was not found in testing but out in the wild.

"Several in-service reports have been received from operators that the auto-throttle remained engaged in the IDLE mode when the flight crew advanced the thrust levers to conduct a balked landing. Once airborne, the thrust levers moved back to idle."
I am not allowed to post links but just Google "AIR-20-19"
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Old 17th Dec 2020, 09:53
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EASA Special Airworthiness Information Bulletin AIR-20-19.

No mention of applicability to 747, only 777/787.
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Old 17th Dec 2020, 14:00
  #73 (permalink)  
 
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I would think the reason that most pilots don't think about the batteries now is that it is no longer an issue. The fix has worked and I cannot think of any further incidents. Also Boeing South Carolina was purely set up as a manufacturing site with no history of aircraft production. I am sure most of the people there are grateful to have a job and would be just as happy building washing machines. However, I would hope they still take pride in their work. I am sure if you were to visit Boeing in Seattle there would be no shortage of people who have been involved in aviation all their life and would have a great deal of insight into the product.
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Old 17th Dec 2020, 15:12
  #74 (permalink)  
 
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Originally Posted by double-oscar View Post
The fix has worked and I cannot think of any further incidents.
The sad part is that Li-Ion + metal box weights more than NiCd it was meant to replace.
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Old 17th Dec 2020, 15:46
  #75 (permalink)  
 
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Sadly that is true. But if the batteries continue to perform without issue then one day the metal boxs may be removed to save weight.
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Old 17th Dec 2020, 16:23
  #76 (permalink)  
 
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"Several in-service reports have been received from operators that the auto-throttle remained engaged in the IDLE mode when the flight crew advanced the thrust levers to conduct a balked landing. Once airborne, the thrust levers moved back to idle."
Isnt this is what caused the 777 accident at Dubai...
once there is weight on wheels, the ac is in LAND mode, therefore the autothrottles will not advance thrust, even when pressing TOGA.
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Old 17th Dec 2020, 16:53
  #77 (permalink)  
 
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I read this as a slightly different issue - sounds like a bug introduced at a particular firmware update, rather than known design logic.
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Old 17th Dec 2020, 18:54
  #78 (permalink)  
 
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double-oscar

If they had used the better Lithium chemistry LiFePO4 which can not catch fire, instead of Lithium Ion which if anything goes wrong goes into thermal running away.
So bad design and choices in both type of chemistry and not putting them into a fire safe box from the start.. The best would be redesign with LiFePO4s and dump the steel box.

The trend in vehicles and aircraft is for LiFePO4 batteries to replace all forms of batteries.
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Old 18th Dec 2020, 01:34
  #79 (permalink)  
 
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Originally Posted by Grunff View Post
The sad part is that Li-Ion + metal box weights more than NiCd it was meant to replace.
The problem was that NiCd didn't have the necessary energy density - in short a NiCd of the needed capacity wouldn't fit in the available space. So they redesigned the Li battery with enough isolation between the cells that if a cell shorted and ran away, it couldn't propagate to additional cells. Unfortunately, the damage to the failed batteries was such that they couldn't definitely determine the cause of the failure, so they couldn't prove they'd fixed the root cause - necessitating the steel box in a sort of belt and suspenders solution.
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Old 18th Dec 2020, 05:20
  #80 (permalink)  
 
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As SLF on this aircraft, I re-evaluate the risks of flying on it every time I am forced to book it. Perhaps it is the prerogative of a pilot to consign his awareness of this issue to the back of his mind, but I trust he understands exactly how he will react when it all goes pear shaped.

It is true that we have not heard much about 787 battery fires lately, is that because they are not happening or the containment is working as designed.
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