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Door blows out during ground test on Boeing 777X jet

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Door blows out during ground test on Boeing 777X jet

Old 7th Sep 2019, 18:58
  #41 (permalink)  
 
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Originally Posted by Less Hair View Post
Didn't they flatten the frames inside the X-cabin in order to win some inches of cabin diameter for the 777X?
Thinner insulation and redesigned sidewalls. Nothing structural.

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Old 7th Sep 2019, 18:59
  #42 (permalink)  
 
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Don't want to interrupt but do we now know which door blew out? I would really want to know not only if it's passenger or cargo but which one of those. It could be an emergency exit. Now THAT would be very interesting.
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Old 7th Sep 2019, 19:04
  #43 (permalink)  
 
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CFRP allows a higher design strain than Al which is mostly beneficial. Non circular fuselage section would cause quite large displacements due to pressure, especially flattening to gain some space in the cabin floor area would put the floor in compression when the hull is pressurized. While I can think of ways to manage that it does not sound like a very good idea.
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Old 7th Sep 2019, 19:53
  #44 (permalink)  
 
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Originally Posted by DaveReidUK View Post
Thinner insulation and redesigned sidewalls. Nothing structural.
I would say redesigning the fuselage frames making the frame height lower but probably increase the thickness of the material in the frame in order the make the cabin wider is a significant structural modification.
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Old 7th Sep 2019, 20:00
  #45 (permalink)  
 
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Changing the frames is a design cycle, while not necessarily a major change it would still be far from trivial.
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Old 7th Sep 2019, 20:01
  #46 (permalink)  
 
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Originally Posted by DaveReidUK View Post
Thinner insulation and redesigned sidewalls. Nothing structural.
The fuselage redesign was most definitely structural - they made the side wall structure 'thinner' to open up more interior space.

As Aihkio notes, I wonder if it is related to how the fuselage was being held down. When they did the ultimate load test on the 767 nearly 40 years ago, they never broke the wings because the fuselage broke first. They were already above the 150% load limit when the fuselage let loose so they didn't need to repeat the test.

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Old 7th Sep 2019, 20:14
  #47 (permalink)  
 
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This starts to restore my confidence in Boeing. The occasional <censored> moment during testing means that you are really testing, rather than going through the motions. Something valuable was learned, and not the hard way. The shareholders don't like this sort of thing but they can get stuffed. People actually have to fly this plane so let's make it as safe as possible. It will get done eventually.

I wonder if this means that they have to build a new test frame?
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Old 7th Sep 2019, 20:25
  #48 (permalink)  
 
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I suppose a picture of the blown out door has not yet been leaked?
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Old 7th Sep 2019, 20:32
  #49 (permalink)  
 
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Originally Posted by Dave Therhino View Post
The article is a bit amateurish. Even with the poor article information, it's clear that the test they were doing was the positive g wing loading ultimate load test. Ultimate load is defined as 1.5 times the limit load. I don't know what limit positive load factor is used for the new 777, but it is required to be at least 2.5 g. So their target was to apply loads corresponding to the airplane pulling at least 3.75 g. That test is required by regulation to be done with the fuselage pressurized to the maximum cabin pressure differential. They apparently got a surprise before they made it to the target load. They are trying to give the impression that the door just popped out. However, plug doors don't just pop out. I suspect some significant structural failure of the fuselage occurred to cause the door to be released like that.
Most cargo doors are not plug type.
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Old 7th Sep 2019, 20:41
  #50 (permalink)  
 
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Originally Posted by tdracer View Post
The fuselage redesign was most definitely structural - they made the side wall structure 'thinner' to open up more interior space.
I stand corrected - I would agree that thinner profile frames are indeed structural (as opposed to sidewalls, which aren't).

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Old 7th Sep 2019, 20:42
  #51 (permalink)  
 
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Back when we (Fairchild-Republic) were testing the Swearingen Metro 4, the cargo door blew off, and sailed 50 feet across the lab ... The area was un-occupied so no harm, no foul, but after that, a cargo net blocked it's path in case there was a repeat ...
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Old 7th Sep 2019, 21:09
  #52 (permalink)  
 
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The A380 wing failed below the 1.5 limit in testing. It’s not uncommon to have issues in the testing phase. I don’t believe they even retested the A380 wing. That is after all the point of testing. Could be no design changes are required or it could be a major engineering effort. At this point no one knows.
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Old 7th Sep 2019, 21:25
  #53 (permalink)  
 
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Point of clarification here.

The wings were NOT being tested at the SAME TIME as the cabin pressure test.

They were simply doing the cabin pressure test while it was on the stand. (which was prudent, given the results)

As far as when it failed in the test, will be the issue. If it failed under static, or final load test, that is a huge problem. If it failed on ultimate (150% of final load) that is not such an issue, just depends at which pressure it failed.

As a side note, given this was a new airframe, with few compression cycles...it should have handled the loads no problem...an airframe with many compression cycles..that is different...this really could be an issue, but who knows.

I suppose a picture of the blown out door has not yet been leaked?
Press noted Boeing locked the facility down. Employees showing up on Friday were not able to access the building.

Last edited by Smythe; 7th Sep 2019 at 21:41.
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Old 7th Sep 2019, 22:00
  #54 (permalink)  
 
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Reasons for testing to failure

From memory (documentary on previous similar tests and FEA modelling a long time ago), testing achieves the following:
- shows the design and construction matches model predictions during normal conditions (say up to working loads)
- shows the same up to design loads (often working plus a percentage e.g. 150% of cabin differential)
- shoes the reliability of the model at the extreme edges (testing to failure)

When testing to failure, you often find out if the nonlinearities in real life were adequately built into the model (think of all the various stresses causing strains and deflections in different directions combining with each other) and - hopefully - you have correctly predicted the weakest point and failure mode at which structure eventually fails.

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Old 7th Sep 2019, 22:08
  #55 (permalink)  
 
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Originally Posted by Smythe View Post
Point of clarification here.

The wings were NOT being tested at the SAME TIME as the cabin pressure test.

They were simply doing the cabin pressure test while it was on the stand. (which was prudent, given the results)
That appears to contradict the Komo News report (on which the Seattle Times article is based):

A door blew off a Boeing 777X as the new plane was undergoing what was supposed to be its final structural inspection by federal regulators.

The test is meant to push the plane beyond its limits. Engineers had the plane pressurized and on the ground. They loaded it up well beyond capacity and bent its wings in an extreme manner, in a way almost certain to never happen in the real world.

As the ground test was underway and as engineers and FAA inspectors watched, a door blew off the plane.
Door blows off Boeing 777X during stress test

It's hard to imagine a bunch of FAA inspectors watching just a simple pressurisation test. What's your source for the alternative account ?
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Old 8th Sep 2019, 00:01
  #56 (permalink)  
 
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I guess I understand why they locked the building down but I think it is a mistake. Usually you don't want that picture of what is a fairly normal sort of engineering snafu (this would hardly be a story except for the MAX) out there with scary headlines, but one of the big problems with the whole MAX debacle was the lack of transparency and circle the wagons approach to the disaster by Boeing. If they let the press in to sniff around and made engineers available, I think it would go a long way to reinforcing the "Boeing comeback" narrative that we need to start seeing pretty soon. "This highlights our commitment to building the safest planes ever", "the engineers are back in charge", "we won't release it until it is right" sorts of PR taglines practically write themselves.

What are they worried about, the stock is going to take a short term hit?
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Old 8th Sep 2019, 00:53
  #57 (permalink)  
 
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Originally Posted by Water pilot View Post
I guess I understand why they locked the building down but I think it is a mistake. Usually you don't want that picture of what is a fairly normal sort of engineering snafu (this would hardly be a story except for the MAX) out there with scary headlines, but one of the big problems with the whole MAX debacle was the lack of transparency and circle the wagons approach to the disaster by Boeing. If they let the press in to sniff around and made engineers available, I think it would go a long way to reinforcing the "Boeing comeback" narrative that we need to start seeing pretty soon. "This highlights our commitment to building the safest planes ever", "the engineers are back in charge", "we won't release it until it is right" sorts of PR taglines practically write themselves.

What are they worried about, the stock is going to take a short term hit?
Probably not locked down, just restricted access to post-test investigation only, else all local employees would come take a look kicking through the debris BTDT
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Old 8th Sep 2019, 01:54
  #58 (permalink)  
 
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Originally Posted by Less Hair View Post
Didn't they flatten the frames inside the X-cabin in order to win some inches of cabin diameter for the 777X? And hasn't the floor structure material been modified compared to the -300ER? Methinks it's made of CFRP now. Might lead to different bending under extreme cabin pressure?
​​​​​​
The original floor grid is CFRP as is the new 777x floor grid. The cabin is the same diameter because the floor beams are the same width dimension wise. It's possible they may have squeezed some extra width from the inside plastic wall linings but seriously doubt they made the frames thinner. Most of the changes are due to wing changing to CFRP.

Edit: ok I stand corrected. Boeing site says additional 2" on each side for a total interior width that is 4" wider than legacy 777. I will have to see if the frames were changed.

Another possible issue is the cabin altitude is designed to be 6000ft similar to the 787. That would increase pressure on the structure especially at more than 100% load. Not sure what cabin altitude is for 777 legacy.

Last edited by sockfocksAP; 8th Sep 2019 at 02:07.
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Old 8th Sep 2019, 02:40
  #59 (permalink)  
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Prior B777 FWD and AFT main cargo doors had piano hinges, and are therefore non plug doors. The AFT BULK door is an inward swinging plug door. The main cabin doors are outward opening plug doors.

A blow out of a MCD could require a failure of the structure around the door to occur, That could occur through failure around the #3 doors when subjected to both high differential pressure and distortion from wing bending testing... sure would be interesting to look at. The wing tests load transfer to the region of the cargo doors does not appear likely, to the extent needed to defeat the locking mechanism. A simple failure from overpressure of the locking mechanism, with or without structural compromise of the primary structure is improbable, TBC has been building that structure for some time, and that doesn't appear to be a new generation technology application.

TBC will know already exactly what happened, and what is needed to rectify the problem. If it s production process defect, it wont take long. If it is a structural issue around the door it will take longer but it won't be a major schedule disruption. Photos and video will tell an interesting story, as will the structural evidence.
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Old 8th Sep 2019, 06:08
  #60 (permalink)  
 
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Frames were changed from sheet metal to milled aluminum and reduced by 2" thickness each, giving a total of 4" additional space.
So they might be as strong as on the "traditional" 777 but more flexible (stiffness increases at the order of 4 with thickness), causing more deformation to the door surround structure and putting more loads on the locking system.
We will see.

At 787 times we would already had all the pictures circulating the web...
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