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737NGs have cracked 'pickle forks' after finding several in the jets.

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737NGs have cracked 'pickle forks' after finding several in the jets.

Old 16th Oct 2019, 19:15
  #261 (permalink)  
 
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Talking of oversize holes, I used to work for a helicopter manufacturer who designed and embodied a flotation bag modification for the British Army. They used the forward undercarriage mountings as the main attachment points for the flotation bags. Unfortunately they carried out the modification at a time when the aircraft was stripped down and jacked up for heavy maintenance. When the aircraft was rebuilt, lowered off jacks and fuelled up, The 8mm holes didn't even come close to lining up. The solution was to drill out one set of holes to 12mm and the other set of holes to 13mm then use the original 8mm bolts with very big washers to clamp the thing up. Cringeworthy

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Old 16th Oct 2019, 22:53
  #262 (permalink)  
 
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6 thou? How could such a gross oversize get through? I'd expect an interference fit and 6 thou would have been obvious. Even close fit is on 5-15 ten thou and 6 thou should have been clearly too loose when installing.
Yes it would be obvious if the hole in ONE piece was perfectly in line with the hole in the other piece. But my **GUESS **is that the hole in the pickle fork was drilled in a jig, and the hole in the Fail safe strap was drilled/enlarged on final assembly, and most probably never reamed as an assembly. Hand drilling a hole can easily result in an out of round hole or slightly oversize. An we do not know the exact assembly process. Or IF interference holes/fasteners were specified. trying to hammer in an supposed light interference hole during assembly creates other problems. For example one could coldwork a hole, and not ream i giving an elongated hole which partially defeats the whole purpose. There is of course the incorrect ' logic ' that reaming a coldworked hole destroys the advantage of prestress around the hole.


Properly done, with correct size mandrel, the stressed area of significance typically exists for one radius external to the origional hole eg start with a 1/4 nominal hole, radius = 1/8 inch. = giving a radial stressed area equal to about 1/2 inch diameter. And usually due to how the aluminum part was processed/rolled, the resulting hole will be slightly elongated ( ellipitical ) by as much as a few thousandths, again depending on material and hole size. Thus to mmaintain a proper interference fit, a follow up ream is required. The preceeding is an overly simplIfied explantion of course.

Sort of a side note- if you want to raise the hair on your friendly stress person, talk about vertical scratches in a structural hole... which then leads to trying to make a sleeve with a spiral opening. Which made early attempts to make a practical sleeve a real problem. After much soul searching, a simple vertical split in the coldworking sleeve was tried, worked great. But still the issue was a major discussion of what about- what if.... etc. So a significant test program was initiated in 60's-70's , with groups of holes and individual holes coldworked with various sleeve split orientations to see if eventual failure was along the vertical split opening or somehow related. Bottom line- end result- no significant relationship re sleeve orientation and eventual overload- fatigue failure.
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Old 17th Oct 2019, 05:34
  #263 (permalink)  
 
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Originally Posted by ST Dog View Post
Agree and matches my experience.



6 thou? How could such a gross oversize get through? I'd expect an interference fit and 6 thou would have been obvious. Even close fit is on 5-15 ten thou and 6 thou should have been clearly too loose when installing.
You are right on.
Most Hi-Lok installations are interference fit and we use a Rivet Gun [Variable Trigger] with a Flush Set with Brass Face to drive the Hi-Lok into the structure.
.006 O/S Hole the Hi-Lok would fall into the hole or be easily pushed into the hole with the fingers.
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Old 17th Oct 2019, 13:27
  #264 (permalink)  
 
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newly enlisted, Hello all around.

Boeing seems to have handed out information that
Classic, NG and MAX do not show the same design.
(i.e. pickle fork issue is deemed to be a distinct NG problem)

What differentiates the NG and MAX pickle fork designs?
Or lies the diference just in having changed suppliers?
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Old 17th Oct 2019, 15:56
  #265 (permalink)  
 
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Originally Posted by Grebe View Post
Yes it would be obvious if the hole in ONE piece was perfectly in line with the hole in the other piece. But my **GUESS **is that the hole in the pickle fork was drilled in a jig, and the hole in the Fail safe strap was drilled/enlarged on final assembly, and most probably never reamed as an assembly.
If the full stack wasn't drilled, cold worked and then final reamed that's a process problem.
I've been involved with similar stack ups and they were always clamped up then final work was done on the assembly.

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Old 19th Oct 2019, 00:22
  #266 (permalink)  
 
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The Boeing 737 - 800 has cracking issues all over the aircraft including the Aft Pressure Bulkhead - Main Frames in main cabin where the overhead bins attach to the frame. Numerous cracks on the -800 main cabin Frames at the overhead bin lower mounts were discovered during the first Major Check.
[After 5 years in service]
The NG and later aircraft structures - in my opinion - do not even compare to the early generation 707-727-737-747. Lots of the major structure parts on NG's were made with lighter gage materials including frames- stingers- skins- bulkheads in an effort to save weight.

The skin and stringers above the main cabin floor line required bonded doublers called "acoustic dampeners" to reduce the vibration and buzzing of the airframe on the -800.
The ones on the stringer hats look like railroad tracks. The ones on the skin has a corrugated look.

I expect for many more cracking issues to arise as the NG Fleets age.
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Old 19th Oct 2019, 15:19
  #267 (permalink)  
 
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I agree, in the quest to save weight there are a lot of thinner gauge parts. The cargo bays also suffer from the cracking of minor parts.
The Aft Pressure Bulkhead inspection is a hangover from the Classics, these were known to crack in the "Y" Chord area. I'm not aware of any cracks being found on the NGs.
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Old 19th Oct 2019, 17:51
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Originally Posted by Webby737 View Post
I agree, in the quest to save weight there are a lot of thinner gauge parts. The cargo bays also suffer from the cracking of minor parts.
The Aft Pressure Bulkhead inspection is a hangover from the Classics, these were known to crack in the "Y" Chord area. I'm not aware of any cracks being found on the NGs.
Of note,- the first 737 NG flew in 1996- just before theMdc buyout and the intallation of the MDC management in various levels on mahogony row.

Then started the major change in 737 production and the emphasis on ' shareholder value " - the faster- cheaper game. All sorts of inspection and procedures were ' trimmed ' and now the rest is history. Name a major program in commercial that since that date has not had late deliveries, over budget, criminal activity resulting in club fed time, shareholder lawsuits for ' lack of candor ' screwing over of unions, moving corporate HQ, etc.

MDC has been more than a " cancer" its been a plague. And apparently the worst is yet to come . .

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Old 25th Oct 2019, 12:00
  #269 (permalink)  
 
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9 out of 42 at Korean Air and others airlines in South Korea 737NG's grounded!
https://simpleflying.com/south-korea...9-boeing-737s/
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Old 25th Oct 2019, 12:41
  #270 (permalink)  
 
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Originally Posted by Grebe View Post
MDC has been more than a " cancer" its been a plague. And apparently the worst is yet to come . .
That is not only an aviation thing.... it's called "capitalism" or "liberalism" at it's best. The thing we all swear is the saviour of this world, is beginning to show the signs of "old age"....

Maybe it's time someone sit down, look at how things work in the world, and see if it's possible to come up with a new philosophy that can actually handle the "problems" all the old ones generate...
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Old 25th Oct 2019, 15:07
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Originally Posted by jmmoric View Post
That is not only an aviation thing.... it's called "capitalism" or "liberalism" at it's best. The thing we all swear is the saviour of this world, is beginning to show the signs of "old age"....

Maybe it's time someone sit down, look at how things work in the world, and see if it's possible to come up with a new philosophy that can actually handle the "problems" all the old ones generate...
Don't think capitalism is the issue, the problem is when short term financial metrics dominate all other considerations.
It is almost always a lot easier and more lucrative for management to goose the share price with a big stock repurchase program that to risk a new investment that may not pay off.
The pernicious longer term effect include a surrender of market position, but the culprits will likely have retired by then. Nearer term, the short term mind set drives efforts to minimize all costs, including worker compensation, development efforts and compliance standards.
Seen that firms that did take investment risks, such as IBM with the S360 or Boeing with the 747, were hugely rewarded, one must assume that there has been a loss of courage in the industrial management mindset, perhaps driven by pressures generated by 'shareholder activists'.
Perhaps punitive short term capital gains taxes might help return the focus to longer term investment, or incentives for longer term returns such as extended vesting schedules, but no consensus has yet developed on this.
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Old 25th Oct 2019, 17:44
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Originally Posted by etudiant View Post
Don't think capitalism is the issue...

It is almost always a lot easier and more lucrative for management to goose the share price with a big stock repurchase program that to risk a new investment that may not pay off.

... the short term mind set drives efforts to minimize all costs, including worker compensation, development efforts and compliance standards.
That's the stage of capitalism we are in, now.
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Old 26th Oct 2019, 04:19
  #273 (permalink)  
 
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Any more news on picklefork issue from workers or BA AOG crew ?
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Old 27th Oct 2019, 17:04
  #274 (permalink)  
 
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Anybody got the total number at this point? With the 9 Korean NGs and the Ryanair, we gotta be pushing 50
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Old 27th Oct 2019, 23:00
  #275 (permalink)  
 
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So how much money did the new style pickle fork save Boeing ? How much are they going to be on the hook for the repair ?

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Old 29th Oct 2019, 15:52
  #276 (permalink)  
 
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Wiki says that 7,031 B737 NGs have been delivered.

Only those NGs that have exceeded 30,000 cycles need to be checked within 7 days, (or 22,600 cycles within + 1000 cycles).

FAA estimate that only 1911 (US aircraft) are affected of the 7,031 that have been delivered so far (presumably because most haven't yet reached 30,000 cycles).

This will be an ongoing problem for many years to come as each and every one of the 7,031 delivered air frames reaches the AD cycle inspection requirements.

Say 5% of inspected aircraft fail the AD at 30,000+ cycles, what percentage of the remainder will subsequently fail the AD Inspection at say 40,000, 50,000, 60,000 cycles etc?

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Old 29th Oct 2019, 16:49
  #277 (permalink)  
 
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Just curious how many airframes have ‘failed’ so far ?
Thanks
David
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Old 29th Oct 2019, 17:04
  #278 (permalink)  
 
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Originally Posted by FlexibleResponse View Post
FAA estimate that only 1911 (US aircraft) are affected of the 7,031 that have been delivered so far (presumably because most haven't yet reached 30,000 cycles).
The FAA's determination is simply the number of NGs on the N register (i.e. around 27% of the world fleet), not based on individual aircraft cycles.

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Old 30th Oct 2019, 10:01
  #279 (permalink)  
 
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Qantas will inspect 33 of its Boeing 737 aircraft by the end of this week after it discovered structural cracks on one of the short-haul jets that are the backbone of its domestic operations.

https://www.smh.com.au/business/comp...30-p535xo.html
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Old 30th Oct 2019, 22:30
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Guardian says of 810 jets inspected so far 5% have failed
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