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

[568]

Low time airframe

https://komonews.com/news/local/exclusive-unexpected-cracking-found-on-critical-boeing-737ng-equipment

It will be interesting to see how this is dealt with by Boeing.
I sincerely hope it is resolved in a timely manner.

[Bend alot]

I must say I am not surprised, there have been some serious allegations about the build quality of the NG.

[568]

I must say I am not surprised, there have been some serious allegations about the build quality of the NG.

Yes, it was only a matter of time.
Boeing is going to find this a tough PR exercise.

[meleagertoo]

Despite several thousand hours on the NG I have never heard of pickle forks and the OP's link doesn't work.

Anyone care to explain?

[RickNRoll]

Link (http://komonews.com/news/local/exclusive-unexpected-cracking-found-on-critical-boeing-737ng-equipment) FTFY

The pickly pecker is the type of thing that if it fails you crash. Joins the wingbox to the body.

[GordonR_Cape]

Despite several thousand hours on the NG I have never heard of pickle forks and the OP's link doesn't work.

Anyone care to explain?

Generic reportage: https://www.reuters.com/article/us-usa-boeing-faa/u-s-faa-requiring-inspections-for-cracks-on-some-737-ng-planes-idUSKBN1WD02E

The U.S. Federal Aviation Administration late on Friday said it would require operators of some Boeing (BA.N) 737 NG jetliners to conduct inspections for structural cracks and make repairs as needed following the discovery of cracks on a small number of planes.

The FAA said Boeing notified it of the issue “after it discovered the cracks while conducting modifications on a heavily used aircraft.” Subsequent inspections “uncovered similar cracks in a small number of additional planes.” Boeing said on Friday it has been in contact with 737 NG operators about a cracking issue, but added that “no in-service issues have been reported.”

Neither the FAA nor Boeing immediately said how many planes were impacted by the required inspections.

KOMO News reported on Friday the issue involved cracked “pickle forks” in some 737 NG jets. The pickle fork attaches the plane’s fuselage, or body, to the wing structure and manages forces. A failure of the part in flight could pose a serious risk. KOMO said workers found a severely cracked pickle fork on a Boeing 737NG earlier this month.

[Bend alot]

Despite several thousand hours on the NG I have never heard of pickle forks and the OP's link doesn't work.

Anyone care to explain?
Basically Boeing is in a pickle - sort of wings departing aircraft type of pickle.

So what is the difference to the MAX pickle forks?

I expected them to be the same.

[Water pilot]

Here is a picture that I found (https://www.facebook.com/photo.php?fbid=10201139046908249&set=o.365957056808594&type=3&eid=ARDg_fSvHW4_d7fN4Arh4DK-QZwtkT7UwGww6v76Wsg5Gkb3h1412OTqv_w0aH43l9VEztTekqtlQ2dO&__xts__%5B0%5D=68.ARCnOddq8J7knI4zx2ZeUkR-ROqAnQyvCgM0a9O1S9pjjdSCtqWSdyKG3DG9hc6yb_8u5zGwNXTWkLtu4MWI QJykRb2neL4IXcy_WO8XpV3gVSzNKzD-M9_0x8L82vw6BehO4Jj4g3UQ76hxhL37DGme6KHb12E1U-6128XimM_KnPASgUz9opfoJae8uypjHoFpzjkfoF2DqLa38VCR2IiNY4bsMj IeV7ELbAwL7UFP2I13kTmP_SF7DGn-py_6XhNoKv1oeN4Z-D5UwisQ_pXVIj7zqebrQ9UEcIPFj9VMBJ5z-RHZAEgiJQS5R8jHBdJIL1JrpMKbOuxxlXCo31c&__tn__=EHH-R)

[etudiant]

Better report on the issue, with images:
Boeing workers found new cracks on Boeing 737NG (not MAX). ? News In Flight (http://newsinflight.com/2019/09/28/boeing-workers-found-new-cracks-on-boeing-737ng-not-max/)

The wing to body attachment is a demanding structure and failures here would not be easily tolerated.

[Water pilot]

Pickle Fork LEAN manufacturing changes (https://www.epa.gov/lean/boeing-auburn-machine-fabrication)

Large Aluminum Parts Cell: 777 Side of Body Fittings (pickle fork)The pickle fork cell produces the body fittings that attach the wing to the body of the plane. The MBU previously produced the pickle fork using batch and queue techniques. When implementing Lean, the primary initiatives for pickle fork production were to create a product-focused cell, increase material efficiencies, and more effectively manage quality within the cell.

The pickle fork cell's capabilities include large part machining, close tolerance boring, hand drilling and finishing, assembly, and coordinate measuring machine inspection. In addition, like the Stow Bin Arch cell, the pickle fork cell maintains its own "store." The store contains the maximum number of parts required on the floor and uses cutouts as a visual control to maintain the proper inventory levels within the cell. Visual controls are also used to standardize and improve work quality. Color coded systems are used to ensure that the proper drills are being used to perform the right task at the right time in production.

To increase materials efficiency, the main component of the pickle fork is now produced out of forged, restrike aluminum. Previously the part was produced from block aluminum, which generated a significant amount of scrap because the pickle fork component was cut and shaped from the block. The pickle fork forgings now arrive in the approximate shape of the component so less aluminum is scrapped. In addition, the type of aluminum previously used for the pickle fork required shipping to California for stress relieving and return back to Auburn for continued production. The current aluminum forgings do not require stress treatment.



So there has been a manufacturing change, but I don't know from the document when that happened to understand if it has anything to do with this issue.

[Grebe]

It will be interesting to see or find out just where the cracks are. Obviously at this time, its just a guess. However, as a GUESS and based on experience dealing with fastener issues in large parts on 707 and 767 ( 707 that had been in service for a long time ) and tooling for 767-here is my SWAG based on the relatively low key descriptions.

A) The cracks are probably around or spreading from Fastener holes, probably those drilled " by hand" during the LEAN manufacturing process which are less than about 3/8 in diameter.
B) As such there is of course an argument that the crack would simply progress to the next hole in the pattern ( since drilling a small hole at the ' end ' of such crack is considered to be a ' crack stopper ' - which is true for a lot of ' sheet metal ' issues.

C) again , just a guess, but for 40 plus years, thre has been available and used a three to four step process to prevent such cracks, which can be done for all sizes of hole, even large holes during fabrication while still in large tooling- drill plates , etc.

D) in general- the steps are 1) drill a hole slightly smaller than final size 2) insert a thin sleeve into hole 3) insert a special mandrel such that when pulled back thru the hole it expands the sleeve and hole. 4) Ream the hole which will usually be slightly out of round to final size.

On assembly, insert bolt as a tight fit.
E) in some cases and sizes, the same process can be used without a sleeve but with a expanding mandrel.

F) This leaves a major prestress around the hole and provides a significant improvement in fatigue life.

The process was patented by Boeing in the late 1960, and a local firm called Fatigue technology was founded- developed from the previous firm called Industrial Wire and metal forming as I recall. And major first use ( from memory ) was on AWACS.
The process- tooling has been the subject of several related patents, and is still used by virtually all aircraft manufacturers
It can be used to prevent or stop cracks from further progress.

Again MY SWAG is that to save time some $$$ - or due to a temporary lack of sleeves or just plain skipping the sequence ( hard to detect when inspection is only on final hole size )

So depending on location and accessibility, the fix would be to remove bolt, expand hole, ream hole, insert new oversize bolt and voila, a terminating fix.

Just have to wait and see- If someone has access to documentation as to real issue and location, would be interesting to see how close I came

[piperpa46]

Basically Boeing is in a pickle - sort of wings departing aircraft type of pickle.

So what is the difference to the MAX pickle forks?

I expected them to be the same.
No Max has flown 35000 cycles.


But I hope that isn't the reason they say Max isn't involved.

[568]

Link works now.
It was copied from another web browser.

[Fly Aiprt]

Crafted a sketch from a Boeing patent illustration :


https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/526x390/o7dn_700a981d1633464ffb12a6c3c8618107c26a48d9.jpg


This aircraft includes what is called a "pickle fork" fitting at the front and rear main spars of the main wing. In the cross-sectional view, a main spar of the wing is visible, to which a pair of pickle fork fittings 210 are fixedly attached. The pickle fork fittings 210 extend upward into the side wall of the fuselage 204, and thus transmit horizontal and vertical forces, represented by arrows 214, and bending moments, represented by arrows 216, from the wing 202 into the fuselage 204. Because of this configuration, when the wing 202 deflects, as shown in dashed lines at 220, the pickle fork fittings 210 also deflect, as shown in dashed lines at 218, causing corresponding deflection and deformation of the fuselage 204. It is to be understood that the magnitude of deflection of the wing shown and of the pickle fork members 210 shown at 218 may be exaggerated for illustrative purposes.

[Big Pistons Forever]

What the bean counter MBA's executives will never understand. You can have your part fast and/or cheap and/or good. When the insist that they want it cheap and fast they never seems to get they going to give up the "good" and it will bite them in the ass.

[568]

Crafted a sketch from a Boeing patent illustration :


https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/526x390/o7dn_700a981d1633464ffb12a6c3c8618107c26a48d9.jpg

Thanks for the graphic.

[GordonR_Cape]

The patent for pickle forks as aircraft wing-to-fuselage joint dates to 2013: https://patents.google.com/patent/US20150097076A1/en
In particular, the present application relates to an aircraft wing-to-fuselage joint with an active suspension connection.

2013-10-09 Application filed by Boeing Co
2013-10-09 Priority to US14/049,995
2013-10-09 Assigned to THE BOEING COMPANY
2015-04-09 Publication of US20150097076A1

It is not clear what mechanism was used for the NG prior to this. It is also not clear when this was first used on the NG (or some variant prior to the current patent).

My guess is that to achieve 35,000 flight cycles (assuming less than a decade of use) would require some kind of test aircraft, not normal passenger service.

[b1lanc]

Just confirmed with a NG capt that his airline is only inspecting certain aircraft. Wonder what the criteria are for inspection? The news in flight article also references 'certain' NG aircraft.

[biscuit74]

Pickle Fork LEAN manufacturing changes (https://www.epa.gov/lean/boeing-auburn-machine-fabrication)

So there has been a manufacturing change, but I don't know from the document when that happened to understand if it has anything to do with this issue.

That seems a reasonable possibility, which no doubt will be being looked into. Changing to a forged from a machined part will certainly change stresses within the material and is likely to affect crystal structure. The comment that post manufacture stress relief is no longer required may be relevant too !

'Big Pistons' is right - you can have fast, cheap or good. Hard to get all three.

[Fly Aiprt]

It is not clear what mechanism was used for the NG prior to this. It is also not clear when this was first used on the NG (or some variant prior to the current patent)

Komo says the 737 NG has 4 pickle forks, so I would presume that every 737 is configured according to the excerpt above.

[Tomaski]

Wonder what the criteria are for inspection?

Probably based on total cycles and/or production lot of the pickle fork component.

[QA1]

Pickle fork cracking was an issue on the 767. IIRC, depending on the extent of the damage, a repair consisted of removing some materiel or complete replacement of the affected pickle fork.

Either way it was a pig of a job.

[Winemaker]

What the bean counter MBA's executives will never understand. You can have your part fast and/or cheap and/or good. When the insist that they want it cheap and fast they never seems to get they going to give up the "good" and it will bite them in the ass.

Yeah. When I was doing mechanical design we used to say 'You can have it right or you can have it now, but you can't have it right now'. Pretty sure that still applies.

[Grebe]

The patent for pickle forks as aircraft wing-to-fuselage joint dates to 2013:


It is not clear what mechanism was used for the NG prior to this. It is also not clear when this was first used on the NG (or some variant prior to the current patent).

My guess is that to achieve 35,000 flight cycles (assuming less than a decade of use) would require some kind of test aircraft, not normal passenger service.


Sorry the patent is strictly about a suspension method design to REPLACE the boeing ' standard " picklefork design used on 737,747,757,767 and 777. Dont know about the 787 but suspect it is similar. This is not to say parts are interchangeable between the models.
Typically the pickle fork is used in conjunction with as common BA part-technique called a PLUS CHORD which joins the wingbox to the wing skin panels- so called since it looks like a plus sign or double plus sign from an end view of a long slightly curved "bar" running fore and aft

As to the 35,000 hours - depending on airline, a usage of 10 hours/day average would give 3600 hours/year and 36,000 hours in about 10 years.

The NG has been around in service for about two decades- and I would be surprised if the pickle fork for the MAX was much different than the NG. Cheaper that way :*

[DieselOx]

There is nothing inherently wrong with changing from batch to lean manufacturing. I've been involved with many lean implementation efforts, in an ISO 9001 compliant environment, from small (one part moving from machined to cast, similar to this one, but the size of your fist, and no lives on the line), to entire production lines.

You need to do your homework, use rigorous techniques and processes, and at the end of it, test final parts and assemblies as rigorously as the original. A complex, utterly critical part like this one would need a herculean effort to get right. I'm not full of the warm fuzzies about Boeing's ability to execute an effort like this in the last 20 years, from what I've read here and elsewhere about Boeing's strategic realignments.

[Fly Aiprt]

A picture of the pickle fork attachment.

According to reddit.com
https://www.reddit.com/r/news/comments/dagbg8/unexpected_cracking_found_on_critical_boeing_737/



https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/669x907/r4l8zmk_81df3b41c5db25402510774b6b279b8bd7f81d41.png

[FlexibleResponse]

There is also the possibility/probability that the addition of the Split Scimitar winglets has had an adverse effect on the wing bending loads carried by the pickle forks.

Apparently the spanwise lift distribution has shifted the centre of lift further outboard on the wings which would necessarily give rise to greater wing bending loads at the wing attachment points from both static flight and gust loads.

Possibly those B737s that were designed from the outset to have Split Scimitar winglets might have strengthened pickleforks to account for the increase in bending loads.

But those B737s (eg, 800, NG) that were fitted with the after-market mod Scimitar installation (without beefing up the wing attach load path design) would necessarily suffer a reduced wing attachment fatigue life due to the higher loads imposed by the addition of the Split Scimitar winglets.

Perhaps more engineering learned members than I might like to comment?

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/741x731/atwinglets_diagram_5120ddbd0171259ee5aa19d76174c19bcdb96c53. jpg

[Grebe]

But those B737s (eg, 800, NG) that were fitted with the after-market mod Scimitar installation (without beefing up the wing attach load path design) would necessarily suffer a reduced wing attachment fatigue life due to the higher loads imposed by the addition of the Split Scimitar winglets.

Perhaps more engineering learned members than I might like to comment?

excellent point- unfortunately there are probably very few if any of the old beards left who would know for sure

I do know that one of the arguments re winglets for the first NG types was just that- increased bending loads. While one could assume that was properly taken care of- the viral infection of the MDC types in the aero design groups coupled with the cheaper-faster- mantra may well have overlooked that issue.

It remains to be seen just where the cracks were found.

[megan]

Beefed up it is, depending on line number the wing beef up adds between 35.4 and 52.1Kg, though no mention of forks.

737-800SSW | Aviation Partners Boeing (http://www.aviationpartnersboeing.com/products_737_800SSW.php)

https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/540x450/product_737_800_ssw_sysdesc_53741ec55630bfed2f0f0b2719bfd2cf 56ea4b8a.jpg

[Maisk Rotum]

This could really Fork Boeing

[Sailvi767]

This could really Fork Boeing

Not really, cracks occur in virtually every airframe built. They are expected over time and addressed through inspection and repair. This would not even have made the news at all were it not for the max issues.

[biscuit74]

Interesting point, 'FlexibleResponse'. I seem to recall that the wingtip extensions fitted to Buccaneers were said to have contributed to the wing spar fatigue failure in 1980.
However, as 'Sailvi767' says, cracks occur in most structures; the trick is to know how and when to inspect before these become critical.

[GordonR_Cape]

Not really, cracks occur in virtually every airframe built. They are expected over time and addressed through inspection and repair. This would not even have made the news at all were it not for the max issues.

The original article indicates that this is not a benign issue, unless you believe the reports to be factually incorrect:
During a recent inspection, workers found a severely cracked pickle fork on a Boeing 737NG. The plane is relatively young, having logged approximately 35,000 flight cycles when the damage was found.

A retired Boeing engineer who asked to remain anonymous tells us, "It's unusual to have a crack in the pickle fork. It's not designed to crack that way at all. Period."

He says it's particularly concerning because it was found so early in the plane's service.

Another source tells us Boeing quickly reported the issue with the single plane to the FAA last week, and now more planes with similar cracking have been found.

[Bend alot]

"Teams in Seattle and Washington, D.C are working on this. A source within the federal government says FAA inspectors were excited and happy to get the call from Boeing.
The source says they are "...elated that the bloodline of safety is alive at Boeing." That same source worries about how economic concerns for Boeing impact safety."


That reads as if the FAA had/have doubts about the bloodline of safety at Boeing - then the last sentence doubt the CEO's public statements on safety at Boeing.

The retiree - seems to think it is pretty urgent - even a grounding of a small number of NG's would create a serious issue for Boeing - the FAA will need to be VERY transparent with the other regulators over this, especially if the cracking is due to some of the manufacture allegations floating around.

The retired engineer tells KOMO the cracks were really surprising, used an expletive, then said, "This is not good news," and added, "It's really urgent to investigate."

[WingNut60]

D) in general- the steps are 1) drill a hole slightly smaller than final size 2) insert a thin sleeve into hole 3) insert a special mandrel such that when pulled back thru the hole it expands the sleeve and hole. 4) Ream the hole which will usually be slightly out of round to final size.

On assembly, insert bolt as a tight fit.
E) in some cases and sizes, the same process can be used without a sleeve but with a expanding mandrel.

.......

Is the sleeve of the same material as the parent metal?
Is the sleeve effectively swaged into place and then reamed, rather than the parent metal?

I have seen something similar using a roller reamer. That is, a process that just swages the parent metal to size.
But have never encountered use of a sleeve.
Note! Not to be confused with roller reamers as used in oil drilling.

Just interested in the process.

[Aihkio]

Yes, wing lift distribution affects the max bending moment but it does not affect the loads transfered to the fuselage. The total lift is not affected by the distribution. What might cause a slight difference is the larger displacements caused by larger moment but as a guess that is not the first concern.

[Water pilot]

To me it reads as sarcasm or damning by faint praise. They are "elated" that Boeing informed them of a (potential) problem with the doohickey that holds the wings onto the plane?

[Speed of Sound]

The fact that this has been discovered in relatively low cycle aircraft suggests to me that this is a manufacturing/materials issue rather than time-dependant metal fatigue.

Also, only certain aircraft are being inspected which makes me think that they have very quickly established a commonality among the affected airframes which could be a single production batch, a single production location or a single supply of raw materials.

[b1lanc]

To me it reads as sarcasm or damning by faint praise. They are "elated" that Boeing informed them of a (potential) problem with the doohickey that holds the wings onto the plane?

One might ask whether the bloodline of safety is alive at the FAA as well......

Have to wonder if this will expand to the 757 and 767 with the new winglets added assuming the scimitar is the cause.

[Scuffers]

Is the sleeve of the same material as the parent metal?
Is the sleeve effectively swaged into place and then reamed, rather than the parent metal?

I have seen something similar using a roller reamer. That is, a process that just swages the parent metal to size.
But have never encountered use of a sleeve.
Note! Not to be confused with roller reamers as used in oil drilling.

Just interested in the process.
from an engineering perspective, using an in-situ sleeve is usually done then the stresses for the fixing exceed the properties of the host material, the sleeve's job is to spread the load over a larger area (assuming a cylindrical sleeve, the increase in diameter increases the load area in the base material).

the other way is to burnish the surface, typical burnishing tools are like a bar with many smaller rollers around it that then compress the host material to size, this is often done as the finishing process for bearing journals in aluminium used on camshafts etc.

here's some example tools: https://monaghantooling.com/precision-metal-finishing/burnishing/

[Grebe]

Is the sleeve of the same material as the parent metal?
Is the sleeve effectively swaged into place and then reamed, rather than the parent metal?

I have seen something similar using a roller reamer. That is, a process that just swages the parent metal to size.
But have never encountered use of a sleeve.
Note! Not to be confused with roller reamers as used in oil drilling.

Just interested in the process.


RE sleeve- no the sleeve is SPLIT and partially rolled together and is typically lubricated with a dry lube, and after expansion simply falls out or is easily removed. Look up the ( at least in Boeing ) the term ' coldworking ' and the firm in tukwilla called Fatigue Technology for more details.Fatigue Technology

401 Andover Park E, Tukwila, WA 98188, United States

They are a few blocks from Southcenter. Little known fact - one of the owners- perhaps now deceased was Burke Gibson-


Since the sleeves are NOT reuseable, and since they held some - but not all of the patents on the tooling ( pullers and certain adaptors ) they made- making a boatload of $$$.

And Lou Champoux was really more than a consultant - he was the inventor. :cool:

And to add or forestall the next ' logical' question re splt sleeve. Initially, Lou tried to use a spiral split sleeve due to concerns re a straight axial 'line' in the coldworked hole being a discontinut in the stress pattern. Almost impossible to make. So a straight simple split was tried- then the question was would the location of the axial ' line ' affect the load pattern and fatigue results ? After bucu tests the answer was nope.

By the way a large mandrel ( 1 inch approx ) lubricated with cetyl alchol as I recall has been used/tested to coldwork bolt holes in railroad tracks to improve fatigue life.

[Halfnut]

Pickle Fork LEAN manufacturing changes (https://www.epa.gov/lean/boeing-auburn-machine-fabrication)



So there has been a manufacturing change, but I don't know from the document when that happened to understand if it has anything to do with this issue.


That link says the change was FOR the 777 and NOT the 737.

[B727223Fan]

As someone who cut their teeth on Boeing Structures with the B 727 -223 and also a few of years on B-757-200 it is very sad to see what has become of Boeing Airplanes. I also have about 6 years experience on B 737 - 800 Structures. To borrow an expression from a TV Commercial the B 737-800 " Is Not Your Daddy's Boeing". In my OPINION it is an example of Lean MFG Gone Wild. I can tell you that Boeing Airplanes do develop cracks and corrosion in Primary Structure Members over time. What is concerning about this story and my experience with the
B 737 -800 is how early into the service life these Structure members are cracking.The B 727's were much older when we started seeing these kinds of problems. A lot of the problems with the B 737 -800 APPEARS to be Design issues to save weight as compared with the B 727 that was built like a tank. I do not recall issues with the B 727 Pickle Forks but the Wing Rib Chords were cracking on the 727 much later in the life cycle of the Airframe.
Example B 737-800 - In an apparent effort to save weight the Skin and Stingers above the cabin floor line were made in a manner that Boeing had to go back and add Bonded Doublers to the Skin and Stringer Hats. These were added to stop vibrations and buzzing of the Airframe and are called Acoustic Dampeners . We experienced a lot of cracking on the Main Frames where the Lower brackets of the Overhead Bins attach to the Frame. We discovered these on numerous B 737-800 frames in their 1st Heavy C Checks which were relatively low time aircraft. The repair includes stop drilling / routing out the crack - cold working the holes - and installing a doubler. We did not see this on the B 727 and B 757 Generation aircraft this early into the life cycle. All these repairs just add weight back to the aircraft that Boeing seemed to be avoiding in the original design and MFG. .
The first generation B-737 were built like the B 707 and B 727 Airframes : Heavy Duty. Even with the Stringer 10 Skin Lap Corrosion issues they were much better built airframes in my opinion. The Aloha B 737 Proved this in Hawaii.Pictures are available on Goggle Images because this forum will not let me upload pictures.

[B727223Fan]

I think you are on to something here because many of the B737 -800 wings had to be modified on the outer part of the wing structure before the winglets could be installed. Maybe the Wing loading at the Pickle Forks changed due to the installation of winglets.

[B727223Fan]

This could really Fork Boeing

The Crew and Passengers could be in a real "Pickle" if the pickle fork fails in flight.

[WingNut60]

from an engineering perspective, using an in-situ sleeve is usually done then the stresses for the fixing exceed the properties of the host material, the sleeve's job is to spread the load over a larger area (assuming a cylindrical sleeve, the increase in diameter increases the load area in the base material).

the other way is to burnish the surface, typical burnishing tools are like a bar with many smaller rollers around it that then compress the host material to size, this is often done as the finishing process for bearing journals in aluminium used on camshafts etc.

here's some example tools: https://monaghantooling.com/precision-metal-finishing/burnishing/

OK. I was already familiar with the "burnishing" process.
Your burnishing tool is what I am referring to as a roller reamer.
But I was not familiar with the use of the sleeve, which I now understand, in principle anyway.
Each roller of a roller reamer (burnishing tool) actually pushes a little bow wave of material ahead of it.
The hertzian contact stress so imposed has the potential, in itself to create microcracks, that potential could be obviated by use of the sleeve.
It also explains why the sleeves are not re-used.

I'm still interested to know whether the sleeve material is the same as or similar to the parent metal: harder or softer?

[Grebe]

I'm still interested to know whether the sleeve material is the same as or similar to the parent metal: harder or softer?

This is going far afield- suggest you take the time to read available catalogs and such from Fatigue technology
generally ( from long ago memory ) sleeves were steel when used in aluminum, and I ** think* heat treated. were there different ones used in steel or in 6AL4V titanium ?- dont think so. Lots of earlier discussion and testing re internal or external sleeve lubrication . But that was 30 to 40 years ago.

My point is/was it is and has been a common technique used world wide for over 40 years in the industry . Why not just drop the detailsm and wait till we find out just where the cracks are-were. BTW- lou champoux was at the desk next to mine for a year or so - and there is much more involved then needs explanation here.

[inducedrag]

https://youtu.be/IaWdEtANi-0

[WingNut60]

This is going far afield- suggest you take the time to read available catalogs and such from Fatigue technology
generally ( from long ago memory ) sleeves were steel when used in aluminum, and I ** think* heat treated. were there different ones used in steel or in 6AL4V titanium ?- dont think so. Lots of earlier discussion and testing re internal or external sleeve lubrication . But that was 30 to 40 years ago.

My point is/was it is and has been a common technique used world wide for over 40 years in the industry . Why not just drop the detailsm and wait till we find out just where the cracks are-were. BTW- lou champoux was at the desk next to mine for a year or so - and there is much more involved then needs explanation here.

Thanks for the input. As mentioned earlier, I was just interested in the general process, not how it might or might not apply to pickle forks.
I asked again about about the sleeve material because I thought you might know. I'd have settled for an "I don't know".

[Grebe]

Thanks for the input. As mentioned earlier, I was just interested in the general process, not how it might or might not apply to pickle forks.
I asked again about about the sleeve material because I thought you might know. I'd have settled for an "I don't know".


The correct answer is it depends there are several specialized variations of the process including leaving sleeves in place etc -PLEASE take the time to look up for free and read the basic catalog.

END END END

[DaveReidUK]

Also, only certain aircraft are being inspected which makes me think that they have very quickly established a commonality among the affected airframes which could be a single production batch, a single production location or a single supply of raw materials.

That seems far more likely than the so far unsubstantiated rumour that the cracks affect only aircraft retrofitted with the SS winglets.

If the latter had been true, the association would have been made by now and we would all know about it.

[cats_five]

Despite several thousand hours on the NG I have never heard of pickle forks and the OP's link doesn't work.

Anyone care to explain?

The link works for me.

"A pickle fork is the part that helps attach a plane's fuselage to its wing structure. It helps manage the stress, torque and aerodynamic forces that bend the connection between the wings and the body of the jet.

Engineers design pickle forks to last the lifetime of the plane, more than 90,000 landings and takeoffs, a term known as "flight cycles" in the aviation industry, without developing cracks. There could be dire results if the pickle fork system on the jet fails in flight."

[flynerd]

I think you are on to something here because many of the B737 -800 wings had to be modified on the outer part of the wing structure before the winglets could be installed. Maybe the Wing loading at the Pickle Forks changed due to the installation of winglets.

I doubt that. The mass of the fuselage would be the same with or without winglets. So the load on the pickle forks would not be altered by the addition of winglets or bigger wings or whatever.... Lift = gravity

[Bend alot]

I doubt that. The mass of the fuselage would be the same with or without winglets. So the load on the pickle forks would not be altered by the addition of winglets or bigger wings or whatever.... Lift = gravity
The bending moment at the pickle forks will vary on any change to the wing length, profile, weight or any other factor.

They transfer loads in all directions not just a fuse mass to wings.

[Aihkio]

The fuselage does not carry any of the wing bending, only secondary effects from displacement. There is a very heavy structure often called the wing box that keeps the wings together. And yes, L=m*(g+x") added with a small number from horizontal tail.

[Fly Aiprt]

See color sketch at https://www.pprune.org/showpost.php?p=10581606&postcount=14

Bending moment 216, deformed pickle fork (exaggerated) 218

[Aihkio]

That is a so called secondary moment that is caused be the displacement of the wing box. It very small in comparison to the primary bending that is carried by the box. The fuselage has to be flexible enough not to carry the loads. It is really a question of relative stiffnesses.

[Bend alot]

That is a so called secondary moment that is caused be the displacement of the wing box. It very small in comparison to the primary bending that is carried by the box. The fuselage has to be flexible enough not to carry the loads. It is really a question of relative stiffnesses.
Actually a case of surprise cracks in the pickle forks.

[B727223Fan]

I doubt that. The mass of the fuselage would be the same with or without winglets. So the load on the pickle forks would not be altered by the addition of winglets or bigger wings or whatever.... Lift = gravity

The pickle fork is attached to the wing SPAR which is a primary load carrying member of the wing.

[ironbutt57]

The pickle fork is attached to the wing SPAR which is a primary load carrying member of the wing.

or the center wing box anyway

[B727223Fan]

Please reference posting #26 in this thread. The illustration shows the Pickle Fork attached to the Wing Spar.

[Water pilot]

Yikes, this is not just some surface cracking:

The Federal Aviation Administration is expected to order all airlines to inspect all Boeing 737NGs with 22,600 or more flight cycles after three planes were found with critical equipment cracked all the way through. One of the three planes in question was being converted from passenger to cargo service in China. Only 15 had been inspected for the issue when the three damaged planes were found.

Most of those 737NG planes will be required to have an inspection performed within 1,000 flight cycles.

But planes with more than 30,000 flight cycles will need to be inspected within a week.

Some overtime headed your way? (https://komonews.com/news/local/faa-to-order-inspections-on-737ngs-after-3-planes-found-with-cracks-in-critical-equipment)

[Pilot DAR]

The illustration shows the Pickle Fork attached to the Wing Spar.

Yes, it does, and generally, and in the case of Boeing jets, the wing box is enclosed by wing spars at the forward and rear faces of the wing box. So, the "pickle forks" are attached to the spars and to the wing box, as considered as a larger assembly including the spars.

Wing bending could have a small effect on the wing box to fuselage connection, in transmitting bending loads from the wing box into the fuselage. I expect that the pickle forks would also be subjected to asymmetric loads associated with yaw, where the vertical stabilizer and wing (including possible differential power) act in opposition to twist the fuselage to wing connection. I'm aware of other types where the loads applied into the airframe from the vertical stabilizer and rudder are of concern.

[six string]

so, to sum it up, as long as we keep positive G’s the fuselage will remain sitting on the wing box. Simples! ;)

[B727223Fan]

I know of a U.S Carrier that has many 737 NG's that have more than 22, 600 cycles. Just the type of publicity Boeing needed after the 737 MAX debacle.

[Bend alot]

Yikes, this is not just some surface cracking:



Some overtime headed your way? (https://komonews.com/news/local/faa-to-order-inspections-on-737ngs-after-3-planes-found-with-cracks-in-critical-equipment)
I guess stop drilling is out of the question then!

All NG's to be inspected and so far 3 out of 15 aircraft have cracks.

With only 15 aircraft sampled that 30,000 cycle limit might drop.

[B727223Fan]

In case you didn't realize I have been inside the Wing Center section numerous times when I was younger. We entered thru the Fuel Tank Plate opening on the lower side of the wing center section..In Fact we had to install Fuel Cell Bladders with special lacing cord on some of our B 727's in the Center Section. So I'm very familiar with the Wing Center Section Structure and the "Bottle Bolt" castings and Bottle Bolts [also called Pins] where the left and right wings attach to the Center Section. In fact we accessed the rear Bottle Bolts thru the wheel wells and used Liquid Nitrogen / Dry Ice to shrink them before installation. The wings had to be shored before we removed the Bottle Bolts for inspection and/or replacement of the casting. I could provide more details but this thread is not the place to do it.

[Speed of Sound]

In fact on Heavy C Checks the floorboards are removed in the fuselage

Floorboards?

I know that the 737 is an old design but had no idea that Boeing was still using wood! :eek:

[golfyankeesierra]

Floorboards?

I know that the 737 is an old design but had no idea that Boeing was still using wood! :eek:
He did say “when I was younger”..

[Webby737]

It will be interesting to see what the forthcoming AD/SB will contain.
I would assume that it will require entry to the centre tank with quite a bit of sealant removal, so it won't be a 5 minute inspection.
If it wasn't for the spotlight on Boeing because of the MAX, we would probably of never heard of this in the mainstream media, these sort of problems exist on many aircraft types, it's not just Boeing products, there's plenty of similar inspections on Airbus aircraft.
@ B727223Fan, I remember the B727 well, we used to inspect the Frames that the forward wing Bottle Pin attached to, STA 740 if I remember correctly, these used to crack in the lower lobe (accessed through the Fwd Cargo Bay), the repair was either a stop drill and external stainless steel doubler or a Frame replacement.
We also used to find cracks in the frames common to the forward and aft bulkheads of the MLG wheel well (STA 870 & STA 950), these used to crack near STR 10 - STR 14 in the window belt area probably due to corrosion.
Of course at the time these were 30 year old aircraft so some defects were to be expected.

[Pilot DAR]

Wing Center Section Structure and the "Bottle Bolt" castings

I would expect structural components in Boeing wings to be comprised of forged parts, rather than castings. The weight penalty, combined with less predicable mechanical characteristics of castings would make them undesirable for such an important structure.

[infrequentflyer789]

Floorboards?

I know that the 737 is an old design but had no idea that Boeing was still using wood! :eek:

Allegedly as recently as this century they were building planes (787) with plywood doors... :E

[Speed of Sound]

Allegedly as recently as this century they were building planes (787) with plywood doors... :E

Oh yes, the famous fake Dreamliner launch in 2007! :O

[Grebe]

I would expect structural components in Boeing wings to be comprised of forged parts, rather than castings. The weight penalty, combined with less predicable mechanical characteristics of castings would make them undesirable for such an important structure.
its very easy to confuse a high quality casting which is painted with a forging which is painted. Especially when such is a specialized aluminum alloy..

[ironbutt57]

Floorboards?

I know that the 737 is an old design but had no idea that Boeing was still using wood! :eek:

apparently they all do, before the airplane departs, the passengers are all onBOARD arent they, after the BOARDing process is complete...

[ironbutt57]

Yes, it does, and generally, and in the case of Boeing jets, the wing box is enclosed by wing spars at the forward and rear faces of the wing box. So, the "pickle forks" are attached to the spars and to the wing box, as considered as a larger assembly including the spars.


https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/500x375/800_section_44_from_southwest_blog_0ff1dba52ab9ca98d20eeb90f bd4e31e9dcc1da1.jpg
center wing box, and what appears to be the right rear "pickle fork"

[ironbutt57]

maybe the ones that have cracked pickle forks are the ones that took a train trip down to the bottom of a gorge:}

[Bend alot]

Seems the inspection is fast at one hour.

https://leehamnews.com/2019/09/30/boeings-737-in-another-pickle/

[Grebe]

Seems the inspection is fast at one hour.

https://leehamnews.com/2019/09/30/boeings-737-in-another-pickle/
Also note the claim that inspections are to be done with a borescope-

Hint- borescopes are normally used to inspect ..... HOLES.... and ROUND things, but sometimes areas hard to see - sort of like a colonoscpy- same device. If it only takes one hour, most likely does not include removal of much- or remove a fastener and that cracks are expected to be visible. Suggest we wait for pics- drawings- or more details. AD supposed to be out in a day or so

[B727223Fan]

[QUOTE=Bend alot;10584485]Seems the inspection is fast at one hour.


Thank you for posting the info link.. Much more informative than previous info.

[B727223Fan]

Webby737;

You are correct about Sta 740 Bulkhead in the aft area of the Fwd Cargo compartment. We would actually cut a 14" x 18" access opening in the bulkhead web to gain access to the FWD Bottle Bolt Casting when they required replacement. Most of ours were being replaced due to Corrosion. Once the Job was finished we would install a doubler over the cutout with Hi-Loks. STA 950 was also the FWD Bulkhead in the Aft Cargo compartment.

[Chris2303]

maybe the ones that have cracked pickle forks are the ones that took a train trip down to the bottom of a gorge:}

Weren't they written off?

[ironbutt57]

Weren't they written off?

yes I'm sure they were...(see the smiley face)

[Pilot DAR]

its very easy to confuse a high quality casting which is painted with a forging which is painted

Indeed, by simply looking at the part, it could be very difficult to distinguish between cast or forged as the means of construction. Other than if a forged part were appropriate for the application in the aircraft design, certainly as a pickle fork would be, it is unlikely in the extreme that a cast part would also exist for that application. Castings have very different applications than forgings, and greater factors of safety required for the design (meaning a heavier part). I am aware that in another aviation industry, counterfeit parts were cast to appear to be replacement parts where a forged part was the correct part. Such use would have been horribly unsafe, and that was the highlight of the presentation. I'm not that least suggesting that is a factor here, other than to draw attention to the fact that there is a vital difference between cast and forged in aircraft part construction, and it's important to be aware of the difference if you're working on the plane. The means of construction difference extends after installation to how the part could corrode, or otherwise have defects. We're dealing with that these days with Cessna 210 wing spar carry through forging inspection and defects.

[Water pilot]

One hour seems optimistic - every day I am reminded that there is a huge difference between theory and practice. Will it be clean enough inside there to see something as subtle as a crack?

[Webby737]

One hour seems optimistic - every day I am reminded that there is a huge difference between theory and practice. Will it be clean enough inside there to see something as subtle as a crack?
Quite true,
I would assume that the area or at the very least the bolt heads/tails would be covered in sealant.

[B727223Fan]

The one Hour time estimate was probably written by some engineer who has never actually performed the task.

My job as a Structure AMT is to verify the Correct Part Number AND the Correct Effectivity assigned to the Aircraft that I'm installing the part on. Also verifying the Part Number on the documents that come with the Part. The part number is already determined for me in Boeing Drawings- Boeing Illustrated Parts List - Engineering Documents- Ect.
I do not have to know whether the part is a forging -casting - extrusion- ext. That is the job of Boeing and my Engineering Dept to instruct me which part to use. My job is to follow their written Instructions.

[B727223Fan]

Dopsonj : Thank you for posting the link to the pictures.

[Vendee]

One hour seems optimistic - every day I am reminded that there is a huge difference between theory and practice. Will it be clean enough inside there to see something as subtle as a crack?

In my experience, the time quoted for an inspection is purely the time it takes to inspect. It doesn't include any work required to get access to the inspection area and restoring the aircraft to a flight condition, including any functional testing.

[BARKINGMAD]

Is there any connection (no pun intended!) between these parts and the structural parts dating from around the millenium supplied by a sub-contractor & supposedly made using computer guided tools?

See my postings various on this topic some years ago.

These parts required hammers and/or redrilling by hand on the assembly shopfloor in order for them to fit and stimulated the report by the victimised supervisors.

Maybe Boeing Board should lock up their senior management and restart with some old engineers and some old pilots in the new fresh design department?
That’s assuming they’ve got any dosh left to pay the rent on the Nissan huts they’ll start out with on this new exciting venture?

What a sad fate for a once great and respected aeroplane manufacturer.

[Nomad2]

I watched a documentary on Boeing recently. There was some covert filming get in the North Carolina plant.

One employee made a very illuminating comment, when asked about the work the factory was doing, and how they were doing it.

"We're not building them to fly, we're making them to sell".

Nail on the head, I thought.

But at least the share price is up...

[Thrust Augmentation]

Is there any connection (no pun intended!) between these parts and the structural parts dating from around the millenium supplied by a sub-contractor & supposedly made using computer guided tools?

That had also crossed my mind - possibly a connection to the chords & components manufactured by Ducommun to new, tighter tolerances using sledgehammers & magic markers...... Tighter tolerances that were required for NG certification, but in reality didn't exist. Apparently this is the revolutionary new computerised manufacturing process in action;


https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/640x480/handforming_a_d3278f7042cea0471ed2fa84ef0214a240670c0e.jpg

[Loose rivets]

I recall an FO correcting me when I said that the leading edges of a BAC 1-11 wing were then 'taken to another location and annealed.' He explained the difference between annealing and normalizing.

Wasn't there mention earlier in the thread about the casting of Pickle Forks? I took the answers to mean, originally they were milled from the solid, but later cast with substantial oversize and then milled down to size. I know the metal cad be recovered, but the effects on the finished casting are serious science. I'm given to understand that even the way a hole is drilled is incredibly critical; the speed and sharpness of the tip being stipulated by the boffins.

[Grebe]

I took the answers to mean, originally they were milled from the solid, but later cast with substantial oversize and then milled down to size

Sorrly charlie -where did you get that " answer"

Its doubtful that that item was/is a casting

But why not check with a credible source ? ASK Boeing or the Vendor !

[fdr]

That had also crossed my mind - possibly a connection to the chords & components manufactured by Ducommun to new, tighter tolerances using sledgehammers & magic markers...... Tighter tolerances that were required for NG certification, but in reality didn't exist. Apparently this is the revolutionary new computerised manufacturing process in action;


https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/640x480/handforming_a_d3278f7042cea0471ed2fa84ef0214a240670c0e.jpg



That photo is what should be hanging around the neck of the OEM's corporate leaders, it encapsulates where the problem within the fish comes from. When the penny drops, and that gets finally acknowledged, then perhaps the OEM can get back to being a global leader.


[The worker in this photo is working on a part that was a "CNC" manufactured part... which resulted in extended maintenance inspections due to the precision of the CNC manufacturing process. The court documents indicated no CNC capability existed. The OEM's QA people were the messengers that ended up sueing WITHOUT SUCCESS for dismissal for doing their damned job. Nothing was ever done to replace these parts as far as I am aware.

[Pilot DAR]

Its doubtful that that item was/is a casting

Speaking as a "boffin", I think it's doubtful too. FAR 25.621 specifies factors to be applied to cast parts, and they are pretty penalizing from the perspective of weight and inspection. Though I have approved designs incorporating cast parts, these parts were in very low stress applications, with low failure severity, and easily inspected. I have changed the production technique for several parts from "cast" to "forged" to improve the product and save weight. And yes, we specify some holes and surfaces pretty closely too. I have nothing to do with Boeings, though it is very unlikely that I would approve a cast part in that application.

Of course, once a part is approved as a part of the type design, as said, it is not the role of subsequent technicians to necessarily understand how the part is made, and to make their own determinations as to airworthiness, other than in accordance with approved techniques and standards. Just put the right part in the plane applying the correct technique.

We all have a role to play in the safe operation of aircraft. For some of us, it may be at the beginning, specifying the manufacturing techniques and standards of quality. For others, it's maintenance or operation of the aircraft. We all have our own "areas" in which detail is important, and misunderstanding must be prevented.

[Speed of Sound]

The OEM's QA people were the messengers that ended up sueing WITHOUT SUCCESS for dismissal for doing their damned job. Nothing was ever done to replace these parts as far as I am aware.

A disgraceful episode where Boeing QA inspectors responsible for acquisition of those 737 parts were told that they were rejecting too many sub standard parts from Ducommon. When they asked how they could keep up with production targets they were told to use the sub standard parts by either re drilling holes or using hammers to make the parts fit. When they took this to the FAA and the US Dept of Justice they lost their jobs.

For those thinking that Boeing’s cavalier attitude to safety is a modern thing, these events were 20 years ago.

[Takwis]

I recall an FO correcting me when I said that the leading edges of a BAC 1-11 wing were then 'taken to another location and annealed.' He explained the difference between annealing and normalizing.

Wasn't there mention earlier in the thread about the casting of Pickle Forks? I took the answers to mean, originally they were milled from the solid, but later cast with substantial oversize and then milled down to size. I know the metal cad be recovered, but the effects on the finished casting are serious science. I'm given to understand that even the way a hole is drilled is incredibly critical; the speed and sharpness of the tip being stipulated by the boffins.

The first article I read on the pickle forks (sorry, can't find it now) said that originally, the part was cut from billet aluminum, creating a lot of waste. It also had to then be shipped to a subcontractor on California for 'normalization'. The new forks are forged, (not cast), and 'don't need to be normalized', or shipped to California. (I suspect that maybe they still do.)

Aha! From Waterpilot's comment (#10) above: "To increase materials efficiency, the main component of the pickle fork is now produced out of forged, restrike aluminum. Previously the part was produced from block aluminum, which generated a significant amount of scrap because the pickle fork component was cut and shaped from the block. The pickle fork forgings now arrive in the approximate shape of the component so less aluminum is scrapped. In addition, the type of aluminum previously used for the pickle fork required shipping to California for stress relieving and return back to Auburn for continued production. The current aluminum forgings do not require stress treatment."

[JamesT73J]

This has been an educational and informative thread. Hopefully this is all resolved safely.

[Longtimer]

FAA orders airlines to inspect dozens of Boeing 737s for structural cracksBoeing discovered cracks on a few of its planes undergoing maintenance in ChinaThomson Reuters · Posted: Oct 03, 2019 9:41 AM ET Last Updated: an hour agoThe U.S. Federal Aviation Administration said on Wednesday that aircraft operators must inspect 165 Boeing 737 NG airliners for structural cracks within seven days after the issue was found on a small number of planes.

Boeing Co notified the FAA of the issue after it discovered cracks on an aircraft undergoing modifications in China. The FAA said subsequent inspections found similar cracks in a small number of additional planes. The FAA said planes with fewer flights will eventually get inspected.
The article says the The order covers a total of 1,911 U.S. registered planes. The inspections can be done visually and should require about an hour per airplane, the FAA said.
Complete story can be viewed at: https://www.cbc.ca/news/business/boeing-737-1.5307170

[B727223Fan]

The Actual AD.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/b7003a93c909869e8625848800467eb9/$FILE/2019-20-02.pdf

[WingNut60]

The first article I read on the pickle forks (sorry, can't find it now) said that originally, the part was cut from billet aluminum, creating a lot of waste. It also had to then be shipped to a subcontractor on California for 'normalization'. The new forks are forged, (not cast), and 'don't need to be normalized', or shipped to California. (I suspect that maybe they still do.)

Aha! From Waterpilot's comment (#10) above: "To increase materials efficiency, the main component of the pickle fork is now produced out of forged, restrike aluminum. Previously the part was produced from block aluminum, which generated a significant amount of scrap because the pickle fork component was cut and shaped from the block. The pickle fork forgings now arrive in the approximate shape of the component so less aluminum is scrapped. In addition, the type of aluminum previously used for the pickle fork required shipping to California for stress relieving and return back to Auburn for continued production. The current aluminum forgings do not require stress treatment."

Interesting that, restrike.
The restrike die operation is, fundamentally, a solid forming operation. The main difference is that a restrike die is used after most of the major forming already has been performed suggesting that the components may still start life as block aluminium / aluminum.

[clearedtocross]

The AD that calls for repetitive inspections on a large lot of 737 is out and can be read here
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/b7003a93c909869e8625848800467eb9/%24FILE/2019-20-02.pdf

[aterpster]

The AD that calls for repetitive inspections on a large lot of 737 is out and can be read here
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/b7003a93c909869e8625848800467eb9/%24FILE/2019-20-02.pdf

That's a whole lot of 737s.

[EEngr]

The patent for pickle forks as aircraft wing-to-fuselage joint dates to 2013: https://patents.google.com/patent/US20150097076A1/en

That patent is for an 'active' suspension system. See below:
https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/1420x2000/us20150097076a1_20150409_d00003_cc81d566473e8aeae34f72466d96 0bb7e2a4a0fe.png
The pickle fork diagram is included as a description of prior art. And probably predates this patent by some years.

[EEngr]

Interesting that, restrike.
The restrike die operation is, fundamentally, a solid forming operation. The main difference is that a restrike die is used after most of the major forming already has been performed suggesting that the components may still start life as block aluminium / aluminum.

Or as a casting in the approximate size/shape of the finished part.

aluminum.

There's the problem. It lost an 'i' somewhere in the process. :ouch:

[Grebe]

The pickle fork diagram is included as a description of prior art. And probably predates this patent by some years.

Some years = approx 40 years or maybe more and generally still in use

[Longtimer]

The FAA says the inspection would only take an hour. Is that accurate?

[ST Dog]

That's a whole lot of 737s.

It's all of the 373NGs.
The immediate action for 30k cycles, and the rest within 1000 cycles.
Then there the repeat inspection every 3500 cycles.

would be interesting to see the Boeing Multi-Operator Message MOM-MOM-19-0536-01B.
I'm assuming that's not public.

[ST Dog]

The FAA says the inspection would only take an hour. Is that accurate?

The AD says 1hr. I'm sure that number comes from Boeing.

[Longtimer]

The AD says 1hr. I'm sure that number comes from Boeing.
Perhaps but maybe someone in the "REAL" world will share their experience and perhaps what has to be removed to uncover the "pickles" .

[568]

Regarding the Boeing MOM:

From the FAA AD itself:
"This service information also provides procedures for reporting inspection results to Boeing. This service information is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in the ADDRESSES section".

Companies have access to the MOM (which is sent to the relevant operators) and actions for reporting back to Boeing when the inspections have been made.
This information isn't normally shared to the public.

[Smythe]

Basically, they have to check ALL 737's to determine the extent of the issue.

Film at 11

[Dave Therhino]

The AD requires eventual inspection of all aircraft with more than 22,600 flight cycles. The FAA in the AD preamble estimated that to currently be about 1900 of the NG airplanes.

The part of the pickle fork fitting that is required to be inspected is exposed in the top forward corners of the wheel wells. With all the equipment installed near that location, it is not possible to get your head into positions that allow an adequate direct visual inspection of each of the fittings. Photos of that area that are adequate to detect the cracks have been taken by holding a cell phone up in that area. The AD requires an inspection using a borescope. There is no work required to gain access for the inspection. You just need a ladder and a borescope. It can be done in less than one hour. If you find a crack you are grounded until an approved repair is made.

[Dave Therhino]

The Boeing MOM referenced in the AD is available to the public in the public rule making docket, which can be viewed at:

https://www.regulations.gov/document?D=FAA-2019-0711-0002

[Grebe]

The Boeing MOM referenced in the AD is available to the public in the public rule making docket, which can be viewed at:

https://www.regulations.gov/document?D=FAA-2019-0711-0002


Just my opinion based on a fair amount of background re fasteners, holes, coldworking, tooling, and a very very small bit of repair issues

First- thanks to dave for the document complete with pics

second - I will draw your attention to the FACT that it was/is the Fail safe strap portion of the PF - not the PF- as the scare press would infer-

third- note that most - many NG will need nothing done/inspected till the next check - and an estimate of 1 hour for inspection is not unreasonable- which does not count time to possibly clean area, maybe take photos and complete paperwork.

Fourth - Even assuming the crack went to both holes and to both edges, the ' wings' will not fall off since the larger bolts ABOVE the smaller ones take the load. Under that event, then a major rework of some type might well be needed.

Fifth - the obvious cure to prevent such happening would be during production to ensure at time of assembly, the holes in that area be drilled, coldworked, reamed, and interference fit bolts installed. A few extra steps- relatively easy to do during assembly at wichita. It is possible that such coldworking was supposed to be done- but was missed since it involves an extra drill and ream operation during assembly. No easy way to ensure it was done.

I'll refer you to my post number 11 in this thread for more details

28th Sep 2019, 07:45
#11 (https://www.pprune.org/10581584-post11.html) (permalink (https://www.pprune.org/rumours-news/625886-737ngs-have-cracked-pickle-forks-after-finding-several-jets.html#post10581584))

[Dave Therhino]

Grebe - regarding your second point: Some of the initially inspected airplanes had both the pickle fork fitting outer chord AND the fail safe strap cracked in a given location. This is mentioned in the AD discussion section. It's shown in the first page of pictures in the Boeing document as well.

[Grebe]

Grebe - regarding your second point: Some of the initially inspected airplanes had both the pickle fork fitting outer chord AND the fail safe strap cracked in a given location. This is mentioned in the AD discussion section. It's shown in the first page of pictures in the Boeing document as well.


True but my point in #4 I believe still applies

Fourth - Even assuming the crack went to both holes and to both edges, the ' wings' will not fall off since the larger bolts ABOVE the smaller ones take the load. Under that event, then a major rework of some type might well be needed.

And I do not recall - perhaps missed it that if " a crack " was found - planes would be grounded ( ferry flight only )

[crewmeal]

Could someone tell me the difference between a 737NG and a 737-800. Also I see there are different varients of the 800 version. For example Egyptair fly the 866 varient. Is it to do with range?

[Viscount Way]

Could someone tell me the difference between a 737NG and a 737-800. Also I see there are different varients of the 800 version. For example Egyptair fly the 866 varient. Is it to do with range?

866 is a Customer Code which identifies an 800 Series for Egyptair. A United Airlines 800 would be an 824 for example. It’s a method Boeing uses to sort out and customise technical manuals etc.

[B727223Fan]

Could someone tell me the difference between a 737NG and a 737-800. Also I see there are different varients of the 800 version. For example Egyptair fly the 866 varient. Is it to do with range?


"Boeing 737 Next Generation (737NG) is the overarching name given to a fleet of aircraft that began production in 1991 (https://www.aerospace-technology.com/projects/boeing737_ng/). It includes the Boeing 737-600, Boeing 737-700, Boeing 737-800 and Boeing 737-900 — variations with different seating capacity. The 737NG featured (https://boeing.mediaroom.com/1997-12-17-First-Boeing-737-700-Goes-to-Southwest-Airlines) improved fuel capacity, a 25 percent larger wing capacity, and an ability to fly 900 more nautical miles than earlier 737 models. Southwest Airlines was the world's first airline to take delivery in 1997 (https://boeing.mediaroom.com/1997-12-17-First-Boeing-737-700-Goes-to-Southwest-Airlines), and by April 2012, 4,000 Boeing 737NGs had been delivered (https://www.aerospace-technology.com/projects/boeing737_ng/) around the world.

Two decades after the debut of the 737NG, Boeing announced plans for a new model: the Boeing 737 Max 8."

"

[B727223Fan]

Could someone tell me the difference between a 737NG and a 737-800. Also I see there are different varients of the 800 version. For example Egyptair fly the 866 varient. Is it to do with range?

American Airlines 800's are designated as Boeing 737 - 823. here is some more info.

https://airlinesfleet.com/american-airlines-fleet-boeing-737-800-details-and-pictures/

[568]

The Boeing MOM referenced in the AD is available to the public in the public rule making docket, which can be viewed at:

https://www.regulations.gov/document?D=FAA-2019-0711-0002

Thanks for the information and link.
If cracks are found, then do you know what steps need to be taken (interior stripped around the wing box area for example) to get to the problem area?

Appreciate your accurate information in many of your posts.

[b1lanc]

My 737-900ER flight this morning was switched to a 757-200OW flown up from Salt Lake to Boise over night - gate agent announced it was the largest plane they had ever used at Boise. Wouldn't surprise me if the airlines are acting aggressively on this one.

[Takwis]

Could someone tell me the difference between a 737NG and a 737-800. Also I see there are different varients of the 800 version. For example Egyptair fly the 866 varient. Is it to do with range?

The "Next Gen" airplanes included the 737-600, -700, -800, and -900. BBJs (Boeing Business Jets) of the same timeframe are also "next gen".

[Dave Therhino]

Thanks for the information and link.
If cracks are found, then do you know what steps need to be taken (interior stripped around the wing box area for example) to get to the problem area?

Appreciate your accurate information in many of your posts.

Hi 568,

I have not seen any information yet about proposed repair schemes other than replacing the entire cracked fitting with a new one. That obviously is a not a quick repair, but I don't know exactly what steps would be involved.

[568]

Hi 568,

I have not seen any information yet about proposed repair schemes other than replacing the entire cracked fitting with a new one. That obviously is a not a quick repair, but I don't know exactly what steps would be involved.

Dave,

Thanks for the response.
Seems this may be quite a lengthy repair job so I will be interested in seeing the details of the repair procedure when published.

[B727223Fan]

Floorboards?

I know that the 737 is an old design but had no idea that Boeing was still using wood! :eek:



Yeah- We still use claw hammers and nail guns to remove and install the floorboards.

Boeing Floorboard Tape.

https://www.e-aircraftsupply.com/products/na/7367714/GSC2195813022

[Grebe]

YIKES ! significant issue re cracks from another site if true

50 percent of those > 25000 cycles in one airline checked with cracks :(

First 10 acft checked 5 cracked
By Jetson on Saturday, Oct 5th 2019 19:41Z

My company started the AD checks two days ago.
By the A.D. Aircrafts with 25.000 or more cycles have 7 days to have the pickles checked otherwise will be grounded.

Aircrafts with less than 25.000 cycles have longer schedules.

In 5 of 10 first aircrafts checked (all with more than 25.000 cycles) the cracks were found and are grounded. They don’t have any idea for how long since there is no definitive bulletin to repair it (the A.D. only states which aircrafts will be checked first and to have all aircrafts with cracks grounded until further instruction)

They are guessing they will be grounded for more than 40 days.
=========
https://www.avherald.com/h?article=4cd92d2a&opt=0

[B727223Fan]

This is the problem with an Airline buying and operating too many of one type of aircraft. I remember reading a story where it stated that American Airlines owns 300 737-800's. Imagine if 50 percent of them require the 7 day inspection and 50 % of them are cracked. That would wreak havoc on Airline schedules and available seats. In my 45 years in aviation I do not ever remember a commercial airliner being grounded as long as the 737 MAX.

[hans brinker]

In other news: Pickle forks prices going up...

[cappt]

Just stick a fork in it!

[b1lanc]

YIKES ! significant issue re cracks from another site if true

50 percent of those > 25000 cycles in one airline checked with cracks :(

First 10 acft checked 5 cracked
By Jetson on Saturday, Oct 5th 2019 19:41Z

My company started the AD checks two days ago.
By the A.D. Aircrafts with 25.000 or more cycles have 7 days to have the pickles checked otherwise will be grounded.

Aircrafts with less than 25.000 cycles have longer schedules.

In 5 of 10 first aircrafts checked (all with more than 25.000 cycles) the cracks were found and are grounded. They don’t have any idea for how long since there is no definitive bulletin to repair it (the A.D. only states which aircrafts will be checked first and to have all aircrafts with cracks grounded until further instruction)

They are guessing they will be grounded for more than 40 days.
=========

Flew through ATL last night - not uncommon to see one or two AC at the maintenance shop - usually larger types and most often in hangar. There were a number of Delta and AA 737NGs parked outside the Delta shop - almost as many AA as Delta. As far as I can tell, AA isn't one of Delta's TechOps customers.

[jimjim1]

I'll refer you to my post number 11 in this thread for more details

28th Sep 2019, 07:45
#11 (https://www.pprune.org/10581584-post11.html) (permalink (https://www.pprune.org/rumours-news/625886-737ngs-have-cracked-pickle-forks-after-finding-several-jets.html#post10581584))

For some reason links to pprune often fail to work properly.
Think this is fixed below but I can only be sure once actually posted. I will test it once posted. Sometimes the links work when that have been put in a quote box as above.
https://www.pprune.org/rumours-news/625886-737ngs-have-cracked-pickle-forks-after-finding-several-jets.html#post10581584

[Hot 'n' High]

........ And I do not recall - perhaps missed it that if " a crack " was found - planes would be grounded ( ferry flight only )Hi Grebe, I think the "grounding" of affected aircraft is implied rather than explicitly stated.

From what I can see, the MOM just talks of reporting all findings but then states in the penultimate Para, “Depending on findings, a ferry flight may be permitted”.

The AD, however, has an instruction to “…. repair if any cracking is found” (Para 1 of the AD and subsequently the last Para of P2 of the AD) and also talks of Ferry Flights to move the [affected] aircraft “….. to a location where the airplane can be repaired if any crack is found.” (at Para (I) on the penultimate page of the AD). It also states that repairs should be made ".... using a method approved by the FAA or .".

There seems to be no “….. carry out repairs within…...” statement – it looks like a case of “if cracked – repair iaw Instruction XXXX and you may be given an exception for a ferry flight if needed to get the repair done elsewhere” - not that the AD quotes any "instructions" - it's all a bit vague! Maybe there is something in the Boeing Manuals (ie an Instruction XXXX) re size/nature of cracks before repair is needed as as often the case but I don’t have that sort of info to hand. From my experience, in Primary Structure, often there is little if no leeway before a repair is needed - but that should all be laid down in the Maint Manuals.

Again, I may be missing something but that’s how I read it FWIW. Not sure what you think. Cheers, [B]H ‘n’ H

[B727223Fan]

Here are the US 737 NG Numbers from a web page story.

"In the United States, Boeing 737NGs are operated by the following US-based airlines:"

Alaska Airlines (138 in fleet)
American Airlines (304)
Delta Air Lines (217)
Southwest Airlines (695)
Sun Country (18)
Swift Air (4)
United Airlines (329)

[Pilot DAR]

Though I'm not involved with B737 maintenance, I am involved in a "cracked forging" inspection program with another type. In my opinion, in terms of a primary structure forging the only "repair" which might be approved could be dressing out of a very tiny crack, otherwise it will be repair of the airplane by replacement of the cracked part. I'll be surprised of a crack so small to be permitted to be dressed out could be detected before getting too long to require part replacement. It is generally otherwise not possible to "repair" a primary structure forged part (as by adding an element to share the load across the crack). A reference to "repair" [of the airplane] will likely be by part replacement. Letting alone the magnitude of the task to replace the pickle fork, another concern will be the availability of replacement parts. Industry can hope that Boeing had a large run of forgings made, and they sit either partly or fully completed. As forgings are a long lead time & and special process part, that are commonly made in batches, rather than as needed.

A forged part may be incorporated in a primary structure design, because that single part is a very efficient means to carry the load. If that part cannot carry the load (because it has become cracked), there typically is not a parallel load path available within that space or attachment to carry the load via an alternate path, so putting a strap across the cracked area is not a likely repair. By the time you did that, you'd have to bypass the entire design load into the same fastener holes, so you may as well replace the defective part.

The reference to an FAA or Boeing approved repair is a subtle reference to the fact that there is no other approved repair scheme to be found - you must request an approval for the proposed repair from either the FAA or Boeing. Otherwise there would be a "repair in accordance with...." statement in the AD. Perhaps in the future there may be, as suggested, but not yet. And, cunningly, the AD wording requires a defect found to be reported, because it serves industry well to have the data about defects. This because I expect that the Boeing maintenance manual might already describe or allow repair of the airplane by replacement of a defective part. So if an operator found a crack, and had a replacement part in stock, they might be able to simply replace the defective part in accordance with existing Boeing instructions. That's fine, but the initial defect must still be reported for statistical reasons.

[pettinger93]

Replacing cracked 'pickle forks' with new, but identical, forgings just kicks the problem down the road. Presumably, the replacement forgings have the same weakness, and will have a tendency to crack in the same way, so the part will need to be re-designed and re-manufactured, to stop the problem for the longer term. Those aircraft that have the forging replaced now may have to do it all again when better forgings are available.

[SLF3]

If the pickle forks are supposed to be good for the design life of the air frame it is very unlikely there will be a lot of spares on a shelf. Lead time on forgings can be months.

[Hot 'n' High]

.... but the initial defect must still be reported for statistical reasons.

All agreed Pilot DAR tho I read it as "nil returns" also required in cases where the aircraft was found to be OK when inspected to give a statistical feel for the issue/ensure all relevant A/C have been checked.

In such areas, usually you are talking of limited scratches/nicks being blended out from my memory. Usually a crack was a "here we go" moment and leads to a world of pain and grief as you suggest (replacement and all that entails). However, I have come across main lift frames in the RW world having repairs but my memory is such that I can't remember how the original frames were produced - they were fairly robust tho! Do recall a good cue to inspect the frame "out of phase" was when the aircrew started saying how smoothly the aircraft was now flying all of a sudden! :} A whole new meaning of "stress relief"!!!!

I just got the feeling, given no repair details have been quoted yet (that we know of), that Boeing/the FAA are still getting to grips with exactly what they have on their plates here - as will the poor operators! As pettinger93 and SLF3 observe, a permenant solution would require a redesign - unless you just "life" the forging and accept an ongoing cost in the interim/future. Whatever it is, sounds like it's not going to be fun. :hmm:

[ManaAdaSystem]

If I understand this correctly, the pickle forks are checked during major checks of the aircraft.
Why have nobody seen this before?

[B727223Fan]

Replacing cracked 'pickle forks' with new, but identical, forgings just kicks the problem down the road. Presumably, the replacement forgings have the same weakness, and will have a tendency to crack in the same way, so the part will need to be re-designed and re-manufactured, to stop the problem for the longer term. Those aircraft that have the forging replaced now may have to do it all again when better forgings are available.

Excerpt from the AD.

"The FAA considers this AD interim action. The inspection reports that are required by this AD will enable the manufacturer to obtain better insight into the nature, cause, and extent of the cracking, and eventually to develop final action to address the unsafe condition. Once final action has been identified, the FAA might consider further rulemaking."

"Develop Final Action" could mean the re-design and manufacturing processes of the pickle forks.

[david340r]

Same component on the Max? Maybe time to start some parting out?

[b1lanc]

Same component on the Max? Maybe time to start some parting out?

I was wondering the same. Boeing has been adamant that it did not affect the Max - maybe because it's grounded?

[infrequentflyer789]

YIKES ! significant issue re cracks from another site if true

50 percent of those > 25000 cycles in one airline checked with cracks :(


Leehams is reporting today that the incidence is 5% over the first 500 inspected. https://leehamnews.com/2019/10/08/boeings-737-in-another-pickle-part-2/#more-31313

The airline with 50% may just be unlucky, more likely some factor in their operation leads to higher loads in that area. Article says retrofit winglets may also be a factor.

The other not-so-bad news is expected repair time of 3 weeks (not as bad as your 40 days) and that 25 sets of new forks are currently available - what happens when those are gone may be interesting, IF the MAX part is the same then presumably some will be available due to slowing production, if not and the 25 were all the spares in stock then I guess later groundings could be longer.

[Grebe]

Leehams is reporting today that the incidence is 5% over the first 500 inspected. https://leehamnews.com/2019/10/08/boeings-737-in-another-pickle-part-2/#more-31313

The airline with 50% may just be unlucky, more likely some factor in their operation leads to higher loads in that area. Article says retrofit winglets may also be a factor.

The other not-so-bad news is expected repair time of 3 weeks (not as bad as your 40 days) and that 25 sets of new forks are currently available - what happens when those are gone may be interesting, IF the MAX part is the same then presumably some will be available due to slowing production, if not and the 25 were all the spares in stock then I guess later groundings could be longer.

UHHHH- how long to remove fuselage aft of wingbox, remove ' old-cracked fork ' replace with " new" fork, reinstall fuselage , etc

And how much cost and whom pays for part failing prematurely ?

[Bend alot]

5% of 500 is 25, so I would guess 0 are currently available.

Will the inspection time be lowered?

[golfyankeesierra]

Apparently the winglets are a major (part of the) cause for the cracks. The Leeham news article mentions the possibility of counting cycles from the moment (aftermarket) winglets were mounted.

How about removing those winglets ASAP?

[WingNut60]

UHHHH- how long to remove fuselage aft of wingbox, remove ' old-cracked fork ' replace with " new" fork, reinstall fuselage , etc

And how much cost and whom pays for part failing prematurely ?

With no knowledge at all to guide me, can someone close to this level of repair (replacement of pickle forks) please explain, in brief, how it would be done.
In my mind I see the entire fuselage being lifted off the wing, just to provide enough access.
Or, can you get the pickle forks in through the hold?
Splitting off the rear fuselage section seems, in my mind, to be totally unachievable in 3 weeks.
And, aren't there both front and rear pickle forks?

[tdracer]

And how much cost and whom pays for part failing prematurely ?

Boeing typically guarantees a certain cycle/hour fatigue life, and Boeing would cover at least part of the repair costs assuming it failed below those life limits.
However, if the cracks are indeed associated with retrofit winglets - that's an STC outside of Boeing's direct control and all bets are off.
I do know that new build 737s with winglets get changes to the wing structure to account for the different loads and load paths associated with the winglets. I don't know about the 737, but I used to know a guy that worked for the company that did the STC winglet mod for the 757 and 767 - he said the structural changes they needed to make to the wings were extensive (and expensive) - but the fuel burn savings were so high that for longer range aircraft the payback only took about a year.

[Grebe]

With no knowledge at all to guide me, can someone close to this level of repair (replacement of pickle forks) please explain, in brief, how it would be done.
In my mind I see the entire fuselage being lifted off the wing, just to provide enough access.
Or, can you get the pickle forks in through the hold?
Splitting off the rear fuselage section seems, in my mind, to be totally unachievable in 3 weeks.
And, aren't there both front and rear pickle forks?

The fuselage does not really ' sit ' on top of the wingbox re production assembly. the pickle forks fore and aft re the fuselage are typical production breaks think of slicing the fuselage with a knife just in front of the front wing spar and just behind the rear wing spar. a close look at the fuselage sections in almost any simple production or 737 handout showing the different sections will show essentially where the production breaks are . So in overly simple ( description only ) terms, for rear pickle fork, undo the production break at rear spar section of wingbox, move it back a bit , undo picklefork from the fuselage section above the wing box and along the rear spar attachment to the wingbox , replace picklefork, and then rebolt the whole thing together again. Lots of overtime to do it in two three weeks. :)

I've found a pic that comes close to showing the fuselage body differences between front and rear spars
look closely at the slight diff in green coating above rear spar fuselage ( panel join ) and ditto in front of wing front spar. Its subtle, expand pic and you can see. the pickle fork extends part way up the fuselage in those two areas

https://www.ainonline.com/aviation-news/air-transport/2018-09-11/boeing-plays-catch-737

[WingNut60]

Does having 25 PCS in stock indicate that they do anticipate having to replace them occasionally?
That is, is this a not unheard of occurence in service, just very uncommon.
Or would they be held in case one is damaged or rejected for some undefined reason on the assembly line.

[b1lanc]

I do know that new build 737s with winglets get changes to the wing structure to account for the different loads and load paths associated with the winglets.

Changes to the wing inboard from the winglets I've seen diagrams of - changes inboard from the pylons?

[B727223Fan]

WingNut60;

I've never replaced pickle forks but can tell you that when replacing major structure members it is not uncommon to require shoring and/or pre-loading of the fuselage and/or wings..

If all the parts and tooling are available with skilled structure mechanics 3 weeks is not unreasonable.

Another issue is that once an area is opened up for repair other issues can arise such as corrosion or cracks and that has to be addressed also. That has the potential to add repair time to the aircraft.

[tdracer]

Changes to the wing inboard from the winglets I've seen diagrams of - changes inboard from the pylons?

Sorry, but you're getting well beyond my area of expertise (which is engines, not structures).

[Mark Van Herd]

Does having 25 PCS in stock indicate that they do anticipate having to replace them occasionally?
That is, is this a not unheard of occurence in service, just very uncommon.
Or would they be held in case one is damaged or rejected for some undefined reason on the assembly line.
Are we assuming they are going to just replace them with existing stock and hope they don't crack again or will Boeing be re engineering and strengthening them and then hoping something else further down the Load paths won't break?
Regards

[The AvgasDinosaur]

Same component on the Max? Maybe time to start some parting out?
Does the MAX share the same ‘pickle fork’ component as the NG ? Are they in fact interchangeable if so there is no shortage for NG replacements as it is still in production and the 25 mentioned are just those held or earmarked for NG replacements if ever required, if not how long should it take to restart and ramp up production?
Is there no mandatory requirement on a manufacturer to guarantee supply of airworthiness critical components during the service life of a type?
Be lucky
David

[Tomaski]

Does the MAX share the same ‘pickle fork’ component as the NG ? Are they in fact interchangeable if so there is no shortage for NG replacements as it is still in production and the 25 mentioned are just those held or earmarked for NG replacements if ever required, if not how long should it take to restart and ramp up production?
Is there no mandatory requirement on a manufacturer to guarantee supply of airworthiness critical components during the service life of a type?
Be lucky
David

This Leeham News piece provides a good update: link to article (https://leehamnews.com/2019/09/30/boeings-737-in-another-pickle/)

[The AvgasDinosaur]

This Leeham News piece provides a good update: link to article (https://leehamnews.com/2019/09/30/boeings-737-in-another-pickle/)

Tomaski,
Many thanks for a very informative link.
Your time and trouble very much appreciated.
Be lucky
David

[India Four Two]

So in overly simple ( description only ) terms, for rear pickle fork, undo the production break at rear spar section of wingbox, move it back a bit , undo ...

Is that feasible? What about the wiring looms and hydraulic/fuel pipes?

[Grebe]

Is that feasible? What about the wiring looms and hydraulic/fuel pipes?


I said it was a simple description- yes there are bucu other things involved- most figured out ahead of time by the AOG crew for major items to be disconnected, removed, etc. Then an experienced crew will notyonly document each step, but most likely find other items not planned.
One would be amazed at just how good the crews are- and do similar work almost anywhere in the world under extreme conditions.

In the late 40's and ealy 50's when douglas was top dog in commercial- Douglas proudly had the absolute best equivalent to an AOG crew and parts. Boeing at that time had the when you drive it off the lot ,its yours,- have a nice day.

But with the advent of the 707, Boeing finally realized that that attitude would not help sales, The result was to set up the current Boeing AOG system. Douglas cut theirs for cost savings and outrageous charges, the rest is history...

[futurama]

Leehams is reporting today that the incidence is 5% over the first 500 inspected. https://leehamnews.com/2019/10/08/boeings-737-in-another-pickle-part-2/#more-31313

An interesting data point: as of yesterday Southwest found only two jets with cracked pickle forks. They have some of the oldest 737NGs (being the launch customer for the 737-700, many of which were slated to be retired this year) -- and presumably inspected their oldest aircraft first to comply with the AD's 7-day limit.

[nerf]

Gol airlines in Brazil just reported 11 more. They have a fleet of 125 - many of them too new to have been inspected. Even in the unlikely event that they inspected everything, that’s 8.8%. So my guess is that the 5% number from today is significantly too low.

I can’t post links because this is my first post, but you can see the specific planes in the fleet if you search for Gol airlines on planespotters dot net. Their fleet looks like a roughly 80/20 mix of 737-800s and 700s.

[Smythe]

According to the news, the ac the FA wanted checked were 165 of SW aircraft.

Yes, it does appear to be the -700 variant.

Now GOL has grounded 11.

In govt testing, there is typically a validation sample size, it will be interesting if the sample size positives, warrant further testing.

Will be interesting to see how many WJ and UA ground...

Given the cost, (well, with no repair options in the AD, and none from BA,) and anticipated retirements, wonder how many will be written off.
I have not seen a -700 BCF program like the -800.

[sgs233a]

That the SW -700s may have been some of the earliest US aircraft inspected made me wonder..... How common are these parts between NG (and perhaps classic, original, and MAX) models? Ie, if it's the same PN for all the NG aircraft, and the -700 is one of the lighter NG variants, one might expect to find relatively more cracks, all else being equal, on the heavier variants like the -800 and -900...

[b1lanc]

An interesting data point: as of yesterday Southwest found only two jets with cracked pickle forks. They have some of the oldest 737NGs (being the launch customer for the 737-700, many of which were slated to be retired this year) -- and presumably inspected their oldest aircraft first to comply with the AD's 7-day limit.
Depending upon how many were inspected, that's an interesting stat for two reasons - the airframes with the most likely number of high cycles seems pretty clean. As I understand from SW, the 700s mostly stayed with the blended winglets, more of the 800 series were converted to the split.
Even more curious since the Jet Airways being modified by Boeing (possibly for Prime) and the original culprits were 800s?

[Grebe]

I said it was a simple description- yes there are bucu other things involved- most figured out ahead of time by the AOG crew for major items to be disconnected, removed, etc. Then an experienced crew will notyonly document each step, but most likely find other items not planned.
One would be amazed at just how good the crews are- and do similar work almost anywhere in the world under extreme conditions.

In the late 40's and ealy 50's when douglas was top dog in commercial- Douglas proudly had the absolute best equivalent to an AOG crew and parts. Boeing at that time had the when you drive it off the lot ,its yours,- have a nice day.

But with the advent of the 707, Boeing finally realized that that attitude would not help sales, The result was to set up the current Boeing AOG system. Douglas cut theirs for cost savings and outrageous charges, the rest is history...

How good are the AOG crew

https://aviation-safety.net/database/record.php?id=19751216-0

And look up the pics

https://aviation-safety.net/photo/6353/Boeing-747-246B-JA8122

it was repaired and put back in service

[etudiant]

Depending upon how many were inspected, that's an interesting stat for two reasons - the airframes with the most likely number of high cycles seems pretty clean. As I understand from SW, the 700s mostly stayed with the blended winglets, more of the 800 series were converted to the split.
Even more curious since the Jet Airways being modified by Boeing (possibly for Prime) and the original culprits were 800s?

There had been comments earlier that the pickle fork manufacturing process had been changed, with the newer method no longer hogging the piece out of a block of aluminum, but rather starting with a preformed part.
If the change in manufacturing process is a factor, one would expect the older aircraft to show few problems.

[Grebe]

There had been comments earlier that the pickle fork manufacturing process had been changed, with the newer method no longer hogging the piece out of a block of aluminum, but rather starting with a preformed part.
If the change in manufacturing process is a factor, one would expect the older aircraft to show few problems.
Think you are confusing 777 program with 737 program

Check again on source

[Aihkio]

Even at its its worst the effect of winglets on the root moment of the wing is very minor. Lift equals weight is the main factor. At the tip of the wing winglets can have a relatively large effect on the structure but that is it.

[etudiant]

Think you are confusing 777 program with 737 program

Check again on source

You are quite right. The article referred to the 777 rather than to the 737 pickle fork manufacturing process. My mistake.

[libellegeoff]

Yes, wing lift distribution affects the max bending moment but it does not affect the loads transfered to the fuselage. The total lift is not affected by the distribution. What might cause a slight difference is the larger displacements caused by larger moment but as a guess that is not the first concern.

I afraid it does affect the loads into the fuselage.

you are right in that the "Shear Loads" must be the same, as the weight inboard of the wing-root is the same, so the wings have to lift the same weight, however the bending moment going into the fuselage is increase, because the lift is further outboard. So the combination of loads going into the fuselage changes. These forks look like they "Predominantly" take vertical load, but the load transfer in this part of an aircraft is extremely complex and different loads combine in different ways, all depending on the various component stiffness.

Maximum loads and fatigue loads will have changed by a different factor or %, this looks like fatigue and I'd expect the fatigue loads to increase by a higher % that the static cases when putting a large winglet on the end of the tip

[Aihkio]

The effect on the fuselage comes from slightly different angular didplacement at the wing root. Pickle fork is not really ment to transfer these resulting loads as the ribs in place are not ment to carry the loads but to bend and not break.

This a secondary load effect and while sometimes problematic not_too_stiff structures carry them. Make everything stiff and one has problems with them. In optimised structures strength and stiffness must both be handled.

[BDAttitude]

https://www.dallasnews.com/business/airlines/2019/10/09/southwest-airlines-finds-cracked-parts-two-boeing-737-ng-jets/
https://www.reuters.com/article/us-usa-boeing-southwest/southwest-gol-ground-13-boeing-737-ng-airplanes-after-checks-idUSKBN1WO2CJ

[b1lanc]

Bjorn has a good update on where the cracks have been found and some collateral damage potential. Initial repair line at Victorville.
https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/326x261/rear_pickle_fork_with_crack_area__758fc14a314e6aa67f583234b1 f1357fdb38d154.png


https://leehamnews.com/2019/10/08/boeings-737-in-another-pickle-part-2/

[Aihkio]

The Boeing patent seen has a suggested replacement structure that would solve this problem. Think pickle fork as a previous generation solution.

Another way to think this is to treat the displacement as irresistible (it practically is) and design around it. The easiest way to do it is to make the rib at that station more flexible.

[SLF3]

From another site, posted yesterday. Bloomberg is reporting 36 out of 686 now. So 5.25%.

https://www.bloomberg.com/news/articles/2019-10-09/cracks-found-on-more-than-5-of-older-boeing-737s-in-inspections (https://www.bloomberg.com/news/articles/2019-10-09/cracks-found-on-more-than-5-of-older-boeing-737s-in-inspections)

[nerf]

My guess is that Gol inspected primarily 800s, while Southwest inspected primarily 700s so far.

Gol grounded 11 out of their fleet of 115. So just under 10% so far. And it's highly unlikely they inspected them all because many of their planes are less than 7 years old. That number will probably go up as they continue inspecting.

Gol flies mostly 800 series - I count 91 800s and 24 700s.

The Southwest fleet is mostly 700s. They have 207 800s, but I'm guessing they started by inspecting the older 700s.

There have been 5,104 800 series jets produced vs only 1,164 700 series. If this is primarily an 800 problem, that's bad for Boeing.

Southwest might just get winged by this - they have plenty of 700s. Ryanair, which flies almost exclusively 800s, could see big losses - even if their fleet is new enough to have no cracks(unlikely), the book value of their fleet (which they borrow against) would plummet.

One interesting fact: Boeing's weight in the Dow Jones is 9.65%. Far and away more than any other company. If Boeing gets wrecked by this, the economy gets hit hard.

[Longtimer]

count now 38 and rising.Cracks found in 38 of 800 Boeing 737 NG jets inspected globallyBoeing Co said Thursday that airlines had inspected 810 of the company's 737 NG jets around the world, and found 38 structural cracks requiring repair and replacement.Boeing and airline officials say the planes will be grounded until repairs are madeThomson Reuters · Posted: Oct 10, 2019 12:54 PM ET Last Updated: 3 hours ago https://www.cbc.ca/news/business/boeing-cracks-found-on-737-jets-1.5316394?cmp=rss

[Chris2303]

I don't know that I would be trusting Boeing's numbers.

[futurama]

Interesting that Alaska Airlines, American Airlines and United have reported zero cracking so far (as of the 7-day deadline for highest cycle planes). Together they have some of the world's largest (& oldest NG) fleets.

Gol on the other hand has 11. What's the difference? The winglets?

[Tomaski]

Interesting that Alaska Airlines, American Airlines and United have reported zero cracking so far (as of the 7-day deadline for highest cycle planes). Together they have some of the world's largest (& oldest NG) fleets.

Gol on the other hand has 11. I believe they have "aftermarket" winglets so maybe that is indeed a difference.

It would be interesting to compare crack incidence with type of winglet and how many cycles since they've been installed. Some of these aircraft may have accumulated a lot of their cycles prior to having winglets installed.

[Grebe]

It would be interesting to compare crack incidence with type of winglet and how many cycles since they've been installed. Some of these aircraft may have accumulated a lot of their cycles prior to having winglets installed.

Just a guess - depending on route structure- eg short 1 to 2 hours per cycle versus maybe 4 to 6 housrs per cycle, the landing weights may be significantly greater for the short cycle- less fuel burn, tank up first flight full, and make maybe 3 to 5 cycles before refueling

versus tank up first flight, make only two cycles before refueling, etc. Could account for difference in overall fleet use versus ' heavy' landings.

comments ??

[tdracer]

It would be interesting to compare crack incidence with type of winglet and how many cycles since they've been installed. Some of these aircraft may have accumulated a lot of their cycles prior to having winglets installed.

Also, retrofit winglets vs. production build winglets. I'm sure Boeing is looking very closely at the inspection results to see what sort of patterns there might be to which aircraft have cracks - winglets, sub-models (600-700-800-900), line numbers, etc. as well as hours and cycles.

Chris2303, you do know that it was Boeing that first discovered the cracks while doing 737 Freighter conversions, and self reported the issue to the FAA, right?

[misd-agin]

Interesting that Alaska Airlines, American Airlines and United have reported zero cracking so far (as of the 7-day deadline for highest cycle planes). Together they have some of the world's largest (& oldest NG) fleets.

Gol on the other hand has 11. What's the difference? The winglets?

Another poster stated that they didn't have the higher cycle counts so the 'age' of their aircraft isn't as high as perhaps SW's might be due to short flights = higher cycles.

[B727223Fan]

Interesting that Alaska Airlines, American Airlines and United have reported zero cracking so far (as of the 7-day deadline for highest cycle planes). Together they have some of the world's largest (& oldest NG) fleets.

Gol on the other hand has 11. What's the difference? The winglets?

AA B-737 - 800 Flies with Winglets .

Most Likely very high cycles on the GOL aircraft as compared with the AA B 737 NG's.

Past History : Aloha FLT 243 B 737 -200 had 89,680 CYCLES and ONLY 35,496 HOURS when it encountered in-flight structural failure of the upper fuselage.

This is opposite Ratio of Cycles/ Hours of most airlines. This aircraft had a very high number of Cycles due to to Island Hopping with short flight times.

.

https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/480x360/hqdefault_041675f116e98fb5a4b5950b2db8a6fd91070c15.jpg
https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/473x280/aloha_vol_243_7151707fbf91bad4c9d9cae691dc95dfb54e781b.jpg



https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/1280x850/american_airlines_boeing_737_800_n895nn_yvr_21976171692__f31 39a33e2618d9b2195eec436f46e6dcf44f379.jpg

[Scuffers]

Interesting that Alaska Airlines, American Airlines and United have reported zero cracking so far (as of the 7-day deadline for highest cycle planes). Together they have some of the world's largest (& oldest NG) fleets.

Gol on the other hand has 11. What's the difference? The winglets?
OK, as an engineer, I am struggling to understand how winglets would make any difference to the loading on this fork?

My thinking is this, the plane's body mass has to be supported by the wings, makes no odds if the wings are bigger/smaller or more/less efficient, they still have to hold up the same mass.

[pilot9248]

Scuffers, it is simple enough to design a fitting for one (static) load case, but in reality the joints will see dynamic variable amplitude loads in various planes, which certainly change with different wing geometry.

[Fly Aiprt]

OK, as an engineer, I am struggling to understand how winglets would make any difference to the loading on this fork?

My thinking is this, the plane's body mass has to be supported by the wings, makes no odds if the wings are bigger/smaller or more/less efficient, they still have to hold up the same mass.

If the wing and fuselage structure were infinitely rigid, indeed there would be not problem
But there is no such thing as a perfectly rigid body, and the wings and fuselage do flex under flight loads.
And wing bending involves bending moment at the wingroot.
Now if one changes the wing geometry (winglets, etc.), the point of application of the flight loads changes, and so the bending moments at the root do change for any given flight condition.

[Aihkio]

Through lift redistribution winglets probably have a very small increasing effect on wing root bending moment. That is not the point though. The fuselage section on top of the wing box is not going to be able to carry any part of it anyway. That fuselage part should be designed to carry a forced angular displacement from the wing bending. A very different exercise from carrying load. The pickle fork design carries the resulting (from rib stiffness and displacement) moment to the rib and if the rib is too stiff breaks the fork.

[Bend alot]

OK, as an engineer, I am struggling to understand how winglets would make any difference to the loading on this fork?

My thinking is this, the plane's body mass has to be supported by the wings, makes no odds if the wings are bigger/smaller or more/less efficient, they still have to hold up the same mass.
No winglet and the wing tip will flap in the breeze.

Add a thing to the wing tip to stop it doing the flapping - where will that load go?

Now make that thing bigger and more loads will go to the same place - far from the wing tip!

[Smythe]

OK, as an engineer, I am struggling to understand how winglets would make any difference to the loading on this fork?

My thinking is this, the plane's body mass has to be supported by the wings, makes no odds if the wings are bigger/smaller or more/less efficient, they still have to hold up the same mass.


Watch the winglets bounce around the next time you fly, then watch wings without them....cyclical loading with the extra mass at the end of the moment arm.
https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/326x261/yamlo51_bb14fecb5684606119a023d9aa7721aac33c01d1.png
Source: leeham
https://leehamnews.com/2019/10/08/boeings-737-in-another-pickle-part-2/

[occasional]

OK, as an engineer, I am struggling to understand how winglets would make any difference to the loading on this fork?

My thinking is this, the plane's body mass has to be supported by the wings, makes no odds if the wings are bigger/smaller or more/less efficient, they still have to hold up the same mass.

But the mass can, and does, move up and down as it flies along.

[rickyricks]

Is there any connection between this issue with pickle forks and the Ducommun scandel some time back? If the pickle forks were installed without the correct drilling procedures, for example, then one ought to expect some early cracking to appear.

[Aihkio]

Potentially yes. I suspect that the people really in the know have their lips riveted shut.

[Fly Aiprt]

Potentially yes. I suspect that the people really in the know have their lips riveted shut.

Isn't it the role of the FAA to investigate ?

[Aihkio]

Isn't it the role of the FAA to investigate ?
I understood that the first time around the Ducommun finding the FAA was not interested at all.

[Fly Aiprt]

I understood that the first time around the Ducommun finding the FAA was not interested at all.

So the FAA doesn't oversee aircraft production processes ?

[Aihkio]

So the FAA doesn't oversee aircraft production processes ?

I am not walking on very thick ice here but as a first guess directly no. In many other ways yes.

[Fly Aiprt]

I am not walking on very thick ice here but as a first guess directly no.

Then, who does ?

[Scuffers]

Watch the winglets bounce around the next time you fly, then watch wings without them....cyclical loading with the extra mass at the end of the moment arm.
https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/326x261/yamlo51_bb14fecb5684606119a023d9aa7721aac33c01d1.png
Source: leeham
https://leehamnews.com/2019/10/08/boeings-737-in-another-pickle-part-2/

so you're suggesting it's fatigue from the wings wagging and the winglets change the resonant frequency?

I can see that, right up to the point that surely the airframe is designed to cope with this? and adding mass to the wing will lower it's resonant frequency?

I don't subscribe to this, I would suggest it' way more likely that a change in manufacturing has caused this.

[Aihkio]

Then, who does ?

Hmmm..... Who might that be? In charge of a Boeing airplane production ......

[Fly Aiprt]

Hmmm..... Who might that be? In charge of a Boeing airplane production ......

;-)
Of course I know...
The point is, despite all this turmoil the FAA doesn't seem willing to regain an overseer position vis a vis Boeing.

[maxxer]

https://investors.boeing.com/investors/fact-sheets/default.aspx

Doesnt look good if the only horse they have is the 787

[Fonsini]

I recall watching a documentary about Boeing whistleblowers who worked in QA reporting issues with sub-standard outsourced 737NG components a while back.

I wonder if those chickens have come home to roost....

Oh Boeing, how the mighty have fallen.

[rickyricks]

I recall watching a documentary about Boeing whistleblowers who worked in QA reporting issues with sub-standard outsourced 737NG components a while back.

I wonder if those chickens have come home to roost....

Oh Boeing, how the mighty have fallen.
I believe that would be the Ducommun scandal I referred to earlier? One other thing. I read somewhere that pickle forks are made from AA7075-T3 - does anyone know this to be true? Most 7xxx alloys are not used in tension, which seems to be the role of a pickle fork, and certainly not in a naturally aged temper (i.e. age hardened at room temperature) as such tempers are unstable in 7xxx alloys. I would have thought a 2xxx damage tolerant alloy more appropriate for pickle forks.

[Grebe]

I believe that would be the Ducommun scandal I referred to earlier? One other thing. I read somewhere that pickle forks are made from AA7075-T3 - does anyone know this to be true? Most 7xxx alloys are not used in tension, which seems to be the role of a pickle fork, and certainly not in a naturally aged temper (i.e. age hardened at room temperature) as such tempers are unstable in 7xxx alloys. I would have thought a 2xxx damage tolerant alloy more appropriate for pickle forks.
You might be correct re diff in alloy and temper. May well be the diff between costs and production techniques between the alloys- all "solved" by using the cheapest.


But the above being said- This SLF non structural engineer suggests that the landing loads and skipped production techniques re hole prep ( drill, coldwork, ream, interference fit being the baseline ) when skipped ( saves time ) and/or improperly checked tooling size ( coldwork mandrel ) is the most likely issue. ( see Fatigue technology ) disclaimer I have NO ties to Fatigue technology- almost opposite for ancient reasons not pertinent here

Add the file to fit- pound to suit- and here we are.

[B727223Fan]

Grebe : and/or improperly checked tooling size ( coldwork mandrel ) is the most likely issue. ( see Fatigue technology )

If the cracks are originating at the fastener holes I do agree with your statement.

Cold Working of holes is very important to relieve stresses as well as proper fastener hole size and proper installation of Hi-Loks.
Hi-Loks are usually installed interference or close tolerance fit.

https://www.aerofastener.com/products/hi-lok-pins

Shot Peening and Flap Peening are also important post assembly maintenance processes on various structural members and parts that also relieves stresses.

Note: I posted this info for folks who have never cold worked holes or installed Hi-Loks.

[ST Dog]

If the pickle forks were installed without the correct drilling procedures, for example, then one ought to expect some early cracking to appear.

My suspicion is incorrect cold working one or both fasteners. Could have been incorrectly specified too.

[Grebe]

Grebe : and/or improperly checked tooling size ( coldwork mandrel ) is the most likely issue. ( see Fatigue technology )

If the cracks are originating at the fastener holes I do agree with your statement.

Cold Working of holes is very important to relieve stresses as well as proper fastener hole size and proper installation of Hi-Loks.
Hi-Loks are usually installed interference or close tolerance fit.

https://www.aerofastener.com/products/hi-lok-pins

Shot Peening and Flap Peening are also important post assembly maintenance processes on various structural members and parts that also relieves stresses.

Note: I posted this info for folks who have never cold worked holes or installed Hi-Loks.

Thanks - also applies to lock-bolts which use a swaged collar- and at one time early on in 737 program ' taper-loks" may have been used but I'm not sure.

As to cracks and holes - somewhere in this thread are some photos which show exactly that- and early on I had postulated just that kind of problem.

MY guess then and now - is probalby a production change tg ensure coldworking of that area, and a repair of non cracked holes via coldwork and first oversize- awkward to be sure- but cheaper in long run

[daved123]

[QUOTE=B727223Fan;
Note: I posted this info for folks who have never cold worked holes or installed Hi-Loks.[/QUOTE]
That would be me then - which prompted a google and found a good explanation at ENG-TIPS
Thanks for the lead
DaveD

[GogogoStopSTOP]

Dave could you post a link to this Boeing inspection data and possible images of the cracks, thanks.

[Grebe]

The Boeing MOM referenced in the AD is available to the public in the public rule making docket, which can be viewed at:

https://www.regulations.gov/document?D=FAA-2019-0711-0002

The pdf contains great pics of actual cracks I've repeated it here since many recent posters have probably missed it

[Cheltman]

I read that when it was changed to a forging there was a material spec change. Does anyone know what grade of aluminium it now is?

[Grebe]

I read that when it was changed to a forging there was a material spec change. Does anyone know what grade of aluminium it now is?
AFIK it was always a forging - do you have any credible source that it was other ?

[Loose rivets]

Mention on PPRuNe about them being milled from the solid. They talked of waste but I assume the dross was collected. Whether it can be recast or used for something else I don't know.

A mill can make short work of a lot of metal, but it's possible that high speed milling might not be normalizable - or whatever has to happen to it.

[nonsense]

OK, as an engineer, I am struggling to understand how winglets would make any difference to the loading on this fork?

My thinking is this, the plane's body mass has to be supported by the wings, makes no odds if the wings are bigger/smaller or more/less efficient, they still have to hold up the same mass.

Remember first year solid mechanics?
Bending moment is the product of force by distance.
An aircraft supported at the wingtips would exert a much higher bending moment at the wing roots than one supported beneath the engines, close to the fuselage.
The winglets alter the distribution of the wing outwards by making the wing tips more efficient, thus increasing the bending moment at the fuselage.

If the wing and fuselage structure were infinitely rigid, indeed there would be not problem.
Regardless of the stiffness of the structure, increasing the lift at the wingtips moves the effective location of the total lift in the wing outwards, increasing the bending moment at the fuselage.

[Smythe]

I can see that, right up to the point that surely the airframe is designed to cope with this? and adding mass to the wing will lower it's resonant frequency?

The airframe was not designed to handle the load from the winglets...the winglets came later...

I find it interesting that only pax ac have found cracks so far...

The issue was found by Boeing Shanghai on the new C2F line July 2019).....What about all of the previous C2F conversions done by others..., why was nothing found there?

Are freighters (and C2F) not included in the group the FAA wants tested?

[Pilot DAR]

I'm thinking about it differently, and, purely speculating, as 737's are outside the scope of my work. As the cracks appear at the last aft fastener holes of a four fastener cluster, I'm not thinking that there is a lot of motion or load between those four fasteners, they're going to act as a unit, even if the spar is bending a little in that area. The presence of a crack indicates a load exceeding the local capacity right there, it's not the whole cluster, just that one last line of two fasteners. So what load separates the area of structure of that cluster of four fasteners (and those above) from those below? Not so much wing bending, but yaw torsion between the wing and the fuselage. The force which would have to be resisted if lots of rudder were being applied. I've always wondered about the applicability of Va in the yaw axis, and this defect continues my wonder about that. As those pickle fork fittings would appear to be the sole structure which resist a wing to fuselage yaw load transfer, perhaps they're just not quite up to it. The presence of winglets could aggravate a yaw reaction a little (winglets would not reduce yaw reaction anyway!).

But, of course, that's all speculation on my part. I'm just thinking about aging aircraft and primary structure cracks, as I'm dealing with them on other aircraft these days. Obviously a load in direction or magnitude, or both, is exceeding what the engineers accounted for, and as we consider repairs, we must consider what load is being carried, which was originally inadequately considered.

[Grebe]

I'm thinking about it differently, and, purely speculating, as 737's are outside the scope of my work. As the cracks appear at the last aft fastener holes of a four fastener cluster, I'm not thinking that there is a lot of motion or load between those four fasteners, they're going to act as a unit, even if the spar is bending a little in that area. The presence of a crack indicates a load exceeding the local capacity right there, it's not the whole cluster, just that one last line of two fasteners. So what load separates the area of structure of that cluster of four fasteners (and those above) from those below? Not so much wing bending, but yaw torsion between the wing and the fuselage. The force which would have to be resisted if lots of rudder were being applied. I've always wondered about the applicability of Va in the yaw axis, and this defect continues my wonder about that. As those pickle fork fittings would appear to be the sole structure which resist a wing to fuselage yaw load transfer, perhaps they're just not quite up to it. The presence of winglets could aggravate a yaw reaction a little (winglets would not reduce yaw reaction anyway!).

But, of course, that's all speculation on my part. I'm just thinking about aging aircraft and primary structure cracks, as I'm dealing with them on other aircraft these days. Obviously a load in direction or magnitude, or both, is exceeding what the engineers accounted for, and as we consider repairs, we must consider what load is being carried, which was originally inadequately considered.

FWIW I note some sort of clevis fitting in the pics near the cracked area- which is on the rear spar to wing box area. Could the clevis area be part of the landing gear arrangement and during landing with a heavy load ( short haul/cycle ) and/or hard landings wind up pushing partly sideways thru the landing gear ' side struts' or some sort of connection ???.

BE interesting to find the flight time vs cycles for the carriers that have found the highest incidence of cracks or other high-over stressed indications.

[B727223Fan]

"The airframe was not designed to handle the load from the winglets...the winglets came later..."


The outer wing was modified with different structure parts before the winglets were installed on the post factory retro-fit NG aircraft.


"For example, a BBJ retrofit, accomplished according to an FAA supplemental-type certificate, involves the following tasks. (This listing does not constitute a complete work instruction package.)"

Removal and replacement of the outboard upper and lower skin panels .
Removal and replacement of rib 25, which is third from the outermost rib ).
Installation of stiffeners across rib 25.
Cutting of the closure rib (rib 27) and trimming of the two spars
Installation of the new center section of rib 27 and the new winglet attach fitting
Installation of the spar attach fittings .
Installation of the aft-position light.
Installation of the winglet ."
"For airplanes in production, the wings are strengthened throughout the wingbox to accommodate the winglet loads with full use of the speed brakes to the in-flight detent position. The in-production modification meets the same design criteria as those for the retrofit. However, during production, structural strengthening is accomplished by increasing the gage of spars, stringers, ribs, and panels. Rib 27 incorporates bolt hole patterns that allow attachment of either a winglet or a standard wingtip. The winglet is installed in final assembly."

http://www.boeing.com/commercial/aeromagazine/aero_17/winglet_story.html

[M609]

SAS has found cracks on two aircraft. One that is allready leaving their fleet. The other one will have the pickle fork replaced.

[DaveReidUK]

Are freighters (and C2F) not included in the group the FAA wants tested?

The AD applies to all N-registered 737NGs. It doesn't differentiate between passenger and cargo aircraft.

[HarryMann]

Despite several thousand hours on the NG I have never heard of pickle forks and the OP's link doesn't work.

Anyone care to explain?
i believe we in the UK call them what they are... fishplates 😊

[Fly Aiprt]

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/705x1061/3h9q_042b7dd0714bfdc75835474d6391458ebed1bb2c.jpg

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/1126x1331/s59f_955cd45698148983cb4fc4d22598a615af8633e1.jpg

[Smythe]

"The airframe was not designed to handle the load from the winglets...the winglets came later..."

The outer wing was modified with different structure parts before the winglets were installed on the post factory retro-fit NG aircraft.

This was strengthening for the wingtip and replacement of the spar with one with boltholes for the winglet...the only stiffened element was the spar third in from the wingtip...

The rest of the wing and the pickle fork connector between the winbox and fuselage remained unchanged.

The AD applies to all N-registered 737NGs. It doesn't differentiate between passenger and cargo aircraft.

Thanks...it seems odd the cracks (so far) have only been found on the pax version....

[ManaAdaSystem]

SAS has found cracks on two aircraft. One that is allready leaving their fleet. The other one will have the pickle fork replaced.



One 700 with winglets and one without.
Any idea of the number of cycles?
NG’s have been with SAS for a very long time. From the late 90’s?

[GordonR_Cape]

Thanks...it seems odd the cracks (so far) have only been found on the pax version....

Probably just numbers in service, as a fraction of the NG fleet. I don't have all the figures, but the majority of cargo operators seem to be using the B737 Classic (-300 to -500). See: https://en.wikipedia.org/wiki/List_of_Boeing_737_operators

[B727223Fan]

The production models had even more structure modifications.

"However, during production, structural strengthening is accomplished by increasing the GAGE of spars, stringers, ribs, and panels.".


"For airplanes in production, the wings are strengthened Throughout the wingbox to accommodate the winglet loads with full use of the speed brakes to the in-flight detent position. The in-production modification meets the same design criteria as those for the retrofit. However, during production, structural strengthening is accomplished by increasing the gage of spars, stringers, ribs, and panels. Rib 27 incorporates bolt hole patterns that allow attachment of either a winglet or a standard wingtip. The winglet is installed in final assembly."


I don't think anyone here has suggested that changes were actually made to the fail safe strap / pickle fork at the wing center section on the winglet models..
In fact my posted link states that inboard wing changes were minimal or unnecessary. Maybe Boeing should re-think this position.
It is apparent that the early Generation NG aircraft were designed / produced / sold without winglets in mind.



"Structural changes.
After completing the studies of the toe angle and speed-brake angle, structural material for the mid- to outboard wingbox was still required. (Because the inboard wing had sufficient strength margins, structural changes to that area were minimal or unnecessary.) To minimize the adverse effects of the wing structural modifications on flutter, wing torsional stiffness was maximized in relation to bending stiffness."

After reading the link info [#221] it appears to me that Boeing strengthened the mid and outer wing but did not make any structure modifications to the inner wing or wing center section.
[made the outer wing stronger which had the effect of transmitting more wing loading into the wing center section that was not modified]

[Winemaker]

After reading the link info [#221] it appears to me that Boeing strengthened the mid and outer wing but did not make any structure modifications to the inner wing or wing center section.
[made the outer wing stronger which had the effect of transmitting more wing loading into the wing center section that was not modified]

I may be stupid, but I don't see how the wing load is greater with the winglet. The load is aircraft weight and g loading; that hasn't changed. I can see stiffening the wing tip as the winglet is increasing the local loading, but the final load carried by the wing box is constant. The wing load profile will change, but not the total load.

[Grebe]

I may be stupid, but I don't see how the wing load is greater with the winglet. The load is aircraft weight and g loading; that hasn't changed. I can see stiffening the wing tip as the winglet is increasing the local loading, but the final load carried by the wing box is constant. The wing load profile will change, but not the total load.


Uhhh look at the wing- with and without a winglet. Compare to lever arm pivoted about one side of the wingbox. Without a winglet, assume a ( hypothetical for ease of calculation ) load of say 1000 lbs 20 feet from pivot poInt= 20000 foot lbs acting on pivot point at edge of wingbox

Now with a winglet, assume a load ( due to aerodynamics in both cases ) of say 1000 lbs at 22 feet from pivot poInt = 22000 foot lbs .
This is because in simplified terms, the winglet changes the aero load ( lift) distribution a bit further outboard, thus increasing the ' lever' arm.
I have deliberately not counted extra weight of winglet, or tried to model actual aero lift numbers, etc. Simplified numbers for illustration only- not an aero engineer, etc.

For a detailed description- go to Aeropartners site.

"For airplanes in production, the wings are strengthened throughout the wingbox to accommodate the winglet loads with full use of the speed brakes to the in-flight detent position. The in-production modification meets the same design criteria as those for the retrofit. However, during production, structural strengthening is accomplished by increasing the gage of spars, stringers, ribs, and panels. Rib 27 incorporates bolt hole patterns that allow attachment of either a winglet or a standard wingtip. The winglet is installed in final assembly."

http://www.boeing.com/commercial/aer...let_story.html (http://www.boeing.com/commercial/aeromagazine/aero_17/winglet_story.html)
Then point is its the LEVER arm change in lift distribution that adds to the torque-bending loads at the junction of wing and wingbox, NOT jusrt the minimal difference in weight and slightly longer wing.:cool:

[DaveReidUK]

I may be stupid, but I don't see how the wing load is greater with the winglet. The load is aircraft weight and g loading; that hasn't changed. I can see stiffening the wing tip as the winglet is increasing the local loading, but the final load carried by the wing box is constant. The wing load profile will change, but not the total load.

There are two pairs of pickle forks on the 737, with the AD referring to cracks found in the rear pair (at STA 663.75).

It's possible that the presence/absence of winglets alters the lift distribution along the wing, and if that moves the C of P then it may well be that the proportion of the wing load carried respectively by the front/rear pickle forks changes, even if the total load remains constant.

[Fly Aiprt]

The wing load profile will change, but not the total load.

So the bending and torsional moments will change.

This might help :
https://tamarackaero.com/insights/2016/07/01/a-geek-data-crash-course-on-winglets


https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/960x720/slide10_e70a44367668d56d180f85086cceccaef1cc36ff.png

[KelvinD]

Are these "pickle forks" or fishplates related to the items that were reportedly poorly manufactured years ago?
https://www.pprune.org/archive/index.php/t-239918.html
There is an Al Jazeera you tube video, produced in 2010 on this same topic. As far as I could gather, the US Dept of Justice stepped in and halted law suits etc relating to the issues raised by a couple of whistle blowers. In the video, reference is made to 3 737NG accidents which all had one thing in common: the fuselage in each case broke into 3 parts upon impact in pretty much the same location. I was a bit baffled by the terminology used in the documentary, they refer to "failsafe cords" (or chords?)
https://www.youtube.com/watch?v=IaWdEtANi-0
At around 11mins in to the film, you will see evidence from Boeing that one of the most common defects with the parts as supplied from the manufacturer was "hole mislocated".
(unrelated to the safety issue, I was baffled by the process here: The parts are manufactured in California, shipped by train to Wichita where they get joined up with other parts to become fuselage sections. Which are then shipped by train to Seattle, presumably going via California??)

[Winemaker]

Ah, thanks. I hadn't looked at the wing as a torque generator on the center structure, but it obviously is, and moving the load outboard would increase the torque because of the changed moment arm and, consequently, increase the load carried through the pickle fork(s). I hope I've got this right now!

[Grebe]

Are these "pickle forks" or fishplates related to the items that were reportedly poorly manufactured years ago?
https://www.pprune.org/archive/index.php/t-239918.html
There is an Al Jazeera you tube video, produced in 2010 on this same topic. As far as I could gather, the US Dept of Justice stepped in and halted law suits etc relating to the issues raised by a couple of whistle blowers. In the video, reference is made to 3 737NG accidents which all had one thing in common: the fuselage in each case broke into 3 parts upon impact in pretty much the same location. I was a bit baffled by the terminology used in the documentary, they refer to "failsafe cords" (or chords?)
https://www.youtube.com/watch?v=IaWdEtANi-0
At around 11mins in to the film, you will see evidence from Boeing that one of the most common defects with the parts as supplied from the manufacturer was "hole mislocated".
(unrelated to the safety issue, I was baffled by the process here: The parts are manufactured in California, shipped by train to Wichita where they get joined up with other parts to become fuselage sections. Which are then shipped by train to Seattle, presumably going via California??)

NO there is no relationship between those parts and the picklefork issue- and trains do NOT go thru calif to get to seattle ( normally )

[Grebe]

Ah, thanks. I hadn't looked at the wing as a torque generator on the center structure, but it obviously is, and moving the load outboard would increase the torque because of the changed moment arm and, consequently, increase the load carried through the pickle fork(s). I hope I've got this right now!

YEP ! of course in the real world, there are a multitude of other factors to be considered making the actual values at different flight or certification regimes difficult to know and maybe even measure. But the basics are still the same.

:)

[david340r]

If I understand correctly moving centres of lift outwards also moves them backwards requiring h stab to, on average, trim slightly more nose up than without, thereby slightly increasing any tensile loads that may be imposed on the rear forks?.

[Grebe]

If I understand correctly moving centres of lift outwards also moves them backwards requiring h stab to, on average, trim slightly more nose up than without, thereby slightly increasing any tensile loads that may be imposed on the rear forks?.


That is way out of my wheelhouse- need both an aero and structural engine- ear :) and a senior level birdman..

[Aihkio]

Moving lift towards the tips increases AND wings with normal airfoil sections have AND tendency anyway. To counter AND moment one needs a downward force from horizontal tail. As far as I can see this all adds up to a compressive load on the fork.

[ManaAdaSystem]

So if winglets are the cause, how do you guys explain the cracked -700 without winglets?

[Fly Aiprt]

So if winglets are the cause, how do you guys explain the cracked -700 without winglets?

We don't know much at the moment, but they might be a contributing factor.

[B727223Fan]

So if winglets are the cause, how do you guys explain the cracked -700 without winglets?

Most of the discussion on this thread about winglets is the additional stresses that they impose on a wing. I don't think anyone has stated here that winglets are the sole possible reason for the cracking of the pickle fork There are other possible reasons why the pickle fork could crack including High CYCLES vs Hours.Folks on this thread have brought up many possibilities for the cracking of the pickle fork including improper manufacturing or assembly processes.

[Chris2303]

There are other possible reasons why the pickle fork could crack including High CYCLES vs Hours.Folks on this thread have brought up many possibilities for the cracking of the pickle fork including improper manufacturing or assembly processes.

Any chance that repeated overweight or hard landings could have been the cause

[Takwis]

737s cannot jettison fuel.

[lc3m4n23]

The actual cause of the pickle fork cracks is because of the the holes being over drilled by around 6 thousands. The holes are grossly oversize and the bolts that run through the part and the fail safe strap are not supporting the part. The bolts are supposed to be snug fit so when a plane lands the bolts and part share equal stress and not have a stress issue. The bolts are not touching the sides of the holes hardly at all therefore any gap between the bolt and the part contributes to all stress being put on the fork part and fail safe strap, which has holes where the bolts are.

[etudiant]

The actual cause of the pickle fork cracks is because of the the holes being over drilled by around 6 thousands. The holes are grossly oversize and the bolts that run through the part and the fail safe strap are not supporting the part. The bolts are supposed to be snug fit so when a plane lands the bolts and part share equal stress and not have a stress issue. The bolts are not touching the sides of the holes hardly at all therefore any gap between the bolt and the part contributes to all stress being put on the fork part and fail safe strap, which has holes where the bolts are.

Wow, if that is true, there is a serious manufacturing deficiency. Is there any source reference that you can share?

[Grebe]

IF- BIG IF the claim that holes are-were oversize as claimed ( some worker- bee who is involved in repair-replace would know ) then ther problem is almost exactly as I postulated back on sept 11 - see below. depending on the defined process - which SHOULD have required the holes on final assembly in that area be properly drilled- reamed- inspected as a minimum ( and skipped or pencil whipped ) - or IMHO been properly coldworked, then the problem could be fleetwide. Although it would be awkward - it **may** be possible to schedule lower cycle planes to have those holes in that area reamed, coldworked, and proper interference fit fasteners installed before say 15,000 to 20,000 cycles.

So much for faster - cheaper- - by god we didn't do that on the Boeing- westervelt B-1, and its just an extra time consuming thing to do on assembly and meet or beat the BAR ( chart ). Just a SWAG- but I'll bet that process IF done- specified up thru about 1998-99 may have been dropped. :\


It will be interesting to see or find out just where the cracks are. Obviously at this time, its just a guess. However, as a GUESS and based on experience dealing with fastener issues in large parts on 707 and 767 ( 707 that had been in service for a long time ) and tooling for 767-here is my SWAG based on the relatively low key descriptions.

A) The cracks are probably around or spreading from Fastener holes, probably those drilled " by hand" during the LEAN manufacturing process which are less than about 3/8 in diameter.
B) As such there is of course an argument that the crack would simply progress to the next hole in the pattern ( since drilling a small hole at the ' end ' of such crack is considered to be a ' crack stopper ' - which is true for a lot of ' sheet metal ' issues.

C) again , just a guess, but for 40 plus years, thre has been available and used a three to four step process to prevent such cracks, which can be done for all sizes of hole, even large holes during fabrication while still in large tooling- drill plates , etc.

D) in general- the steps are 1) drill a hole slightly smaller than final size 2) insert a thin sleeve into hole 3) insert a special mandrel such that when pulled back thru the hole it expands the sleeve and hole. 4) Ream the hole which will usually be slightly out of round to final size.

On assembly, insert bolt as a tight fit.
E) in some cases and sizes, the same process can be used without a sleeve but with a expanding mandrel.

F) This leaves a major prestress around the hole and provides a significant improvement in fatigue life.

The process was patented by Boeing in the late 1960, and a local firm called Fatigue technology was founded- developed from the previous firm called Industrial Wire and metal forming as I recall. And major first use ( from memory ) was on AWACS.
The process- tooling has been the subject of several related patents, and is still used by virtually all aircraft manufacturers
It can be used to prevent or stop cracks from further progress.

Again MY SWAG is that to save time some $$$ - or due to a temporary lack of sleeves or just plain skipping the sequence ( hard to detect when inspection is only on final hole size )

So depending on location and accessibility, the fix would be to remove bolt, expand hole, ream hole, insert new oversize bolt and voila, a terminating fix.

Just have to wait and see- If someone has access to documentation as to real issue and location, would be interesting to see how close I came

[nonsense]

In a clamped joint with high tensile bolts, the bolts are not (supposed to be) subjected to shear loads, which are carried by friction between the surfaces which are clamped together by the bolts. Holes have clearance and individual bolts are not subjected to load in sequence, failing before the next bolt takes load.

[Aihkio]

There is a chance of calculating a bolt joint where - as Nonsense said- bolts do not carry shear. With shear carrying bolts and variable hole diameters and varying location tolerances not a chance. In spite of the calculation capacity existing experimental data is still used, that database is huge.