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

Low time airframe

https://komonews.com/news/local/excl...37ng-equipment

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

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.

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-u...-idUSKBN1WD02E

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.

Better report on the issue, with images:
Boeing workers found new cracks on Boeing 737NG (not MAX). ? News In Flight

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

Pickle Fork LEAN manufacturing changes

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.

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

No Max has flown 35000 cycles.


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

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

Crafted a sketch from a Boeing patent illustration :


https://cimg9.ibsrv.net/gimg/pprune....07c26a48d9.jpg

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.

Thanks for the graphic.

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

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.

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.

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

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

Not the first time
 

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.

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.

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 :*

A picture of the pickle fork attachment.

According to reddit.com
https://www.reddit.com/r/news/commen...al_boeing_737/



https://cimg2.ibsrv.net/gimg/pprune....8bd7f81d41.png

Wing bending load increase with Split Scimitar Winglets
 

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....9bcdb96c53.jpg

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.

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

https://cimg3.ibsrv.net/gimg/pprune....cf56ea4b8a.jpg

This could really Fork Boeing

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.

The original article indicates that this is not a benign issue, unless you believe the reports to be factually incorrect:

"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."

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.

Wing lift distribution effect
 

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.

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.

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/precisio...ng/burnishing/