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

[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]

Originally Posted by 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. 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]

Originally Posted by Tomaski

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]

Originally Posted by Tomaski

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]

Originally Posted by 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?

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]

Originally Posted by 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?

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.

.

[Scuffers]

Originally Posted by 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?

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]

Originally Posted by Scuffers

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]

Originally Posted by Scuffers

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.

Source: leeham
https://leehamnews.com/2019/10/08/bo...pickle-part-2/

[occasional]

Originally Posted by Scuffers

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]

Originally Posted by Aihkio

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]

Originally Posted by Fly Aiprt

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]

Originally Posted by Aihkio

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]

Originally Posted by Aihkio

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

Then, who does ?