727Man
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Re: 737NG Pickle fork issue

Mon Oct 07, 2019 11:44 am

Jacob2877 wrote:
727Man wrote:
trpmb6 wrote:

As has already been reported the -900 is a different design.


Two -900's and two -700's so far have had cracks found.


Not what I’ve read. I read it was 3 737-800


Sorry, I should have said in addition to the 7 -800’s (at that time).
 
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lightsaber
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Re: 737NG Pickle fork issue

Mon Oct 07, 2019 11:57 am

727Man wrote:
Jacob2877 wrote:
727Man wrote:

Two -900's and two -700's so far have had cracks found.


Not what I’ve read. I read it was 3 737-800


Sorry, I should have said in addition to the 7 -800’s (at that time).

Do you have links? One reason we want tail numbers is double counting is a certainty. Your 7+2+2 are far higher than anything else I'm reading. Personally, I would be surprised at any -900 as the -700/-800 were released earlier.

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Amiga500
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Re: 737NG Pickle fork issue

Mon Oct 07, 2019 12:18 pm

I suspect airlines & lessors will be seeking a degree of (or all) compensation from Boeing for any rectification work needed.

If they bought a product on the understanding it would be good till 90k FC, its not exactly meeting spec if its failing at a 3rd of that.
 
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Spacepope
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Re: 737NG Pickle fork issue

Mon Oct 07, 2019 12:46 pm

lightsaber wrote:
727Man wrote:
Jacob2877 wrote:

Not what I’ve read. I read it was 3 737-800


Sorry, I should have said in addition to the 7 -800’s (at that time).

Do you have links? One reason we want tail numbers is double counting is a certainty. Your 7+2+2 are far higher than anything else I'm reading. Personally, I would be surprised at any -900 as the -700/-800 were released earlier.

Lightsaber


I second the list of individual frames, though I'd be less surprised with the 900s being affected, since though they were beefed up compared tho the lighter models, they're still heavier and have a pretty high landing speed so the forces per cycle have to be higher on average.
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scbriml
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Re: 737NG Pickle fork issue

Tue Oct 08, 2019 8:42 pm

Leeham reports that 5% of the first 500 planes inspected have the issue, so that’s 25 so far.
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mjoelnir
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Re: 737NG Pickle fork issue

Tue Oct 08, 2019 9:07 pm

https://leehamnews.com/2019/10/08/boein ... le-part-2/

5% of the 500 checked frames have cracks. Youngest frame with cracks has 23,600 cycles. Frames with cracks are grounded.
 
ShamrockBoi330
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Re: 737NG Pickle fork issue

Tue Oct 08, 2019 9:40 pm

I know its only 5% of airframes tested, but Is this compounding the MAX issue for anyone?

Any word or rumours who the 5% belong to?
 
Palop
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Re: 737NG Pickle fork issue

Tue Oct 08, 2019 9:55 pm

I found the Leeham article interesting in that the winglets may be a contributing factor by changing the bending moment in the wing in an unexpected and unaccounted for way.
I know that the Max have a different pickle fork, but I was curious if this may have ramifications for the Maxes as well. Did Boeing do fatigue testing on the Max? And if so, how?
 
JayinKitsap
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Re: 737NG Pickle fork issue

Tue Oct 08, 2019 9:55 pm

Looking at the diagram @ leeham the red crack marking is across the lower outer bolt hole of the outer chord, possibly both bolt holes at this location. The primary normal loads are compression in the fork as it transfers the fuse forces down to the spar. However, this outer chord is connecting the fork to the skin of the aircraft. With the opening for the gear cutting the skin off below this there are a lot of 3D forces here. The downward shear at this bolt would cause high tension in this plate corner, coupled with the oscillation of the tail and fuse causing large cycle counts. Not good.

This plate probably needs to get thicker, possibly a stiffener added to cut out side bending effects and possibly a doubler plate on the shell at this pair of bolts.
 
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lightsaber
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 12:47 am

Repeat of Leeham link:

https://leehamnews.com/2019/10/08/boein ... le-part-2/

3 week repair. There are 25 shipsets of pickle forks, enough to repair all found (my interpretation of the link).

The low cycle 23,600 aircraft surprised me.

The article notes the normal process of a standard temporary repair is being developed as well as a permanent repair (that process takes a long time to certify).

Worse than I thought, better than I feared. The path to a fix is on the way.

Not good Boeing is about to get great at pickle fork R&R.

Lightsaber

Late edit:

Obviously from my above posts I thought far fewer would be found!
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smokeybandit
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 1:16 am

Any indication of which airlines are affected?

And what does "cracked" really mean here? Like, the pickle fork is about to fall apart? Or are these tiny cracks that really don't affect structural integrity, just they aren't parts that were ever intended to have cracks?
 
freakyrat
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 3:12 am

Palop wrote:
I found the Leeham article interesting in that the winglets may be a contributing factor by changing the bending moment in the wing in an unexpected and unaccounted for way.
I know that the Max have a different pickle fork, but I was curious if this may have ramifications for the Maxes as well. Did Boeing do fatigue testing on the Max? And if so, how?


I'm no engineer but I remember when winglets came out and were installed on the 737. My first ride on a winglet equipped one I wondered as I watched the wing bend upward during flight if this bending motion was putting undue stress somewhere on the airframe. Looks like we are now finding this out.
 
jetmatt777
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 3:20 am

The winglets do seem to add quite a bit of bending that I never noticed before they were installed.

I assume the split scimitar would add more force to the bending moment, as it is a heavier installation.

I am sure they did their homework, so let’s see if that is actually the issue identified through the analysis. It’s a bit premature to say. It could be anything including just a pour metallurgy batch, wings take a ton of force.
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Someone83
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 9:02 am

smokeybandit wrote:
Any indication of which airlines are affected?

And what does "cracked" really mean here? Like, the pickle fork is about to fall apart? Or are these tiny cracks that really don't affect structural integrity, just they aren't parts that were ever intended to have cracks?


Believe i read Southwest confirmed two of their aircraft was affected
 
mjoelnir
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 10:00 am

smokeybandit wrote:
Any indication of which airlines are affected?

And what does "cracked" really mean here? Like, the pickle fork is about to fall apart? Or are these tiny cracks that really don't affect structural integrity, just they aren't parts that were ever intended to have cracks?


Cracked means that the aircraft gets grounded until it is repaired, so I assume it affects structural integrity.

IMO the FAA should remove the 90,000 cycle designation from the 737NG and install an inspect and repair regime instead. This first AD regarding inspection is in reality just to get an measure of the severity of this problem.
 
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 4:01 pm

mjoelnir wrote:
smokeybandit wrote:
Any indication of which airlines are affected?

And what does "cracked" really mean here? Like, the pickle fork is about to fall apart? Or are these tiny cracks that really don't affect structural integrity, just they aren't parts that were ever intended to have cracks?


Cracked means that the aircraft gets grounded until it is repaired, so I assume it affects structural integrity.

IMO the FAA should remove the 90,000 cycle designation from the 737NG and install an inspect and repair regime instead. This first AD regarding inspection is in reality just to get an measure of the severity of this problem.

There will be more ADs, the inspection intervals will shorten. But removing the 90,000 cycle life? Have we proven it isn't a manufacturing issue?

The A380 and A320 both were found to need wing reinforcement. The 60,000 cycle limit wasn't removed for the A320 or 36,000 for A380. Instead a repair was approved. New build aircraft are built to a certified modification. Or Embraer wing spars. Or...

There will be a temporary repair approved. There will be a permanent repair approved less than replacing the pickle forks. It will take a few years, but Boeing will get back to full duration on these.
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mjoelnir
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 7:14 pm

lightsaber wrote:
mjoelnir wrote:
smokeybandit wrote:
Any indication of which airlines are affected?

And what does "cracked" really mean here? Like, the pickle fork is about to fall apart? Or are these tiny cracks that really don't affect structural integrity, just they aren't parts that were ever intended to have cracks?


Cracked means that the aircraft gets grounded until it is repaired, so I assume it affects structural integrity.

IMO the FAA should remove the 90,000 cycle designation from the 737NG and install an inspect and repair regime instead. This first AD regarding inspection is in reality just to get an measure of the severity of this problem.

There will be more ADs, the inspection intervals will shorten. But removing the 90,000 cycle life? Have we proven it isn't a manufacturing issue?

The A380 and A320 both were found to need wing reinforcement. The 60,000 cycle limit wasn't removed for the A320 or 36,000 for A380. Instead a repair was approved. New build aircraft are built to a certified modification. Or Embraer wing spars. Or...

There will be a temporary repair approved. There will be a permanent repair approved less than replacing the pickle forks. It will take a few years, but Boeing will get back to full duration on these.


The A320 did not start out with a 60,000 cycle limit. The original approved limit was 48,000 cycles and 60,000 hours. The limits were extended after further fatigue testing and checking of frames reaching the early lifetime limits. The wing cracks on the A380 were found due to the fatigue testing. It would be interesting to get a reference to wing cracks on the A320, as I have not heard of that.

The 737NG got its lifetime limits out of the box. The pickle forks are part of the lifetime parts, no limited lifetime expected. no checking regime, but the current AD, in place.. Cracking was not found through fatigue testing, but by chance at the conversion of older 737-800 to freighters.
 
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 7:26 pm

mjoelnir wrote:
lightsaber wrote:
mjoelnir wrote:

Cracked means that the aircraft gets grounded until it is repaired, so I assume it affects structural integrity.

IMO the FAA should remove the 90,000 cycle designation from the 737NG and install an inspect and repair regime instead. This first AD regarding inspection is in reality just to get an measure of the severity of this problem.

There will be more ADs, the inspection intervals will shorten. But removing the 90,000 cycle life? Have we proven it isn't a manufacturing issue?

The A380 and A320 both were found to need wing reinforcement. The 60,000 cycle limit wasn't removed for the A320 or 36,000 for A380. Instead a repair was approved. New build aircraft are built to a certified modification. Or Embraer wing spars. Or...

There will be a temporary repair approved. There will be a permanent repair approved less than replacing the pickle forks. It will take a few years, but Boeing will get back to full duration on these.


The A320 did not start out with a 60,000 cycle limit. The original approved limit was 48,000 cycles and 60,000 hours. The limits were extended after further fatigue testing and checking of frames reaching the early lifetime limits. The wing cracks on the A380 were found due to the fatigue testing. It would be interesting to get a reference to wing cracks on the A320, as I have not heard of that.

The 737NG got its lifetime limits out of the box. The pickle forks are part of the lifetime parts, no limited lifetime expected. no checking regime, but the current AD, in place.. Cracking was not found through fatigue testing, but by chance at the conversion of older 737-800 to freighters.

Wasn't the A380 wing crack issue found during the repair of VH-OQA (MSN 014) after QF32?

To be fair, the 737NG was an evolution of a mature airframe, that had been flying for decades, while the A320 was a brand new design. Not saying whether it was right or wrong to give the NG 90,000FC life limit "out of the box", but it was backed by decades of data.
 
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 9:34 pm

ShamrockBoi330 wrote:
I know its only 5% of airframes tested, but Is this compounding the MAX issue for anyone?

Any word or rumours who the 5% belong to?
5% of tested is a lot.
 
sodbuster
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 9:42 pm

34 aircraft with cracks....3 -900's, but most -800's and -700's.
 
kalvado
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 9:51 pm

sodbuster wrote:
34 aircraft with cracks....3 -900's, but most -800's and -700's.

Is there a list anywhere? Yesterday there were 25 cracked ones.. Do we expect 100 by the end of the week at such rate?
 
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 10:37 pm

 
Jacob2877
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 11:05 pm

Yes, it would be helpful if someone had a list. I would like to know where it was found that Southwest Airlines had two that were grounded because of the pickle fork issue.
 
bob75013
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 11:19 pm

Jacob2877 wrote:
Yes, it would be helpful if someone had a list. I would like to know where it was found that Southwest Airlines had two that were grounded because of the pickle fork issue.


https://www.wfaa.com/article/travel/sou ... eda5b84684
 
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 11:22 pm

mjoelnir wrote:
lightsaber wrote:
mjoelnir wrote:

Cracked means that the aircraft gets grounded until it is repaired, so I assume it affects structural integrity.

IMO the FAA should remove the 90,000 cycle designation from the 737NG and install an inspect and repair regime instead. This first AD regarding inspection is in reality just to get an measure of the severity of this problem.

There will be more ADs, the inspection intervals will shorten. But removing the 90,000 cycle life? Have we proven it isn't a manufacturing issue?

The A380 and A320 both were found to need wing reinforcement. The 60,000 cycle limit wasn't removed for the A320 or 36,000 for A380. Instead a repair was approved. New build aircraft are built to a certified modification. Or Embraer wing spars. Or...

There will be a temporary repair approved. There will be a permanent repair approved less than replacing the pickle forks. It will take a few years, but Boeing will get back to full duration on these.


The A320 did not start out with a 60,000 cycle limit. The original approved limit was 48,000 cycles and 60,000 hours. The limits were extended after further fatigue testing and checking of frames reaching the early lifetime limits. The wing cracks on the A380 were found due to the fatigue testing. It would be interesting to get a reference to wing cracks on the A320, as I have not heard of that.

The 737NG got its lifetime limits out of the box. The pickle forks are part of the lifetime parts, no limited lifetime expected. no checking regime, but the current AD, in place.. Cracking was not found through fatigue testing, but by chance at the conversion of older 737-800 to freighters.

It was played down as A320 corrosion.

http://i.stuff.co.nz/business/3402061/C ... rbus-wings
This was found after the 60k extension.

Airbus didn't find their issue in fatigue testing either and far earlier than 48,000 cycles. The Airbus finding was a surprise. It turned out island hopping was brutal on A319/A320 family wings.

My point is that there will be a repair. The regulations do not specify how a problem is found. The first finding was at about 36,000 cycles. The pickle forks with a life of 90,000 cycles must be inspected every 30,000 cycles.

The fact there are so many found after 35,000 tells us these passed. Now the low cycle incident is of concern.

So for now, ground if cracks found and increase inspections. 25 findings out of 500 is bad, but not unprecedented.

There will be shorter inspection intervals until a standard repair is found that returns the life to design.

That repair cannot happen until a new stress analysis is performed. Just as a temporary repair will be found.

There is a process. The cycle test was with a maximum allowed stress (it is well known for aluminum vs. cycles for life). Just knowing the youngest happened at 20,600 cycles and many later tells us the actual stress level. Boeing has good stress engineers that will find a permanent and temporary repair.

The A380 wing cracks are an example. They happened incredibly early. Well before the inspection. Only found because of a RR uncontained engine failure.

The process is intentionally non-punititive to have self disclosure. The was a 738BCF where that self disclosure found the problem and created the AD.

There is a checking regimen. Every HMC. If you cannot inspect visually, x-ray. I assume the HMV required inspection might be altered/improved.

I'm not sure what you are trying to imply.

Legally, there was a self reported finding. The FAA issued an AD on inspections. The data from those inspections will result in a new AD on modified inspection intervals.

Rework is always an approved repair (return to drawing) or pickle fork replacement.

Permanent repairs take time.

Lightsaber
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ShamrockBoi330
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 11:23 pm

bob75013 wrote:
Jacob2877 wrote:
Yes, it would be helpful if someone had a list. I would like to know where it was found that Southwest Airlines had two that were grounded because of the pickle fork issue.


https://www.wfaa.com/article/travel/sou ... eda5b84684


Seeking Alpha are saying Southwest x 2, Gol x 11.... so 13 identified as grounded so far!

https://seekingalpha.com/news/3504888?source=ansh
 
acechip
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 11:26 pm

A question would be, why was this not discovered during a regular heavy check at say, 20k cycles? Why did it have to be discovered accidentally during a freighter conversion? Is that because of the 90k cycle safe life limit?
 
iamlucky13
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 11:32 pm

mjoelnir wrote:
smokeybandit wrote:
Any indication of which airlines are affected?

And what does "cracked" really mean here? Like, the pickle fork is about to fall apart? Or are these tiny cracks that really don't affect structural integrity, just they aren't parts that were ever intended to have cracks?


Cracked means that the aircraft gets grounded until it is repaired, so I assume it affects structural integrity.

IMO the FAA should remove the 90,000 cycle designation from the 737NG and install an inspect and repair regime instead. This first AD regarding inspection is in reality just to get an measure of the severity of this problem.


My interpretation is it is assumed to affect structural integrity, so grounding is necessary prudence unless it can be demonstrated otherwise.

If analysis or testing can demonstrate that a certain "allowable" maximum crack size can still withstand maximum design loads after a certain number of additional cycles, I suppose that could allow limited continuing operation before the repair must be completed. I don't know what kinds of cases this sort of logic can be applied to, but I know there are other cases where allowables are determined for non-conformances.

Life cycle rating should depend on how reliably this can be identified by inspections before it becomes critical and repaired.
 
prebennorholm
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 11:44 pm

WayexTDI wrote:
To be fair, the 737NG was an evolution of a mature airframe, that had been flying for decades, while the A320 was a brand new design. Not saying whether it was right or wrong to give the NG 90,000FC life limit "out of the box", but it was backed by decades of data.

The NG got an entirely new wing with 23% greater span, 35% greater area, 30% increased wing fuel tank capacity, and heaviest NG has 32% higher MTOW than heaviest Classic.

So pickle fork wise the NG can just as well be considered an all new plane. Certainly pickle forks can't be shared among Classics and NGs.
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ikramerica
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Re: 737NG Pickle fork issue

Wed Oct 09, 2019 11:52 pm

lightsaber wrote:
mjoelnir wrote:
lightsaber wrote:
There will be more ADs, the inspection intervals will shorten. But removing the 90,000 cycle life? Have we proven it isn't a manufacturing issue?

The A380 and A320 both were found to need wing reinforcement. The 60,000 cycle limit wasn't removed for the A320 or 36,000 for A380. Instead a repair was approved. New build aircraft are built to a certified modification. Or Embraer wing spars. Or...

There will be a temporary repair approved. There will be a permanent repair approved less than replacing the pickle forks. It will take a few years, but Boeing will get back to full duration on these.


The A320 did not start out with a 60,000 cycle limit. The original approved limit was 48,000 cycles and 60,000 hours. The limits were extended after further fatigue testing and checking of frames reaching the early lifetime limits. The wing cracks on the A380 were found due to the fatigue testing. It would be interesting to get a reference to wing cracks on the A320, as I have not heard of that.

The 737NG got its lifetime limits out of the box. The pickle forks are part of the lifetime parts, no limited lifetime expected. no checking regime, but the current AD, in place.. Cracking was not found through fatigue testing, but by chance at the conversion of older 737-800 to freighters.

It was played down as A320 corrosion.

http://i.stuff.co.nz/business/3402061/C ... rbus-wings
This was found after the 60k extension.

Airbus didn't find their issue in fatigue testing either and far earlier than 48,000 cycles. The Airbus finding was a surprise. It turned out island hopping was brutal on A319/A320 family wings.

My point is that there will be a repair. The regulations do not specify how a problem is found. The first finding was at about 36,000 cycles. The pickle forks with a life of 90,000 cycles must be inspected every 30,000 cycles.

The fact there are so many found after 35,000 tells us these passed. Now the low cycle incident is of concern.

So for now, ground if cracks found and increase inspections. 25 findings out of 500 is bad, but not unprecedented.

There will be shorter inspection intervals until a standard repair is found that returns the life to design.

That repair cannot happen until a new stress analysis is performed. Just as a temporary repair will be found.

There is a process. The cycle test was with a maximum allowed stress (it is well known for aluminum vs. cycles for life). Just knowing the youngest happened at 20,600 cycles and many later tells us the actual stress level. Boeing has good stress engineers that will find a permanent and temporary repair.

The A380 wing cracks are an example. They happened incredibly early. Well before the inspection. Only found because of a RR uncontained engine failure.

The process is intentionally non-punititive to have self disclosure. The was a 738BCF where that self disclosure found the problem and created the AD.

There is a checking regimen. Every HMC. If you cannot inspect visually, x-ray. I assume the HMV required inspection might be altered/improved.

I'm not sure what you are trying to imply.

Legally, there was a self reported finding. The FAA issued an AD on inspections. The data from those inspections will result in a new AD on modified inspection intervals.

Rework is always an approved repair (return to drawing) or pickle fork replacement.

Permanent repairs take time.

Lightsaber

I would say, assuming they are inspected at 30, that there are so many failing soon after means it’s a major safety issue.

I would hope an imaging inspection where they are examined internally is required, or that ALL planes will require reinforcement.
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lightsaber
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Re: 737NG Pickle fork issue

Thu Oct 10, 2019 12:06 am

I realized people here are probably not familiar with standard crack repair processes.
1. Drill out the ends of the crack so the cracks ceases to propogate.
2. Reinforce the affected area in a way that reduces stress to safe levels.

In undergraduate study, I was taught if the wing box in a certain area cracked never fly on that plane again. I happen to know a certain popular aircraft family cracks there and it isn't a North American made aircraft. a mechanic friend of mine was assigned to repair one of these wing boxes and allowed me to watch, his management approved. The mechanic drilled the crack and rivit holes for the doubler. QA inspected and took photos, including back side with a boroscope, doubler was installed, and more photos taken.

What I remember most is being mocked for not taking notes as fast as the repair occured.

There is no reason why such a pickle fork repair doesn't happen.

It will be a required repair. On the aircraft I mentioned, if no crack forms, only the doubler is required. Later frames had that part of the wing box barely reinforced. Weight was removed elsewhere to make the wingbox overall lighter in new builds. The doubler and rivits weighed about 800grams or about 1.8 pounds. :yawn:

That example taught me not to freak out about cracks.

I've seen videos of a cracked landing gear bay replaced. I was shown as I incorrectly stated you couldn't replace that. Oops.

I've seen the solution was to cut a 10 cm hole in another part so less force is transmitted to the cracking part. (Hole cut part flexed instead of transferring the load.)

I am not dismissing the severity. For 25 aircraft, a new pair of pickle forks is required. Those aircraft will require a future repair to keep the pickle forks from cracking again. All 737NG with winglets or scimitars will require the repair.

It is possible the high engine weight of the MAX removes the issue.

Let us put this in perspective. The 737NG was in service 21+ years (since December 1997) before the issue was found.

I suspect the repair will be engineered to extend pickle fork life to the full 110,000 cycle life of the 737.

Lightsaber
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iamlucky13
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Re: 737NG Pickle fork issue

Thu Oct 10, 2019 12:08 am

acechip wrote:
A question would be, why was this not discovered during a regular heavy check at say, 20k cycles? Why did it have to be discovered accidentally during a freighter conversion? Is that because of the 90k cycle safe life limit?


I'm not sure the "accidentally" is quite an accurate description.

Leeham reported one frame had cracking found at 23,600 cycles. Other aircraft showing cracking are apparently in the general ballpark of 30,000 cycles. If Leeham is correct that heavy checks are done every 6 years, then that would mean very roughly 12,000, 24,000, and 36,000 cycles.

It is a reasonable guess that none of these aircraft had the cracks present at the time of their last heavy check.

Speaking of which, don't cargo conversions tend to happen when a frame is coming up on a heavy check, because the check can be done more cost effectively then, and the air frame price is lower?

As an additional note, the AD estimated the inspections currently being done at only 1 hour work time (and if I remember right, 1 hour paperwork time). While it's unfortunate to have to add additional maintenance cost, it won't be onerous if a relatively frequent inspection interval is mandated due to this.
 
sodbuster
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Re: 737NG Pickle fork issue

Thu Oct 10, 2019 12:08 am

GOL going to VCV for frame replacement. Watch flight aware.
 
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Re: 737NG Pickle fork issue

Thu Oct 10, 2019 12:32 am

iamlucky13 wrote:
Leeham reported one frame had cracking found at 23,600 cycles. Other aircraft showing cracking are apparently in the general ballpark of 30,000 cycles. If Leeham is correct that heavy checks are done every 6 years, then that would mean very roughly 12,000, 24,000, and 36,000 cycles.

It is a reasonable guess that none of these aircraft had the cracks present at the time of their last heavy check.

Last I looked, the HMV could be almost 7 years on corrosion, so it is reasonable that the youngest frame found was at the 2nd HMV. The original frame was at lease expiration where the 3rd HMV was being performed in parallel to freight conversion.

It is possible early WN -700s passed their 3rd HMV as so many cycles were performed without winglets. (I speculate).

It could be that the winglets moved the natural frequency of forces on the pickle fork to a stress multiplying frequency.

I calculate 12,000 to 20,000 cycles between HMV.

So we can agree:
1st cracks at the conversion/HMV. Probably of an aircraft that received winglets early (I speculate).

Cracks on the low cycle airframe probably during HMV.

Other aircraft were almost certainly ok at prior HMV.

The more I think about it, I think hours with winglets might be the metric, not cycles. But I am speculating.

Lightsaber
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mjoelnir
Posts: 8508
Joined: Sun Feb 03, 2013 11:06 pm

Re: 737NG Pickle fork issue

Thu Oct 10, 2019 12:41 am

lightsaber wrote:
mjoelnir wrote:
lightsaber wrote:
There will be more ADs, the inspection intervals will shorten. But removing the 90,000 cycle life? Have we proven it isn't a manufacturing issue?

The A380 and A320 both were found to need wing reinforcement. The 60,000 cycle limit wasn't removed for the A320 or 36,000 for A380. Instead a repair was approved. New build aircraft are built to a certified modification. Or Embraer wing spars. Or...

There will be a temporary repair approved. There will be a permanent repair approved less than replacing the pickle forks. It will take a few years, but Boeing will get back to full duration on these.


The A320 did not start out with a 60,000 cycle limit. The original approved limit was 48,000 cycles and 60,000 hours. The limits were extended after further fatigue testing and checking of frames reaching the early lifetime limits. The wing cracks on the A380 were found due to the fatigue testing. It would be interesting to get a reference to wing cracks on the A320, as I have not heard of that.

The 737NG got its lifetime limits out of the box. The pickle forks are part of the lifetime parts, no limited lifetime expected. no checking regime, but the current AD, in place.. Cracking was not found through fatigue testing, but by chance at the conversion of older 737-800 to freighters.

It was played down as A320 corrosion.

http://i.stuff.co.nz/business/3402061/C ... rbus-wings
This was found after the 60k extension.

Airbus didn't find their issue in fatigue testing either and far earlier than 48,000 cycles. The Airbus finding was a surprise. It turned out island hopping was brutal on A319/A320 family wings.

My point is that there will be a repair. The regulations do not specify how a problem is found. The first finding was at about 36,000 cycles. The pickle forks with a life of 90,000 cycles must be inspected every 30,000 cycles.

The fact there are so many found after 35,000 tells us these passed. Now the low cycle incident is of concern.

So for now, ground if cracks found and increase inspections. 25 findings out of 500 is bad, but not unprecedented.

There will be shorter inspection intervals until a standard repair is found that returns the life to design.

That repair cannot happen until a new stress analysis is performed. Just as a temporary repair will be found.

There is a process. The cycle test was with a maximum allowed stress (it is well known for aluminum vs. cycles for life). Just knowing the youngest happened at 20,600 cycles and many later tells us the actual stress level. Boeing has good stress engineers that will find a permanent and temporary repair.

The A380 wing cracks are an example. They happened incredibly early. Well before the inspection. Only found because of a RR uncontained engine failure.

The process is intentionally non-punititive to have self disclosure. The was a 738BCF where that self disclosure found the problem and created the AD.

There is a checking regimen. Every HMC. If you cannot inspect visually, x-ray. I assume the HMV required inspection might be altered/improved.

I'm not sure what you are trying to imply.

Legally, there was a self reported finding. The FAA issued an AD on inspections. The data from those inspections will result in a new AD on modified inspection intervals.

Rework is always an approved repair (return to drawing) or pickle fork replacement.

Permanent repairs take time.

Lightsaber


So you compare skin corrosion on a wing with the cracking of in internal structural part. Skin corrosion is usually even detectable by normal sight inspections and than confirmed by measuring thickness.

There was no inspection regime for 737NG pickle forks at 30,000 cycles, that is new with the last AD. It was a part configured for 90,000 cycles no special inspections needed before that time.

What I am trying to imply is, that it would perhaps had been prudent, after the big changes from the classic to the NG, to run a NG frame through fatigue testing.
If you do not realize the difference to find things by fatigue testing, rather than by accident...

You legally self reported finding would have been criminal if not reported.
 
sodbuster
Posts: 19
Joined: Sun Mar 23, 2014 5:08 pm

Re: 737NG Pickle fork issue

Thu Oct 10, 2019 1:32 am

The issue is short runways and heavy braking. Winglets also add into the equation. Which is why GOL has 8 aircraft affected. 800 and 900 have same frames..
 
RickNRoll
Posts: 1789
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Re: 737NG Pickle fork issue

Thu Oct 10, 2019 2:25 am

This is not a problem like the MAX but for those Airlines that use the NG and the MAX each NG that is out of service is going to be unusually painful.
 
prebennorholm
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Re: 737NG Pickle fork issue

Thu Oct 10, 2019 3:21 am

mjoelnir wrote:
What I am trying to imply is, that it would perhaps had been prudent, after the big changes from the classic to the NG, to run a NG frame through fatigue testing.
If you do not realize the difference to find things by fatigue testing, rather than by accident...

I find it hard to imagine that new fatigue testing wasn't done on the NG before certification of that 25-30% bigger and heavier frame.

The dimentions cannot just be scaled. Changing the dimentions will also change elastic properties of the structures. Changing elastic properties will always also mean changing cracking resistance properties.

Theoretically changed elasticity and cracking resistance can be calculated for minor scaling, but beyond a few percent scaling it becomes very complicated for such complex structures. Maybe that was actually what they did back in the 90'es, and in that case we likely just look back on a 20+ years old calculation error.

Thank God it was discovered in time. Premature cracking on quite old planes is normally not a big issue since it cannot be avoided. The special thing about this pickle fork issue is that it would normally not be discovered at D checks, and it was discovered only "by accident". One of the primary reasons for having D checks is to discover and correct such cracking before it becomes dangerous.
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seahawk
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Re: 737NG Pickle fork issue

Thu Oct 10, 2019 6:10 am

It was done, but it is still testing. In that case it seems like winglets and use of short runways are both indicators.
 
mjoelnir
Posts: 8508
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Re: 737NG Pickle fork issue

Thu Oct 10, 2019 8:11 am

iamlucky13 wrote:
acechip wrote:
A question would be, why was this not discovered during a regular heavy check at say, 20k cycles? Why did it have to be discovered accidentally during a freighter conversion? Is that because of the 90k cycle safe life limit?


I'm not sure the "accidentally" is quite an accurate description.

Leeham reported one frame had cracking found at 23,600 cycles. Other aircraft showing cracking are apparently in the general ballpark of 30,000 cycles. If Leeham is correct that heavy checks are done every 6 years, then that would mean very roughly 12,000, 24,000, and 36,000 cycles.

It is a reasonable guess that none of these aircraft had the cracks present at the time of their last heavy check.

Speaking of which, don't cargo conversions tend to happen when a frame is coming up on a heavy check, because the check can be done more cost effectively then, and the air frame price is lower?

As an additional note, the AD estimated the inspections currently being done at only 1 hour work time (and if I remember right, 1 hour paperwork time). While it's unfortunate to have to add additional maintenance cost, it won't be onerous if a relatively frequent inspection interval is mandated due to this.


The accidental is in regards to the first cracks detected on the three frames during freighter conversion. No cracks had been detected during, a) fatigue testing of a frame, AFAIK not specially done for the NG, or B) during regulare checks.
AFAIK none of the heavy checks would look for this cracks,

All subsequent frames with cracks have been found during checks mandated by the AD. Frames above 30,000 cycles got one week and frames above 22,600 cycles got a year to do this check. Most of the frames found with cracks I expect to be frames above the 30,000 cycle limit, because of the short time frame for the check on those frames. At least one frame in the lower cycle range has been found with cracks, so I expect the next AD to shorten the time given for the frames above 22,600 and below 30,000 cycles and it would be perhaps prudent to check still younger frames.
Last edited by mjoelnir on Thu Oct 10, 2019 8:20 am, edited 1 time in total.
 
FluidFlow
Posts: 292
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Re: 737NG Pickle fork issue

Thu Oct 10, 2019 8:17 am

According to the Seattle Times there are now 36 aircraft grounded out of 686 tested. A repair station is now being set up in Victorville.

If the pickle fork is really affected on every single 737NG then this is a problem for Boeing because the pickle fork should last for the whole life time of the aircraft. I guess the repair costs and the compensation for the 3 weeks of grounding will probably be paid for by Boeing (product liability). As the NG is at the end of its production cycle, every single NG could be and probably will be over time affected. Thats over 6700 repairs over the next 10-20 years, which would be 1-2 aircraft per day, with a duration of 21 days for the repair, thats between 20-40 aircraft affected at the same time. So lets hope it is an isolated case only affecting a limited amount of pickle forks due to a bad delivery and not a construction fault effecting all of them.

Here is the source: https://www.seattletimes.com/business/boeing-aerospace/cracks-found-on-more-than-5-of-older-boeing-737s-in-pickle-fork-inspections/
 
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scbriml
Posts: 17476
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Re: 737NG Pickle fork issue

Thu Oct 10, 2019 8:58 am

FluidFlow wrote:
According to the Seattle Times there are now 36 aircraft grounded out of 686 tested. A repair station is now being set up in Victorville.


So that's now 5.25% of the tested fleet having the problem.
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planecane
Posts: 1145
Joined: Thu Feb 09, 2017 4:58 pm

Re: 737NG Pickle fork issue

Thu Oct 10, 2019 10:00 am

FluidFlow wrote:
According to the Seattle Times there are now 36 aircraft grounded out of 686 tested. A repair station is now being set up in Victorville.

If the pickle fork is really affected on every single 737NG then this is a problem for Boeing because the pickle fork should last for the whole life time of the aircraft. I guess the repair costs and the compensation for the 3 weeks of grounding will probably be paid for by Boeing (product liability). As the NG is at the end of its production cycle, every single NG could be and probably will be over time affected. Thats over 6700 repairs over the next 10-20 years, which would be 1-2 aircraft per day, with a duration of 21 days for the repair, thats between 20-40 aircraft affected at the same time. So lets hope it is an isolated case only affecting a limited amount of pickle forks due to a bad delivery and not a construction fault effecting all of them.

Here is the source: https://www.seattletimes.com/business/boeing-aerospace/cracks-found-on-more-than-5-of-older-boeing-737s-in-pickle-fork-inspections/


The 21 day repair is to replace the pickle forks with new ones. As lightsaber said, a reinforcement modification will be developed and installed on all aircraft BEFORE the cracks develop. This modification will certainly be far less expensive and time consuming. As lightsaber also said, once a repair is certified, a repair and reinforcement will be able to be done on aircraft with cracks that doesn't involve replacing the pickle forks with new ones. This will also be a less costly and time consuming repair.

They aren't just going to inspect and replace pickle forks when cracks are found for the rest of the 737NG service life.
 
leghorn
Posts: 901
Joined: Sun Jan 22, 2017 9:13 am

Re: 737NG Pickle fork issue

Thu Oct 10, 2019 10:09 am

One has to wonder why this hasn't been found on ex-Ryanair planes. They've been sent to freight companies and have been used across Europe intensively on short hops. I guess they are heavily affected but at least the news comes during the low season.
 
Armadillo1
Posts: 518
Joined: Thu Apr 20, 2017 5:14 pm

Re: 737NG Pickle fork issue

Thu Oct 10, 2019 10:11 am

how old ex-Ryanair planes now?
 
leghorn
Posts: 901
Joined: Sun Jan 22, 2017 9:13 am

Re: 737NG Pickle fork issue

Thu Oct 10, 2019 10:20 am

Armadillo1 wrote:
how old ex-Ryanair planes now?

Older than they were as they waited a long time to strike a deal on Maxes for a very long time and those planes have been used on short routes like Dublin-British Midlands for 16 hours a day.
 
VSMUT
Posts: 3038
Joined: Mon Aug 08, 2016 11:40 am

Re: 737NG Pickle fork issue

Thu Oct 10, 2019 10:24 am

 
Someone83
Posts: 4390
Joined: Sun Sep 17, 2006 5:47 pm

Re: 737NG Pickle fork issue

Thu Oct 10, 2019 10:25 am

seahawk wrote:
It was done, but it is still testing. In that case it seems like winglets and use of short runways are both indicators.


Yes, but not exclusive

LN-RPK with SAS doesn’t have winglets. However, it had been used a lot on domestic Norwegian flights
 
FluidFlow
Posts: 292
Joined: Wed Apr 10, 2019 6:39 am

Re: 737NG Pickle fork issue

Thu Oct 10, 2019 10:59 am

planecane wrote:
FluidFlow wrote:
According to the Seattle Times there are now 36 aircraft grounded out of 686 tested. A repair station is now being set up in Victorville.

If the pickle fork is really affected on every single 737NG then this is a problem for Boeing because the pickle fork should last for the whole life time of the aircraft. I guess the repair costs and the compensation for the 3 weeks of grounding will probably be paid for by Boeing (product liability). As the NG is at the end of its production cycle, every single NG could be and probably will be over time affected. Thats over 6700 repairs over the next 10-20 years, which would be 1-2 aircraft per day, with a duration of 21 days for the repair, thats between 20-40 aircraft affected at the same time. So lets hope it is an isolated case only affecting a limited amount of pickle forks due to a bad delivery and not a construction fault effecting all of them.

Here is the source: https://www.seattletimes.com/business/boeing-aerospace/cracks-found-on-more-than-5-of-older-boeing-737s-in-pickle-fork-inspections/


The 21 day repair is to replace the pickle forks with new ones. As lightsaber said, a reinforcement modification will be developed and installed on all aircraft BEFORE the cracks develop. This modification will certainly be far less expensive and time consuming. As lightsaber also said, once a repair is certified, a repair and reinforcement will be able to be done on aircraft with cracks that doesn't involve replacing the pickle forks with new ones. This will also be a less costly and time consuming repair.

They aren't just going to inspect and replace pickle forks when cracks are found for the rest of the 737NG service life.


Alright, that's good news.

Does anyone here has a rough estimation what a fix like this would cost? The development, testing and certification will probably cost a bit. Afterwards when it can be done on premise from the airline maintenance it should be rather cheap, a few hours of work.
 
kalvado
Posts: 2014
Joined: Wed Mar 01, 2006 4:29 am

Re: 737NG Pickle fork issue

Thu Oct 10, 2019 11:36 am

FluidFlow wrote:
planecane wrote:
FluidFlow wrote:
According to the Seattle Times there are now 36 aircraft grounded out of 686 tested. A repair station is now being set up in Victorville.

If the pickle fork is really affected on every single 737NG then this is a problem for Boeing because the pickle fork should last for the whole life time of the aircraft. I guess the repair costs and the compensation for the 3 weeks of grounding will probably be paid for by Boeing (product liability). As the NG is at the end of its production cycle, every single NG could be and probably will be over time affected. Thats over 6700 repairs over the next 10-20 years, which would be 1-2 aircraft per day, with a duration of 21 days for the repair, thats between 20-40 aircraft affected at the same time. So lets hope it is an isolated case only affecting a limited amount of pickle forks due to a bad delivery and not a construction fault effecting all of them.

Here is the source: https://www.seattletimes.com/business/boeing-aerospace/cracks-found-on-more-than-5-of-older-boeing-737s-in-pickle-fork-inspections/


The 21 day repair is to replace the pickle forks with new ones. As lightsaber said, a reinforcement modification will be developed and installed on all aircraft BEFORE the cracks develop. This modification will certainly be far less expensive and time consuming. As lightsaber also said, once a repair is certified, a repair and reinforcement will be able to be done on aircraft with cracks that doesn't involve replacing the pickle forks with new ones. This will also be a less costly and time consuming repair.

They aren't just going to inspect and replace pickle forks when cracks are found for the rest of the 737NG service life.


Alright, that's good news.

Does anyone here has a rough estimation what a fix like this would cost? The development, testing and certification will probably cost a bit. Afterwards when it can be done on premise from the airline maintenance it should be rather cheap, a few hours of work.

Few hours including removal and reinstall of wing root fairing?

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