737NGs have cracked 'pickle forks' after finding several in the jets.
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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.
"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.
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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.
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Leehams is reporting today that the incidence is 5% over the first 500 inspected. https://leehamnews.com/2019/10/08/bo...-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.
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.
And how much cost and whom pays for part failing prematurely ?
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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?
How about removing those winglets ASAP?
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?
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.
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.
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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?
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?
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-n...lays-catch-737
Last edited by Grebe; 9th Oct 2019 at 05:14. Reason: added pic and italics to clarify
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.
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.
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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.
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.
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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.
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.
Regards
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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
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
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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
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This Leeham News piece provides a good update: link to article
Many thanks for a very informative link.
Your time and trouble very much appreciated.
Be lucky
David
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 ...