Boeing in yet another technical pickle!

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TheGreenGoblin
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Boeing in yet another technical pickle!

#1 Post by TheGreenGoblin » Mon Sep 30, 2019 9:30 am

A pickle fork to be exact

"The FAA has ordered operators of some of the hard-working fleet of Boeing 737NGs to conduct inspections for cracks in a critical structural assembly that have shown up in some NGs. Boeing found cracks in a plane that had about 35,000 cycles on it, less than half the 90,000 that the “pickle fork” is designed to last. The pickle fork is the main structural attachment between the wings and the fuselage and is supposed to last the life of the aircraft. Cracks were found in a few other aircraft. It’s not clear how many of the 7,000 NGs in service will need to take a break for the inspections but Boeing says it’s spreading the word. “Over the coming days, we will work closely with our customers to implement a recommended inspection plan for certain airplanes in the fleet,” the company told the BBC in a statement. It’s also not clear what the potential fix might entail and how long it would take an aircraft out of service."

737NG cracks...
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Re: Boeing in yet another technical pickle!

#2 Post by Pontius Navigator » Mon Sep 30, 2019 12:18 pm

So do they look at 35k plus aircraft or test a few younger ones first. The Valiant story again where young aircraft were assumed safe but a check carried out to be sure. I think the youngest was at 40 hours. Then they found zero hours spars (sic) also with fatigue cracks.

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Re: Boeing in yet another technical pickle!

#3 Post by TheGreenGoblin » Mon Sep 30, 2019 4:20 pm

Pontius Navigator wrote:
Mon Sep 30, 2019 12:18 pm
So do they look at 35k plus aircraft or test a few younger ones first. The Valiant story again where young aircraft were assumed safe but a check carried out to be sure. I think the youngest was at 40 hours. Then they found zero hours spars (sic) also with fatigue cracks.
With respect to the 737NG one assumes assumes they that will take a number of random samples (suitably sized) from the complete set of aircraft sold to date covering all sectors and usage patterns , the set of aircraft with less than 35000 hours and the set of aircraft with more than than 35000 hours and just to be sure check the boundaries by looking at aircraft with zero hours (i.e. new) and the set of aircraft at or near max number of hours to date. They will, I assume, issue some sort of directive to all 737NG operators.

With respect to the Valiant I read somewhere that the change of role of the aircraft from high altitude to low altitude penetration had resulted in an unexpectedly shorter spar life, the air being denser and it being bumpier in and around the weeds. The discovery of 0 hours spars with cracks must have pointed to some sort of manufacturing/installation anomaly surely (I know, don't call you Shirely)?
The cracks are not an issue for MAXes
Er, that might be because most of those released for operation have low hours and are sitting grounded in hangars, on taxiways or even car parks...
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Re: Boeing in yet another technical pickle!

#4 Post by Pontius Navigator » Mon Sep 30, 2019 4:50 pm

TGG, the Valiant problem was to do with the formulation of the alloy and its crystalline structure. The spars became fatigued just sitting in the stores.

One hopes the Boeing problem is not as fundamental but it suggests there are unexpected stresses present, the question is when does this first manifest itself and how long before the pickle fork fails.

As you say, they will need to check a number of aircraft around that 35k example.

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Re: Boeing in yet another technical pickle!

#5 Post by TheGreenGoblin » Mon Sep 30, 2019 5:28 pm

Pontius Navigator wrote:
Mon Sep 30, 2019 4:50 pm
TGG, the Valiant problem was to do with the formulation of the alloy and its crystalline structure. The spars became fatigued just sitting in the stores.
Just had a look in more depth based on your good advice and your correct root cause analysis points to an alloy called DTD683 and a flawed lifing strategy called Safe Life as opposed to Fail Safe. Always great to learn something new. Thank you.

DTD683

Fail Safe, Safe Life

Apparently the alloy's issues were known before the Valiant was designed, as it was used in other types including the Shackleton, but the designers assessed that it would suffice for use in the Valiant high level role, but their calculations and and assumptions were proved to be woefully wrong!
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Re: Boeing in yet another technical pickle!

#6 Post by llondel » Mon Sep 30, 2019 5:37 pm

I remember watching what was probably an Open University materials science programme on a bit of metal in the Canberra bomber to which they bolted the wings. That started with a cylindrical billet which was heated then stood on end and flattened into a vaguely rectangular slab. All to do with the grain of the metal and how by doing it that way rather than with a rolled flat slab was better and more resistant to fatigue.

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Re: Boeing in yet another technical pickle!

#7 Post by TheGreenGoblin » Mon Sep 30, 2019 6:39 pm

llondel wrote:
Mon Sep 30, 2019 5:37 pm
I remember watching what was probably an Open University materials science programme on a bit of metal in the Canberra bomber to which they bolted the wings. That started with a cylindrical billet which was heated then stood on end and flattened into a vaguely rectangular slab. All to do with the grain of the metal and how by doing it that way rather than with a rolled flat slab was better and more resistant to fatigue.
Given that the V Force bombers were more bleeding edge than even leading edge, it not surprising that things occasionally creaked, cracked and even broke. Even the Vulcan wasn't immune...

The Canberra for its part must be regarded as one of the most successful British military aircraft of all time.




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Re: Boeing in yet another technical pickle!

#8 Post by Boac » Sun Oct 06, 2019 9:23 am

This web page gives a good coverage of the problem. https://samchui.com/2019/10/05/faa-issu ... ZmyFWZ7mcQ

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Re: Boeing in yet another technical pickle!

#9 Post by Alisoncc » Sun Oct 06, 2019 10:57 am

TheGreenGoblin wrote:
Mon Sep 30, 2019 6:39 pm
Given that the V Force bombers were more bleeding edge than even leading edge, it not surprising that things occasionally creaked, cracked and even broke. Even the Vulcan wasn't immune...
Re: Vulcan crash at RAF Syerston 20th Sept 1958 Battle of Britain day in video. Our school ATC had organised an RAF mini bus to take us up from Nottingham for the day. So Yup I was there, but it wasn't my fault.
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Re: Boeing in yet another technical pickle!

#10 Post by TheGreenGoblin » Sun Oct 06, 2019 11:45 am

Alisoncc wrote:
Sun Oct 06, 2019 10:57 am
Re: Vulcan crash at RAF Syerston 20th Sept 1958 Battle of Britain day in video. Our school ATC had organised an RAF mini bus to take us up from Nottingham for the day. So Yup I was there, but it wasn't my fault.
Alisoncc it must have been quite a shocking thing to see. Nobody expects to see an aircraft wing give way, least of all the mighty delta on the Vulcan I imagine!

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Re: Boeing in yet another technical pickle!

#11 Post by ian16th » Sun Oct 06, 2019 12:30 pm

Alisoncc wrote:
Sun Oct 06, 2019 10:57 am
20th Sept 1958 Battle of Britain
That day I was poured onto a train at Orange SNCF station, heading overnight to Paris, then on to Yatesbury for my Fitter Bomber course.
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Re: Boeing in yet another technical pickle!

#12 Post by Fox3WheresMyBanana » Sun Oct 06, 2019 12:43 pm

Not a lecture would pass in Materials Science without my professors laughingly mentioning the stupidity of trusting one's life to monocoque aluminium structures, it being known that I was the idiot on an RAF Cadetship.

It was the first thing that popped into my brain when I noticed one of the large panels over an intake flapping madly around shortly after take-off one sunny morning.

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Re: Boeing in yet another technical pickle!

#13 Post by Pontius Navigator » Sun Oct 06, 2019 2:52 pm

Airlines that have found cracks must repeat the inspection thereafter at intervals not to exceed 3,500 flight cycles.
Two things occur to me:

1. They were very quick to pluck a number out of the air.

2. That seems a very long time between checks. If one flight cycle is a take-off flight and landing, and even with 4 flights in a day, that is over 8 years between checks.

I found this: " A Boeing 747 can endure about 35,000 pressurization cycles and flights—roughly 135,000 to 165,000 flight hours—before metal fatigue sets in. ". As the pickle forked 737 had 35,000 cycles that would seem to fit the expected fatigue life. Their check after 3,500 cycles suggested they just stuck a finger up and chose 10%.

I am beginning to suspect that the problem was not a surprise.

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Re: Boeing in yet another technical pickle!

#14 Post by Boac » Mon Oct 07, 2019 12:51 pm

I see nothing but more doom and gloom for Boeing here. If replacement is the fix, taking NGs out of service to replace the parts on top of a depleted fleet due to Max issues - airlines will not be very happy. It will not be a 'quick' replacement job, either.

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Re: Boeing in yet another technical pickle!

#15 Post by ian16th » Mon Oct 07, 2019 2:19 pm

Wasn't the Hawaiian event due to high cycles and short hours?
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Re: Boeing in yet another technical pickle!

#16 Post by Fox3WheresMyBanana » Mon Oct 07, 2019 6:48 pm

The factors in choosing a cycle time for fatigue cracking inspections depends, IIRC, on the critical crack length in the component, the rate of crack growth based on experience, the crack length which is detectable (depends on ease of access and equipment available), and the consequences of a failure.
I doubt the 3,500 cycles has just been picked out of thin air.
The critical crack length on a 747 fuselage is in most places about 13 inches, so you can just use the usual walkround as it's pretty obvious when there's a problem.

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Re: Boeing in yet another technical pickle!

#17 Post by Boac » Wed Oct 09, 2019 1:49 pm

Boeing said yesterday Tuesday that an unidentified business jet customer had ordered one 737 MAX jet.

Phew! That'll help.................wonder what it cost?

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Re: Boeing in yet another technical pickle!

#18 Post by Fox3WheresMyBanana » Wed Oct 09, 2019 2:06 pm

Is that one whole order ;)))

Jeez, it looks worse putting that out than saying nothing.

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Re: Boeing in yet another technical pickle!

#19 Post by Boac » Wed Oct 09, 2019 3:25 pm

Has anyone heard anything about the state of the front pickleforks?

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Re: Boeing in yet another technical pickle!

#20 Post by Boac » Wed Oct 09, 2019 9:28 pm

Aeroflot cancels order for 22 787s.

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