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747-8 Uncontained Engine Failure?  
User currently offlinetp1040 From United States of America, joined Apr 2011, 223 posts, RR: 0
Posted (2 years 3 months 5 days 18 hours ago) and read 45676 times:

This was mentioned in the 747-8 production thread.

A 747-8 had a rejected takeoff at ZSPD. On 11/9, it seems that during takeoff, an Air Bridge Cargo crew got unusual indications on one of the GEnx-2B67 engines. Shut down, rejected take off, parts scattered on the runway. Indicating a possible uncontained engine failure.

http://www.jacdec.de/news/news.htm


At least this GEnx did not start a grass fire.

94 replies: All unread, showing first 25:
 
User currently offlinestarrion From United States of America, joined Jul 2003, 1129 posts, RR: 2
Reply 1, posted (2 years 3 months 5 days 18 hours ago) and read 45598 times:

Well that would appear to answer the question about whether the AI incident was a one-off or not.

I believe there may be a market for no-doze and antacids at the GE engine plant.



Knowledge Replaces Fear
User currently offlineJumboJim747 From Australia, joined Oct 2004, 2465 posts, RR: 44
Reply 2, posted (2 years 3 months 5 days 18 hours ago) and read 45292 times:

It seams more engines are failing lately cauld it be due to higher then normal production and the workers are getting a bit sloppy?


On a wing and a prayer
User currently offlineKC135TopBoom From United States of America, joined Jan 2005, 12178 posts, RR: 51
Reply 3, posted (2 years 3 months 5 days 18 hours ago) and read 45129 times:

Quoting tp1040 (Thread starter):
Indicating a possible uncontained engine failure.

No, if the engine parts come out the tail pipe, as they are suppose to, it is not an uncontained failure, it is a contained failure. If the parts come out the intake or the sides of the engine, then it is an uncontained failure.

Quoting JumboJim747 (Reply 2):
It seams more engines are failing lately cauld it be due to higher then normal production and the workers are getting a bit sloppy?

You may be onto something there. This is the second GEnx to fail, although one was the -1B and the other is a -2B. RR had an uncontained failure of a Trent-900 a few years ago on a QF A-380, and the Trent-1000 of the NH B-787s had to have their gear box replaced.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 4, posted (2 years 3 months 5 days 17 hours ago) and read 45022 times:

Quoting tp1040 (Thread starter):
Shut down, rejected take off, parts scattered on the runway. Indicating a possible uncontained engine failure.

An uncontained failure requires that there be holes in the nacelle. It's very very easy to detect. The maintenance crew would see it almost instantly on a cursory inspection. The normal failure mode is for parts to go out the front (relatively unusual) or the back (very normal). Those are not uncontained failures.

Tom.


User currently offlineSEPilot From United States of America, joined Dec 2006, 7097 posts, RR: 46
Reply 5, posted (2 years 3 months 5 days 17 hours ago) and read 44831 times:

I do not find it surprising that any radically new design engine should have a couple of hiccupIs; the one that surprised me was the GE90-110/115, which went an extraordinarily long time before the first failure. Infant mortality is common among electronic devices; I think it also applies to a lesser extent to mechanical products. If there is a defect in either manufacturing or design, it often shows up early.


The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlinetp1040 From United States of America, joined Apr 2011, 223 posts, RR: 0
Reply 6, posted (2 years 3 months 5 days 16 hours ago) and read 44100 times:

I just using JADEC's terminology and calling it a possible uncontained failure. Parts came out the back, but the report called it a possible UC engine failure due to the fact that exact details were unknown.

User currently offlineDocLightning From United States of America, joined Nov 2005, 20333 posts, RR: 59
Reply 7, posted (2 years 3 months 5 days 15 hours ago) and read 44000 times:

So this is two GEnX engines having a failure. The -1B and -2B are very similar with mostly fan size being the difference, IIRC.

In my opinion, this suggests a design issue more than a manufacturing issue, although it is certainly possible that the failure was caused by a defective part common to both engines.

Quoting SEPilot (Reply 5):

I do not find it surprising that any radically new design engine should have a couple of hiccupIs;

I think that spitting debris out the back indicates a bit more than a "hiccup."


User currently offlineKarelXWB From Netherlands, joined Jul 2012, 13068 posts, RR: 35
Reply 8, posted (2 years 3 months 5 days 15 hours ago) and read 43812 times:

Quoting KC135TopBoom (Reply 3):
and the Trent-1000 of the NH B-787s had to have their gear box replaced.

And don't forget the Trent 1000 failure on a 787 testbed back in 2010.

http://www.flightglobal.com/news/art...-trent-1000-engine-failure-346215/



Only two things are infinite, the universe and human stupidity. And I'm not sure about the universe.
User currently offlineStitch From United States of America, joined Jul 2005, 31375 posts, RR: 85
Reply 9, posted (2 years 3 months 5 days 15 hours ago) and read 43757 times:
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Quoting DocLightning (Reply 7):
The -1B and -2B are very similar with mostly fan size being the difference, IIRC.

Another major change was adding back two-thirds of the blades in the LPT (with PiP1 for the GEnx1B and as the baseline for the GEnx2B).


User currently offlinesweair From Sweden, joined Nov 2011, 1831 posts, RR: 0
Reply 10, posted (2 years 3 months 5 days 14 hours ago) and read 43103 times:

A design error should have been caught during testing? May it be some sort of material weakness, stuff like this happens.

Anyway this is bad, very bad and these two programs don't need any more delays or holdups.


User currently offlinegoosebayguy From United Kingdom, joined Sep 2009, 415 posts, RR: 0
Reply 11, posted (2 years 3 months 5 days 14 hours ago) and read 42805 times:

Truth is that engines are always pushing at the limits of technology yet we demand total reliability. One small problem could lead to huge delays in delivery and then who pays for such delays? Boeing have paid for the 787 delays but will GE pay for any 747-8 delays? Just think what will happen if RR find they're are late delivering the XWB for the A350! The cost could be monumental to RR. GE need to get a handle on this problem and quickly. A third event could lead to the 747-8 being grounded!

User currently offlineimiakhtar From , joined Dec 1969, posts, RR:
Reply 12, posted (2 years 3 months 5 days 14 hours ago) and read 42646 times:

Quoting KarelXWB (Reply 8):
And don't forget the Trent 1000 failure on a 787 testbed back in 2010.

That was due to an engine being tested beyond design parameters.

Contrary to popular belief, RR engines are not prone to uncontained engine failures. Since 1994, there have only been three such RR failures: the T900 on the A380, a T700 HPT that failed on an Edelweiss A330 due to untested engine oil and an RB-211 in 1994 (not sure if -524 or -535).

Meanwhile the GE manufactured CF6, a very mature design, has been spitting out turbine parts (often spectacularly) on a yearly basis since it's introduction.


User currently offlinebrilondon From Canada, joined Aug 2005, 4414 posts, RR: 2
Reply 13, posted (2 years 3 months 5 days 14 hours ago) and read 42389 times:

Quoting JumboJim747 (Reply 2):

It seams more engines are failing lately cauld it be due to higher then normal production and the workers are getting a bit sloppy?

Too many checks and balances for this to be the case. This would be the case if they made the jet engines in one day which I highly doubt.



Rush for ever; Yankees all the way!!
User currently offlineMaddogJT8D From United States of America, joined Oct 2009, 402 posts, RR: 1
Reply 14, posted (2 years 3 months 5 days 14 hours ago) and read 42318 times:

Quoting imiakhtar (Reply 12):

Didn't an RR powered Delta 777 have an uncontained failure a year or two ago on the runway in Atlanta?


User currently offlineWarpSpeed From United States of America, joined Feb 2010, 595 posts, RR: 3
Reply 15, posted (2 years 3 months 5 days 14 hours ago) and read 42235 times:

Quoting DocLightning (Reply 7):
So this is two GEnX engines having a failure. The -1B and -2B are very similar with mostly fan size being the difference, IIRC.

In my opinion, this suggests a design issue more than a manufacturing issue, although it is certainly possible that the failure was caused by a defective part common to both engines.

Glad that both incidents occurred during take-off runs as opposed to in-flight.

The WSJ is now reporting this story and indicates the failure stems from the same problem as the July incident.



DaHjaj jaj QaQ Daghajjaj !!!!
User currently offlineStitch From United States of America, joined Jul 2005, 31375 posts, RR: 85
Reply 16, posted (2 years 3 months 5 days 13 hours ago) and read 41211 times:
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Quoting WarpSpeed (Reply 15):
The WSJ is now reporting this story and indicates the failure stems from the same problem as the July incident.

That article also says that GE has been testing all of the GEnx engines in service and that the Air Bridge Cargo bird was one of about a dozen that had not yet been tested. It also notes that GE is now applying a new coating to the engine shaft to protect the surface metal from corrosion and contamination.

So it sounds more like a materials issue than a design issue. As I noted up-thread, GE made major revisions to the LPT module for the GEnx2B and GEnx1B PIP1, but they were mostly to add back blades, vanes and injectors after examination proved GE had been too aggressive in reducing their count with the initial GEnx design.


User currently offlineADent From United States of America, joined Dec 2006, 1404 posts, RR: 2
Reply 17, posted (2 years 3 months 5 days 13 hours ago) and read 41146 times:

Quoting MaddogJT8D (Reply 14):
Didn't an RR powered Delta 777 have an uncontained failure a year or two ago on the runway in Atlanta?

On 02JAN2009 a Delta 777 had a blade failure that caused a dent in the fuselage. It was powered by a Roll-Royce Trent 895-17 engine.

See http://www.ntsb.gov/aviationquery/br...ef.aspx?ev_id=20090105X01036&key=1 . ( ENG09IA002 )

Quote:
The examination of the right engine revealed one fan blade was fractured through the root section with the fractured dovetail section remaining in the fan disk’s blade slot. All of the remaining fan blades had hard body impact damage to the leading edges. An examination of the fan blades with an ultraviolet light did not result in any fluorescence. There were several holes through the inlet duct. The examination of the fuselage revealed a 3 1/2-inch diameter dent that was approximately 3/8-inch deep that was located forward of the 2R door just above the window belt, but below the Delta Air Lines company logo.


User currently offlineHAWK21M From India, joined Jan 2001, 31702 posts, RR: 56
Reply 18, posted (2 years 3 months 5 days 13 hours ago) and read 40941 times:

Uncontained or not......This is the 2nd time.......the cause of it needs to be asertained.....If its a design flaw then thats really sad news.....


Think of the brighter side!
User currently offlinelightsaber From United States of America, joined Jan 2005, 13518 posts, RR: 100
Reply 19, posted (2 years 3 months 5 days 13 hours ago) and read 40955 times:
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Please change the title. This looks to be, as others have noted, a contained failure.

Quoting starrion (Reply 1):
Well that would appear to answer the question about whether the AI incident was a one-off or not.

I believe there may be a market for no-doze and antacids at the GE engine plant.

  

Quoting KC135TopBoom (Reply 3):

No, if the engine parts come out the tail pipe, as they are suppose to, it is not an uncontained failure, it is a contained failure. If the parts come out the intake or the sides of the engine, then it is an uncontained failure.

Nitpick: Parts may go out the intake in a contained failure. I'm for the 'punctured nacelle' definition for uncontained.   

Quoting WarpSpeed (Reply 15):
The WSJ is now reporting this story and indicates the failure stems from the same problem as the July incident.

Reuters, but lacks the detail of the WSJ noting the similar failure:
http://www.reuters.com/article/2012/...gine-failure-idUSL1E8KDHDF20120913

Quoting Stitch (Reply 16):
As I noted up-thread, GE made major revisions to the LPT module for the GEnx2B and GEnx1B PIP1, but they were mostly to add back blades, vanes and injectors after examination proved GE had been too aggressive in reducing their count with the initial GEnx design.

Was the failed 787 powerplant a 'base engine' or and engine with the PIP?

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently online747classic From Netherlands, joined Aug 2009, 2214 posts, RR: 14
Reply 20, posted (2 years 3 months 5 days 13 hours ago) and read 40651 times:

Quoting WarpSpeed (Reply 15):
The WSJ is now reporting this story and indicates the failure stems from the same problem as the July incident

The same article also reported : A preliminary inspection revealed the damage was in the low-pressure turbine and was contained.

Quoting lightsaber (Reply 19):
Was the failed 787 powerplant a 'base engine' or and engine with the PIP?

AFAIK It was a GEnx-1B (PIP1) engine.



Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineEPA001 From Netherlands, joined Sep 2006, 4934 posts, RR: 40
Reply 21, posted (2 years 3 months 5 days 13 hours ago) and read 39584 times:
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Quoting 747classic (Reply 20):
The same article also reported : A preliminary inspection revealed the damage was in the low-pressure turbine and was contained.

Still, this is not good. Hope GE will sort out the issue soon.


User currently offlineWarpSpeed From United States of America, joined Feb 2010, 595 posts, RR: 3
Reply 22, posted (2 years 3 months 5 days 13 hours ago) and read 39373 times:

Quoting EPA001 (Reply 21):
Still, this is not good. Hope GE will sort out the issue soon.

They may already know. The WSJ article also mentioned that GE is applying a new coating to the engine shaft to protect the surface metal from corrosion and contamination.



DaHjaj jaj QaQ Daghajjaj !!!!
User currently offlinelightsaber From United States of America, joined Jan 2005, 13518 posts, RR: 100
Reply 23, posted (2 years 3 months 5 days 12 hours ago) and read 38718 times:
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Does anyone doubt that when these nuts fails that the low turbines destroy themselves fast enough to prevent a dangerous RPM in the low turbine?    Ok, I'm amused that GE's safety feature has proven itself twice. However, false positives are bad...

How I wish I knew the pedigree of the two failed engine nuts. How old was the nut that failed on each engine? Now, these are fan over-speed protection devices, so they must be designed to fail. But where these early build parts (time for corrosion), or from a certain batch (coating in question?).

Quoting 747classic (Reply 20):
AFAIK It was a GEnx-1B (PIP1) engine.

Thank you.

So did the connection change with the GEnX-2B and PIP1? e.g., a vendor or process change?

The failures only seem to happen with the newer low turbines. Is there a certain frequency in the new turbines that exacerbates any flaw in the nut? Or were the failures coincidence and one of the non-PIP1 GEnX-1B will spray a low turbine soon?   

Quoting WarpSpeed (Reply 22):
The WSJ article also mentioned that GE is applying a new coating to the engine shaft to protect the surface metal from corrosion and contamination.

I've seen coating changes dramatically increase part lives. By a factor of 8.

However, I would question the inspection process on the part too.

Here is a detailed question no one outside of GE/NATSB should know: Where on the nut is the failure happening. There are two cases. If they are at the same location, I would question an inherent manufacturing flaw too. Tolerances might need to become tighter.

Quoting HAWK21M (Reply 18):
the cause of it needs to be ascertained

GE is big on ROOT cause analysis. ETOPS 330 is riding on this. If GE can prove that what they were inspecting for was in the failed engine, then they will just move forward with their current plan. If this latest failure wouldn't have been found in the inspection, Scooby would say "Roh Roh."

Quoting 747classic (Reply 20):
A preliminary inspection revealed the damage was in the low-pressure turbine

   Yea, blades hitting stators do create a wee bit of damage.


Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlinemffoda From United States of America, joined Apr 2010, 1109 posts, RR: 0
Reply 24, posted (2 years 3 months 5 days 11 hours ago) and read 37398 times:

Quoting 747classic (Reply 20):
Quoting lightsaber (Reply 19):
Was the failed 787 powerplant a 'base engine' or and engine with the PIP?

AFAIK It was a GEnx-1B (PIP1) engine.

I may be wrong... But I thought the GEnx-2b has not yet received a PIP. My understanding was that 1st PIP for the GEnx-2b would available in Q3 2013. And it would be based on the 1st PIP (already in service on the 787) and the 2nd PIP (later this year) from the GEnx-1b?

I remember this form the Cargolux dispute... anyway, I could be wrong?   



harder than woodpecker lips...
User currently offlineKC135TopBoom From United States of America, joined Jan 2005, 12178 posts, RR: 51
Reply 25, posted (2 years 3 months 5 days 11 hours ago) and read 37152 times:

Quoting goosebayguy (Reply 11):
A third event could lead to the 747-8 being grounded!

Why? One event was on a B-787 and this one is on a B-747. Two different airplanes with two different versions of the engine, with different thrust.

Quoting mffoda (Reply 24):
But I thought the GEnx-2b has not yet received a PIP. My understanding was that 1st PIP for the GEnx-2b would available in Q3 2013. And it would be based on the 1st PIP (already in service on the 787) and the 2nd PIP (later this year) from the GEnx-1b?

That's what I thought too. The GEnx-2B doesn't get its PIP-1 until next year. Is that not correct?

As of August 2012 Boeing has delivered 20 B-747-8Fs and 7 B-747-8I/BBJs (4 VIP/BBJs and 3 to LH).


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 26, posted (2 years 3 months 5 days 11 hours ago) and read 37054 times:

Quoting DocLightning (Reply 7):
In my opinion, this suggests a design issue more than a manufacturing issue, although it is certainly possible that the failure was caused by a defective part common to both engines.

How does this suggest a design issue? These aren't the high time engines...in fact, they're low time engines relative to the fleet leaders. That very strongly suggests it's *not* a design issue, but something in the manufacturing or environmental; there has to be something funny about these engines or the way they were operated.

Quoting sweair (Reply 10):
A design error should have been caught during testing?

Of the kind that shows up on low-time engines, yes. The design error that shows up in the fleet rather than in testing is the one that is tied to fatigue or life degradation.

Quoting WarpSpeed (Reply 15):
Glad that both incidents occurred during take-off runs as opposed to in-flight.

That's the highest stress time for the engine shaft...if it's indeed a shaft problem, this is what you'd expect to happen.

Quoting WarpSpeed (Reply 15):
The WSJ is now reporting this story and indicates the failure stems from the same problem as the July incident.

That was quick.

Quoting HAWK21M (Reply 18):
Uncontained or not......This is the 2nd time.......

If it's the the same failure, yes.

Quoting HAWK21M (Reply 18):
the cause of it needs to be asertained....

You can bet that will happen; nobody wants to now know why.

Quoting HAWK21M (Reply 18):
If its a design flaw then thats really sad news.....

Agreed, but it's hard to see how it could be at this point.

Tom.


User currently offlineBoeingVista From Australia, joined Jan 2009, 1584 posts, RR: 3
Reply 27, posted (2 years 3 months 5 days 10 hours ago) and read 35685 times:

Quoting Stitch (Reply 16):
That article also says that GE has been testing all of the GEnx engines in service and that the Air Bridge Cargo bird was one of about a dozen that had not yet been tested

Tested or inspected? What exactly would GE be testing for.

Quoting lightsaber (Reply 23):
Here is a detailed question no one outside of GE/NATSB should know: Where on the nut is the failure happening. There are two cases. If they are at the same location, I would question an inherent manufacturing flaw too. Tolerances might need to become tighter.

Maybe GE stress calculations are just wrong, as you would know in engineering sometimes you get schooled by experience. Unexpected harmonics for example (maybe when setting power?), can raise stresses very quickly. Anyway something real world is not playing ball with GE's assumptions.

Will the NTSB be investigating this failure, they should be

Quoting KC135TopBoom (Reply 25):

Why? One event was on a B-787 and this one is on a B-747. Two different airplanes with two different versions of the engine, with different thrust.

But essentially the same engine. If the failed part is the mid shaft net and this is the same in both engines then a 3rd similar failure in a GEnx series engine would raise serious questions.

Quoting tdscanuck (Reply 26):
How does this suggest a design issue? These aren't the high time engines...in fact, they're low time engines relative to the fleet leaders. That very strongly suggests it's *not* a design issue, but something in the manufacturing or environmental; there has to be something funny about these engines or the way they were operated.

Could even just be an assembly issue like the A380 wing skins but nothing can be ruled out at this point.



BV
User currently offlineStitch From United States of America, joined Jul 2005, 31375 posts, RR: 85
Reply 28, posted (2 years 3 months 5 days 9 hours ago) and read 34669 times:
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Quoting mffoda (Reply 24):
I may be wrong... But I thought the GEnx-2b has not yet received a PIP.
Quoting KC135TopBoom (Reply 25):
That's what I thought too.

The GEnx2B entered service with the revised LPT that was introduced with PIP1 on the GEnx1B.



Quoting BoeingVista (Reply 27):
Tested or inspected?

The article merely said "tested".

Quote:

The NTSB and GE are conducting a metallurgical analysis of the engine and its components. Of the 118 GEnx engines in operation, about a dozen on non-passenger freighter aircraft have yet to be tested, including the one in Shanghai. Those tests will be completed by next week.


User currently offlineBlueSky1976 From Poland, joined Jul 2004, 1909 posts, RR: 4
Reply 29, posted (2 years 3 months 5 days 9 hours ago) and read 34416 times:

Quoting SEPilot (Reply 5):
I do not find it surprising that any radically new design engine should have a couple of hiccupIs; the one that surprised me was the GE90-110/115, which went an extraordinarily long time before the first failure.

GE90-115 had quite a number of in-flight shut downs during its infancy with forced emergency landings. The most famous one was with AF 777-300ER in Siberia.



Now get your f***ing Jumbo Jet off my airport!!! - AC/DC "Ain't No Fun To Be a Millionaire"
User currently offlinemffoda From United States of America, joined Apr 2010, 1109 posts, RR: 0
Reply 30, posted (2 years 3 months 5 days 8 hours ago) and read 33743 times:

Quoting Stitch (Reply 28):
Quoting mffoda (Reply 24):
I may be wrong... But I thought the GEnx-2b has not yet received a PIP.
Quoting KC135TopBoom (Reply 25):
That's what I thought too.

The GEnx2B entered service with the revised LPT that was introduced with PIP1 on the GEnx1B.

I'm not doubting you Stitch...

Its just I can't find anything when I google "GEnx-2b PIP certification"?? The nearest thing regarding the PIP's comes from GE's website.

http://www.geaviation.com/press/genx/genx_20110823.html

Quote:

"August 23, 2011

EVENDALE, OHIO -- GE has received type certification from the U.S Federal Aviation Administration on its Performance Improvement Package (PIP) I for the GEnx-1B engine that will power the Boeing 787 Dreamliner. The Part 33 certification was issued on August 12.

"The entire GEnx team-from the product line to engineering to supply chain--has worked extremely hard on the PIP 1 on the GEnx-1B engine, and I'm proud of their dedication to enhancing the engine's performance for our GEnx customers," said Bill Fitzgerald, vice president and general manager of the GEnx engine program.

The PIP 1 on the GEnx-1B engine includes a redesign of the low pressure turbine airfoils. These enhancements will provide a substantial improvement to the specific fuel consumption (SFC) for the GEnx-1B engine. The first GEnx-1B engines will enter service on the Boeing 787 in the fourth quarter of this year.

Testing is underway on a PIP II on the GEnx-1B engine. The PIP II will include upgrades to the high pressure compressor to bring additional fuel consumption improvements. GE anticipates the PIP II to certify next year with entry into service by early 2013.

GE Aviation is also developing a PIP for the GEnx-2B engine. This package will incorporate elements from the GEnx-1B PIP I and PIP II programs."



Do you have a link I could check out?

Regards,



harder than woodpecker lips...
User currently offlinesweair From Sweden, joined Nov 2011, 1831 posts, RR: 0
Reply 31, posted (2 years 3 months 5 days 3 hours ago) and read 27094 times:

I have a hunch its some sort of metallurgic problem, composition of a certain batch of metal maybe differing from the norm.

User currently online747classic From Netherlands, joined Aug 2009, 2214 posts, RR: 14
Reply 32, posted (2 years 3 months 5 days 1 hour ago) and read 25521 times:

The GEnx-2B (747-8 series) had the low pressure turbine update already from the start. The next and so far the only scheduled update (called PIP) is still being tested and will be certified end 2013.

The GEnx-1B (787) had the low pressure turbine update (and other improvements) with PIP1, that has been certified at June 14 2012. The PIP2 is also not certified yet, but will be certified before the PIP on the GEnx-2B (748) engine.

The question remains : is the low pressure shaft exactly identical on both engine types or is only the design the same.

The core engine (high pressure spool) is identical on both engines.

However the low pressure system is different :

The GEnx-1B (787) engine has a 111 inch fan + 4 stage LPC driven by a 7 stage LPT, max 2778 RPM

The GEnx-2B (748) engine has a 105 inch fan + 3 stage LPC driven by a 6 stage LPT, max 3026 RPM

Here you can see the assembly of a GEnx-2B, at elapsed time 0.27 you can see the low pressure shaft :
http://www.youtube.com/watch?v=sv5C5I67SNA&feature=related

[Edited 2012-09-14 03:16:48]


Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineOzGlobal From France, joined Nov 2004, 2732 posts, RR: 4
Reply 33, posted (2 years 3 months 4 days 23 hours ago) and read 24347 times:

Quoting brilondon (Reply 13):
Quoting JumboJim747 (Reply 2):

It seams more engines are failing lately cauld it be due to higher then normal production and the workers are getting a bit sloppy?

Too many checks and balances for this to be the case. This would be the case if they made the jet engines in one day which I highly doubt.

Really, the A380 Trent 9000 incident was clear poor quality of manufacture and sloppy workmanship.



When all's said and done, there'll be more said than done.
User currently offlineHAWK21M From India, joined Jan 2001, 31702 posts, RR: 56
Reply 34, posted (2 years 3 months 4 days 22 hours ago) and read 23256 times:

Would a month be an ideal time frame to get a detailed investigative report of the snag or would 3 months be more realistic.


Think of the brighter side!
User currently offlineStitch From United States of America, joined Jul 2005, 31375 posts, RR: 85
Reply 35, posted (2 years 3 months 4 days 21 hours ago) and read 21355 times:
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Quoting mffoda (Reply 30):
Its just I can't find anything when I google "GEnx-2b PIP certification"??

As 747classic noted, the GEnx2B had the new LPT from the start - it was not retrofitted via a PIP.


User currently offlinelightsaber From United States of America, joined Jan 2005, 13518 posts, RR: 100
Reply 36, posted (2 years 3 months 4 days 20 hours ago) and read 20360 times:
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Quoting BoeingVista (Reply 27):
Maybe GE stress calculations are just wrong, as you would know in engineering sometimes you get schooled by experience. Unexpected harmonics for example (maybe when setting power?), can raise stresses very quickly

I wouldn't say wrong, I would say a missed assumption such as a harmonic. Changing the number of turbine blades will change the harmonics.

And Rotor Dynamics is *not* an easy science. If the 'designed to fail' join is flexing more than plan, that extra stress will have it fail early.

But I am not privy to the details.

Quoting OzGlobal (Reply 33):
Really, the A380 Trent 9000 incident was clear poor quality of manufacture and sloppy workmanship

   I flare tubing better than what shipped on the Trent 900 and my technicians won't let me flare tubing as their quality is 100X better than mine!

Quoting sweair (Reply 31):
I have a hunch its some sort of metallurgic problem, composition of a certain batch of metal maybe differing from the norm.

Unlikely. GE would be like Pratt and be able to identify while holes out of the ground the metal came from. The part that is failing will have extreme metallurgical control. I suspect either a un-analyzed manufacturing flaw or it is indeed a coating issue.

Quoting 747classic (Reply 32):
The GEnx-1B (787) engine has a 111 inch fan + 4 stage LPC driven by a 7 stage LPT, max 2778 RPM

The GEnx-2B (748) engine has a 105 inch fan + 3 stage LPC driven by a 6 stage LPT, max 3026 RPM

I had forgotten the RPM difference was so high. That makes the failures odd... GE has designed such features before. What did they do wrong this time? I threw out a bunch of cases as we can assume GE had competent engineers and manufacturing control. It is going to be an important detail that adds stress that creates the issue.

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently online747classic From Netherlands, joined Aug 2009, 2214 posts, RR: 14
Reply 37, posted (2 years 3 months 4 days 14 hours ago) and read 17989 times:

NTSB Urgent Recommendation to FAA : Inspect GEnx Fan Mid Shafts Immediately .

See aviation week :

http://www.aviationweek.com/Blogs.as...23f09a-5cc4-4752-a1cc-6bb1d09569bc

And :
http://www.ntsb.gov/doclib/recletters/2012/A-12-052-053.pdf

Highlights :

- The first failure (GEnx-1B) at Charleston was caused by a fractured forward end of the Fan Mid shaft (FMS), that separated at the rear of the threads.

- The fracture was no fatigue cracking.

- Further examination revealed a faceted, quasi-cleavage fracture morphology that is typical of environmentally assisted cracking of certain high strength steel alloys such as that used on the GEnx FMS.

- A second (zero flight hour) GEnx-1B FMS with a fracture was found during engine checks.

- The investigation into the cause of the environmentally assisted cracking that occurred at both fractured FMSs is continuing.

- The damage noted on the photographs of the GEnx-2B (Shanghai) is consistent with that observed on the engine that failed at Charleston.

- The GEnx-1B FMS is slightly longer than that in the -2B engine. However, the threaded end of the FMS; the manner in which it is clamped with the retaining nut and the assembly procedures, material specifications, and operating environment are similar between the two models. Therefore, the FMS in GEnx-2B engines may be susceptible to the same type of failure observed with the GEnX-1B FMS.

- the NTSB recommends that the FAA require operators to accomplish repetitive inspections of the FMS in all (on-wing and spare) GE GEnx-1B and -2B engines at a sufficiently short interval that would permit multiple inspections and the detection of a crack before it could reach critical length and the FMS fractures.

[Edited 2012-09-14 14:58:23]


Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlinecf6ppe From United States of America, joined Mar 2006, 352 posts, RR: 0
Reply 38, posted (2 years 3 months 4 days 13 hours ago) and read 17821 times:

Quoting 747classic (Reply 37):
NTSB Urgent Recommendation to FAA : Inspect GEnx Fan Midshafts Immediately .

See aviation week :

http://www.aviationweek.com/Blogs.as...23f09a-5cc4-4752-a1cc-6bb1d09569bc

And :
http://www.ntsb.gov/doclib/recletters/2012/A-12-052-053.pdf

Thank you for the second link...

Reading the NTSB doc (on a Friday afternoon) brought back memories of Emergency Airworthiness Directives being issued on any given Friday afternoon and my weekend plans being adjusted.

The linked NTSB document fills in quite a few details for the recent 787 at Charleston and now the B748 FMS problems.

Hopefully, GEAE has already talked to the operators and Boeing re: the problem. I always found GE to keep us on the operators side informed and ahead of the game plan.


User currently offlinePW100 From Netherlands, joined Jan 2002, 2581 posts, RR: 13
Reply 39, posted (2 years 3 months 4 days 11 hours ago) and read 17534 times:

Apologies if this is too extensive or in-depth, but this is what I find really fascinating, as a turbine engine nut(case), as some call me . . .. These are the situations aviation will be learning from, and which will make future flight safety so much better!


Quoting 747classic (Reply 37):
NTSB Urgent Recommendation to FAA : Inspect GEnx Fan Mid Shafts Immediately .

And :
http://www.ntsb.gov/doclib/recletters/2012/A-12-052-053.pdf

That is a mighty interesting and a mighty scaring document. Not only do we now have two fractured shafts, destroying two engines in the process (incidentally both a -1 and a -2), it now turns out that there also was a third engine removed from service with a cracked shaft before that actually failed catastrophically. You can bet that this shaft will be under intense investigation.


[speculation mode]

From own experience, the failure described in the above referenced document sounds like a metallurgic problem, with crack initiation embedded inside the parent material.

Typically these type of shafts are produced from a high strength steel. The bearing and flange mating diameters are difficult to produce within the required accuracy of less than 0.0001 in, and still have the material properties required for their tight-fit clearances. So usually nickel based platings are applied as top layers on these critical surfaces.


Nickel plating is applied through a galvanic electroplating process, where the part is submerged in a plating bath. Through a cathode-anode type reaction, the nickel grows on the part to form a thin layer of a nickel based top layer. This layer is then machined to the spec dimensions.

If the nickel plating process is not fully controlled and understood, it could lead to a condition known as "hydrogen embrittlement".

The hydrogen embrittlement phenomena can occur through a couple of different mechanisms:
* extensive time between plating process and post-plating heat treatment, which is required to "fix the loose hydrogen atoms";
* temperature setting at heat treatment too low or too high;
* excessive plating time in plating tank, because of:
* too low current or voltage settings, extending the plating time to grow the plating layer thickness to the required spec;
* plating bath contamination;
* active plating content in bath too low.

What happens is that (excessive) hydrogen atoms embedded in the steel, will work its way out of the matrix (diffuse), and expand in volume. That increases internal stresses in the part, which can increase to such high values, that spontaneous crack initiation starts WITHOUT the part being loaded (i.e. without the engine running). The only thing needed is TIME and (room) temperature.

Depending on very specific deficiencies in process parameters, crack initiation can take a couple of months or upto several years. It's a continuous process that can not really be stopped.
Depending on service time, crack growth can take a coupe of thousands hours or cycles, but can also take as less as ten hours service time.

It could be that these shafts were produced years ago, and sitting idle - even in controlled atmosphere/preserved state - resulted in progressive crack initiation if incorrect process parameters were applied. So now the first time the engine is brought to meaningful power level . . . snap . . .

[/speculation mode]

I would not be surprised if this would result in a grounding order. Even if there was no grounding order, odds are pretty high that all these FMS shafts will get a (mandatory) initial life limit through an AD. And that could be a very limited useful life. Think anywhere between 0 and 1000 cycles.

Rest assured, many people are now working 24/7 to dig into the manufacturing history of ALL FMS shafts produced to date, looking at all imaginable process parameters, from raw material, to plating process parameters, to final machining/grinding specs etct. etc, all to the finest detail.

GE will find the cause and correct it. It could take months, if not longer to come up with a fix. Perhaps many shafts need to be replaced (Been there, seen that. Actually, this is still very much active today on "my" engine type . . . . ).

Rgds,
PW100

Disclaimer: I'm not a metallurgist, so I may be off in some of the process details described above.



Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 40, posted (2 years 3 months 4 days 11 hours ago) and read 17472 times:

Quoting 747classic (Reply 37):
NTSB Urgent Recommendation to FAA : Inspect GEnx Fan Mid Shafts Immediately .

I started a thread that deals with this one issue (that of the NTSB recommendations):

Ntsb Issues Recommendations RE: GEnx Failures (by KELPkid Sep 14 2012 in Civil Aviation)

Just thought I'd let you guys know  



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlinemffoda From United States of America, joined Apr 2010, 1109 posts, RR: 0
Reply 41, posted (2 years 3 months 4 days 8 hours ago) and read 17168 times:

So here is the latest form FG on this matter.

http://www.flightglobal.com/news/art...enx-powered-787-and-747-8s-376525/


"The recommendations issued by the National Transportation Safety Board (NTSB) offer the clearest explanation yet for the rash of zero- or low-time GEnx engine failures since 28 July.

The NTSB letter sent to the Federal Aviation Administration also reveals that an analysis of the fan midshaft fractures do not point to metal fatigue as a likely cause. The fan midshaft connects the low pressure turbine to the fan and booster stages at the forward end of the engine.

Instead, the cracks in the critical engine component are "typical of environmentally assisted cracking of certain high strength alloys such as that used on the GEnx [fan midshaft]", the NTSB letter says. The NTSB is continuing to investigate what is triggering the environmentally assisted cracking. According to GE, such metals crack as a result of galvanic corrosion caused by a moist environment with the presence of hydrogen.

A potential trigger of the galvanic corrision could have been revealed earlier this week. In a statement issued by GE on 11 September, the company said it has changed the coating process for the fan midshaft on the production line as a result of the engine failures. GE says today that the new coating process changes the dry film applied to the midshaft, and replaces the lubricant used when a retaining nut is clamped to the midshaft.

The NTSB's letter to the FAA indicates all three engine failures discovered to date could be linked to the same cause"


edit:

Actually from NTSB, and FG reporting.

[Edited 2012-09-14 19:48:30]


harder than woodpecker lips...
User currently offlineStitch From United States of America, joined Jul 2005, 31375 posts, RR: 85
Reply 42, posted (2 years 3 months 4 days 8 hours ago) and read 17134 times:
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So looks like they know what's causing it and have a fix.

Any idea if the part can be swapped in the field?


User currently offlinemffoda From United States of America, joined Apr 2010, 1109 posts, RR: 0
Reply 43, posted (2 years 3 months 4 days 7 hours ago) and read 17072 times:

Quoting Stitch (Reply 42):
So looks like they know what's causing it and have a fix.

Any idea if the part can be swapped in the field?

Stitch, are you directing that question at me?

Because, I was just outside re-coating a couple of dozen Fan mid-shaft's... but it started to rain. So I'll have to get back you on the field swapping thing. (Sorry couldn't resist)  



harder than woodpecker lips...
User currently offlineBoeingVista From Australia, joined Jan 2009, 1584 posts, RR: 3
Reply 44, posted (2 years 3 months 4 days 6 hours ago) and read 16957 times:

Quoting Stitch (Reply 42):
So looks like they know what's causing it and have a fix.

Any idea if the part can be swapped in the field?

I think its a bit early to say that they have a fix, shafts with the new coating will (should) have to undergo at least as much testing as they devoted to the original process which is now found to be flawed.

I can't see how you would swap out a mid shaft in the field, the entire booster stage seems to be assembled on it.

Two things that could lead to the grounding of the GEnx series are 1) An inspected FMS fails, 2) FMS fails after V1 and aircraft becomes airborne leading inevitably to a high profile incident.

How likely are either of these to happen? Probably 50/50 i'd say.

3) Of course the FAA could just order a grounding but I can't see that at the moment without a further incident.



BV
User currently offlinemffoda From United States of America, joined Apr 2010, 1109 posts, RR: 0
Reply 45, posted (2 years 3 months 4 days 6 hours ago) and read 16908 times:

Quoting BoeingVista (Reply 44):
I think its a bit early to say that they have a fix, shafts with the new coating will (should) have to undergo at least as much testing as they devoted to the original process which is now found to be flawed.

This sounds very similar to the Trent1000 gearbox issue regarding corrosion in some crown gears. Granted not in the same location, but the new coating process seemed to be easily handed without much disruption? Why would think this process has to go though more testing then the Trent's had to?



harder than woodpecker lips...
User currently offlineBoeingVista From Australia, joined Jan 2009, 1584 posts, RR: 3
Reply 46, posted (2 years 3 months 4 days 5 hours ago) and read 16849 times:

Quoting mffoda (Reply 45):
This sounds very similar to the Trent1000 gearbox issue regarding corrosion in some crown gears. Granted not in the same location, but the new coating process seemed to be easily handed without much disruption? Why would think this process has to go though more testing then the Trent's had to?

I think that the Trent issue was flakes of coating departing from gears, here we have a totally different issue which appears to be "hydrogen" induced cracking of the actual material.

Other obvious differences would be operating environment, temperature, stresses, materials and the fact that the component failed losing integrity.. Do GE want to be back in the same place in 6 months when the new process also proves to be less than optimum?

These 2 issues are totally different.

Rereading the NTSB bulletin, they may be hinting they are moving towards GEnx grounding or at least revoking ETOPS

Quote:
Because of the short time to failure and the fact that all of the engines on any single airplane, whether the 787 or the 747-8, have all operated for the same period of time, the NTSB is not only concerned about the potential for further fractures occurring, but also the possibility that multiple engines on the same airplane could experience an FMS failure. Although the FMS fracture that occurred on the 787 at Charleston and the incident that occurred on the 747-8 at Shanghai both happened on the runway and the pilots were able, respectively, to abort the test and the takeoff, the NTSB is concerned about the possibility of an FMS fracture occurring in flight at the limits of an airplane’s extended twin-engine overwater operations, or ETOPS,5 range and the airplane having to operate with one engine inoperative for up to 5 1/2 hours.

Is a pretty strong hint that they are not at all happy about this situation



BV
User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 47, posted (2 years 3 months 4 days 3 hours ago) and read 16673 times:

Quoting BoeingVista (Reply 46):
Is a pretty strong hint that they are not at all happy about this situation

After reading the NTSB letter I can understand them, the ultrasound method that GE has developed can detect cracks which has grown to 0.05 inch. That means an unknown number of engines operate with cracks which are smaller then that (the Hydrogen corrosion as described by PW100 develops a multitude of cracks at the end of the thread).

Now that would not be such a big problem if it was not for this part of the message:

"In addition, the nature of the cracking that was noted on the FMS from ESNs 956-121 and 956-175 did not provide a predictable crack propagation rate that a typical fatigue crack would have. The NTSB believes that repetitive inspections are necessary to ensure that, once an initial inspection has been performed, new or sub-detection-level cracks do not propagate and cause additional failures. Therefore, the NTSB recommends that the FAA require operators to accomplish repetitive inspections of the FMS in all (on-wing and spare) GE GEnx-1B and -2B engines at a sufficiently short interval that would permit multiple inspections and the detection of a crack before it could reach critical length and the FMS fractures."

It seems to be difficult to predict how fast those less then 0.05 inch cracks, which will go undetected, will grown and start to endanger the engines integrity. They say "sufficiently short intervals", that must mean they have at least an hypothesis about the max crack propagation speed, otherwise we would have seen immediate grounding of all GEnx. When the first engine appear which have visible cracks that are longer then this assumed speed there is mega trouble (real trouble is already present   ), let's hope this does not happen.

About the crack propagation speed, if I understand PW100 right we are talking calender time rather then cycles for this phenomenon (which I had not heard of before, I know about stress corrosion, galvanic ....., but not this one).

BTW, this is not comparable to the T1000 issue, IMO ANA grounded their fleet for very little reason, the gearboxes had "a potential long-term problem" with no in field incidents. Here we have 2 on wing engines turning into windmills and one more being on the way + any number in the process of developing over time dangerous cracks in one of the engines critical parts.

[Edited 2012-09-15 00:32:03]


Non French in France
User currently offlinePW100 From Netherlands, joined Jan 2002, 2581 posts, RR: 13
Reply 48, posted (2 years 3 months 4 days 3 hours ago) and read 16501 times:

Quoting ferpe (Reply 47):
About the crack propagation speed, if I understand PW100 right we are talking rather calendar time then cycles for this phenomenon

Correct. The running time of the engine is unrelated to crack initiation.

It appears that we have to distinguish two phenomena: crack initiation, and crack growth. Although they may have the same effect, I see it as that the crack initiation is the starter phenomena, due to the hydrogen embrittlement as described in my earlier post.
Crack growth, is the result of loads and stressed on the part as a result of regular operation.

The shaft has considerable safety margins, and a small crack will not allow the shaft to fail. I have seen shafts of "my" engine type with cracks running around the circumference for over 120 degrees where the shaft did not fail (yet).
The problem is that the crack initiation phenomena, if undetected, can grow significantly over calendar time, even if the engine is not operating. The crack initiation is dependent on many process variables that are very hard, if not impossible to predict. Also multiple crack initiations may be present, making any effort on failure prediction even harder.

Quoting ferpe (Reply 47):
BTW, this is not comparable to the T1000 issue, IMO ANA grounded their fleet for very little reason, the gearboxes had "a potential long-term problem" with no in field incidents. Here we have 2 on wing engines turning into windmills and one more being on the way + any number in the process of developing over time dangerous cracks in one of the engines critical parts

Agree. The T1000 was indeed a long term problem. This GEnX is completely different from nature, and can not be predicted. And therefore your observation is spot on:

Quoting ferpe (Reply 47):
Now that would not be such a big problem if it was not for this part of the message:
Quoting BoeingVista (Reply 44):
Of course the FAA could just order a grounding but I can't see that at the moment without a further incident.

You mean three cracked shafts - including two catastrophic failures - in a four-week time span on a newly introduced engine with only a limited number of engines in operation is not enough? How many more incidents do you need? You rather want to wait until a 787 comes down with two failed shafts? In this business GE can consider them extremely lucky to have as much as three significant warnings.

Quoting Stitch (Reply 42):
So looks like they know what's causing it and have a fix.

I would expect that at minimum all shafts with the old process coating must be replaced. This could affect 100 - 200 engines. Don't be surprised if they get a hard life-limit of say six months, maybe a year. In the meantime, repetitive ultrasonic inspections would be required at intervals as short as one month.

Quoting Stitch (Reply 42):
Any idea if the part can be swapped in the field?

Although I have no experience at all with large GE engines, I would be very surprised if such an important part, embedded very deep in the engine could be changed in the field. It smells to me as engine shop level work.
I would also expect that as a FOM (Follow Up Maintenance) a test cell run would be required after replacement of the shaft to verify dynamic vibrations, rated performance, and make sure no internal oil leaks are present (you have to expose main bearings, and thus bearing cavities to replace the shaft).

PW100



Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
User currently offlinegoosebayguy From United Kingdom, joined Sep 2009, 415 posts, RR: 0
Reply 49, posted (2 years 3 months 4 days 2 hours ago) and read 16488 times:

No chance of ETOPs for a while here.

User currently offlineBoeingVista From Australia, joined Jan 2009, 1584 posts, RR: 3
Reply 50, posted (2 years 3 months 4 days 2 hours ago) and read 16438 times:

Quoting PW100 (Reply 48):
You mean three cracked shafts - including two catastrophic failures - in a four-week time span on a newly introduced engine with only a limited number of engines in operation is not enough? How many more incidents do you need? You rather want to wait until a 787 comes down with two failed shafts? In this business GE can consider them extremely lucky to have as much as three significant warnings.

I agree that 3 incidents should be enough for the FAA to do something but they seem to be taking the weekend off, they have even ordered the inspections recommended by the NTSB. With the type of crack initiation and propagation suggested it doesn't take a genius to see a scenario where you lose an engine at V1, and then have to TOGA another one and snap another FMS clearly this is a problem even with a 4 engined aircraft let alone a 2 engined aircraft and you have a very heavy glider transitioning into a large crater.

I see very serious questions here and am most surprised that more people are not asking them.

The more you think about what we know of these failures the more scary what we do not know becomes (non detected cracks, propagation rates); from a risk management perspective you have to wonder if this situation should not lead to an immediate GEnx grounding, but it wont until something fatal happens.

[Edited 2012-09-15 01:56:52]


BV
User currently offlinesweair From Sweden, joined Nov 2011, 1831 posts, RR: 0
Reply 51, posted (2 years 3 months 4 days 2 hours ago) and read 16370 times:

I may not have been wrong about it being a metallurgical issue, this is advanced stuff and on the nano level, chrystal forms and particle alignments etc

There are numerous metallurgical failures in history with grave consequences, Titanic being one very famous one, ok that was part metallurgic.

Though I am surprised that this was not caught during the exhaustive testing of today. Back to the metal lab GE!

I guess future engine certification will become even tougher?


User currently online747classic From Netherlands, joined Aug 2009, 2214 posts, RR: 14
Reply 52, posted (2 years 3 months 4 days 2 hours ago) and read 16418 times:

Quoting BoeingVista (Reply 46):
Rereading the NTSB bulletin, they may be hinting they are moving towards GEnx grounding or at least revoking ETOPS

According the rules : If ExTended OPerationS (ETOPS) is revoked for all GEnx powered aircraft, operated under part 121 and 135 :

- The 787/GE will be far the most affected (back to 60 minutes )

- The 747-8I will go back to 180 minutes.

- The 747-8F will NOT be affected (exempted, because more than 2 engines installed and cargo only)

Are above mentioned implications correct ?

[Edited 2012-09-15 02:07:02]


Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlinesweair From Sweden, joined Nov 2011, 1831 posts, RR: 0
Reply 53, posted (2 years 3 months 4 days ago) and read 16220 times:

How would RR follow this? If something like this happens do competitors follow closely and check their own gear? I can imagine materials and some parts being used by both GE and RR?

Coatings and corrosion causing problems for both, it seems that way?


User currently offlineBoeingVista From Australia, joined Jan 2009, 1584 posts, RR: 3
Reply 54, posted (2 years 3 months 4 days ago) and read 16205 times:

Quoting sweair (Reply 53):
How would RR follow this? If something like this happens do competitors follow closely and check their own gear? I can imagine materials and some parts being used by both GE and RR?

You know I wouldn't think that they were that similar because all of the parts and materials are propriety and most probably under patents. Shaft assembly is most likely different too as GE is 2 shaft and RR is 3.

But I imagine that rival manufacturers recheck areas that competitors have trouble with, the most (in)famous example of this being the Airbus 787 dossier.



BV
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 55, posted (2 years 3 months 3 days 22 hours ago) and read 15863 times:

Quoting BoeingVista (Reply 46):
Rereading the NTSB bulletin, they may be hinting they are moving towards GEnx grounding or at least revoking ETOPS

The NTSB can't do either of those things. The NTSB can only recomment; the FAA is the one who has to take action.

Quoting ferpe (Reply 47):
About the crack propagation speed, if I understand PW100 right we are talking calender time rather then cycles for this phenomenon (which I had not heard of before, I know about stress corrosion, galvanic ....., but not this one).

It will be both. Environmental cracking typically goes with calendar time but is highly temperature sensitive, which will couple it in to engine operating time as well. In addition, crack growth once a crack is initiated is mostly a cycle phenomenon.

Quoting PW100 (Reply 48):
You mean three cracked shafts - including two catastrophic failures - in a four-week time span on a newly introduced engine with only a limited number of engines in operation is not enough?

How are you defining "catastrophic failure"? There are lots of failure modes that will shut down an engine. I agree this is spectacular but, in terms of system-level safety, it's no better or worse than, say, a fuel pump failure.

Quoting PW100 (Reply 48):
I would expect that at minimum all shafts with the old process coating must be replaced. This could affect 100 - 200 engines. Don't be surprised if they get a hard life-limit of say six months, maybe a year.

Not gonna happen. GE doesn't have the capacity to inject 100-200 additional engines into the fleet in 6 months. They will find some kind of interim mitigation (probably inspection + treatment) to protect the affected engines.

Quoting PW100 (Reply 48):
In the meantime, repetitive ultrasonic inspections would be required at intervals as short as one month.

One month inspections wouldn't be much of a burden; lots of other existing maintenance tasks happen far more frequently. If they can get away with a monthly ultrasound they should consider themselves very lucky.

Quoting goosebayguy (Reply 49):

No chance of ETOPs for a while here.

It's all about probabilities. If they develop an inspection criteria that keeps the risk of failure between inspections at an acceptable level there's no reason to pull ETOPS.

Quoting BoeingVista (Reply 50):
The more you think about what we know of these failures the more scary what we do not know becomes (non detected cracks, propagation rates);

Non-detected cracks are normal, expected, and planned for. That's the entire point of damage tolerant design. It's the propagation rate that's screwing things up here. That's likely to be due to a a crack initiation mode they didn't expect at that location, rather than a flat-out unknown mechanism.

Tom.


User currently offlineBoeingVista From Australia, joined Jan 2009, 1584 posts, RR: 3
Reply 56, posted (2 years 3 months 3 days 21 hours ago) and read 15804 times:

Quoting tdscanuck (Reply 55):

The NTSB can't do either of those things. The NTSB can only recomment; the FAA is the one who has to take action.

Yes, true and here's the thing, the NTSB have recommended that these engines are inspected before they are allowed to fly and the FAA has remained silent hence presumably these aircraft are merrily flying across the globe. Is it usual for an urgent recommendation from the NTSB to be ignored by the FAA.

Quoting tdscanuck (Reply 55):
Non-detected cracks are normal, expected, and planned for. That's the entire point of damage tolerant design. It's the propagation rate that's screwing things up here. That's likely to be due to a a crack initiation mode they didn't expect at that location, rather than a flat-out unknown mechanism.

Your statement is contradictory, if they didn't expect it it can hardly be described as normal, nor can the failures be described as planned for especially on 2 units that had never even flown! It may not be an unknown mechanism but it cannot be said to be understood at this point.



BV
User currently offlineStitch From United States of America, joined Jul 2005, 31375 posts, RR: 85
Reply 57, posted (2 years 3 months 3 days 21 hours ago) and read 15788 times:
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Quoting BoeingVista (Reply 56):
Is it usual for an urgent recommendation from the NTSB to be ignored by the FAA.

It's not unheard of. The FAA has dual mandates - both to protect US aviation and to promote it. So calling for a grounding of the GEnx is going to impact GE and Boeing (Boeing has 14 787-8s preparing for delivery with GEnx power and five more under construction, plus the 747-8).

That being said, the FAA is not going to want to risk a hull loss, so I expect they'll mandate tighter inspections in the interim while working with GE on a permanent fix and engine swap program.


User currently offlinekanban From United States of America, joined Jan 2008, 3839 posts, RR: 27
Reply 58, posted (2 years 3 months 3 days 20 hours ago) and read 15645 times:
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I suspect that one of the reasons this didn't show up earlier was GE having too much inventory manufactured head of time that sat on shelves quietly cracking. They may be able to isolate by serial number shafts from those production runs and by addressing those for first replacement, allowing a longer time for fleet change out... on the other hand, the situation causing the embrittlement may have covered many more production lots and still be present today. You can bet all the plating parameter logs are being gone over.

this is similar to a 747 landing gear issue 30 years ago where several lots of axles suffered hydrogen embrittlement (a few snapped).. as I recall it was a faulty temp controller during chrome plating..


User currently offlinePW100 From Netherlands, joined Jan 2002, 2581 posts, RR: 13
Reply 59, posted (2 years 3 months 3 days 19 hours ago) and read 15519 times:

Quoting tdscanuck (Reply 55):
How are you defining "catastrophic failure"? There are lots of failure modes that will shut down an engine. I agree this is spectacular but, in terms of system-level safety, it's no better or worse than, say, a fuel pump failure

That should read catastrophic in terms of engine destruction, not at airframe level. Sorry for not being more clear.

Quoting tdscanuck (Reply 55):
. . . in terms of system-level safety, it's no better or worse than, say, a fuel pump failure

I'm not sure if I agree with this. Failures of this magnitude at full power have an inherent level of uncertainty with them, which may not always be fully understood for the simple reason it is almost impossible to test at airframe level. If I was on board in flight, and I must choose, I'm pretty sure which one to choose . . . .

Quoting tdscanuck (Reply 55):
One month inspections wouldn't be much of a burden; lots of other existing maintenance tasks happen far more frequently. If they can get away with a monthly ultrasound they should consider themselves very lucky.

I do hope that is the case.
However an ultrasonic inspection is by no means straight forward. Aside from accessibility of the part (does it require partial engine disassembly?), main problem is that for a suitable ultrasonic inspection, one needs (a set of) exactly the same type of component(s) (FMS in this case), or at least a meaningful relevant section of subject component. This sample component needs to have pre-calibrated cracks, which are then used to bench mark the ultrasonic reading from the component that is being inspected. You can’t just stick an ultrasonic probe in there and judge a reading off a scope without in-situ system calibration/bench marking. It just doesn't work like that.

For GE, to produce these calibrated sample shafts and get them out to the field in any meaningful numbers (as required for repetitive ultrasonic inspections) in a short time frame is going to be very challenging. In this respect, one month is considered very short.

Rgds,
PW100



Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 60, posted (2 years 3 months 3 days 18 hours ago) and read 15341 times:

Quoting BoeingVista (Reply 56):
Is it usual for an urgent recommendation from the NTSB to be ignored by the FAA.

Not particularly. The NTSB, properly, has only one mandate: find out what happened and determine what you'd do to prevent it happening again. They have no obligation (on purpose) to assess feasibility of those corrective actions. The FAA is responsible for if/how to implement any NTSB recommendations. Lots of NTSB recommendations never happen because they're massively uneconomical.

Quoting BoeingVista (Reply 56):
Your statement is contradictory, if they didn't expect it it can hardly be described as normal, nor can the failures be described as planned for especially on 2 units that had never even flown!

No, it's not contradictory. They expected cracks. That's how damage tolerance works. They used an inspection process that could reliably pick up cracks >= 0.05". You assume that you have cracks smaller than that, then use you fracture mechanics to figure out how those cracks will grow. You design the part so that there's a gap between the critical crack length and the detectable crack length. Then you set the inspection interval or life limit so that a crack that was just below 0.05" when you did the first inspection will be above 0.05" (detectable) but below the critical length by the next inspection. Thus you expect to pick up growing cracks before they become problems.

This all depends on proper understanding of crack initiation and growth. If they have a crack initiation mechanism they didn't expect then the growth rates will be all screwed up and the actual interval for a crack to reach critical length will be shorter than the life limit/inspection interval.

Quoting PW100 (Reply 59):
Quoting tdscanuck (Reply 55):
. . . in terms of system-level safety, it's no better or worse than, say, a fuel pump failure

I'm not sure if I agree with this. Failures of this magnitude at full power have an inherent level of uncertainty with them

Well, GE did design this feature in specifically to prevent a rotor burst in the event of a shaft failure, so in some ways it's doing its job. None of the failures have been uncontained or damaged the airframe. Not that you want the failure in the first place, but it sure looks like their containment strategy is working.

Tom.


User currently offlinelightsaber From United States of America, joined Jan 2005, 13518 posts, RR: 100
Reply 61, posted (2 years 3 months 3 days 17 hours ago) and read 15238 times:
Support Airliners.net - become a First Class Member!

Quoting 747classic (Reply 37):
NTSB Urgent Recommendation to FAA : Inspect GEnx Fan Mid Shafts Immediately .

I think we can agree that is required. I would think the insurance companies wouldn't ignore this one!

Quoting 747classic (Reply 37):
- The investigation into the cause of the environmentally assisted cracking that occurred at both fractured FMSs is continuing.

- The damage noted on the photographs of the GEnx-2B (Shanghai) is consistent with that observed on the engine that failed at Charleston.

Ruh roh. Not a warm fuzzy feeling.

Quoting 747classic (Reply 37):
http://www.ntsb.gov/doclib/recletters/2012/A-12-052-053.pdf

I see I'm not the only one reading that to suspect ETOPS 330 until this is resolved to the FAA's satisfaction.

Quoting BoeingVista (Reply 46):
Rereading the NTSB bulletin, they may be hinting they are moving towards GEnx grounding or at least revoking ETOPS

I doubt grounding. Certainly the inspection interval for ETOPS will be... a pain in the arse.

ETOPS 180 is still possible, just with expensive inspections. GE had better find a way to ensure crack free shafts ASAP. Yes, I'm aware everything is designed to have the unavoidable 0.005" cracks. GE has a part too sensitive to cracks. I wonder how much is how the nut is forced onto the shaft?

Quoting ferpe (Reply 47):
That means an unknown number of engines operate with cracks which are smaller then that

  

Quoting PW100 (Reply 48):
You mean three cracked shafts - including two catastrophic failures - in a four-week time span on a newly introduced engine with only a limited number of engines in operation is not enough? How many more incidents do you need? You rather want to wait until a 787 comes down with two failed shafts? In this business GE can consider them extremely lucky to have as much as three significant warnings.

GE has been lucky. They have a wide spread problem.

Quoting kanban (Reply 58):

I suspect that one of the reasons this didn't show up earlier was GE having too much inventory manufactured head of time that sat on shelves quietly cracking.

They violated lean production.   A big part of lean is to find issue quickly before they go out in numbers.

I wonder if this is why QR was holding off 787 deliveries?   

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlineqantasguy From United States of America, joined Oct 2003, 164 posts, RR: 0
Reply 62, posted (2 years 3 months 3 days 17 hours ago) and read 15241 times:

Those of us old enough may remember the teething problems with the JT9 on the first 747s. Multiple failures and even a bent shaft. There was also an "Ovalization" issue too until there were braces fitted. IIRC.


Airplanes Flown on..B-727-100, B-727-200, DC-9, F-27, B-707, B-717, B-737, B-747SP, B-747-100, B-747-200, B-747-300, B74
User currently offlineRevelation From United States of America, joined Feb 2005, 12920 posts, RR: 25
Reply 63, posted (2 years 3 months 3 days 14 hours ago) and read 14943 times:

Quoting Stitch (Reply 57):
The FAA has dual mandates - both to protect US aviation and to promote it.

According to http://www.eaa.org/govt/default_Mar_2011.asp that is no longer true:

Quote:

following the ValuJet 592 accident, and a subsequent perceived lack of oversight of the airlines by the FAA, Congress eliminated the FAA’s dual mandate and focused its charter solely on safety.



Inspiration, move me brightly!
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 64, posted (2 years 3 months 3 days 14 hours ago) and read 14957 times:

Quoting Revelation (Reply 63):

Quoting Stitch (Reply 57):
The FAA has dual mandates - both to protect US aviation and to promote it.

According to http://www.eaa.org/govt/default_Mar_2011.asp that is no longer true:

According to the FAA as of about 2 minutes ago:
"Our mission is to provide the safest, most efficient aerospace system in the world."
http://www.faa.gov/about/

The dual mission is now safety + efficiency.

Tom.


User currently offlineDaysleeper From UK - England, joined Dec 2009, 873 posts, RR: 1
Reply 65, posted (2 years 3 months 3 days 14 hours ago) and read 14886 times:

Quoting tdscanuck (Reply 64):

According to the FAA as of about 2 minutes ago:
"Our mission is to provide the safest, most efficient aerospace system in the world."
http://www.faa.gov/about/

The dual mission is now safety + efficiency.

I wonder what they mean exactly by "efficient" - For instance, if they did happen to learn of a serious problem with a US Airline, but fixing it would effect it's "efficiency" of operation then they would have exactly the same conflict of interest as before.


Why can't their mission be just to provide the safest aerospace system in the world?


Same crap, new name......


User currently offlinericknroll From Afghanistan, joined Jan 2012, 896 posts, RR: 0
Reply 66, posted (2 years 3 months 3 days 13 hours ago) and read 14752 times:

Quoting BoeingVista (Reply 56):
Yes, true and here's the thing, the NTSB have recommended that these engines are inspected before they are allowed to fly and the FAA has remained silent hence presumably these aircraft are merrily flying across the globe. Is it usual for an urgent recommendation from the NTSB to be ignored by the FAA.

According to Ben Sandilands "A broader issue arising from the urgent alert (which has the same legal liability effect as an order to comply) is its potential to prevent the engines from being 180 minutes ETOPS certified on delivery."

That is, from an insurance point of view, NTSB have to be complied with even without an FAA directive. Is that true?


User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 67, posted (2 years 3 months 3 days 13 hours ago) and read 14753 times:

Re the ultrasound measurement method, according to NTSB GE have now measured through all engines except some freighter ones. This is in some 6 weeks or less as they had to understand the problem and develop the method.

IMO they can't have to much dis-assembly to do in such a case.

- Is it so that they can stick the probe into the hollow axle from the front, by taking of the fan spinner and get axcess to the FMS, then slide the probe to the location of the thread?

- If not, how to they get access without taking of the fan case and the booster case? When you later mount these 2 cases and rotating parts I would imagine you would have to check the balance and as PW100 says to a check run. This can not be done on premise, it must be done at an MRO shop? I can not imagine that GE has achieved that for all running pax 787 and 748 GEnx in the 4 weeks available.



Non French in France
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 68, posted (2 years 3 months 3 days 11 hours ago) and read 14587 times:

Quoting Daysleeper (Reply 65):
I wonder what they mean exactly by "efficient"

They basically mean "acceptable trade between safety and cost." It drives most people nuts to think about, but that's how the whole industry actually works.

Quoting Daysleeper (Reply 65):
For instance, if they did happen to learn of a serious problem with a US Airline, but fixing it would effect it's "efficiency" of operation then they would have exactly the same conflict of interest as before.

They'll always hew to the side of safety. If it's actually a serious problem the safety exposure will be so large that it will always trump the economic cost.

Quoting Daysleeper (Reply 65):
Why can't their mission be just to provide the safest aerospace system in the world?

Because then we'd never fly. The only way to be completely safe in aviation is to never takeoff. Slight more this side of reality, if we didn't accept any statistical level of risk at all, air travel would be so expensive that nobody would do it.

Quoting ricknroll (Reply 66):
That is, from an insurance point of view, NTSB have to be complied with even without an FAA directive. Is that true?

That's between the airlines and their insurance companies. The NTSB can't legally force the airlines to alter their operations.

Quoting ferpe (Reply 67):
- If not, how to they get access without taking of the fan case and the booster case? When you later mount these 2 cases and rotating parts I would imagine you would have to check the balance and as PW100 says to a check run. This can not be done on premise, it must be done at an MRO shop?

You generally go in through the inspection plugs (small threaded holes all along the case), possibly down the tower shaft in this case. As long as you didn't alter the physical structure of the rotating parts in the process of the inspection then you shouldn't have to do a balance run. You can do a normal leak check & run anywhere without an MRO.

Tom.


User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 69, posted (2 years 3 months 3 days 5 hours ago) and read 14134 times:

Quoting tdscanuck (Reply 68):
You generally go in through the inspection plugs (small threaded holes all along the case), possibly down the tower shaft in this case.

What do you mean with the tower shaft? The shaft picking up the power to the gearbox?

I found a picture that I think is accurate, it is from a 3D animator called Mike James who modeled the 787 and got a good cut-through picture from GE apparantly from which he could model the GEnx:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/genx_inner_shaft_with_break_point800x450.jpg

If I have understood things right the Forward Middle shaft (FMS) is the part of the inner axle going forward from the forward bearing box (shown in the picture as the constrained area of the axle) and tying the LPT to the FAN/booster with the nut at the forward end. In that case my arrow shows where the cracks start. This is pretty much at inside the booster stage with variable guide wane stators and what have you, not ideal for access to the shaft. Given that the nut is just behind the spinner, would it be easier to get to it from the front? Here also a cut-through that has been shown before with the FMS marked:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/hiw_genx_1600_w_arrow.jpg

Now the interesting part is how GE designed the shaft axial and lateral fixture, the forward bearing box contains an axial bearing which then only fixes the shaft in the forward direction, the aft direction is then free to move the distance it takes the LPT to reach it's stator (to stop overrevs if the shaft goes). I guess there must be some aft fixing but this gets to a breakout force when the LPT is running, otherwise how to they stop the shaft from moving aft when idle?

Someone in the know should enlighten us (at least me  )

Edit: At more brain usage one could envision that only the aft bearing box does the axial fixing, the flanges on the shaft should denote that I guess. Anway, how do you get the axial aft play when you want it (when the axle goes) but not in normal wear and tear?

[Edited 2012-09-15 23:13:19]


Non French in France
User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 70, posted (2 years 3 months 3 days 1 hour ago) and read 13799 times:

There are others that have found the shaft in isolation:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/LPshaft.jpg

I guess it is called the middle fan shaft as there is a part going on it aft of the LPT mounting flare extending to the aft of the engine. But this is the interesting part of the total shaft (some 80-90% of it).

And finally here a picture of the fan rotating hub being inserted into the fan case from the GEnx assembly video. One can see the nut and as a dark part inside the nut the shaft. Only the spinner comes on top of this part, the fan blades gets fitted in the groves/seats of the rotating hub:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/GEnxclampingnut.jpg

This is a test engine, one can see 4 cables going out to the fan blade seats, most likely to measure the forces in these.

[Edited 2012-09-16 03:22:34]


Non French in France
User currently offlineBoeingVista From Australia, joined Jan 2009, 1584 posts, RR: 3
Reply 71, posted (2 years 3 months 3 days ago) and read 13713 times:

Quoting ferpe (Reply 69):
If I have understood things right the Forward Middle shaft (FMS) is the part of the inner axle going forward from the forward bearing box (shown in the picture as the constrained area of the axle) and tying the LPT to the FAN/booster with the nut at the forward end. In that case my arrow shows where the cracks start.

I think that your red arrow is in the wrong place, the nut and FMS join point is the front taper parallel with the LP fan stators probably 1m into the engine.



BV
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 72, posted (2 years 3 months 2 days 21 hours ago) and read 13407 times:

Quoting ferpe (Reply 69):
What do you mean with the tower shaft? The shaft picking up the power to the gearbox?

Yes.

Quoting ferpe (Reply 69):
Anway, how do you get the axial aft play when you want it (when the axle goes) but not in normal wear and tear?

I think the forward bearing provides forward and aft restraint; when the axle goes the turbine is free to move forward or back in a mechanical sense but the pressure gradient in the engine will drive it backwards.

Tom.


User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 73, posted (2 years 3 months 2 days 21 hours ago) and read 13373 times:

Quoting BoeingVista (Reply 71):
I think that your red arrow is in the wrong place, the nut and FMS join point is the front taper parallel with the LP fan stators probably 1m into the engine.

Might very well be but then the second picture group is wrong as well (I did not make that, found it on the internet). As I understand it there is only one retaining "nut" on this whole shaft, it is the one at the front securing the fan onto the splines you see clearly in the second post. The shaft IMO has 2 parts, they can also be seen in the exploded view as the front of the middle shaft, which is shown as a stub where I have the blue arrow (also what the original poster of this picture pointed out, dunno if it was PW100) and then you can see the end of this shaft as the trumped like flare just in front of the LPT assemebly, the aft part of the shaft is the axle underneath the explanation "exhaust nozzle". The shaft parts are joined with integral threaded parts IMO, no nuts there.

In the assembly video one has to understand GE has threaded a long stub axle onto the front threads (dark blue, probably for alignment of the high-pressure core + booster/fan during the assembly) onto which the high pressure core/booster/fan is threaded before being pushed onto the mid shaft. This is later removed and the nut is securing the fan/booster rotor onto the axle splines. Thus the nut is carrying the fan loads if the axle splined part is not an interference fit (it is probably a conical fit for centricity).



Non French in France
User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 74, posted (2 years 3 months 2 days 20 hours ago) and read 13354 times:

Quoting tdscanuck (Reply 72):
I think the forward bearing provides forward and aft restraint; when the axle goes the turbine is free to move forward or back in a mechanical sense but the pressure gradient in the engine will drive it backwards.

That would require the axial bearing to be in front of the shaft failure, I think the bearing is behind. It is sitting on the area with the changed dia just aft of the blue lifting band in post 70. The failure is shown to be in front of that (right or wrong, not my arrow but I happen to concur  ).

Re the gearbox pickup seems to be from fornt of the high-pressure spool, then it is a bit far back for reaching this threaded area (once again if it the right one).



Non French in France
User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 75, posted (2 years 3 months 2 days 20 hours ago) and read 13316 times:

I think we might be mislead by the NTSB/GE nomenclature and the assembly video. NTSB talk of a Fan Midshaft (FMS) failure, IMO this stand for the engine middle shaft (low pressure spool) as opposed to the outer (high pressure spool) or whatever they call that one. But it can also be so that they really mean the middle part of the total shaft, in that case the count the inner part of the fan/booster hub as a shaft and it is indeed the middle part of 1. fan/booster part. 2. middle part all the way to the LPT. 3 aft part rear or the LPT trumpet flare.

Furher, the video shows a very long shaft sticking out from the LPT assembly (actually longer then the engine IMO). As said I think this is the middle shaft with an extra fit shaft threaded onto it.

If the above should be the case the front of the fan middle shaft is then also the point where the middle shaft transmits the LPT torque to the larger dia fan/booster shaft via splines and a retaining nut.

[Edited 2012-09-16 07:33:16]


Non French in France
User currently offlineTristarsteve From Sweden, joined Nov 2005, 4064 posts, RR: 33
Reply 76, posted (2 years 3 months 2 days 18 hours ago) and read 13138 times:

Quoting ferpe (Reply 67):
- If not, how to they get access without taking of the fan case and the booster case? When you later mount these 2 cases and rotating parts I would imagine you would have to check the balance and as PW100 says to a check run. This can not be done on premise, it must be done at an MRO shop?

Not always.
In 1980 I worked for a Tristar operator with RB211-524 engines.
We had a small engine shop who changed the 04 (HP comp and turbine) and the
05 (LP turbine) modules. We then fitted the engine to an aircraft and did the full sequence of engine tests on wing. In usually worked well and we had few test failures. We carried out test 1 to 17, but not in that order, and if all went well I could get the engine serviceable after about 40 mins on the run bay.

Our small engine shop was about the size of a garage for two lorries, and 6 guys worked in there!


User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 77, posted (2 years 3 months 2 days 17 hours ago) and read 13205 times:

So, think I've cracked it, we are all correct (except for the 3D artist but then what do you expect   ).

The LP spool "shaft" from front to back is divided into 3 parts, one of these does not look like a shaft but like a cone, the forward part. One can see the principle here (from a GEnx presentation flash video):



The middle shaft connects to the back end of the fan/booster rotation part, the inner part of that is shaped like a flared cone. Now come the part where Tom was right, the LP spool front bearing is placed at the back end of this cone, see this split view of the parts:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/hiw_genx_1600_zoom.jpg

As the front bearing is part of the booster+fan cone and the thread+spline midshaft front goes inside this and get locked with the nut, when the shaft goes the middle and aft part of the shaft can move aft if the only axial+lateral bearing is placed on the cone. What confused me was that the ball bearing for the high pressure spool is just behind this section, I though both spools had their forward bearing there.

So the axle in post 70 is indeed the one and the thread is the cracking one  Wow! . It is also the last part looking like an axle, connecting to the booster/fan conical innards. It is also the FMS nut one can see from the front but it is at arm-lengths recess at the cones end   .

Given that the fracture place is in front of the splines and these grid into the rear part of the cone I only think you can check the part from the front without dissambling the propulsor from the fan case and then the fan+booster stage from the high pressure spool. You would then also dissasamble the nut and expose the thread, you might as well use non ultrasound methods for crack-searching then.

[Edited 2012-09-16 11:51:46]


Non French in France
User currently offlineBoeingVista From Australia, joined Jan 2009, 1584 posts, RR: 3
Reply 78, posted (2 years 3 months 2 days 9 hours ago) and read 12630 times:

Quoting ferpe (Reply 73):
The shaft IMO has 2 parts, they can also be seen in the exploded view as the front of the middle shaft, which is shown as a stub where I have the blue arrow (also what the original poster of this picture pointed out, dunno if it was PW100) and then you can see the end of this shaft as the trumped like flare just in front of the LPT assemebly

That would be me that posted the original  
Quoting ferpe (Reply 77):
As the front bearing is part of the booster+fan cone and the thread+spline midshaft front goes inside this and get locked with the nut, when the shaft goes the middle and aft part of the shaft can move aft if the only axial+lateral bearing is placed on the cone.

Yup, what he said!

Quoting ferpe (Reply 77):
It is also the FMS nut one can see from the front but it is at arm-lengths recess at the cones end

Yeah about 1m in straight down the middle access would seem to be reasonable, presumably the shaft end is not capped.

Big version: Width: 389 Height: 455 File size: 63kb


This is a GEnx-2b

[Edited 2012-09-16 18:24:27]


BV
User currently offlinecf6ppe From United States of America, joined Mar 2006, 352 posts, RR: 0
Reply 79, posted (2 years 3 months 2 days 6 hours ago) and read 12408 times:

Please reference the following link from the first thread: Debris From B787 Engine Sparks Fire In S.C.

Debris From B787 Engine Sparks Fire In S.C. (by varigb707 Jul 29 2012 in Civil Aviation)

Go to Reply #124 where I explained what the pieces are and how they interact to connect the Fan Rotor, Fan Forward Shaft, Fan MID (not middle) Shaft to the LP Turbine Rotor.

Some of the same graphics and photos are used in both threads so you shouldn't have any trouble figuring out the setup...

The only thing that is different from the CF6s is that GE has introduced the fail safe coupling into the Fan Mid Shaft to Fan Forward Shaft. This results in the LP Turbine Shaft being installed from the rear instead of from the Front in order for the the Fan Mid Shaft and LPT Rotor to be able to shift aft so that the LPT Rotor rubs to a stop against the LPT Stators when the connection between Fan Rotor and LPT Rotor become disconnected, thus avoiding and LPT Rotor burst.

What happens if the LPT Rotor isn't snubbed to a stop following a shaft disconnection is that the LPT Rotor accelerates instantly to a speed where the rotor come unglued. This has been a problem on more than one CF6-50 when the LPT Rotor Stage 1 disk attaching bolts failed and allowed the stage one disk to overspeed and come apart sometimes tearing off the LPT Stator case, LPT rear frame and attached parts including the core exhaust nozzle and centerbody, and even the core cowling which departed the aircraft. GE was working on this problem at the urging of the FAA, etc.

I've been watching this thread and there are a lot of thinkers here, but....

Anyway, my two cents.

Also, thanks for the additional pictures.


User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 80, posted (2 years 3 months 2 days 5 hours ago) and read 12410 times:

Quoting BoeingVista (Reply 78):
That would be me that posted the original

Thanks, you seem to be in the know   .

Quoting BoeingVista (Reply 78):
Yeah about 1m in straight down the middle access would seem to be reasonable, presumably the shaft end is not capped.

The GEnx, GE90 and GP7000 all share the same design principle. I found a high res cutout of the GP7000 which shows this area perfectly, one can see the joining of the shafts, the retaining nut and the cone with the bearing. The cone is a bit shallower and the end is capped in this case (which one can take off to come to the nut to split the shaft or measure the area  Wow! ) :

http://i298.photobucket.com/albums/mm262/ferpe_bucket/GP7000cutoutwithmarkings.jpg

The PW4000 has the same design as well with a forward cone, a mid shaft etc. But here the low spool forward bearing is on the mid shaft clustered with the forward high spools bearing,. Therefore this type of safety mechanism would not work given the bearing take axial loads.



Non French in France
User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 81, posted (2 years 3 months 2 days 5 hours ago) and read 12315 times:

Quoting cf6ppe (Reply 79):
Please reference the following link from the first thread:

Thanks for reminding me, I realize I missed quite some information there   , sorry for all the duplication. Anyway it resulted in a good cutaway that we can use to show the problem area (even if it is the wrong engine   ).

The whole thing started when I asked how they could measure so many engines in such a short time, well they have easy access to the area from the front and can put the probe in the hollow shaft underneath the crack area.


Re stress levels in this area:
- it only carries the axial load imposed by the LPT, the torque (which is considerable to transmit some 70klbf fan+booster force through some 10k RPM shaft) is being taken by the splines.

- If there is local phenomena that expands the material (like hydrogen corrosion) this will impose high stresses however. The axle is not very thick here as well, designed to crack under stress  Wow! .

- The stress from the LPT wanting to drag the whole thing aft is at it's highest at low speed with take-off power, (some 50-60klbf shall be kept in axial check), then the lapse ratio (fan efficiency ratio) will lower this for the rest of take-off and climb. The cruise load is low, some 10klbf. Cruise climb would bring some higher loads but well below the start, the lapse is quite high. A bit scary will be TOGA go arounds, the lapse is not that high at some 160kt or what the final approach speed can be, if the start caused the cracks to grow the TOGA can snap the shaft   .

[Edited 2012-09-16 22:59:44]


Non French in France
User currently offlinetrex8 From United States of America, joined Nov 2002, 4869 posts, RR: 14
Reply 82, posted (2 years 3 months 1 day 8 hours ago) and read 11445 times:
Support Airliners.net - become a First Class Member!

Not sure if this has been linked on any other thread
http://www.flightglobal.com/news/art...enx-powered-787-and-747-8s-376525/


User currently offlineAirlineCritic From Finland, joined Mar 2009, 736 posts, RR: 1
Reply 83, posted (2 years 3 months 1 day 5 hours ago) and read 11224 times:

Quoting trex8 (Reply 82):
Not sure if this has been linked on any other thread

So they are calling for grounding before inspections are done. Interesting.


User currently online747classic From Netherlands, joined Aug 2009, 2214 posts, RR: 14
Reply 84, posted (2 years 2 months 4 weeks 3 hours ago) and read 10410 times:

All active GEnx engines have completed the initial checks, ahead of the completion of a FAA AD.

" GE has developed a field ultrasonic method to inspect the suspect area while the engines remain on the airplanes. The entire process takes between two and three hours to complete, according to the company. Boeing 787 customers have taken delivery of 14 GEnx-1B engines and 747-8 customers have taken 114 GEnx-2Bs.
As a result of findings to date, GE has introduced changes in the production process that address so-called environmentally assisted cracking, or cracks caused by galvanic corrosion in a moist environment. GE has returned to using the same midshaft dry-film coating it used for the GE90-115B. The company abandoned it for the GEnx in an effort to lessen environmental concerns associated with lead use."

See : http://www.ainonline.com/aviation-ne...-genx-inspections-faa-completes-ad



Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently online747classic From Netherlands, joined Aug 2009, 2214 posts, RR: 14
Reply 85, posted (2 years 2 months 4 weeks 1 hour ago) and read 10202 times:

Here is the proposed GEnx FAA Airworthiness Directive (AD) , with a 90 day inspection interval, after the initial inspection, covered in a General Electric Service Bulletin.
This proposal will be effective within 30 days. The mentioned 11 engines are the under FAA ruling operated engines.
Probably all other agencies will follow this ruling.

http://www.gpo.gov/fdsys/pkg/FR-2012-09-21/pdf/2012-23443.pdf

[Edited 2012-09-21 03:10:58]


Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineWarpSpeed From United States of America, joined Feb 2010, 595 posts, RR: 3
Reply 86, posted (2 years 2 months 3 weeks 14 hours ago) and read 9214 times:

Muddied waters: apparently the Shanghai incident is not the same as the cracked mid-shaft experienced in Charleston...

http://seattletimes.com/html/busines...nology/2019276579_geenginexml.html



DaHjaj jaj QaQ Daghajjaj !!!!
User currently offlineDocLightning From United States of America, joined Nov 2005, 20333 posts, RR: 59
Reply 87, posted (2 years 2 months 3 weeks 13 hours ago) and read 9141 times:

Quoting WarpSpeed (Reply 86):
Muddied waters: apparently the Shanghai incident is not the same as the cracked mid-shaft experienced in Charleston...

Uh-oh, that sounds like bad-news bears. Two different issues that caused complete destruction of two brand-new engines?


User currently offlineStitch From United States of America, joined Jul 2005, 31375 posts, RR: 85
Reply 88, posted (2 years 2 months 3 weeks 11 hours ago) and read 8990 times:
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As aeroblogger noted in the 787 production thread, the FAA has issued an AD for the GEnx series of engines - http://www.gpo.gov/fdsys/pkg/FR-2012-09-21/pdf/2012-23443.pdf

User currently offlineBoeingVista From Australia, joined Jan 2009, 1584 posts, RR: 3
Reply 89, posted (2 years 2 months 3 weeks 11 hours ago) and read 8901 times:

Quoting Stitch (Reply 88):
As aeroblogger noted in the 787 production thread, the FAA has issued an AD for the GEnx series of engines -

A more user friendly link AD.nsf/0/3b217124c64a00ae86257a800043d51f/$FILE/2012-19-08.pdf" target="_blank">http://rgl.faa.gov/Regulatory_and_Gu...57a800043d51f/$FILE/2012-19-08.pdf

For the TLDR crowd ultrasound inspections are mandated every 90 days.

Quoting WarpSpeed (Reply 86):
Muddied waters: apparently the Shanghai incident is not the same as the cracked mid-shaft experienced in Charleston...

So I guess we put our speculation hats on again but clearly a 2nd unrelated GEnx failure cannot be good news as there has been already been confirmation that the first failure (FMS) is not a one off occurrence.



BV
User currently online747classic From Netherlands, joined Aug 2009, 2214 posts, RR: 14
Reply 90, posted (2 years 2 months 3 weeks 5 hours ago) and read 8608 times:

Here is the latest official press release of the NTSB :
No cracked Fan Mid Shaft (FMS) was found on the GEnx-2B engine, that failed in Shanghai. The examination and tear-down of that engine is continuing under the direction of the CAAC.

See : http://www.ntsb.gov/news/2012/120927.html



Quoting BoeingVista (Reply 89):

The mentioned link to the FAA AD data base doesn't work.

[Edited 2012-09-27 23:08:32]


Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineBoeingVista From Australia, joined Jan 2009, 1584 posts, RR: 3
Reply 91, posted (2 years 2 months 3 weeks 4 hours ago) and read 8519 times:

Quoting 747classic (Reply 90):
The mentioned link to the FAA AD data base doesn't work.

It was a bit early, try this link...

Link

Quote:
As part the CAAC's investigation and in relation to the NTSB's ongoing investigation of the July 28th engine failure, preliminary findings from the examination of the Shanghai incident engine revealed that the FMS was intact and showed no indications of cracking. The examination and teardown of that engine is continuing under the direction of the CAAC.

I assume that the engine has been shipped back stateside for the teardown.



BV
User currently online747classic From Netherlands, joined Aug 2009, 2214 posts, RR: 14
Reply 92, posted (2 years 2 months 2 weeks 1 day 3 hours ago) and read 7334 times:

Safety Board Suspects Improper Turbine Assembly In GEnx-2B Failure.

Closer inspection of the General Electric GEnx-2B engine that failed last month on an Air Bridge Cargo Boeing 747-8F in Shanghai indicates that a wrongly assembled low pressure turbine part was the likely culprit, rather than the FMS suspected as the cause of a very similar looking GEnx-1B problem on a 787-8 in July.

See : http://www.aviationweek.com/Article....l/avd_10_03_2012_p03-01-502398.xml

[Edited 2012-10-04 00:48:22]


Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineBoeingVista From Australia, joined Jan 2009, 1584 posts, RR: 3
Reply 93, posted (2 years 2 months 2 weeks 1 day 3 hours ago) and read 7289 times:

And of course this means another GE Service bulitin..

http://professional.wsj.com/article/...mod=WSJ_hp_LEFTWhatsNewsCollection

Quote:
General Electric Co. will tell aircraft operators to make another round of inspections on GE engines installed on Boeing Co.'s 787 and newest 747 models.... the service bulletin will call for inspections of the lower pressure turbine, where the engine mounted on a Boeing 747-8 saw damage in the Shanghai incident, a GE spokesman said. That is a different area than where other flaws were found in the same engine type.



BV
User currently online747classic From Netherlands, joined Aug 2009, 2214 posts, RR: 14
Reply 94, posted (2 years 2 months 2 weeks 14 hours ago) and read 6743 times:

General Electric has ordered inspections on all 120 GEnx engines operating on Boeing 747-8s and 787s to check for installation errors of a component that has triggered a GEnx-2B engine failure at a 747-8F at Shanghai (China) last month.

The service bulletin issued on 4 October calls for a one-time inspection of the first stage low-pressure turbine (LPT) nozzle, a non-rotating part that directs the air flow into the trailing LPT stages

See : http://www.flightglobal.com/news/art...in-genx-orders-inspections-377319/



Operating a twin over the ocean, you're always one engine failure from a total emergency.
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