tp1040
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747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 4:17 pm

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.
 
starrion
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 4:26 pm

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.
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jumbojim747
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 4:48 pm

It seams more engines are failing lately cauld it be due to higher then normal production and the workers are getting a bit sloppy?
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kc135topboom
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 5:07 pm

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.
 
tdscanuck
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 5:12 pm

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.
 
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SEPilot
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 5:25 pm

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.
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tp1040
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 7:05 pm

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.
 
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DocLightning
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 7:15 pm

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."
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KarelXWB
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 7:37 pm

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/
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Stitch
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 7:40 pm

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).
 
sweair
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 8:14 pm

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.
 
goosebayguy
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 8:23 pm

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!
 
imiakhtar
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 8:26 pm

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.
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brilondon
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 8:35 pm

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.
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maddogjt8d
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 8:36 pm

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?
 
WarpSpeed
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 8:39 pm

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.
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Stitch
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 9:10 pm

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.
 
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 9:13 pm

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.
 
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HAWK21M
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 9:19 pm

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.....
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lightsaber
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 9:19 pm

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
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747classic
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 9:29 pm

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.
 
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EPA001
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 10:02 pm

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.
 
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 10:09 pm

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.
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lightsaber
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 10:28 pm

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.


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mffoda
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 11:12 pm

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?   
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kc135topboom
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 11:50 pm

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).
 
tdscanuck
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RE: 747-8 Uncontained Engine Failure?

Thu Sep 13, 2012 11:53 pm

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.
 
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 12:56 am

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
 
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Stitch
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 1:41 am

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.
 
BlueSky1976
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 1:53 am

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.
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mffoda
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 2:18 am

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,
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sweair
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 8:03 am

I have a hunch its some sort of metallurgic problem, composition of a certain batch of metal maybe differing from the norm.
 
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747classic
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 10:00 am

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.
 
ozglobal
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 11:18 am

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.
 
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HAWK21M
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 12:11 pm

Would a month be an ideal time frame to get a detailed investigative report of the snag or would 3 months be more realistic.
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Stitch
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 1:52 pm

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.
 
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lightsaber
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 2:43 pm

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.

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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 9:03 pm

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]
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 9:33 pm

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.
 
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 11:23 pm

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.
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KELPkid
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RE: 747-8 Uncontained Engine Failure?

Fri Sep 14, 2012 11:37 pm

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  
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mffoda
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RE: 747-8 Uncontained Engine Failure?

Sat Sep 15, 2012 2:46 am

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]
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Stitch
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RE: 747-8 Uncontained Engine Failure?

Sat Sep 15, 2012 2:50 am

So looks like they know what's causing it and have a fix.

Any idea if the part can be swapped in the field?
 
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RE: 747-8 Uncontained Engine Failure?

Sat Sep 15, 2012 3:21 am

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)  
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RE: 747-8 Uncontained Engine Failure?

Sat Sep 15, 2012 4:21 am

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.
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RE: 747-8 Uncontained Engine Failure?

Sat Sep 15, 2012 4:40 am

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?
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RE: 747-8 Uncontained Engine Failure?

Sat Sep 15, 2012 5:12 am

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
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RE: 747-8 Uncontained Engine Failure?

Sat Sep 15, 2012 7:11 am

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]
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RE: 747-8 Uncontained Engine Failure?

Sat Sep 15, 2012 8:05 am

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
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goosebayguy
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RE: 747-8 Uncontained Engine Failure?

Sat Sep 15, 2012 8:12 am

No chance of ETOPs for a while here.