787 engine failure in Charleston, SC
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From: what U.S. calls Žold EuropeŽ
Boeing Marketing changed to -8, -9 etc.
However, once you really buy the aircraft, you get your full 3 digits.
For example ANA is not operating 787-8, but 787-881. Lufthansa is not operating 747-8 but 747-830. Just the same since 50 years, but marketing needs something new now and then to justify their existence...
However, once you really buy the aircraft, you get your full 3 digits.
For example ANA is not operating 787-8, but 787-881. Lufthansa is not operating 747-8 but 747-830. Just the same since 50 years, but marketing needs something new now and then to justify their existence...
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From: flyover country USA
Machinbird:
It's a known issue going back a few decades before the F-4. After cleaning & replating R-985 pushrod-cover gland nuts (Cadmium plate, no less) we always baked them a couple hours to remove hydrogen entrapped.
I can remember some large spacer washers on the McDonnell F-4 that kept the stabilator centered on the fuselage. These things were way overdesigned to look at them, but they were failing in service because they didn't have the hydrogen driven out of the metal following plating operations. (Improper process specification)
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From: Reading, UK
Boeing Marketing changed to -8, -9 etc.
However, once you really buy the
aircraft, you get your full 3 digits.
For example ANA is not operating
787-8, but 787-881. Lufthansa is not operating 747-8 but 747-830. Just the same
since 50 years, but marketing needs something new now and then to justify their
existence...
However, once you really buy the
aircraft, you get your full 3 digits.
For example ANA is not operating
787-8, but 787-881. Lufthansa is not operating 747-8 but 747-830. Just the same
since 50 years, but marketing needs something new now and then to justify their
existence...
But for the 787, the only certificated variant (as of yesterday's update to the TC) is the -8, with no reference in the TC to individual customer numbers, which suggests that for this aircraft those are purely marketing and/or Boeing internal designations.
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From: Grassy Valley
barit1
In your experience, can the plating process be reversed, the stock re cooked, and then replated? If Hydrogen is entrapped, the fissures have already started, and there is possibility for continued embrittlement, post re-plate?
In one description of the failure, there was reference to "Facets" in the degraded areas. This suggests a propagation of fractures at the level shy of inspection at .05 inches?
This is eerily similar to the Shaft problems RR had in the TRENT, perhaps....
In your experience, can the plating process be reversed, the stock re cooked, and then replated? If Hydrogen is entrapped, the fissures have already started, and there is possibility for continued embrittlement, post re-plate?
In one description of the failure, there was reference to "Facets" in the degraded areas. This suggests a propagation of fractures at the level shy of inspection at .05 inches?
This is eerily similar to the Shaft problems RR had in the TRENT, perhaps....
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From: California
What I find interesting is that these problems show up in products from main-line manufacturers with decades of experience.
I guess that Boeing and GE can breath a sigh of relief that their overly ambitious production rate has still not happened.
f
I guess that Boeing and GE can breath a sigh of relief that their overly ambitious production rate has still not happened.
f
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From: Middle America
I have been a little reluctant to comment on these failures, not knowing for sure what the cause might be. It does appear, however, Hydrogen Embrittlement (HE) may indeed be the cause. In recent newer GE engines (CF6-80C/E or newer), the LPT shaft connects into the Fan Mid Shaft as described by BadgerGrowler. I believe the FMS is made of Maraging steel and the LPT shaft of a different high strength steel. Maraging steel is somewhat sensitive to HE like normal high strength steel and it is only used because of its high shear strength and grain size does play a role in HE. The HE may come from factors in the manufacturing process or raw material (alloy) production, not as a result of operating service. Higher strength is developed by heat treatments but comes at the expense of ductility. Corrosion resistance is also reduced. Typically, high strength steels becomes HE sensitive when heat treated to give tensile strengths above 130,000 psi, perhaps higher for Maraging steel. The part must be subjected to tensile stress as would be the case of a forged shaft. Shafts do not need to be assembled or in service to be under tensile stress. The heat treating process provides most of the residual stresses. Manufacturing processes that utilize acids or electro-plating introduces hydrogen into the part material. I think shafts are electroless plated or vapor deposition coated to prevent corrosion in service.
No matter what, there is a process as barit1 described as "baking". And as he pointed out, parts must be baked within 4 hours of hydrogen exposure, less is better. Parts must be baked at 400℉, and parts must be held at 400℉ for a minimum of 4 hours, longer depending on thickness or size. If the baking process is not done properly, parts can be sitting on the shelf and can begin to show signs of HE. 70% of aerospace components that fail because of HE are related to improper "baking", one or more of the steps outlined above. Since "baking is a batch process, that is more than one component per batch, if one is bad, you can bet the farm that all the components in that batch will be bad. And this takes us to the GE situation.
Boeing essentially put out an original schedule for aircraft build for both the 787 and the 747-800 series. GE, in turn ordered parts to that build schedule, placing orders for long lead time parts first. Then technical issues at Boeing resulted in long delays/postponements for the need of engines. So the engine parts were on hand or partially processed when new delayed schedules for aircraft builds were announced. I am sure they sat on the shelves until needed. Meanwhile, the engine testing and certification programs went on and engines were delivered for flight testing of both aircraft models. IMHO, this is why the problem wasn't discovered during the normal certification process, just an opinion/speculation. Nevertheless, the delay in the program may have hurt rather than helped.
So if the problem is indeed HE, the NTSB AD to GE is to find the rest of the shafts from that "baking" batch or alloy batch ASAP assuming the "baking" process or alloy batch might be the cause. Either way, it would be traceable.
Lyman,
The joint of the LPT shaft to the FMS is not in the hot section of the engine.
TD
No matter what, there is a process as barit1 described as "baking". And as he pointed out, parts must be baked within 4 hours of hydrogen exposure, less is better. Parts must be baked at 400℉, and parts must be held at 400℉ for a minimum of 4 hours, longer depending on thickness or size. If the baking process is not done properly, parts can be sitting on the shelf and can begin to show signs of HE. 70% of aerospace components that fail because of HE are related to improper "baking", one or more of the steps outlined above. Since "baking is a batch process, that is more than one component per batch, if one is bad, you can bet the farm that all the components in that batch will be bad. And this takes us to the GE situation.
Boeing essentially put out an original schedule for aircraft build for both the 787 and the 747-800 series. GE, in turn ordered parts to that build schedule, placing orders for long lead time parts first. Then technical issues at Boeing resulted in long delays/postponements for the need of engines. So the engine parts were on hand or partially processed when new delayed schedules for aircraft builds were announced. I am sure they sat on the shelves until needed. Meanwhile, the engine testing and certification programs went on and engines were delivered for flight testing of both aircraft models. IMHO, this is why the problem wasn't discovered during the normal certification process, just an opinion/speculation. Nevertheless, the delay in the program may have hurt rather than helped.
So if the problem is indeed HE, the NTSB AD to GE is to find the rest of the shafts from that "baking" batch or alloy batch ASAP assuming the "baking" process or alloy batch might be the cause. Either way, it would be traceable.
Lyman,
The joint of the LPT shaft to the FMS is not in the hot section of the engine.
TD
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From: Grassy Valley
Thanks TD, always appreciate your data. A couple questions though, can you be more specific re: the Plating? You mention 'electroless', I am unfamiliar. Also, by vapor, do you mean plasma or powder coat? I like the explanation of the difficulties GE faced due the assumedly schedule busting resin/spinning process.
Also, you mention the "NTSB AD". The NTSB is not a rule making body, but can recommend only. There is an AD? I could not find it in the FAA site. The NTSB does not write drama, and their concern is clear, there would have to be an AD at some stage, lest the "Optional" brigade start to drag their paws on the ground....
My concern for the location of the joint came about when I read that "The shaft migrated aft, and caused clash with the stators, etc."
We have been down that road, my perplexion comes from any possibility of uncontainment of an explosive nature?
thanks again.
Also, you mention the "NTSB AD". The NTSB is not a rule making body, but can recommend only. There is an AD? I could not find it in the FAA site. The NTSB does not write drama, and their concern is clear, there would have to be an AD at some stage, lest the "Optional" brigade start to drag their paws on the ground....
My concern for the location of the joint came about when I read that "The shaft migrated aft, and caused clash with the stators, etc."
We have been down that road, my perplexion comes from any possibility of uncontainment of an explosive nature?
thanks again.
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From: flyover country USA
So long as the turbine rotor/stator geometry is designed so that a rotor axial shift creates a clash of airfoils, it's a "fail safe" design. The rotor will never get the chance to accelerate to a dangerous RPM. This is apparently what has happened in the GEnx failures; the low-energy airfoil debris exits through the core nozzle.
However, even this "benign" shrapnel can create a flight hazard - for example, if hydraulic lines are routed within the horizontal stab LE. A thorough FMECA is the answer here.
(FMECA = Failure Modes, Effects, Criticality, Analysis)
However, even this "benign" shrapnel can create a flight hazard - for example, if hydraulic lines are routed within the horizontal stab LE. A thorough FMECA is the answer here.
(FMECA = Failure Modes, Effects, Criticality, Analysis)
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From: flyover country USA
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From: Grassy Valley
September 18, 2012, 2:52 pm
AINonline is reporting that GE will use "additional Lead" in the formula for the coating that's expected to prevent corrosion on the FMS thread area. GE reduced Lead in the formulation post GE90, to "protect" the Environment from the deleterious effects of Lead. Nice thought. Now, not so much.
Let's hope that a new EIR is not required, Pesky EPA...
Still nothing regarding a forthcoming AD, other than some sources are saying inspections are "required" (can't happen w/o AD). A Seattle paper is reporting that the Manufacturer is "requested" to inspect...
The operator, Atlas, is saying they are "looking at" the request... Atlas is the only carrier under the jurisdiction of the FAA, supposedly.... (AINonline)
AINonline is reporting that GE will use "additional Lead" in the formula for the coating that's expected to prevent corrosion on the FMS thread area. GE reduced Lead in the formulation post GE90, to "protect" the Environment from the deleterious effects of Lead. Nice thought. Now, not so much.
Let's hope that a new EIR is not required, Pesky EPA...
Still nothing regarding a forthcoming AD, other than some sources are saying inspections are "required" (can't happen w/o AD). A Seattle paper is reporting that the Manufacturer is "requested" to inspect...
The operator, Atlas, is saying they are "looking at" the request... Atlas is the only carrier under the jurisdiction of the FAA, supposedly.... (AINonline)
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From: flyover country USA
Still nothing regarding a forthcoming AD, other than some sources are saying inspections are "required" (can't happen w/o AD). A Seattle paper is reporting that the Manufacturer is "requested" to inspect...
And a strongly worded SB will likely hit the street before FAA can process an AD.
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From: Grassy Valley
Hi barit1
I agree, but I also think it is one thing to face the loss of Warranty, and another thing the loss of an aircraft. The willful evasion of an AD is (can be) a criminal offense.
I am concerned at the lackadaisical attitude of the 747-8 operator. Two incidents of brand new engines spitting their guts out into the slipstream. Smoke/fire.
I agree, but I also think it is one thing to face the loss of Warranty, and another thing the loss of an aircraft. The willful evasion of an AD is (can be) a criminal offense.
I am concerned at the lackadaisical attitude of the 747-8 operator. Two incidents of brand new engines spitting their guts out into the slipstream. Smoke/fire.
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From: Middle America
Lyman,
On September 17 the GE spokesman told AIN that all GEnx engines in the field would have undergone inspection by the time the FAA issued its AD this week. The inspection is accomplished on-wing, no need for engine removal unless something is detected.
BTW, electroless plating is a process method of usually applying nickel to a component that has experienced wear, restoring the surface and dimensions to the original limits. Relative to vapor deposition, I am not sure of the exact process used. Since shafts are hollow, the coating is applied to both OD and ID to minimize corrosion from oils, etc., that are vented through the shaft interior.
TD
On September 17 the GE spokesman told AIN that all GEnx engines in the field would have undergone inspection by the time the FAA issued its AD this week. The inspection is accomplished on-wing, no need for engine removal unless something is detected.
BTW, electroless plating is a process method of usually applying nickel to a component that has experienced wear, restoring the surface and dimensions to the original limits. Relative to vapor deposition, I am not sure of the exact process used. Since shafts are hollow, the coating is applied to both OD and ID to minimize corrosion from oils, etc., that are vented through the shaft interior.
TD
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From: Grassy Valley
Once again, TD thanks for the update.
My concern would be that the shafts were cooked in 'batches', and that the cooking is the required step for excluson of atomic Hydrogen. Since the Hydrogen is a result of a galvanic process, (dissimilar metals), what is the assurance that a field negative exonerates the batch? The additional ingredients involve a humid environment (prevalent), and the location at a machined in situs, (thread root). The fix per AIN is Lead formula coating, not plating, so how is the initial plating tested? The ultrasonics, per GE are only resolved to .05 inches. That is a rather large fissure, and less than that threshold leaves rather a lack of confidence, imo. So then we find that the inspections are recurring at short intervals, to protect the client from fracture and failure. Can this engine be field stripped, like the TRENT and its fifteen modules profile? I am having a time of it, picturing how any effective coating can be applied in the field, without strip. Then there are the threads.
Do you know if the threads are coated prior to join with the FFS? The suspect area is the root of the termination of the helical cut made for the thread in the shaft, again, that seems quite the challenge to "view" on wing....
Thanks TD
My concern would be that the shafts were cooked in 'batches', and that the cooking is the required step for excluson of atomic Hydrogen. Since the Hydrogen is a result of a galvanic process, (dissimilar metals), what is the assurance that a field negative exonerates the batch? The additional ingredients involve a humid environment (prevalent), and the location at a machined in situs, (thread root). The fix per AIN is Lead formula coating, not plating, so how is the initial plating tested? The ultrasonics, per GE are only resolved to .05 inches. That is a rather large fissure, and less than that threshold leaves rather a lack of confidence, imo. So then we find that the inspections are recurring at short intervals, to protect the client from fracture and failure. Can this engine be field stripped, like the TRENT and its fifteen modules profile? I am having a time of it, picturing how any effective coating can be applied in the field, without strip. Then there are the threads.
Do you know if the threads are coated prior to join with the FFS? The suspect area is the root of the termination of the helical cut made for the thread in the shaft, again, that seems quite the challenge to "view" on wing....
Thanks TD
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From: Middle America
Lyman,
You are asking questions that can only be answered by seeing the failures first hand, and the failure analysis that would follow, besides knowing in detail the actual complete processing steps. I don't have this information to answer your questions.
TD
You are asking questions that can only be answered by seeing the failures first hand, and the failure analysis that would follow, besides knowing in detail the actual complete processing steps. I don't have this information to answer your questions.
TD
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From: Grassy Valley
Among others, that is a point I am trying to make. This problem is not complex, nor is it worthy of the shadow people are trying to hide it behind. It has to do with the safety that is currently under attack in our industry.
If someone of your professional calibre is in the dark, we all are.
And that is no place to put the people who pay for the equipment, and pay for the agency that is supposed to protect us from the shadows.
A little sunlight would be a good thing.
If someone of your professional calibre is in the dark, we all are.
And that is no place to put the people who pay for the equipment, and pay for the agency that is supposed to protect us from the shadows.
A little sunlight would be a good thing.