QANTAS A380 Uncontained failure.
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DERG
I don't disagree, but not only is your view a bit simplistic, there is question whether an Oil Fire caused the burst.
For instance, as old engineer writes, the Oil's temp rises gradually, and not even to flash point (by measure at the scavenge inlets). Now this doesn't preclude Fire, but, an Oil Fire by definition is an oil fed fire, and there seems to be no Oil missing from the system.
Oil may have accumulated as solids over time (as coke) in critical locales, but no theory of actual fuel for fire is offered. The authority, ATSB, has offered that an Oil Fire "may have initiated a sequence that resulted in Uncontained release", etc. But the theory of bearing heat obtains just as well.
What is the mechanism for fire to be located in the "Annulus" between HPT and IPT? How did the fire heat the Drive Arm from its aft portion (Not known), when the fire was located on the forward side of the disc?
Question. On Figure 8, at the Fan, take note of Blades that appear to have been damaged. Notice two blades past the spinner's top, at ~10 o'clock. Illusion?
I don't disagree, but not only is your view a bit simplistic, there is question whether an Oil Fire caused the burst.
For instance, as old engineer writes, the Oil's temp rises gradually, and not even to flash point (by measure at the scavenge inlets). Now this doesn't preclude Fire, but, an Oil Fire by definition is an oil fed fire, and there seems to be no Oil missing from the system.
Oil may have accumulated as solids over time (as coke) in critical locales, but no theory of actual fuel for fire is offered. The authority, ATSB, has offered that an Oil Fire "may have initiated a sequence that resulted in Uncontained release", etc. But the theory of bearing heat obtains just as well.
What is the mechanism for fire to be located in the "Annulus" between HPT and IPT? How did the fire heat the Drive Arm from its aft portion (Not known), when the fire was located on the forward side of the disc?
Question. On Figure 8, at the Fan, take note of Blades that appear to have been damaged. Notice two blades past the spinner's top, at ~10 o'clock. Illusion?
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DERG
In prior posts we discussed the lack of disclosure by RR and LuftyMx re: Qantas.
It is a glaring and actionable blunder, in my opinion, and the lack of information forthcoming from the Manufacturer and Mx provider will be accomodated at Court, no doubt.
It is well to assign culpability to Oiling, and why not? The Mfg. group has said an oil fire is the cause. What of the degradation of the Oiling System that predicated the Fire? While the claim is that a stub pipe failed, no mention is made of the wear seen in this part (if the image is an actual image of the offending piece). No Oil loss is recorded in the offered data, and wear that was instigated by a possible loss of oiling is not addressed. So we continue with a lack of information, this time the victim is the Public interest, and ultimately (unimagined, one thinks) the manufacturers. This flight came within a hairbreadth of complete loss of the Engine from the wing, a ditching, or a crash. The causes were not a surprise, meaning that someone ignored a basic tenet of Aviation, one that suffers currently due to its unpopularity in the boardroom:SAFETY FIRST, and even before bonus and profit.
More than a few engineers, and non-engineers know precisely what caused the burst, it will come out, through the EASA, the FAA, or at Court.
Best wishes to you for the New Year,
bear
In prior posts we discussed the lack of disclosure by RR and LuftyMx re: Qantas.
It is a glaring and actionable blunder, in my opinion, and the lack of information forthcoming from the Manufacturer and Mx provider will be accomodated at Court, no doubt.
It is well to assign culpability to Oiling, and why not? The Mfg. group has said an oil fire is the cause. What of the degradation of the Oiling System that predicated the Fire? While the claim is that a stub pipe failed, no mention is made of the wear seen in this part (if the image is an actual image of the offending piece). No Oil loss is recorded in the offered data, and wear that was instigated by a possible loss of oiling is not addressed. So we continue with a lack of information, this time the victim is the Public interest, and ultimately (unimagined, one thinks) the manufacturers. This flight came within a hairbreadth of complete loss of the Engine from the wing, a ditching, or a crash. The causes were not a surprise, meaning that someone ignored a basic tenet of Aviation, one that suffers currently due to its unpopularity in the boardroom:SAFETY FIRST, and even before bonus and profit.
More than a few engineers, and non-engineers know precisely what caused the burst, it will come out, through the EASA, the FAA, or at Court.
Best wishes to you for the New Year,
bear
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The hidden accusition against Lufthansa and Lufthansa Technik regarding the C check in September is no new information. It was posted several times before in the old thread to this case. As early as post nr. 240 there was a statement of a Lufthansa Technik spokesman quoted whith the content that Lufthansa Technik has no responsibility for the engines. Quantas has obviously only contracted Lufthansa Technik for the "Body" C-check only.
Under the present contract of "power by the hour" I believe even Quantas is not responsible for the status and service readiness of the engines, itīs sole RR business. There might be excemptions from this strict ruling - subject to contract details - e.g. minor service activities at the stations that are involved in A 380 operation, but thats all.
I think this whole case is much too serious to start apppointing of blame without solid facts at hand.
Under the present contract of "power by the hour" I believe even Quantas is not responsible for the status and service readiness of the engines, itīs sole RR business. There might be excemptions from this strict ruling - subject to contract details - e.g. minor service activities at the stations that are involved in A 380 operation, but thats all.
I think this whole case is much too serious to start apppointing of blame without solid facts at hand.
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DERG & bearfoil
Some interesting information on the A380 and engines from the airline user's point of view (prior to QF-32), perhaps you already saw it. Look at the engine maker's views as well.
Technical issues
Happy New Year to all !!!
Turbine D
Some interesting information on the A380 and engines from the airline user's point of view (prior to QF-32), perhaps you already saw it. Look at the engine maker's views as well.
Technical issues
Happy New Year to all !!!
Turbine D
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Not part of the "Tech" discussion, but an interesting interview with Captain David Evans, who was the supervising check captain.
EXCLUSIVE - Qantas QF32 flight from the cockpit | Aerospace Insight | The Royal Aeronautical Society
EXCLUSIVE - Qantas QF32 flight from the cockpit | Aerospace Insight | The Royal Aeronautical Society
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LH Tech / RR engine repair shop
DERG
that is very correct. RR and LH technik agreed upon installation of a shared repair unit that became established at Arnstadt/Thueringen. As far as I am informed about that company they do the repair on the LH TRENT 900 only , yet they may, sooner or later, also take engines from other airlines.
Wish you and all other participants of this circle a happy and prosperous New Year
that is very correct. RR and LH technik agreed upon installation of a shared repair unit that became established at Arnstadt/Thueringen. As far as I am informed about that company they do the repair on the LH TRENT 900 only , yet they may, sooner or later, also take engines from other airlines.
Wish you and all other participants of this circle a happy and prosperous New Year
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bearfoil
I think it is up to Rolls Royce to develop solutions to the engine tech issues, not a repair/overhaul shop they are partnering with to service the engines.
One hopes LHTek will be instrumental in developing a solution to this engine's issues.
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PICTURES of the damaged wing structure
PICTURES of the damaged wing structure of the Qantas Airbus A380, flight
QF32, 4th November 2010, Nancy-Bird Walton, MSN 0014, Reg. VH-OQA
SpeedShare - Download A380-QFA-MSN014-Damage Overview.pdf
SpeedShare - Download Damages_description_wingtopskin.pdf
QF32, 4th November 2010, Nancy-Bird Walton, MSN 0014, Reg. VH-OQA
SpeedShare - Download A380-QFA-MSN014-Damage Overview.pdf
SpeedShare - Download Damages_description_wingtopskin.pdf
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TurbineD
My intent was to describe LHT as involved in the retro/repair/upgrade. Their service of the id'd engines that failed/faced failure, is critical to the explanation for the defects. From this explanation an understanding of the events can be acquired. Since non-disclosure of vulnerabilities is reported by Qantas, some apprehension is reasonable as to whether this incident will be fully understood by the Public. What is the nature of the actions taken that now create a reduced possibility of in flight Burst?
What of the year-old AD's?? What was/is being replaced other than the famous 'stub' pipe?? Further, there is the question of disclosure of meaningful concerns by the representatives of the Public?? Is the Mission of the EASA to protect Corporate proprietaries? Or is its Mission to protect the safety of the Public in Carriage??
One hopes the latter.
My intent was to describe LHT as involved in the retro/repair/upgrade. Their service of the id'd engines that failed/faced failure, is critical to the explanation for the defects. From this explanation an understanding of the events can be acquired. Since non-disclosure of vulnerabilities is reported by Qantas, some apprehension is reasonable as to whether this incident will be fully understood by the Public. What is the nature of the actions taken that now create a reduced possibility of in flight Burst?
What of the year-old AD's?? What was/is being replaced other than the famous 'stub' pipe?? Further, there is the question of disclosure of meaningful concerns by the representatives of the Public?? Is the Mission of the EASA to protect Corporate proprietaries? Or is its Mission to protect the safety of the Public in Carriage??
One hopes the latter.
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LHT
DERGīs post about that quoted LHT sentence made me dig through many reports and interviews I could find in german media. What I think has happened is, a statement of one LHT member was conveniently shaped to the editors intent. Those statements or quotations of LHT I found to the case is like quote: . . .for the time being . . .we see no reason to not operate the A 380 . .
That would make much more sense than this simply stupid sentence. One day after such a severe accident no one that uses his/her brain will make such a statement.
But to come back to more technical items.
The socalled "A mod" version of the Trent 900 is the engine installed on the first deliveries to QF and SIA
Lufthansa received its first A 380 - D-AIMA - on may, 19 2010. According information I was able to find only one engine on that plane upon delivery was a "A mod" version.
D-AIMA experienced very early into line service upon return from China an inflight shut down - 1 hour prior landing at FRA - of one engine because of quote: "irregularities in the oil system"
That engine was taken off the wing and went into that Arnstadt shop.
Next was the either FOD or birdstrike generated change of one engine on a LH - A 380 somwhere after the Qantas case had happened.
The third change of engine I know of was conducted after RR had issued that recommendation not to use any "A mod" engines until upgraded to later standard.
The forth engine switch to come is scheduled for next week Wednesday or Thursday to have that plane ready for service by Friday.
Interesting information on the side.
This engine was closely monitored since mid December. Other than directed by the EASA EAD 2010 - 0236-E LH checked itīs engine since that EAD not only every 20 cycles as requested, but instead after every ONE flight cycle !! I believe their usage of the type allows for that extra effort.
May be, thatīs the difference between having the engines leased or possesing them as own property ??
Jo
That would make much more sense than this simply stupid sentence. One day after such a severe accident no one that uses his/her brain will make such a statement.
But to come back to more technical items.
The socalled "A mod" version of the Trent 900 is the engine installed on the first deliveries to QF and SIA
Lufthansa received its first A 380 - D-AIMA - on may, 19 2010. According information I was able to find only one engine on that plane upon delivery was a "A mod" version.
D-AIMA experienced very early into line service upon return from China an inflight shut down - 1 hour prior landing at FRA - of one engine because of quote: "irregularities in the oil system"
That engine was taken off the wing and went into that Arnstadt shop.
Next was the either FOD or birdstrike generated change of one engine on a LH - A 380 somwhere after the Qantas case had happened.
The third change of engine I know of was conducted after RR had issued that recommendation not to use any "A mod" engines until upgraded to later standard.
The forth engine switch to come is scheduled for next week Wednesday or Thursday to have that plane ready for service by Friday.
Interesting information on the side.
This engine was closely monitored since mid December. Other than directed by the EASA EAD 2010 - 0236-E LH checked itīs engine since that EAD not only every 20 cycles as requested, but instead after every ONE flight cycle !! I believe their usage of the type allows for that extra effort.
May be, thatīs the difference between having the engines leased or possesing them as own property ??
Jo
Last edited by Annex14; 2nd Jan 2011 at 08:33.
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Old Engineer
That post about bearing technologies is a wealth of information. My tech times are so far away - 1st life I usally say - that I have forgotten a lot about the specialities in that field.
Reading your information a question arose: Is it possible that aside of that AP coating - probably used in high performance jet engines - also Ceramic balls are used in such a desighn??.
From FAG information I took that any of their products used in high tech engines is custom tailored and thus probably far away from what they publish in their normal product listings.
If Ceramic balls are used, would that decrease or increase the consequences of loss of lubrication ??
Thanks in advance
Reading your information a question arose: Is it possible that aside of that AP coating - probably used in high performance jet engines - also Ceramic balls are used in such a desighn??.
From FAG information I took that any of their products used in high tech engines is custom tailored and thus probably far away from what they publish in their normal product listings.
If Ceramic balls are used, would that decrease or increase the consequences of loss of lubrication ??
Thanks in advance
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deposits on IPT fragment
Since we look at the rear side of that IPT disk fragment the question came in my mind what kind of deposit is visible on the picture, Fig. 14, ATSB report. Starting with a shiny polished piece of craftmenship somewhere this dark greyish layer must come from.
Is it the normal agglomeration of exhaustgas that leaked into that space between the rear surface of the disk and the structure connected to or held by that demolished stator ring ?
Or, is it kind of oil cooking coming from an insidious leak somewhere at the rear end of the IPT shaft ?
Another question, how come that the supporting ring underneath the fir tree groves doesnīt show any sighn of wear when it travelled backward towards the nr. 1 nozzle guide vanes ring of the LPT ?? Or did it not at all hit that ring shifting backward, but instead desintegrated before it even got so far ??? How comes that still a ring of that demolished part is hanging inside the wrecked engine??
Is this all possible ??
Is it the normal agglomeration of exhaustgas that leaked into that space between the rear surface of the disk and the structure connected to or held by that demolished stator ring ?
Or, is it kind of oil cooking coming from an insidious leak somewhere at the rear end of the IPT shaft ?
Another question, how come that the supporting ring underneath the fir tree groves doesnīt show any sighn of wear when it travelled backward towards the nr. 1 nozzle guide vanes ring of the LPT ?? Or did it not at all hit that ring shifting backward, but instead desintegrated before it even got so far ??? How comes that still a ring of that demolished part is hanging inside the wrecked engine??
Is this all possible ??
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Annex14
I think the bright shiny to grey color comes naturally over time. This is a hot area of the engine and the combination of temperature and air turns things grey.
The darker coloration and lighter irregular deposit on the surface close to the bore probably came from both heat (darker color) and liquid metal (lighter color) migrating out and solidifying on the disc surface.
As you point out, the rim of the disc (under the dovetail slots) looks remarkably clean. For this section of the disc, there was no apparent metal contact of the disc rim with another component.
I think the metal "ring" that you see hanging in the engine is casing material, some is totally gone, some is bent aft or forward. The in between space is where the disc, blades and nozzles exited the engine. There are two pipe rings that run circumferential around the outside of the casing at a location directly above the IPT rotor blades. I think these pipe rings provide air and are for blade clearance control, mainly at cruise altitude. You can see in the photographed area, they are mainly gone except for a piece of one still showing.
deposits on IPT fragment
The darker coloration and lighter irregular deposit on the surface close to the bore probably came from both heat (darker color) and liquid metal (lighter color) migrating out and solidifying on the disc surface.
As you point out, the rim of the disc (under the dovetail slots) looks remarkably clean. For this section of the disc, there was no apparent metal contact of the disc rim with another component.
I think the metal "ring" that you see hanging in the engine is casing material, some is totally gone, some is bent aft or forward. The in between space is where the disc, blades and nozzles exited the engine. There are two pipe rings that run circumferential around the outside of the casing at a location directly above the IPT rotor blades. I think these pipe rings provide air and are for blade clearance control, mainly at cruise altitude. You can see in the photographed area, they are mainly gone except for a piece of one still showing.
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bearfoil
I agree with your statement. However, I think it to be appropriate to separate aircraft C check maintenance from significant engine inspection. I think there are limited shops you can take an A380 aircraft to have a C check done. What comes to mind at this point would be Airbus, LHTek, Singapore International Airlines and that is about it for now. So Qantas probably didn't have much choice based on their hours and operational schedule. SIA were probably busy C checking their own aircraft. LHTek was probably the only logical choice for the airframe.
The issue of Qantas Trent 9072 engine maintenance, under the Rolls Royce "Total Care Program" seems murky to me at best. I know what the program title says, but what does it mean? If RR had knowledge of technical issues discovered from any of their engine overhaul/repair stations, Germany, Singapore. UK, etc., it is up to them to provide this information to all operators in a timely fashion and in the case of Qantas, notify and take care of any technical issues on the 9072's.
In reality, we will probably never know the details. But the real point is that it should not have happened in the first place if the "checks and balances" during the engine design and review stages had been accomplished properly. There were "lessons learned" that were not learned.
In the US we have the NTSB that investigates incidents and accidents, determines the cause/causes and provides corrective action recommendations to the FAA. The FAA can either chose to accept, partially accept, or reject the NTSB recommendations. There has been a lot of "flak" flying in recent times that the FAA is too close to the airlines and manufacturers in the carrying out of their responsibility of safety to the general public, ignoring many NTSB recommendations. Don't know if the EASA has this sort of problem.
My intent was to describe LHT as involved in the retro/repair/upgrade. Their service of the id'd engines that failed/faced failure, is critical to the explanation for the defects.
The issue of Qantas Trent 9072 engine maintenance, under the Rolls Royce "Total Care Program" seems murky to me at best. I know what the program title says, but what does it mean? If RR had knowledge of technical issues discovered from any of their engine overhaul/repair stations, Germany, Singapore. UK, etc., it is up to them to provide this information to all operators in a timely fashion and in the case of Qantas, notify and take care of any technical issues on the 9072's.
What is the nature of the actions taken that now create a reduced possibility of in flight Burst?
Is the Mission of the EASA to protect Corporate proprietaries? Or is its Mission to protect the safety of the Public in Carriage??
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Turbine D
Thanks. I can appreciate your concern about lessons not learned. There is data about that supports your conclusions. It is technical, unknown to most folks (perhaps especially Qantas' Flight ops).
That deficiencies exist in powerplants on introduction is common knowledge. To my memory, none have ever been identified, and then ignored.
(send a PM)
Thanks. I can appreciate your concern about lessons not learned. There is data about that supports your conclusions. It is technical, unknown to most folks (perhaps especially Qantas' Flight ops).
That deficiencies exist in powerplants on introduction is common knowledge. To my memory, none have ever been identified, and then ignored.
(send a PM)
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Qantas A380s to return to US route, Airbus misses delivery target
The connection between the QF32 failure and high takeoff thrust on certain runways remains very mysterious if indeed there is any connection at all. Has all this delay been just about putting minds at rest and installing mod C engines? Anyway, very glad to see that things are getting back to normal.
I know that some people get a bit excited by near disasters but rememeber that "nearly" never hurt anyone. And you probably can learn as much from near disasters as from the real thing.
A good new year to Airbus, Rolls Royce, Qantas and All and sundry.
QANTAS is expected to announce as early as next week the resumption of its A380 superjumbo flights on its key international route between Australia and the US.
I know that some people get a bit excited by near disasters but rememeber that "nearly" never hurt anyone. And you probably can learn as much from near disasters as from the real thing.
A good new year to Airbus, Rolls Royce, Qantas and All and sundry.
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I note from the article in the travel magazine that the 'new' engines will have to be inspected after every 200 flights, then subsequently after every 100 Flights. Most unusual to see restrictions tighten after re-introduction and initial data.
The Airline person, anonymous, said the route for the 380 (LAX) is on a "wait and see" basis, so no new info there.
Airbus and Qantas are right pissed at RR, and you may want to read a more cogent and trustworthy source than a Sydney based Travel Office release.
The 900 has teething problems, the question remains, are they mitigable? The only way to know this is to examine what the workaround of the 972 truly consists of. Is the retrofit an upgrade that is thought to extend service life to advertised lengths? Or is it merely a buying of time, a compliance with existing AD's to take the heat off of reintroduction?? None of the C engines has enough TOW to give any results that can be analyzed, as of yet, no demands of 72k POT to the cycles or hours that The "A" acquired at time of the Burst.
The engineers who built and had certified the "A" are on the spot. Is it conceivable that these folk hadn't considered their lightweight newby might need upgrading?? How quickly can new internals be designed, built and tested to plug the gap in performance left wide open by the failure of the first iteration?
The bottom line is this. The certificate failed. Instead of re-certification, the Manufacturer is allowed to modify without returning to the procedures. There is no downside to grounding the 972 whilst rebuilding/replacing them, as they need to be off wing anyway. Pretty slick.
It is simply this: Qantas was offered and accepted the Thrust augmented 972 after Airbus found six tons of extra fat on the Whale. The Thrust came from a DEP, a "Chip" that opened the fuel a bit more on an engine that was DEP limited on shorter routes. The Max thrust was used carefully, in limited fashion, so essentially this engine had serious limits on it that made it a hangar Queen, a Route Limited Diva, or a test bed for how Rolls expected to gain market share. Sell engines by opening the throttle, and limiting its life. That isn't a new engine, that is a "warmed up" leftover.
The Airline person, anonymous, said the route for the 380 (LAX) is on a "wait and see" basis, so no new info there.
Airbus and Qantas are right pissed at RR, and you may want to read a more cogent and trustworthy source than a Sydney based Travel Office release.
The 900 has teething problems, the question remains, are they mitigable? The only way to know this is to examine what the workaround of the 972 truly consists of. Is the retrofit an upgrade that is thought to extend service life to advertised lengths? Or is it merely a buying of time, a compliance with existing AD's to take the heat off of reintroduction?? None of the C engines has enough TOW to give any results that can be analyzed, as of yet, no demands of 72k POT to the cycles or hours that The "A" acquired at time of the Burst.
The engineers who built and had certified the "A" are on the spot. Is it conceivable that these folk hadn't considered their lightweight newby might need upgrading?? How quickly can new internals be designed, built and tested to plug the gap in performance left wide open by the failure of the first iteration?
The bottom line is this. The certificate failed. Instead of re-certification, the Manufacturer is allowed to modify without returning to the procedures. There is no downside to grounding the 972 whilst rebuilding/replacing them, as they need to be off wing anyway. Pretty slick.
It is simply this: Qantas was offered and accepted the Thrust augmented 972 after Airbus found six tons of extra fat on the Whale. The Thrust came from a DEP, a "Chip" that opened the fuel a bit more on an engine that was DEP limited on shorter routes. The Max thrust was used carefully, in limited fashion, so essentially this engine had serious limits on it that made it a hangar Queen, a Route Limited Diva, or a test bed for how Rolls expected to gain market share. Sell engines by opening the throttle, and limiting its life. That isn't a new engine, that is a "warmed up" leftover.
Last edited by bearfoil; 2nd Jan 2011 at 13:15.
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The certificate failed.
I think this is quite wrong. There is nothing wrong with the type certification process. Engines meeting the relevant specifications will perform as expected albeit that a new fleet will inevitably have teething problems. In this case the engine was defective and so cannot be expected to perform in the same way as a normal engine because a defective example is not representative of type.
Following the engine failure there was obviously much more focus on teething problems to see if the known issues were linked unexpectedly to the engine failure. Once oil fire becomes a reality the pressure is on to deal conclusively with any already known imperfect oil seal even if it is not an airworthiness issue.
The type is easily capable of the thrust required for the North America flights. What has been at issue apparently has been the durability of the HP/IP support structure now apparently improved to unlimited life cycle through two successive modifications (B and C).
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Yes, the type certificate process is not flawed. The engine is. How did you read my post as critical of the process?
The HP/IP structure is having problems because the engine has new demands on it, and the test process was based on insufficient information. I notice you have relented on your position of "stub pipe duff, let's move on" ??
This iteration of the 900 is expected to produce higher power at higher RPM, an invitation for gremlins to pounce. Vibration, Lightweight, and new components in a design that doesn't share enough of its predecessor's systems to qualify as a "Sister", a follow on, or a family member perhaps.
An "apparently improved" HP/IP structure?? Have you some idea what that would mean, and do you know how long that would take and that it would disable current authorization? Added weight, augmented milling and dimensions, new testing, etc. etc. Stop flailing at windmills.
Contra Rotation, higher discrepant RPM in the same box, and a "Standard" Oil System. Throw in LP vulnerabilities (via "standard" dimension, heft, and tolerances), and would you even consider that this "C" model might have better been named an "A" model of a different lineage??
An "apparently improved HP/IPstructure" Have you some idea what that would entail?? Thicker web, enhanced diaphragm dimension, and additional structure. That means a re-design, and an abandonment of the certificate. That puts the 900 effectively out of production. Over, Finito. The DEP method of sequential thrust enhancement is at risk.
The HP/IP structure is having problems because the engine has new demands on it, and the test process was based on insufficient information. I notice you have relented on your position of "stub pipe duff, let's move on" ??
This iteration of the 900 is expected to produce higher power at higher RPM, an invitation for gremlins to pounce. Vibration, Lightweight, and new components in a design that doesn't share enough of its predecessor's systems to qualify as a "Sister", a follow on, or a family member perhaps.
An "apparently improved" HP/IP structure?? Have you some idea what that would mean, and do you know how long that would take and that it would disable current authorization? Added weight, augmented milling and dimensions, new testing, etc. etc. Stop flailing at windmills.
Contra Rotation, higher discrepant RPM in the same box, and a "Standard" Oil System. Throw in LP vulnerabilities (via "standard" dimension, heft, and tolerances), and would you even consider that this "C" model might have better been named an "A" model of a different lineage??
An "apparently improved HP/IPstructure" Have you some idea what that would entail?? Thicker web, enhanced diaphragm dimension, and additional structure. That means a re-design, and an abandonment of the certificate. That puts the 900 effectively out of production. Over, Finito. The DEP method of sequential thrust enhancement is at risk.