While there seems to be much conversation the cause of "bangs" heard.
How about HP/IP bearing fire, bearing seizure and IP turbine wheel on end of said shaft shearing off could be BANG #1

Bang #2 is when IP turbine disc of huge mass bursts its way out of the turbine case travels upwards and hits the nacelles thankfully overdesigned "firewall" and shatters sending disc segments blades thru the wing, wing to body fairings thru air-conditioning bays, fuselage, fin leading edge etc.
That is the Bangs covered. Much of the gas path theory being discussed with a giant slit in the turbine section to describe the bangs heard is beyond the scope of my experience.

( Please see the above comments with tongue firmly in cheek.)

IP coupling failure. ?? There is an inspection of the IP shaft coupling for wear (trent 900). It is a laborious and tedious task and was being scheduled as per requirements but it is unrelated to this failure.


This does look to be the case but who else is qualified with large engine and metallurgical technology, GE or P&W ? I don't think that will happen.

To look at the root cause of this incident, if it were as simple as quality control issue and poor manufacturing of an oil pipe. RR would have said check your engines and if no fault found fly on. But this did not happen.
RR said fly on but don't use (no de-rate) high thrust even thou "high" thrust was NOT being used at time of the incident SIN - SYD.

The Trent 900 was developed for A380 when there was a perfectly acceptable Trent 800 with 110 inch fan producing more thrust than was required of the new T900 116 inch fan.
What was changed in the core engine? Why was it changed? The T900 is heavier, larger and produces less thrust.

IMHO I think I will be seeing a modification program mandated by RR to replace the turbine bearing section with a module that will look incredibly like the same fixture fitted to a T800 to take the stresses of the engine at the top end of the design thrusts.

As someone has already said “As regulators they do no more than RUBBER STAMP what the manufacturers tell them”
A setback or design flaw, I guess it depends if you are an accountant or an engineer.
2 cents

Bolty McBolt

If you read back, you will find bearing seizure is addressed. Also Stall/Surge. In my opinion, whether the HP/IP Roller bearings failed (I think they did) or not, the problem is at the Rigid coupling, the IP/HP thrust (Ball Bearing) locale. This "Module" is insufficient in service to withstand not only great Thrust, but its own idiosyncracies that disqualify it as TRENT anyway. The weaknesses are not my imagination, they are documented and described by the regulator, and stingily by the Actions of the Manufacturer in attempting to design a new engine whilst it (the 'current' iteration de jour) labors on wing in Public Carriage. The "C" mod is not capable of solving the teething problems to satisfy the parameters of the original certificate. It is a Stop Gap, an attempt to keep the engine viable. The alternative is to admit the engine is not ready for service, and face economic failure, and potential criminal prosecution. Will we see this circuitous fraud in the light of day?? Perhaps. Are you a betting man??

Will the "C" last to the expected service life? I think not, another newer module will replace it, and on, and on. What do you think?

bearfoil:
A commanded engine shutdown is only possible through direct connections from the engine master switch to the HP fuel shutoff valve or from the fire push button to the HP and LP fuel shutoff valves. The EEC's authority to close the HP shutoff valve is limited to a few specific cases (e.g., aborted start sequence or certain protections). The fact that engine 1 could not be shut down indicates defective wiring between the switches and these valves but does not imply that the EEC had any problems in controlling its engine as designed.

Independently of this, I still wonder why exactly engines 1 and 4 went into degraded mode, i.e., what led to the loss of internal and external(?) data (certain pressure and temperature measurements were mentioned in an older post) that is supposed to cause this degredation.

Not randomly. Under normal conditions the active channel is changed with each engine start.

Derg:
if it only would have been so simple - we have had in Poland a case last April when in the plane crash some 96 people died including a President and practically all top brass people (for the sake of this we can assume it should equal to IPT landing at 10 Downing Str). And within a short time what do we have - business (+politics) as usual. Moral issues are treated as tools for reaching the targets. Even the Church has stepped into this minefiled and lost its moral credibility.
Some say it is a sign of stable democracy (true) - but we can also say that politics are just the changing curtain covering ever greedy corporations and ever greedy shareholders - does it mean that We (people) are the problem?

I do also have trust in Australians - they do have to care for safety as their land is kind of really empty inside and surrounded by big waters on the outside ;) - their planes do have to fly safely!

DERG - Oils are approved for use by brand name, not spec. A new brand will need to be extensively tested before clearance including lab tests and endurance running. Testing is the responsibility of the Type Certificate holder, results need to be approved by Certificating Authority.

RB211-535 uses 180deg oil, for many years, with no probs.

Eureka!

A664

My mistake, yes the EEC Channel A/B selection at start is normally alternated.

This prevents the accumulation of dormant faults, normally.

However, between starter cut-out and Idle, the EEC may select a channel change. If one Channel has defects, the other channel will be selected for control. Also, if both channels have defects, the channel in control at identification of defects gets (retains) control.

As to degradation, (#1, #4). The EEC monitors/controls the Engine through motors, solenoids, and relays, while transmitting data to the a/c (Cockpit).

The Channel that is in control can make use of the standby channels logic, inputs and outputs. If a like output is faulted in both, the control Channel is the one that remains in operation. So the EEC communicates with the a/c. It maintains and supplies data for fault analysis to other systems on the aircraft. To what extent each of the other EECs is contingent on the failure (or failure reads) of one or both Channels of #2 I am unclear. Can you help with that??

RE: Fuel cutoff. One assumes that the "protections" limiting EEC authority to halt fuel supply include Overheat, and Fire. At the Burst, N3 was over limit. The Fuel is supplied by the HP Pump, which is driven by the Gearbox shaft, which in turn is connected to N3. Prior to 'shutdown' of #2, one assumes the HP was operating overlimits as well, and for a brief time may have been flooding the nozzles with fuel. Since the assumption is made that N3 at 98% was caused by fuel supply continuing past N1 N2 failure to turn, one also assumes the supply had continued, the supply may have been too "plentiful", and that EEC and or cockpit controls had lagged in protecting the engine from burst. Back to DEP, boosted thrust logic, etc.?

Oil Approval Guide
 

CAAD & DERG

Here is the process:

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/0f6f86064c839816862572c60065ba18/$FILE/ANE-2006-33.7-3A.pdf

Turbine D

Are we agreed then that Regulatory Agencies depend fully on the suppliers for specs and tests? (Manufacturers). ??

Does this require a mission that includes considerations other than Money?

Because at the end of the Day, Rolls, Airbus, and Operators will skate on their responsibilities. That is known. How much can we trust a system that is proved beyond doubt incapable of controlling its turf?? I have no patience or trust in the State of Regulation. They are known to be sycophants of the Firms whose actions they are required by Law to regulate. Is there another way to see it??

Turbine D

The Trent is not a US engine. It is from the UK and is therefore certicated by EASA. So the FAA process you quoted does not strictly speaking apply.

However the FAA process appears to be broadly in line with my summary.

Specifications are not usually tight enough. Hence brand names and careful control of oil suppliers is required

Actually the TRENT 900 isn't really a TRENT. Too fine a Point??

Where does that leave the Regulatory Agencies of, for example, Australia and Canada?

Broad Brush?? If the shoe fits......?? In general, if. after an incident, the immediate divulgence of fact and insult, counter insult diminishes...one is left with What, Exactly? The sure and certain notion that mitigation of reputation, money protection, and market is being "massaged"? Yes, I think. Who remembers how many "A"s came off wing, how many were (still are) subject to sanction?? Thought so. The diminution of actual data in favor of spin is instructive of the lack of concern for safety of ALL the players.

Turbine D
 

Thanks for your considered and very rational views over the past few pages. I think your processes are valid but am curious why the IPT blades were not "cookie cutted" away unpowering the IPT when the IPT migrated rearwards.

For your info, the two bangs were separated by about 1/2 second, so the two bangs were from very different processes. I like your thoughts of an HPC stall (boom) followed by the disc burst (boom). A time plot P30 would be of great help.

Less Hyperbole Please
 

For the contributors who make accusations against LU and RR ethics, I would suggest you look at the current long haul industry engine reliability statistics (6 x better than 180 ETOPS requirements), the failure rates of the 747-400 engines from 1989-1992 (I had two), and the current notices concerning PW and GE engines. The conclusions are clear.

BTW: The RR 972 max oil temp is 196 deg C, measured just before the scavenge filter, so an oil temp of 180 deg C is not uncommon.

CAAD

YES, the engine was originally certified by the EASA, but, it was subsequently certified by the US FAA. As to the oil, this presentation may give you better insight into EASA/FAA relationships.

http://isoclean.net/uploads/GE_turbi..._pres_STLE.pdf

35 Year Pilot

FAA Notice of Proposed Rule Making.

Request for Public comment: Under the existing Rule of 51, Hyperbole Reduction Act, Comment is requested.

I'll do my part, I realize I am a titch over the top. Thank you for noticing in a civil manner.

39 year pilot

TW IMC

The FAA is subject to all Laws of the United States. One of these is the Freedom of Information Act, better known as FOIA.

Under this Act, virtually all information owned by the people is subject to petition to disclose. The FAA will certainly receive all pertinent data from EASA. This makes it Public. There is not a single databit that is immune. I do not know the EU's rules, but I am familiar with FAA's. Whatever Secrecy Foreign firms rely on outside of the USA is nonexistent in this country. Every part, purpose and process utilized in compliance mode and timeline will be incorporated by reference in the FAA's decisions. So in a very real way, the EASA and the FAA are one, though the FAA has marginally bigger stones.

under the top

QF 32
 

Guys,

May I remind us all that the value of this forum is a place for discusion amongst professionals. In particular, the QF32 thread has revealed an enormous amount of experience and very genuine concern in our community.

There is information regarding the QF32 incident that has not been released into the public domain. That much is clear.

Please let us retain a civil attitude and respect towards one another, and an open minded and constructive attitude towards the various views being expressed.

The QF 32 outcome could have been much worse. I think we all wish to prevent such a recurrence?

35Year Pilot

Good question... My thoughts on this would be that the rotor sped up as soon as the power drive arm fractured at the 580 bolts, given the N3 speed at 98% and then it moved aft, with the blades contacting the smooth leading edge of the Stage 1 LPT nozzle inner band forward overhang. Now when this happened, there may have been enough force to shear the blades off, just above the blade platform, depending on some features I will discuss below. There was no contact with the Stage 1 nozzle vane airfoils as they are "recessed" too far aft. Obviously, this is not what you want to have happen from a design point of view to slow the rotor down. You would like blade on vane contact. In the failed engine, it is hard to tell some things relative to the blades. If you look at the recovered portion of the disc photo in the ASTB report, Figure 14, Page 21, you can see distinctly two blade dovetails in the corresponding disc slots (maybe a third, not sure). All the others are missing completely. The thing I wonder about is the fastening method used to keep the blades in the disc, forward and aft. I am pretty sure the mechanism to keep the blades from moving aft is a tang that protrudes downward at the blade dovetail (leading edge side and part of the blade casting) that keeps it from moving aft. The blades are inserted in the disc from the forward side during assembly. To keep the blades from coming out of the disc forward, a retainer clip is inserted in the space under the dovetail of the blade (you can see the open area in the photo) from the aft side of the disc, and it is then bent upward both forward and aft sides, thus locking both blade and clip in place. However, there is no evidence of any clips in the Figure 14 photo. Another important feature that I can't tell is if the blades are shrouded at the tip or un-shrouded. If they are un-shrouded, the blades (some) could be pushed out of the disc slots (whole blades) when contacting the nozzle inner band with some being fractured off as the retainers would fail from the stress/heat. If they are shrouded, I would think all blades would fracture off. We just don't see enough and I am not familiar enough with the Trent 900 blades to know for sure. But, either way, I think it was too late as the rotor was already speeding towards burst point before any contact of the stator behind it. Then there is the possibility the disc/rotor was wobbling as it moved back (uneven contact).

I would agree. If the cockpit voice data recorder could have saved the sounds, it could be overlaid with the rest of the engine data to determine the exact points of the bangs in the failure sequence. Now it will be a guess.
Regards and thanks for your comments,

Turbine D

I do believe there was wobble instantly as the Drive Arm Fractured (circumferentially). The seperation, Disc from Arm, would not be in any way orderly, and an imbalance (a certainty) would impart an elliptical and irregular orbit to the Wheel. My drawings show the IPT Blades (Roots) as below ('within the perimeter') of the Stator Vane "Platform". "Cookie Cutter"** shear off of the Roots would force the Blades through and out the front of the fir tree dovetails. Given the "Shake" of the disc (wobble) in its new orbit, the roots would endure a constant force forward, while being mercilessly vibrated, a suitable explanation for their loss from the Wheel??

I've posted this prior, I don't keep track of things, and I regret if this is but repetition. Naturally, any failure description needs to be indexed with a timeline.

Now as to Boom, a Compressor Stall is possible, but so is explosive loss of LPT Drum (Gas) contents. A loss of this highly energetic gas forward and through the lost dynamic seal of the IPT would explain also the rupture of the case, pehaps in concert with exit of high energy debris. If there is a one half second lag, do you think it possible that flowing fuel from the nozzles, Oil fed fire, and loss of IPT blades could explain events in this manner?? IOW, a gas explosion out the weakened case, holed by the IPT?? This might put the Burst in front of the "Stall", so help would be needed to explain this divergent view as to timeline.

**Acknowledgments to 35 Year Pilot

bearfoil

The problem I see with this is that it would completely wipe out the bearing structure below it and because the IP shaft is so close the the LP shaft, we would see rubbing or damage to the LP shaft. Based on the photos of the pulled LPT module (ASTB Report) there isn't any damage to the LPT shaft.

The recovered portion of the IPT disc (Figure 14 ASTB Report) does not show any damage to the disc posts between the dovetail slots and two of the turbine blade dovetails ("roots") that stayed in the slots look remarkably in good shape. That is why I think the contact point was just above the blade platform (airfoil) or maybe at the blade platform. If it was more toward engine centerline, we would see rubbing of the disc posts.

The way I see it, we are talking about what happened in between 2-3 seconds of time. P30 collapse = compressor stall + bang. This occurred ~3 seconds or less before disc rupture. Now I also think that the IPT disc rupture and the casing ruptures (both IPT and LPT Stage 1 Nozzle + the nozzles) releasing gas pressure would be one bang, all happening within milliseconds of one another.

For some reason, I think the fuel wasn't completely cutoff, but reduced, perhaps because the ECC was programed to recognize a P30 drop (compressor stall) and to provide for rapid recovery (air relight) or the need to restart the engine completely (air restart), but I don't know this for sure. But I think the ECC didn't recognize what else may have happened. This fuel flow could have added to a fire that was subsequently put out by engine shutdown and by the release of the fire extinguishing bottles.

Just some thoughts...

Turbine D

To clarify, I describe the roots and root walls as inside (radially) the Vanes Platform, to provide the same as you state, a fairly undamaged Root system.

This is a new architecture in the 900. The Nozzle Guide Vanes on the TRENT 700 (Edelweiss) are placed directly opposite their IPT Blade counterparts. With a fully fractured Drive Arm (Circumferential), the 700's Blades immediately effaced (rubbed) the Vanes, and slowed the IPT. This is regarded as the event that prevented an otherwise catastrophic burst. It is also thought that not only did the Blade/Vane effacement slow the wheel, it stabilized it, preventing further aft travel and chaotic loss.

In your opinion, what are the design/operational advantages of the "New" architecture in the 900??

Turbine D - The FAA, being sensible people, would not have repeated all of the work done by EASA in certificating the Trent. Similarly they will not be very much involved in routine continued airworthiness or lifing or approval of oils for foreign engines of reputable provenance.

As to the oil, I do not believe the GE presentation you identified precludes the need to identify oils approved for individual engines by brand name. I believe it actually describes an approval process.

Changing the subject a little, I thought that turbine blade root cross sectional areas were sized so as to fail in tension in the event of an overspeed. Thus hopefully limiting the extent of overspeed.

wobble at separation
 

TurbineD, bearfoil
there is no damage at the end bearings (roller) but the damage may be seen closer to front bearings, where the IP shaft splines are located

what bothers me is the way the drive arm of the IP turbine disk if bent (fig 15 from preliminary report) - outward as if the disk was forced first into the axis of rotation and only afterwards has flown away - but would it has enough place to move like this?

How about such alternative explanation:

separation of the IP disc from the shaft has happened longitudinally when the IP shaft has moved rearwards significantly enough to break out the mentioned drive arm with its 580 bolts instantly. Still this would require the IP disk to stay fixed longitudinally to enable the forced break-out. Roller bearing do enable such shaft movement easily as long as the traveled distance stays within the width of the raceway (here the raceways could be estimated at around 1 inch). To press out (break out) the IPT from the shaft it would need to move backwards by less than 15mm resulting from 2mm gap between the IPT and following vanes fixture plane and some distance to impose enough force to break the disk (for a rigid structure like IPT i guess it could be 5..10mm). This could happen only if the IP midshaft (splines) connection would got loose or separated. Suddenly free front end of the rear shaft, not supported by the roller bearings anymore, would wobble and move rearvards driven by the IPT. But than what would break the disk from the shaft? Two possibilities: (1) high energy from the rotating disk (2) significant longitudinal force coming from the screw used to keep splined shafts together. If the splines get loose, two parts of the IP shaft start rotating against each other, front part stays fixed by the roller bearing but the the rear part of IP shaft presses the IP turbine against anything available to slow it a little just enough to get shafts unscrew from one another (4..5 full rotations would be enough) to press-break-out the IP turbine disk drive arm from the IP shaft. Disc goes free to speed up and fly away. No roller bearing get damaged except the bearing supporting the IP shaft which has to support wobbling shaft .

how the splines could have separated - easily if splines are worn out on outside diameter - fire in the bearing box would suddenly heat up the external surface of the shaft which would thermally increase diameter enough to splines get free - no need for Oldham razor here ;)

does it make sense?

WojtekSz

Of course sensible. This is the very mechanism by which EASA and FAA (by reference) alerted the operators would (could likely) cause catastrophe. The Splines serve at an intermediate joint. By definition this joint has clearances, else it would not allow rotation. Excessive wear of the Splines, detailed minutely by the regulator (via Rolls), allow distress at the coupling. The loss of radial commitment due scrubbed splines is the mechanism of failure. But the wear is caused by something. No sane team would field a system of extreme importance that had disqualifying levels of failure at an interval of 400 cycles since new. Yet this is exactly what was encountered by dozens of supplied powerplants to Airbus.

The IP aft shaft and fore shaft create a perfect environment for damage through vibration of their Splines. Any vibration here, at the Thrust Bearings, in close proximity to the HP shaft and LP shaft is amplified by the joint itself, with elements of whip, and bind. If this is the case, wear would be rapid, and progressively worse through the passage of time. The more the wear, the faster it wears. At the end of the sequence, the Splines are 'immune' from a 400 cycle inspection. It would seem to be more prudent to lessen the interval for borescope as the engine's life exceeds its first inspection limit at shop visit. Perhaps it was not a misprint that the "C" Mod was to have its first borescope at 200 cycles, then only 100 after that. So, 300 cycles and then what?? The "D" ?? It cannot happen that way, it is an admission that this engine is being designed on the "fly", with passengers aboard.

The Roller bearings at the end of the IP shaft end up being the area of least expression of wear, their purpose is radial resistance to stress. It is in this dimension that the failure mode at the Drive Arm presents, hence less likelihood for failure here. The Roller bearings run in a smoothe channel, their axial movement appears to be snubbed by their cage. It isn't farfetched to think that since the Axial drift is snubbed at the Ball bearings, no provision to stop the rollers from drifting was supplied. If the vibration at the LP and IP Shaft area is the problem, the Ball Bearings need to resist not only thrust, but radial and also divergent (chaotic) stress. This is obviously of concern. Instead of a conforming stress to the bearings as designed, each ball is subjected to changing stressors, independently of the others. Wear becomes random and irregular, hastening by a great deal the failure of the bearing itself.

Trent 800 >> Trent 900
 

The ongoing discussion about rules and regulations applied or questioned by the one or the other member of this circle are, what I would like to call an additional battlefield to take care off. I admit that my imagination stretches far enough to understand the expressed uncomfortable feelings about institutions, operating like state administrations, but responsible for so sensitive items like certification of aircraft engines. However, to be honest, one must concede that no one within these official bodies is intentionally wrong doing. Thought that needed to be said ones at a time.

Since Bolty McBolt brought up the comparison of Trent 800 and Trent 900 engines, this has drawn my special interest. I looked for a way to compare the engines as far as possible visually. That worked by using those RR issued brochures of the Trent 800 and 900 engines cutaways.

Provided RR has not set up these two pictures at different scales and keeping in mind the relative non precise method of measuring parts on a 26 " screen I found these differences between the two engines.
All length measurements show greater values at the T 800 for IPC, HPC, combustion chamber, etc. than on the T 900. The more it surprises me that the distance between the ball bearing Nr. 1 and Nr. 3 and especially Nr. 2 and Nr. 3 are shorter than those found in the T 900.

In connection with these findings a question to the engineers:

Is the tendency to flutter of a longer rotating cylindrical body - HPC-module - compared to a shorter, more compact desighn to be expected on a lower level ? With other words, could one expect to have a longer cylindrical body accelerated to comparable rotating speeds to run smoother and with lesser vibrations ??
What influence- if at all - does that greater distance between bearing Nr.2 and Nr. 3 have on the stiffness of the supporting structure between these two important bearings ??

What also is very obvious in that comparison of engines is the fact that the construction of the diaphragm / plenum chamber in front of the IPT disk is completely different, as is the desighn of the bearing chamber. Also there is no sealing diaphragm between the rear of the IPT disk and the plenum inside the LPT.

So, as Bolty McBolt has mentioned, why in gods name was that T 900 developed and used on the A 380, having a well desighned, functioning, more powerful and line proven engine in the inventory ??

Handbook of case histories in failure analysis


Handbook of case histories in ... - Google Ksi??ki @ transportation components pp.17
provides and intersting example of excessive spline wear in Mirage III flown by RAAF - due to fretting wear. Very instructive pictures. Most probable cause: incorrect machining error

does it look familiar to incorrect machining of the stub pipe?

source and more info at : Fretting Wear in Lubricated Systems - most important points:

• increasing load or unit pressures tend to generate higher wear rates
• Fretting seems to progress more rapidly in friction couples that have smooth surface finishes and close fits.

Sounds like a great idea (fusing) but it opens up other cans of worms.

A common blade attachment max stress level at 100% operating RPM in tension gives a 50% margin in overspeed. Tensile margins are nice when one considers their interaction with vibratory stress levels in a spinning machine (Goodman Diagram) but if you were to design every disk with something greater than the blade margin you would have an extremely heavy engine.

Then one has to consider the mass of the blade being released in a fused overspeed, and whether its practical to design containment for that event. In the end many things are considered together in protecting against overspeeds with the majority of the consideration being placed on limiting the speed the machine can get without being uncontained.

By-the-way, it's more likely that the stretch in the disk will open up the fir tree and release the whole blade before the attachment would fail (common in a disk over heat event)

Annex14

Can you give me the http: for the Trent 800 RR brochure? I would like to see it.

Thanks,

Turbine D

lomapaeso

Thanks for your insight here. In fact, you can see this opening up in the ASTB Figure 14 of the recovered disc section where the couple of blade dovetails remained in place for whatever reason.

Derg:

thanks ;)
i have posted the link to both books to propose an explanation on how the shaft's splines have gone away as this is the problem RR has to solve. And this may in fact also include some clever redesign work to reduce vibrations, possibly even using some ingenious damping techniques or just making the splines much more durable if reducing vibrations prove to be difficult.
The scavenge oil tube to me is a clear example of extremely poor machining and louse quality control - completely out of the way it is presented in the BBC program on building RR's engines YouTube - Rolls-Royce, How To Build A Jumbo Jet Engine -HQ- (Part 1/4)
it is a MUST see it to learn how much science+effort goes into the engine. Some really interesting things are shown there - i would have written 'suggested reading' but it seems more like 'suggested watching' ?

I think the scavenge tube is fed by a tray, or gallery, responsible for collecting hot Oil at the 'bottom' of the bearing case. I think also the challenge for Rolls is to detune the Thrust case from the LP shaft, keeping in mind that Thrust is borne in other areas besides the Ball Bearings. There are struts in the IP case that connect further forward, assuming a great deal of forward push from the engine.

De-Tuning I think will prove insufficient to correct the problem in the 900. To isolate massive vibratory impetus would more than likely involve strengthening the Shafts by adding metal. Inside Diameter? Outside? Both? This motor is already at maximum relative to clearances, weight, and power. If all it meant was adding weight, easy peasy. There are dimensions that actively resist any solution by addition. These dimensions likewise prevent subtracting structure without losing Thrust. Losing Thrust at 72klbs prevents puffing out the rest of the 80k that was sold, and paid for.

Least possible of all is to change the architecture. The architecture was modified already, and away from a proven model. Go Back?? As Woj points out: Back there lies the 800.

bearfoil
the strange thing with vibrations is that sometimes you can get better results by getting the item actually lighter (remember the famous story of Mr Citroen?). The trick is to get away from certain frequency and you can move up or down in frequency by getting the part stiffer or more flexible, lighter or heavier, or both :)
900 has different proportions to 800 so the internal structure frequencies has changed and solutions from 800 might not fit the new engine. A new equilibrium has to be searched for.

WojtekSz

Thanks for your YouTube post, it was enlightening. I would encourage everyone to look at the Part 2 of this series:
YouTube - How to Build A Jumbo Jet Engine - 2/4 (Full Version)

About half way through, the process used to make the turbine blades is shown in good detail. Both the HPT & IPT blades are made this way (single crystal) with the IPT blade being solid, non-air-cooled. Also, note the machining section. After I looked at this:

35Year Pilot
I take back the idea the blades were pushed out of the dovetail slots. lomapaseo is correct, the disc stretched, releasing most of the blade dovetails from the corresponding disc slots. Also, the blades are shrouded at the tip and are interlocked by means of the z-form shrouds. This means that all the blades probably fractured near the platform upon contact with the LPT nozzle inner band ring. The machining tolerances of the dovetail forms are so tight, they couldn't be pushed out of the disc slots, unless the IPT rotor blades all came out uniformly in mass because of the shroud interlocks, an unlikely scenario.

DERG

I am not a RR guy so the Trent is a slightly different animal from what I am use to seeing as far as the details go. But, basic design principles apply regardless of manufacturer, RR, P&W, GE or EA.

bearfoil & WojtekSz

I am going to give you my thoughts on the Trent 800 vs Trent 900 and IMO, what I might think of the Trent 900 design in a new post.

Turbine D

Trent 800 brochure

mike-wsm

Thanks for the Trent 800 link.

mike-wsm Turbine D
 

mike-wsm Thanks for posting the link. I am just back from an event and would have to start the answer to Turbine D´s request.
Hope it works as it did here.

Turbine D
 

I have also this
Large aircraft engines - Rolls-Royce

May be interesting since it gives access to all the biggies.

DERG
I agree with you on the ever increasing oil temperatures. The tent is being moved closer to the edge of the cliff.

As things are moved closer together as is happening in the newer engine, heat dispersion is a problem, especially when a hot engine is shut down and the soak temperature rises higher than the maximum operating temperature of the oil. IMO, coking is still a problem and major concern even with the newer oils.

Fellows......(Fellettes??)

It's been a real slice. Them videos are telling: "This missing assembly could cost Money, so the situation is critical.." All that marvelous effort by folks who are brilliant, and actually care about their work, who are cut off at the knees by the greed and borderline criminality at the back end.

The machinery is first rate, when given an actual chance by the accountants and marketing. None better. The TRENT has become a fiasco, instead of the Beautiful expression of the Art that it actually is. It gives me goosebumps it is so exquisite.

Underneath the grimy newspaper it is wrapped in by cost cutters, and Marketing knuckleheads, lives a true masterpiece, thought I'd get that straight........

Changing Frequencies now, JB is far more fun, but I'll keep this one in the box.
Don't take no wooden nickels.