QANTAS A380 Uncontained failure.
 

Continued from previous thread here.

Turbine D

You propose a "false bearing" developing between IPT and LPT NR. You also suggest two possible causes for this contact. Fire is one, and Shaft failure another. I would offer that in the two previous failures, the disc was retained because there was not overspeed. In one case, (Miami) the Disc had separated from the Drive Arm in a "Circumferential Fracture". The second is still under investigation. For the reputed cause of QF32 uncontained failure, RR has offered "Oil Fire". Oil Fire in the Roller Bearing case was due to uncontrolled combustion specifically (Your tenet). There is not evidence of oil fire showing on the LPT module, and the gases involved would have to have overcome the Pressure in the IP/LP cavity, no mean feat. So what is left is heat acting on the Drive Arm from the front face, having escaped two sets of seals, and blowing past Roller bearings that presumably were still serviceable. Sounds unlikely, and that leaves Shaft Failure as the cause of disintegration of the IPT. The Shaft failure that comes to mind is the one predicted as a result of Spline wear/failure by the AD's.

Do you have an opinion on the generation and advance of the "Oil Fire"? How do you read the AD's prior to November 4? Do you consider the Splines as exonerated?

Bearfoil

In a design of an engine, fire and shaft failure are important items that must be addressed due to severe resulting consequences. In the Trent 900, I think fire was the culprit, not shaft failure.

I Agree.

Not exactly. The fire did not occur inside the roller bearing box, it occurred in the cavity which is part of the frame next to the IPT disc.

From the EASA AD's:

The IPT rotor did overspeed on the Trent 900 and there was evidence of molten metal splatter on the recovered portion of the fractured disc.
Again, from a EASA AD introducing a electronic software modification:

The LPT shaft was protected during all of this event by the presence of the IPC/IPT shaft. Everything went outward, some rearward but not as much as if the IPT rotor blades had born the brunt clashing with the Stage 1 LPT nozzle vane airfoils.

I think everything in the Trent engine was operating normally. Remember, the engine had been inspected for spline wear and must have passed the requirements for continued operation as no corrective action was required. Obviously spline wear at an early stage of engine life is of concern and requires a more permanent corrective other than shortened periodic inspection. I do wonder if there is unusual vibration or harmonics being passed through the system when splines are wearing so rapidly. This vibration, if present, could affect anything in the torque field.

Turbine D

Have you taken into account the AD amendment which lowered the amount of metal left on the Splines necessary for continued on wing? The original AD requirement was for an off wing strip if any single Spline showed wear of 2mm or more. Later the requirement was relaxed to require an average only of not more than 2mm for all the Splines taken as an aggregate.

Obviously, an average of 2mm wear for all the Splines would allow for some splines to have worn a good deal in excess of the 2mm previously allowed. At certain aspects of Load and Strain, this joint can be bearing several thousand pounds on Two Splines alone. One gets the magnitude of accelerated wear (per cycle) when the damage is expressed in this way. No argument why EASA was demanding borescope of the Splines at every third Landing. Likewise, even with the inspection, seriously rated Thrust and Loading METO.

Now to me, I "get" the "Oil Fire". I understand the willingness of some to claim the new (post uncontained event) AD absolves the Operators of application of sanctions re: the original (and still in force) AD's. To my knowledge the Splines AD's are still in force. If this is so, the manufacturer may be performing retro fits of the internals that caused the Splines to wear so quickly, and replacing "Oil Pipes" at the same time. I am unfamiliar of the Regulatory process that allows an operator/manufacturer to ignore prior and "unrelated" AD's simply because they are honoring new ones?? Can you help with this??

Add: The vibration problem is well known, yet seems to have escaped comment here, will you be the one to elaborate?
Also, the drive gear for the gearbox, Fuel Pump is fixed to the IP Shaft, is there possibility of some loss of metal when the IP Shaft migrates aft?

I take your point re: the Blades/Vanes miss and would like to point out that the friction/clash w/o blade clash would occur at the Drive Arm Return "corner" verse the Stator. If aft migration of the Wheel/Drive Arm was gradual, one can entertain the heat that must have been generated. Lost (molten) metal from the Stator/Drive Arm interface would explain the "splattering" molten metal on the Aft face of the Disc. It is this metal/metal contact I believe the AD references as possibly causing uncontained failure with damage to airframe and humans on the ground. It is for this reason among others that I believe the engine failure was caused not by Fire (forward of the IPT) but heat and damage Aft of it. I don't believe there was time for the Oil Fire to have soaked the IPT from one side, when the Drive Arm failure is not only demonstrable here, but also in two prior events.

A possible source for the ball bearings that resist thrust in this part of the engine is New Hampshire Ball Bearing, HiTech Division. Airbus notes their product as being in the A380. The bearings "Inch Series, Thin Section - Radial and Gothic Arch" are available in 1/2" bore steps up to 10" bore. I have to check Airbus' other bearing suppliers for the A380 before I can be more certain, assuming I can get equally good data (experience teaches this will not be true with every supplier). Their link is at nhbb.com and p29 in the catalog (p30 in the pdf) is wanted, in case of trouble with the link:

http://nhbb.com/files/catalog_pages/HiTech-29-30.pdf

I'm not sure these are big enough for this job, as 13754 lbs thrust is the highest capacity listed, using chrome steel (52100). You can find special products on the site, which mentions that spent oil pickup extensions can be placed on the inner races, and that puller grooves can be put in the outer races, dogs to prevent rotation in the outer housing, etc. NHBB makes custom bearings also; the largest cataloged standard bearings are 1/2" cross-section with 1/4" balls.

One thing to note is that thrust capacity increases with diameter, and is hard to come by. Taken with the fact that machinery is usually designed with only two bearings per shaft, and a flexible coupling is used with more than two, we immediately know where the center bearing is on the LP shaft. It has to be on the larger forward shaft; on, adjacent or near to the boss housing the interior splines. These splines have to accomodate angular deflection between the two sections of the shaft, more at some times than other times.

I have been wondering for some time if the helical twist to the splines is also put to use providing a clamping force for the inner race of this bearing. Given that thrust resistance is so hard to come by in this bearing, I have no doubt that the primary purpose of the twist is to transmit the tension load, created by the aft gas forces on the LPT blades, directly forward to the fan. This reduces the force on this bearing.

Parts of this reasoning can be applied to the IP shaft, which also has a set of splines.

What I am thinking is that if we have an oil fire, we have to look for a source of ignition. Talk about oil flash point (tech board) is all well and good, but the fire point is another, where a pool of oil under an ignited flash will burn without self-extinguishing. That's a bit higher, but the auto-ignition point is substantially higher--404 degrees C in the recommended Mobil Jet Oil II (as shipped from the factory, a highly-inhibited ester synthetic). There seems to be some discussion as to a change in oil in some of the QF32 engines.

Where was the source of energy to ignite this oil fire? Even an explosive mixture of gasoline fumes will not be ignited by just any spark. I think even 15 mA circuit contacts are permitted now in such atmospheres. I used to use a bowl of gasoline to quench the stream of sparks coming off my grinding wheel (the same leaded gas I washed my hands in). Well, definitely don't try this at home :).

One thing that seems worth a look is the effect of the unrestricted ops for oil temp up in the 190s-C, as compared to the more common 160-165-C in some other jet turbines. I'd say the 160-165 considers a limit to viscosity reduction to maintain adequate bearing lubrication and cooler running, although it may consider use (military?) of the Dow non-varnishing synthetic (glycol). The higher temp in the 190s seems to push the 3% evaporation limit in 6.5 hrs (a regulation?), here at 204-C for the supplied oil, on the cutting edge upstream of the measurement. Oil also has the advantage of being someone else's oil, and maybe not the oil type shipped in the engine. Just observations. I could not locate any lubrication recommendations on the NHBB site, except possibly in referenced industry standards (typically costly to obtain now).

TurbineD
 

Thanks for the comprehensive explanation, I am always open to learn more!

I think what all our efforts to clarify the sequence of events hampers is the shortage of reliable information and pictures. A closeup picture of the rear - roller bearing chamber and drive arm residues, or a similar picture from the central ball bearing chamber and LP / IP / HP shaft situation may probably give us the information we now more or less are guessing at.

I also think that the findings of ATSB, stating break of an oil tube and oilfire near the IPT disk are doubtless correct. They have had the pieces in their hands, we have only seen pictures.

Yet, the question must be allowed to ask: what, where and when started the oil fire ? Was it really the pimary cause - the oil fire - or secondary to the extend that it had no influence on the drive arms break up ??
I have a problem to become convinced that the oil fire did it, seen the total time elapsed since take off, the obvious scarce space in front, looking FTA, of the IPT disk and underneath towards the drive arm and the total mass of that disk. Therecovered part - about 1/3 was an estimate - weights about 70 Kg, times 3 makes a total of roughly 210 - 220 Kg or 450 - 500 lbs. I can´t see how that big chunk of metal can be heated beyond desighn limits under the circumstances prevailing.

One other hint that might point to a different cause I have found checking through these graphs added to the ATSB preliminary report, Fig. A2 and Fig. A3. The latter is the one that shows the recording og oil related data. There is that faint drop in pressure - total of about 5 Psi - starting at the same time the oil temperature raise. Oil pressure remains the entire final second above minimum oil pressure requirement - taken from the Certification Form, it even hikes momentarily before disk break up, drops, comes back before final drop. Oil temperature raises steady and falls after break up. The steady rise of oil temperature indicates to my understanding an constant heating in progress.
Meanwhile and untill several seconds after breakup the measured oil quantity remains level.
My conclusion, the final break of the repeatedly mentioned oil tube occured either seconds before, at or immediatly after the breakup. Oil will have become ignited by the hot parts of the engine or the hot engine gases beeing blown into that cavity on break up.
Could be that I am wrong with this entire theory but I thought there a lot indications that I can´t be that far off.

Old Engineer

I think the fire occurred in the chamber that is part of the frame located just forward of the IPT rotor. In a two spool engine, this frame would be best described as a turbine mid-frame. It is a very troublesome and complex component because of its location and the temperature gradients (stresses) that occur on acceleration/deceleration and resulting fatigue. On early two spool, high by-pass engines, this mid-frame was present, but on newer engines it has been eliminated by moving the bearings and bearing structures forward towards the compressor rear frame.

If you look at the Trent 900 cutaway, the frame (a multi-piece fabrication) consists of an outer ring (casing), airfoil like struts in the hot gas path (could be radial or could be tangential) connected to a highly formed and shaped thin wall 360º plenum chamber which supports the bearing system at the inside diameter of the frame. I would suspect each of the major components are of different materials selected for temperature, strength and formability considerations. I would believe the interior of the the struts and plenum are cooled from air drawn off the compressor to cool the oil lines that pass through the struts and plenum which feed the bearings and drain oil from the sump. Although not shown in the cut-away, I think the stub pipe in question is located in this plenum. This is a very hot area of the engine.

The gas path temperature entering this frame would be somewhere around 1800℉ (982ºC) or higher. I say this because the IPT rotor blades, which are solid (non-aircooled) are made of a single crystal high temperature superalloy.

Now if the stub pipe ruptures as they say it did, the oil pours out into the plenum chamber, no doubt causing a change in cavity pressure and perhaps overcoming the cooling air being provided. If the pressure becomes great enough, a failure could result in the plenum itself or the connection of it to the the airfoil struts resulting in a flash fire right next to the IPT rotor disc.
The heat generated increases the temperature of the disc itself, and it wants to stretch starting at the bore giving way to the failure of the power drive arm at the shaft flange 580 bolt holes resulting in the capability to begin to overspeed and move rearward.

That is my theory on how the fire ignition started.

Bearfoil
The way I would read this is that, through the inspections and measurement process of the original AD, it was determined that the wear of the splines was somewhat consistent spline to spline rather than being a skewed situation where some wore much greater than others resulting in the amended AD.

I would believe the AD for spline inspection is a continued requirement until such time a corrective measure is proposed by Rolls Royce and approved by EASA. Then the current spline AD would be replaced with a new one (or revised one) that would instruct the operators to incorporate the change/improvement by a certain time or specific engine cycle completion after the last spline wear inspection. The two AD's are completely separate from one another and accomplishing one (check for oil leaks) does not relieve responsibility to perform the other (spline wear inspection and measurement). I am sure this doesn't make any of the airline operators happy at the moment as it is disruptive to scheduling, etc.

Old Engineer
 

May be this link is of help for your search for the bearings used in Trent 900
Schaeffler Technologies *|*Sectors / Key Industries *|*Publications
Look for the .pdf file "Takeoff to the Future and there on page 13. There they state that all the engine bearings used in the Trent 900 as well as the GP 7200 are their brand.
Hope that helps

Thanks Turbine D for your analysis, to me it makes sense.

You seem to know your way around a jet turbine:) (guess your name stands for turbine designer, is 70 correct though or are you still active?).

The fact that RR did not have guide vane noses who could stop the IPT is interessting, saftey sacrificed on the efficiency altar?:rolleyes:

Re bearings, FAG is one of the renowned bearing companies in the world together with SKF, Timken et al.

The direct link to the PDF file is

http://www.schaeffler.com/remotemedi...9110_de_en.pdf

Check the silhouette cross section of the recovered disk piece with the cross section published above.

Turbine D

I note your take on the AD amendment to allow an averaging of wear for this powerplant's Splines. I don't fully get your conclusion. If the 5mm wear limit was not superseded, the engines would have been "less available" to the operator. An allowance for averaging seems clearly meant to allow any single Spline with maximum wear to continue on wing, whilst its mates had time to "Catch up". I cannot read this amendment another way. If wear had presented as consistent spline/spline, no change in AD would have been considered?? If not consistent, an average allows the weak link to degrade further??

A poster has directed me to assess the chronologies reported in the ATSB prelim. Report. Specifically the N values as they wander, synchronised with the Oil System reads. It is quite revealing. The time line would dispute quite clearly a cause of failure as some Oil System anomaly. Take a look. Check Oil: Pressure, Temperature, and Quantity. It is quite interesting.

lomapaseo

Also, check the ATSB Preliminary Report, A0-2010-089, Page 21, the photo of the disc cross-section, the fracture surface. Additionally, note the wording on Page 21 and 22 as to the description of the disc failure itself.

Take note of the "Oil Tube" image. Enlarge and notice what appears marked as "Misaligned" Counterbore. The arrows point to surfaces that have worn due to vibration and constant relative movement. The missing metal is clearly NOT machined away, evidenced by the round "coving" at the intrusion on to the affected wall. The missing "Rim" material appears to have broken off cleanly, rather than fractured irregularly as the other evidence demonstrates. This would indicate manufacturing problems, but also argue AGAINST an 'off line' end mill. I would propose that this oil line failed primarily due vibration, in situ, and not as the result of some coarse and glaring QA blunder. Replacing this tube to "solve" the Burst issue is therefore unsupportable.

The TRENT is a marvelous Machine. It is ground breaking in its design, and promises many years of loyal and dependable service. Any new machine is probationary, singling out the TRENT for abuse due its "teething problems" is unwarranted. However, shielding these problems from end users is unconscionable.

The lack of disclosure due Qantas, and the apparent complicity of Lufthansa Mx, is in imminent danger of tarnishing the Firm's Reputation. The TRENT remains a marvel, and being dishonest relative to its weaknesses is dangerous.

The FIRM, NOT THE MACHINE.

bearfoil

I am not sure I understand your point here. If you take the chart that has all the oil data on it and then look at the other chart that gives the time line of engine parameters N2%, N3%, etc., the time of the start of oil temperature rise and drop off of oil pressure (0200.20) isn't on the time line of the engine parameter chart which starts at 0200.48. So the oil temperature rise and pressure drop started before the abnormal N2%, N3% fluctuations which began just prior 0201.00. This would indicate to me that something was happening in the oil system prior to the beginning of the "event".

I don't know the inter-workings of the oil system, or where the oil temperature measurements are coming from on the Trent 900 engine. Unless you know that, you can't say for certain oil wasn't in play leading to the engine failure.

bearfoil - but the rest of the world , including those who have seen and handled the part in question seem to take the view that it was mis-machined. These people will include RR engineers, EASA people, Aussie investigators and the AAIB. FAA BEA and Airbus will have also had a piece of the action by now. Do you think some awful conspiracy is in place involving all these organisations?

In this part of the world end mills are rarely used to machine bores. Bores are drilled, reamed or bored, all of which processes provide the minor circumferential scoring seen in the bore. Wear frettage would be much more irregular in appearance.

CAAAD

Keep an open mind, as there is no technical text accompanying the picture, by no mistake, producing judgments such as yours.

The "Misalignment" damage shows a coving at the break with the wall of the pipe. This is not the product of a drill, or bit, or jet. A drill has sharp facets at the terminus of the drilling face, not a deficit that allows for "rounding" in the piece. Notice the "lines" on the surface of the bore. These are obviously not a product of tooling, as they are irregular and non concentric, as well as being out of sync with eachother.

The rim that is missing shows a "shadow" where the pieces departed, and does suggest a problem on manufacture, but shows evidence not of misalignment, but the opposite, a concentric mill, not an elliptical one.

The most important telltale is at the rim itself, the jagged trough of missing metal that includes a particularly ugly remnant of damage, most probably due to profound vibration. This is evidence of the mate to this pipe having a loose and compromised fit, where vibration over time led to degradation of this area.

It is apparent that there was a separation under stress of this joint, at least to me, and may have signalled the initial drop in Oil Pressure.

There are no accompanying comments with this picture, leaving the door open to conjecture. I have seen damage of the sort shown in fittings of this type. From experience, I stand by my comments. Discuss??

Turbine D........... I have some understanding of the 972 oil system architecture, if you'd like, perhaps I could answer some questions?

From the report AO-2010-089:

"Misaligned stub pipe counter-boring is understood to be related to the manufacturing process."

Let's see......Manufacturing defects are understood to have been related to failure......

Fatigue failure of the Stub Pipe...is related to failure.

Fatigue failure of the IT is related to disintegration..........

Fatigue.......Failure........Oil Fire.......IPT Burst.........Deck Chairs.........Titanic.....

bearfoil

OK, I am aware of, but not intimately familiar with two types of oil systems. One of which may or may not be used on the 972 engine.

One is a pressure relief system that limits pressure to some determined maximum pressure by means of a pressure relief valve in the oil pump. In other words, the pump can pump more oil or less oil based on a maximum oil pressure number of the system.

The other is a full flow system. Here, the pump would be sized to give the optimum flow at 100% operating speed and pressure would fall out as a by-product. I think in this system abnormal oil pressure would show up, e.g., high pressure - clogged oil line or plugged lube jet, or low pressure - broken oil line.

Which system does the 972 use?

I would think the oil level is measured in the oil tank which has a oil level indicator and an electronic oil level measuring system connected to flight deck instrumentation, correct?

Now depending on the system used on the 972, what happens should the oil pressure drop and the oil temperature increases as in the case of the Qantas A380?

Where is the oil temperature measured? Each sump at the oil returns? At the oil tank before being set to the fuel or air coolers?

Since the oil temperature data in the ASTB report is only one line per engine, is this an average oil temperature number of the total system?

%rpm - Vibration - Oil status
 

Since I was the one that dug myself through these ATSB graphs, I feel obliged to add on some more detailed information how I got there.
It is correct observed that the time scales at Fig. A2 and Fig A3 are not identical. The N-Graphs leap with 3 sec. from main time mark to main time mark, while in the oil graph the spread is 39 sec. Notwithstanding this deficiency it is possuble to do a correlation using a corrected time scale. I mean sec. are sec. and min. are min. So a logical sequence of events can be build.
I have used for that Excel and when I finished my listing stored it as .pdf file, which I will include into this message. Hope it works.
I would appreciate if those "knowing" would check my list and than come back and tell me what you think. My opinion, though probably not as secure as a trained engineers sight of developments, has found only one explanation left as far as the place and the sequence is concerned. The disaster started in the central ball bearing chamber. Weather it was a bearing that went through the wind or that suspiciuous bevelgear wheel that sits on the HP-shaft,just in front of ball bearing nr. 3 or - as a whistleblower told a british newspaper - a / the bearing chamber vent tube was blocked. Whatsoever it was, it started in front and only at the end of that trail of single failures the IPT disk ran into the LPT stator ring and vanes, eliminating these and itself.

Hope I was able to clarify some questions.

previous message
 

sorry, something went ugly wrong. Thatis no excel file. Will try again
jo

Annex14

Thanks for that data, I managed to get it before the post altered its aspect.

What I notice is that while the Ns and the rpm fluctuate, the Oil reads are fairly stable. I think most noticeable is the quantity, stable at 12 Quarts. Had there been a depletion of Oil feeding the "Oil Fire" I would have expected the quantity to diminish. At twelve, the total in the tank seems representative, and additional oil in the system can be assumed to have remained consistent given depletion (supply) rates and return (scavenge) to replace it. The Temp and Pressure reads fluctuate slightly, but this may be due to vibration caused sensing errors.

There is a possibility that in the mechanical process and timeline of severe internal damage, the Driveline was arrested to the gearbox and pumps. If the Ring gear on the IPShaft (Drive) failed, Fuel flow would stop, as the HP pump is driven by this Driveshaft. I believe the Oil Pump Lines would continue pumping, but if not, it becomes clear that at least from a data standpoint, the Oil System was tracking normally up to and through the casing loss and IT burst. IMO>

If the Pressure had zeroed, the ECAM would show this in red, Aural Warning would trigger, and an ACARS would transmit. Oh, and "Master Caution".

lost data list on QF 32 case
 

So one more time, now with a Adobe generated file. Sorry for all the inconvenience,

file:///Puffer/QF_32_RPM_VIB_OIL_2.pdf

Hope it works now
Jo

Bearfoil
What I can read from these data is, the oil circuit was working, there was no big loss of oil as one could expect after the rupture of an oilpipe that has an inner diameter of about 13 - 14 mm or about half an inch. Miracoulous is that heavy vibration of the HP part while the others stayed fairly calm. That brought in mind our discussion about the bevelgear ring that sits in front of that nr.3 bearing. One has to realize that this part turns as fast as the HP shaft - 11000 rpm !! I have no idea if that driveshaft that runs into the inner gearbos really goes so many rpm or even more because of that difference in teeth involved. Very amazing structure there.
Jo

bearfoil & Annex14

Guess I was too late, all I see are the file data, but can't open any of the files. So, what leads one to draw the conclusion the disaster started in the central ball bearing chamber?

Turbine D

bearfoil, Turbine D, and Annex14:

Let me throw a little more grist into the mill that is grinding away on the behavior of the oil circuit:

Recall in the exclusive interview, the SrCheckCapt said that the FO was himself duplicating the time run past the first engine overtemp warning, thru the brief engine fire warning, and into the second overtemp warning. But the FO did not wait beyond 30 seconds from the first overtemp warning. It was stated FO initiated "engine shutdown procedures"* at 30 seconds from the first overtemp warning. (*or words to that effect)

Let's say that since a fire warning had been seen and engine temps continued to rise, the FO made his first shutdown procedure to shut off the fuel, and empty the (a?) fire bottle(s?) into engine #2. Subsequently, one bottle was reported discharged, IIRC.

Let's assume the fuel to the engine was cut off. I don't recall any comment in the report on this matter-- ie, whether the wires latter found cut would have prevented shutoff of fuel to #2, and discharge of the 2d bottle (or even if this was called for, for #2). I do recall the cut wires per report later prevented this relative to #1. Correct me if I am wrong so far.

What happens to the oil temp when the fuel flow stops? The FOHE progressively become less effective in cooling the oil as the now stagnant fuel cools. (I'm assuming fuel shutoff prevents any fuel recirculation through the FOHE, or at least any significant quantity of fresh fuel in any small(?) recirc that may occur from the engine-driven HP fuel pump (again, if this occurs similar to the BA038 system)).

So the oil temp rises. Significantly? Apparently the oil circulation continues, as ever hotter oil continues to arrive at the oil temp gage in the sump. Unfortunately, the beginning of the oil temp rise occurs at a time we do not have in the published data --am I correct in this? Or does the Annex14 failed Excel post have it? [Maybe it just failed on my machine, altho I have Excel if I haven't disabled its use; anyway I have the raw data in a txt file.]

Would this explain a rise in oil temp --due to the FO's emergency shutdown, all stops out, action --before the blowout; and without the need to assume any malfunction or excessive leakage in the oil circuit prior to the IPT blowout? We know that he began this action before the IPT blowout; there was no comment in that interview, that I recall, as to all the actions or how long they took. The FO, however, was quite alert.

I leave this to you all --I'm buried under trying to understand why FAG rates its turbine bearings at -54C to +120C (I understand the -54), while saying that their fatigue life is infinite (a 1983 concept), unless subject to ... overtemperature... among oil contamination and corrosion; while RR sees no problem with oil temps in the 190Cs. Is that the 7-year on wing bearing fatigue temperature limit (a new concept?)?.

Also now going to run down RHP, a British bearing mfr with the capability to make these bearings for RR, and see what they have to say.

Meanwhile, my own ECAM is telling me IE has encountered a problem, and needs to close. Way past 30 sec now... I've discovered that ignored, data will not be lost...

OE

turbineD
 

Sorry for the inconvenience. I have made an Excel file that shows a timescale at the left side and right of that I have listed N1; N2; N3; oilP;oilT and oilQ.
My idea behind that effort was to get a time corrected correlation of these data.
I will try harder to have that list posted. Will come back later
Jo

old engineer

The TRENT 900 will run on gravity fed Fuel at all demands I believe. The Oil data and other that Annex14 posts, I have; I assume his new link will display it also. His vibration points are instructive.

bearfoil

Yes, I was going to try to time-correlate all that data as well, but I just never had time to do it, so Annex14's effort is appreciated.

On another tack on the issue of bearing failure, I noticed an interesting, and possibly pertinent comment among the various FAG glossy brochure literature. Just happened to catch my eye. It's in the brochure on repair of bearings; IIRC a ball bearing is taken as an example. "Rebuilt to as-new standards" and further on "parts replacement not permitted" or word to that effect.

Somewhere, either in the FAG brochures or elsewhere (daughter page lost when IE had to close, before bookmarking), I discovered a useful account of the process by which high precision ball bearing are made. There are a lot of forming, grinding, tempering, regrinding, and finally lapping to make the races accurate to .0001". But apparently this does not always result in the same particular ten-thousandth from piece to piece (which I deduce from the adverse comment against part replacement, above). The same is done with the spherical balls that run between two particular races, but here the finished balls are ingeniously sorted in size down to the quarter of a ten-thousandth (0.000025").

From this I deduce that the selected inner and outer race are measured for the gap between the running surfaces of the balls, and the appropriate quarter-size of the nominal ten-thousandth tolerance ball diameter is selected. That is, the bearing as an assembly may be interchangeable, but its components are not individually interchangeable --not if you want an "as new" rebuilding of the bearing. This last phrase straight from the horse's mouth at FAG-- and please, we'd like the whole engine and 18 days to do it. Even so, it's apparently a substantial saving over a whole new bearing.

From my own experience, I know that even a drop-in whole new bearing replacement will not necessarily result in "as new." That is because the interference fit between bearing housing and outer race can compress the outer race and reduce its diameter. And that depends on just what the outer race diameter of the replacement piece is, not to mention the housing diameter. I see locating tangs are popular here, for locking the race against rotation, to avoid having to rely on a heavier fit to accomplish this. It's enough of a problem that FAG comments that "as new" can only be restored in a factory setting [I read, their factory].

So, suppose the Singapore repair facility just replaced the spalled outer race? That was the damage, IIRC. What then the bearing life?

Bearings are indeed matched assemblies; inner and outer races (rings) are id'd by serial number, and the set of balls (or rollers) likewise.

Reconditioned bearings have the races reground to accept slightly larger balls or rollers.

This is a standard worldwide practice, I believe, and I'd be very surprised to find a shop unscrupulous enough to shortcut this matching protocol.

QF32 RPM VIB OIL data
 

The following files are posted on behalf of Annex14.

Excel Data(.xls)

Excel Image(.png)

mm43
 

Thank you for helping me posting the list files.

This list shows no self made additions, it´s just data derived from the ATSB Preliminary Report. The time scale starts where the oil pressure starts to drop below the level of the previous trace in Fig. A3. It is also the moment that rise of oil temperature is recorded.
The time frame ends 8 sec. after the breakup occured. The engine is dead but oil status, though starting to drop in all 3 lines is still within certification parameters.
Remarkable is also the period between 02:01:06 and 02:01:09, where first the N2 line drops to zero in half a second followed by N1 shortly after 02:01:06 but obviously ahead or at the same moment the IPT disk vandalized the engine.
Apparently the front end of the engine was already dead while the HP part still ran at 98 % of its max. perm. N3. So there must be still fuel being pumped into the combustion chamber. There is mentioned in the report that the fuel flow was cut back automatically when these high rpm where achieved.

What I left out in the time scale is the timing of some warnings that became switched on and subsequently displayed in the cockpit. That is
02:01:06:30 - OVERHT Engine 2 turbine overheat - ON
02:01:07:30 - Captain Master Caution - ON
02:01:11 - Pylon Overheat Engine 2 - ON

It is very clear by this that - as stated in the crew interviews - the first real reactions by the crew came after the two reported "loud bangs". Subsequent actions than were worked down according the procedures layed down for such cases.

Now to the different possible developments as they have been discussed in this thread.

1. The preliminary version (ATSB / RR)
> oil tube rupture > oil spills into the cavern formed by the supporting structure > oil becomes ignited by the surrounding heat > oil fire weakens the structural integrity of the IPT disk ( because its closer to that cavern than the HPT disk)> circumferential diskfailer at the drive arm> migration of the disk backward into the structure of the LPT thus destroying this and disintegrating due to overstress
What Pro´s and what Con´s ?
Pro - Oil fire can start in that cavern , outside the bearing chamber, weaken
the disk with subsequent consequences
Con - An rupture / break of an oil tube that size involved will fill that cavern,
no oil backflow into the sampling scavenge
- an rupture that dimension will show a) in drop of oilpressure and b) in
steady dropping quantity
- break of oil tube means no sufficient lubrication to the 2 roller bearings
in that chamber, causing damage and destruction of the bearings
- N3 went to the permissable topspeed, N2 turbine rpm likely went to
overspeed - both not very likely with corrupted or damaged bearings

the Forum derived version
> inside the central ball bearing chamber a component started to deteriorate
> strong vibrations of HP shaft developed > IP shaft "decoupled"> heat of
compromised parts ignited an oilfire that corrupted the seals> subsequent
blowout of hot gases that were at higher pressure values foreward ! > migration of the IPT disk rearward > overspeed in few seconds > contact to IPT structure anddesintegration of the disk> oilspill by instantly broken oil tube, start of an oilfire with recorded oil fire remains on the disk

Pro - heavy vibration in HP part, mild in LP and IP
- obviously the oil system worked beyond breakup of disk within
certification parameters
- heavyest fire damage on the cowling is visible foreward of the gap
caused by the disk break up
- solid thrust drop of N1 and N2 with in 3,5 sec - N2 stops in 0,5 sec. and
N1 is down in just 3,5 sec !! about 5 sec prior disk break up
- oil soot on the LP shaft at about the position of ball bearing nr.2,
means gap, leak or fracture of the surrounding IP-shaft
- no oil soot at the position of the roller bearings for IP and HP rear
support
- previous repair of foreward bearing because of spalling (only outer race
???)
Con - no known as primary cause reported cases for the ball bearing chamber
in previous Trent 3 - shaft models
- spline coupling wasn´t a problem before

I stop here, but I think the final report of this incident may have some additions.
Probably also towards another candidate of trouble, the bevelgear drive that has its delivering ring mounted ahead and leaning against the HPC ball bearing.
Just an idea that has caught my attention!
Another item too - no one untill now has said where excactly that demolished and broken oiltube - shown in picture - was mounted - at the rear roller bearing chamber or at the foreward ball bearing chamber ??

Lots of questions, many ideas and much assumption! Okay, RR and the ATSB could overcome that by releasing some more pictures from the interior and /or plainly say what the ongoing investigations have revealed so far.
My opinion is : Knowing is Safety - Not knowing is Unsafe
Jo

Old Engineer about FO emergency actions:
No you don't. The first thing that happens, that the crew is aware of, is two nearly simultaneous loud bangs (the engine failure). No more loud bangs after that. Emergency actions begin after the failure.

At FIRE warning, the chronometer was halted, then restarted after the warning reverted to OverHeat. This is the testimony of SCC Evans.

This event has caused an immediate change to the DEP such that the EEC will shut down an engine of this type prior to certificated delay times. Had the Fuel been pulled earlier than 2:01:11, this Burst may not have happened. What remains is to determine if overspeed even occurred?

If the IT slid back to contact the stationery Stator ring, it surely slowed, and heated up. Had it slipped further, the Blades would have sheared off on the Stator Vanes Platform. Loss of blades drops the N2 to zero, and the N1 as well, as the LPT has nothing in front of it by way of gas. By this time the contact area of the Drive Arm and Stator Ring are fluid, and the Drive Arm gives up completely, the Disc wobbles and disintegrates. The first Bang, was it Stall? Was it caused by IPLP cavity Pressure releasing forward through the bladeless aperture at the IPT Rim? A forward exit of all Gas Path contents that upset all mechanical stresses? The second Bang the Rupture of the Case?? Someone with Turbine sense could look at the reads and the evidence??

From the report.

Not too diffucult to understand surely!

Noted. Do you have some thoughts on the "two" discrete reports? Related to the chronology, would you relate the continuation of N3 to ongoing fuel supply post Burst?

The charts at the back of the report show N3 reducing after the burst. I do not see any N2 overspeed. Ductile failure probably refers to large plastic deformation due to turbine overspeed and overheating.
Two bangs corresponding to two large turbine fragments?

bearfoil

I think the first place to start is to look at an item on the Trent 900 cross-section drawing and also the engine cutaway. Of particular interest, note that the roller bearing for the rear HP spool sits directly below the frame and plenum which I believe contains the stub pipe that would normally feed oil to this roller bearing and the one under the IPT rotor disc. Now this stub pipe, for one reason or another, had begun to fail by means of a fatigue crack initiation, even perhaps undetected on a previous engine cycle or flight that permitted oil to begin to seep out into the plenum cavity. But on this flight upon climb out, the crack progressed to the extent the oil flow into the cavity became great enough to cause abnormal operation of the HP spool rear roller bearing and the spool began vibrating. The roller bearing under the IP rotor disc seemed to be unaffected. However, enough oil had collected in the plenum chamber and given the temperature in this area, ignited. The disc, especially in the bore area, began to heat beyond its material property capability and in a ductile manner began to stretch. It got to the point where restraint (580 bolt holes) was overcome by stretch, and the power drive arm failed at the bolt holes (a disconnect). The N2% begins to fall. The ECU, sensing this calls for more fuel and the N3% begins to rise. N2% steadies momentarily, then drops like a rock. The ECU calls for more fuel flow and the N3% continues to rise. But then the HP compressor outlet pressure starts to drop and fuel flow is reduced by the ECU. With no air feeding the HP compressor, it stalls, BANG! The hot gasses built up in the combustor (580 psi @ 98% N3?) and compressor release both forward and aft (flames) but upon reaching the fan by-pass are blown back by the fan through the bypass and may not have been seen emerging out the front of the engine.

Very quickly then, the free IPT rotor (blades and disc) in an over-speeding mode because of the high N3% moves rearward into the Stage 1 LPT stator ring, contacting it close to the fractured power drive arm continuing to overspeed from the "false bearing effect and then bursts, BANG!

Some Key Points:

The stub pipe may not have completely fractured dumping a large quantity of oil into the plenum at once, more gradual but progressive over time. In fact it could of broken completely through as a result of the breakup in this area of the engine, we don't know the time line.

Over speed of the IP rotor was probably not detected because N2% is measured off the IP compressor.

The rotor overspeed was not slowed because the initial contact with the Stage 1 LPT nozzle was too close to engine centerline. For example, if you turn your bicycle upside down and turn the pedals, try stopping the wheel close to the hub verses stopping it at the rim.

The HP spool rear roller bearing upset was great enough to cause detectable vibration (skidding/uneven contact) but not great enough to cause seizure.

The fuel flow to the combustor was reduced when the P30 pressure collapsed, but may not have been cut off completely, just reduced.

The burning streaks on the fan bypass cowling is characteristic of a major failure in the turbine area, blades, nozzles and discs and the compressor stall that is created.

Essentially, almost everything happened before the flight deck crew had a chance to react other than to begin to shut the engine down after receiving warnings 2 seconds before the disc burst.

I would suspect the ECU was reprogrammed to call for fuel flow reduction at the first sign of N2% fall off and N3% rise which might have prevented the disc burst situation.

Those are my thoughts on this engine failure.

firstfloor wrote:


Well, let me agree (now that I've re-read the 12/3 ATSB report and the 12/8 interview with Sr Chk Capt (SSC) that I cannot know for sure that the FO took any action prior to the disc leaving the A/C thru the wing. But the throttle of #2 could have been retarded to idle in response to the "engine turbine overheat" warning in the cockpit (via ECAM), as this is the procedural response to this warning. And this response, including the FO starting an independent stopwatch, could have been done prior to loss of the turbine disc.

The ATSB report places the "two, almost coincident, 'loud bangs'" at the same time as the activation of the "turbine overheat parameter" at 0201:08. The report places the "turbine disc failure" at 201:11, based on multiple indications of A/C systems failure (the cut wiring in the wing giving the significant indications, I presume). That the two bangs occurred slightly earlier would not contradict the SSC's statement. I assume the FO had the same to say.

I do not wish to say that you cannot be correct in your comment that the engine failure occurred at the "two bangs." However, I prefer to consider the possiblity that the two "almost coincident" bangs could be the result of the flame and "explosion" of a compressor stall exiting the two ends of the 20-foot long engine. Doppler effect aided by the reduced speed of sound could separate the two enough to perceived as separate explosions.

I've luckily been present at only one compressor stall, but there was the definite impression of engine explosion, causing great alarm in the cabin. (Landing approach at 9000 feet through near vicinity of thunderstorm, pitching and bobbing, in a steep approach at low power to avoid a displaced ILS threshold, BLAM, orange glow outside-- a dark afternoon at UIO from the south, downslope shortish runway, overtaken by the city on both thresholds-- in "City of Guayaquil" A320, flagship of the Equadoran fleet.) A panicked woman across the aisle asked, explosion or lightning? I said, Just lightning, don't worry.

So RR would have us believe it's only a broken oil line. For all the detail that's been given about that, the final break in the cracked fitting could have occurred in dismantling the engine. I'm still studying the question of bearing design philosophy in this engine, including choice of permissible oil temperature, which gets more interesting all the time.

As shearing is the most energy-efficient way to cut thru metal, I am not convinced that the disc fragment would have made much noise going through the wing. You can see the impression of teeth going thru the crossframe web, cut like a die-- is this the trace of the oft-mentioned bevel gear?