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bearfoil
24th Dec 2010, 17:31
Continued from previous thread here. (http://www.pprune.org/rumours-news/432704-qantas-a380-uncontained-2-engine-failure.html)

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?

Turbine D
24th Dec 2010, 19:55
Bearfoil

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.

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 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".

I Agree.

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).

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:

An uncontained engine failure has recently occurred on a Rolls-Royce RB211
Trent 900 involving release of high energy debris and resulting in damage to
the aeroplane. Analysis of the available elements from the incident
investigation shows that an oil fire in the High Pressure / Intermediate Pressure
(HP/IP) structure cavity may have initiated a sequence of events leading to
rupture of the drive arm of the IP Turbine (IPT) disc and subsequent overspeed and burst of that same disc.

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:

Engine Fuel & Control – Intermediate Pressure Turbine Overspeed
Protection System Software – Introduction

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.

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?

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.

bearfoil
24th Dec 2010, 22:20
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.

Old Engineer
25th Dec 2010, 05:52
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).

Annex14
25th Dec 2010, 10:09
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 canīt 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 canīt be that far off.

Turbine D
25th Dec 2010, 17:15
Old Engineer

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.

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 360š 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℉ (982šC) 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.

Turbine D
25th Dec 2010, 18:04
Bearfoil
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.


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.

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??

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.

Annex14
26th Dec 2010, 08:18
May be this link is of help for your search for the bearings used in Trent 900
Schaeffler Technologies *|*Sectors / Key Industries *|*Publications (http://www.schaeffler.com/content.schaeffler.de/en/branches/aerospace_group/aerospace_2/aerospace_publications/publications_2.jsp)
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

Ferpe
26th Dec 2010, 11:54
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.

sky9
26th Dec 2010, 14:28
The direct link to the PDF file is

http://www.schaeffler.com/remotemedien/media/_shared_media/library/schaeffler_2/brochure/downloads_1/FL_09110_de_en.pdf

lomapaseo
26th Dec 2010, 14:50
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 ??


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

bearfoil
26th Dec 2010, 15:05
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??

bearfoil
26th Dec 2010, 15:10
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.

Turbine D
26th Dec 2010, 15:32
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.

bearfoil
26th Dec 2010, 15:56
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.

Turbine D
26th Dec 2010, 16:22
bearfoil

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.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.

CAAAD
26th Dec 2010, 16:34
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.

bearfoil
26th Dec 2010, 17:08
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?

Morane
26th Dec 2010, 19:12
From the report AO-2010-089:

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

bearfoil
26th Dec 2010, 19:25
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.....

Turbine D
26th Dec 2010, 19:32
bearfoil

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

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?

Annex14
26th Dec 2010, 21:56
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.

Annex14
26th Dec 2010, 21:59
sorry, something went ugly wrong. Thatis no excel file. Will try again
jo

bearfoil
26th Dec 2010, 22:40
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".

Annex14
26th Dec 2010, 23:00
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

Turbine D
26th Dec 2010, 23:06
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

Old Engineer
26th Dec 2010, 23:18
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

Annex14
26th Dec 2010, 23:28
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

bearfoil
26th Dec 2010, 23:32
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.

Old Engineer
27th Dec 2010, 01:02
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?

barit1
27th Dec 2010, 01:18
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.

mm43
27th Dec 2010, 02:04
The following files are posted on behalf of Annex14.

Excel Data(.xls) (http://countjustonce.com/QF32/QF_32_RPM_VIB_OIL.xls)

Excel Image(.png) (http://countjustonce.com/QF32/QF_32_RPM_VIB_OIL.png)

Annex14
27th Dec 2010, 11:50
Thank you for helping me posting the list files.

This list shows no self made additions, itīs 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 Proīs and what Conīs ?
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 wasnīt 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

firstfloor
27th Dec 2010, 12:03
Old Engineer about FO emergency actions:

We know that he began this action before the IPT blowout


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.

bearfoil
27th Dec 2010, 13:18
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??

firstfloor
27th Dec 2010, 13:38
From the report.


The engine failure

Following a normal takeoff, the crew retracted the landing gear and flaps. The crew reported that, while maintaining 250 kts in the climb and passing 7,000 ft above mean sea level (AMSL), they heard two, almost coincident ‘loud bangs’. The PIC immediately selected altitude and heading hold on the autopilot control panel, and the FO started his chronometer.


Not too diffucult to understand surely!

bearfoil
27th Dec 2010, 13:48
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?

firstfloor
27th Dec 2010, 15:53
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?

Turbine D
27th Dec 2010, 16:55
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.

Old Engineer
27th Dec 2010, 20:32
firstfloor wrote:


Old Engineer about FO emergency actions:

We know that he began this action before the IPT blowout



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.



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?

Turbine D
27th Dec 2010, 21:43
Old Engineer

Here is something perhaps of interest regarding compressor stalls. Note the section that begins at ~ the 6 minute mark. It is the most violent of all stalls in terms of noise and everything else.

YouTube - pt. 2 of 3 Turbofan Jet Engine failure recognition (http://www.youtube.com/watch?v=osAT6mwkr94&feature=related)

Turbine D
27th Dec 2010, 22:26
Old Engineer

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?

I would agree with you on this, partly. However, when that disc broke, it made a BANG just like a test bar failing during tensile testing, only louder.
Note the puncture hole at the top surface of the wing, it corresponds much like the cross-section of the IPT disc. It is hard to say what else came out inside the wing, but I think it isn't the bevel gear, it is too far forward in the engine and it would not appear there is much external damage forward of the HPT rotor.

firstfloor
27th Dec 2010, 23:42
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.


I see where you get this from but bear in mind that there is no CVR at this time so loud bangs cannot be placed on the timeline. Yes the overheat parameter is timed but "at the same time" is vague in the context of the report and does not necessarily refer to the bangs, I would say.

Old Engineer
28th Dec 2010, 04:53
firstfloor

Yes, that is the counter-argument. It is too bad that the CVR is not available.

Turbine D

I hadn't thought of the test machine, and you can't forget that bang. But with that, you're within 3 or 4 feet. But I agree, it would be much louder. Still, the response of the ear is logrithmic, so it wouldn't sound as loud as it actually is, and the passengers are a little farther away. What I regret is that so often the passengers are not questioned with some respect for the information they might have-- here if those opposite the engine had heard only one bang, that would suggest that it was two nearly simultaneous bangs, but at opposite ends of the engine.

Rising oil temp: Today I discovered an explanation for this not mentioned here, that can occur without a broken pipe. I'll put up a post on this tomorrow.

Annex14
28th Dec 2010, 09:27
post nr. 1999 and 2003
I took once again a glance in that FAG internet appearance and those brochures.
I found the - 54 to +120 deg C values you mentioned, and yes, those technical data wouldnīt cover the requirements in an engine at all I assume. So I went on and found this Schaeffler Technologies | Sectors / Key Industries | Product range (http://www.schaeffler.com/content.schaeffler.de/en/branches/aerospace_group/aerospace_2/product_range_7/product_range_7.jsp)
Its general description but at least they state there that they can cover a temperature range from -250 to + 500 deg C.

post nr. 2013
What I take from the holes in the wing picture is , a big piece did the damage to the leading edge structure and front spar. Thats the big hole. The other, smaller one, where a smaller piece puntured a wing tank, resembles very well the cross section of that disintigrated disk.
The assumed trajectory of these two pieces I think are drawn in that sketch on p.18 of the ATSB report. These are missing I think, and should be somewhere to right side of the flightpath. The big piece recovered seems to have left the engine in the oposite direction. Amazing how far it was thrown away from the flightpath.

bearfoil
28th Dec 2010, 13:52
The "bang(s)" are intriguing.

It is possible that what was heard were two separate sources of sound that happened
(close to) simultaneously.

Possibly the IT was 'slumped' (out of shape) and had fractured, but was restrained by the Shaft, although at its virtual limit of integrity.

The Stall may have been initiated by blade loss (stator contact) and reduced N2. With the instantaneous "hybrid" gas path (stall) upsetting the Disc (not to mention the entire engine/pylon), the wheel disintegrated and blew out the case. Two very loud reports, of different cause and sonic "character". One metallic, one gaseous. The pilots may have been (through experience) better able to notice the differing character of each sound, even with "simultaneity". It would explain the final impetus of the Disc failure, especially in light of the Miami machine's retention of disc "integrity" sans "Stall". I don't think it necessary to include overspeed as a component.

Oil Fire certainly would account for added heat, but logically, the heat would be somewhat erratic, and the mode of failure of the wheel is described as 'patent',eg 'in three roughly equal parts'. If true, that would suggest less than a chaotic heat soaking due to fire. A more blended heat soak (evenly distributed) would most likely have been the result of friction at the Drive Arm/Stator (who brought up 'fluid bearing?).

Most important, metallurgically, then, would be a determination of the "Point" of failure, whether Rim (Fire), or Drive Arm. The chronology of the event suggests to me, a 'build' of heat, something I would relate to a slow "Migration" of the Wheel, and a concomitant elevation of Oil temp. It sounds counterintuitive to describe this "failure" as 'gentle' in any way, but a slow build of heat through the structure seems more accurate, given the timeline, than that engendered by something as chaotic as Oil Fire.

Whether the Stub Pipe was born wrong or wore through, its failure appears gradual, and conforms to worries announced in the ADs. Though a three shaft powerplant, any insufficiency of bearing performance at one location, translates immediately to the other bearings. The vibration record (both power and timing) is truly mesmerizing, and tells a tale.

barit1
28th Dec 2010, 15:03
The photo of the recovered disc segment (1/3 sector) strongly suggests it is NOT a rim-originated failure, but rather starting at the bore and extremely rapidly progressing outboard. Such is characteristic of an overspeed burst, and the metal splatter from the 'false bearing' is supportive of this.

The root cause of the rotor burst is the fact that after the IPT disc decoupled from the IPC, the IPT blades remained more-or-less intact in the disc, and continued to convert N3 gas stream energy into torque to accelerate the disc to destruction. Note this sequence is different from the RB211 failure on QF74, 31 Aug., where the blades were destroyed/removed either by blade root failure or by clashing with the LPT nozzle ring.

Don't get me wrong; Oil fire is nasty - you DO NOT want that blowtorch playing on bearings and shafting. But it should not precipitate an overspeed to the point of a rotor burst!

bearfoil
28th Dec 2010, 15:10
Annex14's

assembly of engine parameters is interesting. I am put off by the 'zeroes'. I think neither N1 nor N2 siezed, so is the reading of '0' RPM a hard number, or one generated by the EEC after loss of the actual signals from the engine? N1 and N2 are sensed at the respective Shaft via phonic wheel. Four each, two pair, each pair sending its output to either channel A or channel B of the EEC. N3 is derived from the generator affixed to the gearbox connected via driveshaft to the Ring gear on the HPC Shaft. If the shaft speeds are disabled, the EEC computes "generalized" numbers to send to the cockpit for display. So I am reluctant to assign events to the 'timeline' from the list.

barit1
28th Dec 2010, 15:21
I will also suggest a rationale for the 'double boom'.

1) The A380 is a very large aircraft
2) Sound travels faster through metal than through air
3) The first boom heard in the cockpit could have been propagated by the aircraft structure, and the second by airborne sound wave. The airborne wave might arrive 50-100 milliseconds after the first. This is easily discernible by the ear.

Turbine D
28th Dec 2010, 15:30
bearfoil

The "bang(s)" are intriguing.

It is possible that what was heard were two separate sources of sound that happened
(close to) simultaneously.

I agree with you, one bang was gaseous in nature - the stall, the other mechanical in nature, the disc rupturing. If you assume the following: The disc was free on the shaft, it was being subjected to higher temperature conditions than what it was designed to handle, it was rotating at some speed perhaps not approaching what would normally be burst speed (a degraded burst speed margin due to temperature), and the disc all of a sudden is subjected to a huge shock wave of energy (the stall), it might have been enough to push it "off the cliff" so to speak. Rapid P30 collapse - prelude to a stall, engine overheat - a stall - disc failure within ~ 3 seconds. Too bad the CVR of this wasn't available.

When you think about that disc carrying over 100 turbine blades at high rpm's, the load could approach 1,500,000 pounds or more.

It sure would be nice to have seen a photo of the recovered portion of the disc depicting the forward face (we only see the rear face). I say this because we could perhaps see if it is discolored resulting from a fire. There is a hint of this in the photo of the disc fracture surface, but it may only be a shadowing effect from the camera angle and lighting arrangement. Also, the recovered piece doesn't show any evidence of a rim failure.

bearfoil
28th Dec 2010, 15:34
If the Disc developed a 'circumferential fracture' of the Drive Arm, a la Miami, it very well could have separated from the remnants of the Arm to remain in the case while rotating independently and progressively more elliptically, scrubbing off its blades whilst gaining rapid deviations in planar rotation. At some point, the energy is greater than the thin case's ability to contain it, and it divides itself into the requisite three piece 'suite', to exit. If the Disc separated, but was contained in some elliptical path within the case, it becomes clear the generation of "fold back" of the Arm remnants on the Wheel's failure signature.

At 7000 RPM, sufficient energy is available to accomplish the Burst, an overspeed is not necessarily required.

So it becomes ever more telling; are the reads on the list accurate?

The 'Rigid Coupling' is accused of failure (ATSB), however, it may have failed in the respect of allowing the AftShaft to wander aft, not in losing contact, other than axial, and that sufficient to keep the shaft operating as a unit. (AD's) IMO.

Annex14
28th Dec 2010, 16:10
As I mentioned in my messages before the list was posted through help of mm43 all I did, have the Graphs published in that ATSB report printed enlarged, put them side by side and read of the data shown. It must be clear to everyone that this is not a very sophisticated evaluation method. My intention was, with the data at hand to make a more logical approach to the facts at hand.
So zero in my list means zero in the ATSB graphs. These might be in original prints 2 or 3 time as large and much more precise. What none of us knows How perfect calibration of the recording media was. As is well known, many little drifts off the ideal line can add to a major error.
Hope this explains a bit the content of my list.

Annex14
28th Dec 2010, 16:17
Coincidence of thoughts. Me too have had a look at this picture showing the fracture surface. Upon enlarging it I thought to see the "shade" to the left to be some kind of an airbubble plastic wrap.
Sorry if my wording is sometimes not very correct, but have to translate it from my mothertong.

bearfoil
28th Dec 2010, 16:20
Annex14

I get it now. The zeroes seemed arbitrary, for obvious reasons. I am not very good at computer work, and until I remembered the EEC's role in cockpit reporting management, I was stuck. It's all relative. Thanks again, I think you've opened up a fruitful harvest of data.

Turbine D
28th Dec 2010, 17:06
Annex14

Look at the disc fracture face photo, in the upper left of the disc, just below the dovetail serrations you will note a dark area which is the forward face of the disc. It is this that I wonder about compared to the lighter metallic surface of the rear surface of the disc that is more clearly evident. Is it dark because of the effect of fire/temperature? Or is it dark because of the lighting shadow?

Sometimes these surfaces can tell you somethings relative to conditions that were happening at the time.

Annex14
28th Dec 2010, 19:35
I did check and also amplified those pictures in the ATSB report to 800 x the original size, beyond pixelling starts and there is too much noise.
I must admit that I cannot say wether what one sees in the area you mentioned but also at another one in the lower left base is a dark deposit or just shade. Unfortunately it looks like the picture was taken just off axis, slightly right of the center of the cross section. So either is possible.

However, I also checked for pictures of the disk piece in earlier posts. Check the post nrs. 42; 84 ; 587 ; 680 - they show several aspects that has to be considered. In post 42 is a picture where police officers carry that piece by hand and using some questionable dirty pieces of cloth for that. Post nr. 84 shows that part probably in a private car trunck before or at delivery to the police. Although these pictures show a non professional handling of that important part some kind of deposit remained untouched to some extend.

Post nr. 587 shows that same part on a small lory, also only the rear side of the disk. What is remarkable there are still some darker areas visible may be some kind of deposit ???
Finally there is that false colour picture in post nr. 680. It too shows some darker areas, even in false colour.

What I also have realized is a difference in surface colour of those early pictures compared to the "official" one in the ATSB report. Explanation for that - either the different colours come from repeated treatment, handling and reproduction of the original pictures or the disk was cleaned, hopefully after samples of any foreighn material on the surfaces was secured,
A pitty, I have to say it again, that there are no better and more detailed pictures at hand.

Chu Chu
28th Dec 2010, 21:30
Could the second bang have been the disc segment hitting the wing?

bearfoil
28th Dec 2010, 22:17
No, you'd be hearing a "Thump". Nowhere near the noise of the Burst. And you'd need to be seated close by. The Cockpit did not hear it. The wing is built remarkably lightweight, and even the Spar is no match for the Disc. Knife, Butter....imo. The good news is that the shape of the debris will then be remarkably unfazed by passage thru of the Nickel Alloy Steel; note the cookie cutter deficit, as if the skin were nonexistent.

bearfoil
28th Dec 2010, 22:42
Disc/Color/Surface.

The Discs are highly polished prior to install, the final rub is Colloidal Silica. Similar to jeweler's rouge. Now this Wheel had seen 200plus cycles, and heat debris and friction, Gas components can work their mischief on the shine. In the ATSB picture, my guess would be that the Disc had been cleaned and inspected, but the image is prior to destructive sampling of the metal. The fracture at Drive Arm appears to be "Puddled/Smeared", as if autonomously and randomly 'forged' prior to parting the Shaft remnants of Drive Arm. It wouldn't be a wild guess that the Disc had experienced a circumferential fracture. Note the Drive Arm 'fracture portion of the image'. It is beaten around, and it lacks sharp fracture delineation that the Disc separations show. So lost from the Shaft through circular fracture, a small hesitancy while describing ever more elliptical orbits of the Drive Arm (with consequent 'folding over'), then separation into three large pieces, and immediate exit. The remnants of Blades are suggestive of a gradual loss (tenths of a second?), and an inconsistent failure mode, the blades/roots which are missing may be more indicative of a 'vibratory/centrifugal/non planar' loss.

Turbine D, old engineer, annex14, mm43, first floor.......all

http://www.atsb.gov.au/media/2891297/vh-oqa-fig8.jpg

Take a big look at the severed torque links, and a peek inside the IPLP cave. Does one see the remnant of NGV1LP? Or is that a remnant of the Intermediate Turbine? Also beneath the centrifugal Oil Breather, see the burned Stator ring hanging down?? displaced Much?? Without the Torque tubes (which look like they snapped in tension!!) the engine can swing to its heart's content, not good in Yaw, and one step away from losing the powerplant off the pylon. Thanks to the suspension cleats, no worries!!

Turbine D
29th Dec 2010, 01:02
Chu Chu
Could the second bang have been the disc segment hitting the wing?

I agree with bearfoil. It would appear the disc separated into 4 pieces, the largest being the 135š section recovered. It must have exited the engine downward and to the left based on its recovery point. the other three pieces exited to the right as defined in the ASTB report's diagram.

The recovered piece weighed almost 70 Kg, 150 Lbs. So the total weight of the disc alone, minus the turbine blades approached 400 Lbs. or more.

It was probably rotating at a speed of 7,000+ RPM at the time of failure.

The sound of breakage and the energy released is so immense it would overcome any sound of the pieces going through the wing.

Also, watch the video on compressor stalls and the noise created by the explosion of the gasses going forward and aft, that was in one of my previous posts, the site is given below.

YouTube - pt. 2 of 3 Turbofan Jet Engine failure recognition (http://www.youtube.com/watch?v=osAT6mwkr94&feature=related)

Turbine D
29th Dec 2010, 01:47
bearfoil

Take a big look at the severed torque links, and a peek inside the IPLP cave. Does one see the remnant of NGV1LP?

It looks like a Stage 1 LPT nozzle vane, hanging down, to me.

You can also look at Figures 8 and 13 to see more things.

In Figure 8, you are looking at the Stage 1 LPT blades, the stator in front of this is gone.

In Figure 13, you can see the gas path vanes that are part of the frame the plenum joins to. Also, you can see the peeled back casing that was above the IPT rotor.

The main engine mounts did a good job retaining the engine on the pylon.

bearfoil
29th Dec 2010, 02:19
Turbine D

NGV1LP- Nozzle guide Vanes, #1, Low Pressure Turbine (my shorthand, sorry).

The Stage one Guide vanes and Stator are attached to the Intermediate Pressure case with the IPT, No? One wouldn't expect to see it with the LPT Module on strip, would one?

Note the #1 wheel, LP. The damage (missing blades) is the same as on the front view of the LP Module (why wouldn't it be?).

I agree the Stator hangs down, did you see the outer Vanes Platform? It has separated completely from the IT case (or the case blew away from it). It also is bent as it enters the cavity. One also gets to see the Oil vent from the HPIP bearing case (no sign of heat damage), the oil lines to and from the Oil Breather centrifuge, and the mount for the EEC. The EEC has been removed from the Fan Case, note the 15 leads wrapped in plastic bags and the Four (anti vibration) mount towers. Bleeds are visible, as well as the air dam on the pylon.

Old Engineer
29th Dec 2010, 05:06
bearfoil

Now there is resolution-- 14 megapixels times 3 layers for the colors, I think. Is there a similar camera copy for the report showing the LP shaft that might show the condition of the splines? Not that that would mean anything after two hours of windmilling in an engine casing that could hardly have remained straight...

Am I looking at the inside of one of those large ball bearing thrust bearings as well? My looking around tells me that the entire assembly may be as large as 3-3/4" square (two rings and the included spherical balls), plus parts of the turbine made integral with the rings. I'd want to do some scaling off the pixels relative to the fan diameter, with a little perspective shortening thrown in, if I can locate a line parallel to the shaft-- well, the dolly should be, shouldn't it?

Anyway, the outer race of that bearing looks kinked as well. Could we call that bearing damage? I've found a reason to put bearing damage on the list of usual suspects, even if it had a fully functional oil supply. Tomorrow. Good work, bearfoil, in finding that picture. Does the raw file include any camera data such as lens focal length and size of its sensor chip (or camera model)?

bearfoil
29th Dec 2010, 10:57
http://www.atsb.gov.au/media/2891300/vh-oqa-fig14.jpg

A follow up on my post above re: the Drive Arm/Wheel fraction.

Notice the fracture area at the central arrow. It is beaten while quite hot, imo. Also, the surface of the Drive Arm area appears that it spent some time within the remaining (shaft) area of the Drive Arm, or the inner Stator ring. The failure furrow is worn smooth in this area, while remaining crisp further out. Also, the outer 'layer' of metal is peened off by the inner Arm. The metal spatter appears to be bits of molten Drive Arm, supporting a theory of intense heat from kinetic or Fire products. However, that begs the necessity of the Fire being in the IPLP cavity, not in the area in front of the Wheel (bearing case). In fig 8 we can see what is left of the Stator at its center closest the IPT. Out of view is the area of contact. The Oil quantity hadn't depleted, although it did read once at 11 quarts, but returned to twelve to remain there.

So what of the stub pipe? At ~5/8 inch and a pressure of ~65psi, one would think a serious loss of Oil, but the quantity read doesn't show that. The Temperature of the Oil is elevated, and that shows some tramp heat, but perhaps not a Fire at the area of scavenge??

firstfloor
29th Dec 2010, 11:22
I am trying to follow the arguement so far. It looks like this, Oil leakage, oil fire, heating of drive arm leading to failure (first bang?), turbine wheel overspeed because of disconnect from load (but not instrumented) leading to disintegration (second bang?).

bearfoil
29th Dec 2010, 11:56
firstfloor

I think at 12 quarts, the Powerplant may have been 'leaking' chronically. With the tank at 12, the system had to account for 16 quarts. As to Oil fire, the quantity remained constant prior, through, and after "fire"*. If the IT separated from the Drive Arm, it would certainly overspeed independently of the Shaft**; I think the Shaft maintained its integrity, but slipped at the Thrust area coupling, (axially).

I lean toward an engine Stall with interruption of N2 gas, the first bang, and having blown through the IPLP, and upset the IT to disintegrate, it exited the case, second bang. I kind of think the noise was approximately simultaneous, but due to the character of the reports, each was 'heard'. This is to say the Drive Arm failure caused the N2 loss, which caused the Stall, which caused the Burst, something like that.

*we cannot forget the "Stub Pipe" here. Supposedly it was pouring Oil into the HPIP Plenum, but the reads of Annex14's don't support this.

**but not for long, at least not in some orderly manner, almost immediately would blades start to depart, as they contacted the Stator Guide Vanes. The Wheel would orbit its Shaft with a larger bore radius than it started with, causing severe out of balance issues (see vib HP %RPM). The focus of stage one vibration would be the bearing space shared with HP, I feel that is why the vib was highest at the HPT.

barit1
29th Dec 2010, 12:35
bearfoil:I lean toward an engine Stall with interruption of N2 gas, the first bang, and having blown through the IPLP, and upset the IT to disintegrate, it exited the case, second bang.

An engine that will not tolerate (mechanically) a high-energy compressor stall WILL NOT withstand all the test regimen in development and certification testing. Whatever failings the Trent 900 might have, I find your thesis to be very far-fetched.

Turbine discs are very stout. The 9/11 crashes demonstrated that; of all eight engines that were destroyed that day, all the turbine discs were pretty much intact. To envision a compressor stall inducing a disc burst is "round the bend".

bearfoil
29th Dec 2010, 13:02
barit1

I think you misunderstand my post. The IT failed at the Drive Arm, This left the Disc rotating with its full energy in an out of balance fashion. This is not the first time an IPT has fractured fully from its Drive Arm. The idea is that the Disc would burst and exit with or without the Stall. Forget the Stall. The moment the disc parted its Arm, the clock was running. As the Turbine lost its blades having migrated into the Stator, N2 diminished. At perhaps five hundred pounds and 7500 RPM, the Burst was on its way. A Stall makes the bang, one of two. I list the Stall as the first bang. It could have easily been the second loud report. No need to link the Stall with the failure,[I] if indeed there was a Stall. If there was, it isn't round the bend to think it may have tipped the Disc, aggravating and perhaps speeding the Burst along?

The explosive disintegration of the Wheel is seen. What on Earth does 9/11 have to do with this?? The Disc is 'very stout' therefore it withstands the forces that fail it, ipso facto?

barit1
29th Dec 2010, 13:22
OK - I have little doubt there was a stall somewhere in the whole sequence, but it wasn't a necessary part of the mechanical failure, but rather it was incidental.

Consider also that the drive arm is much less massive than the disc bore, and was directly in the "blowtorch" zone; the bore would take a lot longer to heat up to the point of failing at 7000-8000 rpm. Thus I submit that it was indeed an overspeed that failed the disc, and that requires the IPT blades to remain more-or-less intact after the drive arm separation. (They could readily disappear when passing through the case etc.)

My reference to the 9/11 engines was simply to point out that normal discs running at normal temperature & rpm do not fail even when horribly abused.

But all this is subject to revision based on more evidence.

firstfloor
29th Dec 2010, 13:38
Overspeed is the mechanism described in AD 0262 -

Analysis of the available elements from the incident
investigation shows that an oil fire in the High Pressure / Intermediate Pressure
(HP/IP) structure cavity may have initiated a sequence of events leading to
rupture of the drive arm of the IP Turbine (IPT) disc and subsequent overspeed
and burst of that same disc.


Other complications have no standing per rule of Occam's razor.

Turbine D
29th Dec 2010, 15:59
firstfloor

I agree with your post.

Fire - increasing temperature of IPT disc in the bore area - fracture of drive arm - increase of rotor speed - disc rupture - the end.

In the Trent 772 Edelweiss failure, a similar scenario: Fire - fracture of drive arm - disc does not rupture - the end.

The differences are: The IPT rotor in the Trent was probably turning at lower rpm's (7000 maximum permissible) verses the Trent 900 (8300 maximum permissible).

Temperature at the R850 holes in the Trent 700 disc arm reached 1832℉, a combination of friction and fire according to the NSTB report.

The first contact of the IPT rotor in the Trent 700 would have been at or near the tip of the turbine blades as they contacted the Stage 1 LPT nozzle slowing (breaking effect) the rotational speed of the disc. The Stage 1 LPT nozzle tilts forward at the OD. In my opinion, this feature saved the day in preventing increasing overspeed and disc burst.

The first contact of the IPT rotor in the Trent 900 would have been at the drive arm interface near to the engine centerline creating melting and potential further rotational speed, no breaking effect there. The Stage 1 LPT nozzle does not tilt forward and the airfoils are recessed because of a large forward ID overhang design.

Key factors: Hoop stress at the disc bore - radial stresses in the disc web - temperatures at the bore (keep less than ~500℉) - at the rim (keep less than ~900℉), both depending on the capability of the disc material.

lomapaseo
29th Dec 2010, 19:10
Turbine D

Glad to see that this thread finally ended up in the tech section where it belongs, especially since it's only speculation and not news worthy.

Your post above has come the closest to describing the key factors and differences in the two incidents.

However, once again I would urge you to forget about the significance of friction once the failure scenario has started. At the speeds that turbo machinery runs the interface conditions in a contact environment is nothing but molten metal.

The energy is all in the gas stream, so if you want to corral this energy you have got to get rid of the driving airfoils within the time it takes to blow the flame out the tailpipe. If the airfoils remain for even seconds, it's probably too late.

mm43
29th Dec 2010, 19:42
I've been following this interesting discussion from the beginning on both threads, and other than dropping in the odd graphic have just watched the flow and ebb. However, when looking at a pic taken after the #2 had been demounted and lashed to the trolley, I noted a stray pipe with a rather distressed look to what is now an open end. What would have been carried in this line? I assume this damage was caused by the disc burst.

http://countjustonce.com/QF32/qf32-eng-sec.png

Also, I believe that references have been made to the FDR graphics as published by the ATSB in their Interim Report. Those 5 graphs in their full size (1369 x 976 pixels) can be downloaded as follows:-

QF32-FDR-1 (http://countjustonce.com/QF32/qf32-atsb-1.png)
QF32-FDR-2 (http://countjustonce.com/QF32/qf32-atsb-2.png)
QF32-FDR-3 (http://countjustonce.com/QF32/qf32-atsb-3.png)
QF32-FDR-4 (http://countjustonce.com/QF32/qf32-atsb-4.png)
QF32-FDR-5 (http://countjustonce.com/QF32/qf32-atsb-5.png)

Reference to the engines #2 and #3 N2% scale in image #2 will reveal that the #2 readout has been offset vertically and the scale associated with both engines is corrupt. I suspect the correct scale is that above for N3%.

lomapaseo
29th Dec 2010, 19:57
mm43

I've been following this interesting discussion from the beginning on both threads, and other than dropping in the odd graphic have just watched the flow and ebb. However, when looking at a pic taken after the #2 had been demounted and lashed to the trolley, I noted a stray pipe with a rather distressed look to what is now an open end. What would have been carried in this line? I assume this damage was caused by the disc burst.



Somebody on here may know for sure, but it looks like a structural member to go between the mount points on the engine. Wasp waist engines have a tendancy to distort their cases and rub compressor blade tips without this kind of load carry device.

bearfoil
29th Dec 2010, 19:58
mm43

Not a pipe, in the conduit sense, it is a Torque Link. Both these struts were severed by the exiting HE Debris. See the mates above, at the pylon cleat. These features prevent yaw of the engine. They snub each attempt in tension/compression, as a pair.

The separation of the Disc from the Drive Arm would allow freespool, surely, but not without instantaneous consequences, imo. The Rim of the Disc is aligned with, and short of, the Platform for attachment of Guide Vanes on the Stator. The rim would rub the Platform, but the loose bore of the broken Wheel permits "Elliptical" rotation, something that would shear the Blades of the IT off immediately. The fact is, as the Drive Arm is contacting the Stator, the rim is contacting the Platform. This contact may have happened prior to the Circumferential fracture at the Drive Arm. There is no way of knowing at this point the exact progression of the fail. I do believe that since the Blades would shear instantaneously in either case, overspeed did not progress far, if at all. This makes one think of the consequence of instant unloading of the IPLP barrel, and forward. Who needs a Stall?? The debris and damage shows remarkable scarcity aft of the Stator. Most everything appears to have been blown out the gaps in the case in a forward direction.

Turbine D
29th Dec 2010, 20:01
lomapaseo

Thanks for your post. Your comments regarding the airfoils is well taken. The Trent 900 is an extremely high performing engine that produces higher pressures, temperatures, rotational speeds and thrust, higher stresses go with the package. In this new generation of engines, the turbine airfoils are highly loaded, 3-D designed for optimum aerodynamic performance and there are less of them to save weight meaning they have to work harder to extract more energy in the same axial distance span. I hadn't given this a thought until you brought the subject up, indeed they have to go away fast!

mm43
29th Dec 2010, 20:19
lomapaseo, bearfoil;

Thanks for the feedback. A strut it is, and I have made the connection.

Old Engineer
29th Dec 2010, 21:56
My comments are based on, or inferred from, information which I believe was developed at Stonehouse. It was stated that it was believed to have possible application to a contemplated aircraft designated the A3XX which could carry 450-500 people, among others. It appears to have originated with a technique used in fighter aircraft. Note is made of the fact the fighter and commercial aircraft differ substantially in the frequency of engine inspections, at least those involving tear-down of the engine.

I comment as follows:

The steadily rising oil temps-- from about 170-C to somewhere in the 190s, and at a comparatively leisurely pace (20-some seconds here before everything went pear-shaped), are compatible with a bearing running hot under very high thrust load, due to the inability to maintain an oil film under these conditions. This occurs even though the oil supply is completely normal (normal flow rate, and properly reaching the bearing(s), and being cooled in the normal fashion), in commercial A/C.

In the military precedent, the fighter A/C could totally lose oil flow to bearings due to violent turns, etc. A solution had be sought to this problem that would enable the bearing(s) to survive 30 seconds undamaged during oil starvation.

The inability to maintain an oil film can rapidly lead to spalled races and bearing seizure in plain metallic bearings, even those with several different types of surface hardening. Perhaps by accident or lucky chance, it was found that a coating called AP (advanced phosphate) tended to act as a solid lubricant (or perhaps an oil film would be adsorbed onto its surface?), and was not itself damaged in the process... at least not up to a point. (If there is such a point, it is not in the information I have, nor is a full explanation why the AP coating worked as it did.)

A model of a ball thrust bearing was made, roughly 1" x 1" in section including both races. This is thus about a quarter-scale model of what I tentatively believe to be the size bearing used in the OF32 #2 engine. The test bearing, with the AP coating on both races and the caged spherical balls, was test run for about 6 minutes with the appropriate high thrust loading. The inner and outer races rose to rather different temperatures, but by inspection of the graphs, 200-C is a fair estimate of the average of the two temperatures. This could be said to occur over the initial 40 seconds. The text said the AP coating tended to higher bearing temperatures, but that stabilization at about 200-C was typical. On reduction of the high thrust load back to more normal, the temperature fell without any bearing surface damage detectible.

Perhaps it can be said that there is a trade-off here in the weight of more oil cooling capacity. But maybe this type of AP coating is just going to run at about 200-C regardless (Edit: but only on failure to form the normal oil film). I don't want to get too far beyond my information; I have sought more recent information, but without success at the moment. I do know that such a bearing (or bearings, there are 5) was used in an advanced turbofan engine built by BMW Rolls-Royce AeroEngines.

At the moment, and I always stand to be corrected, I incline toward a bearing problem initiating a bearing overheat problem. Then obviously this will lead to hot lubricant in all the bearings of that engine, and they will all contribute to the overheating of the oil. Well, of course, the unrestricted certification oil temperature of the RR RB211-972 is up in the 190s (194-C? 197-C?).

The warning upon which there was time to take action was the rise and rate of rise of the oil temperature beyond 170-C. But this rise apparently is not communicated to the FD, just to maintenance. I cannot emphasize too strongly that we do not need any oil fire to have this happen. Yes, I've read the official report. I see a lot of clean metal in the area of the missing turbine casing-- a lot of that is clean as a whistle, including one large piece that had rotary symmetry sundered by a vicious, meandering tear. I also see a large, clean ball thrust bearing, with a buckled outer race.

I agree with barit1 that it is unlikely that a compressor stall was the start of this. But drag from a failing bearing may have disturbed the relation among the 3 compressors and 3 turbines leading to a stall. Then the forces involved in this stall may have made the 30-second delay, perhaps ordinarily enough to not incur disc disintegration while seeking stabilization of the engine, a wrong choice in the software. This is now changed in software.

A lot of questions arise out of this information. Did engine #2 have bearings with the AP coating? Or a later coating accomplishing the same purpose? Did vibration and impact from excessive spline wear damage this coating? There is certainly a heavy watch on spline wear. I leave more questions to later.

bearfoil
29th Dec 2010, 22:42
old engineer

I take note of your theory of film loss, and this covers heating of the engine oil. Not enough is being made of high vibration imo, for this is a more damaging way to lose lubricating performance. Though the linear aspect of Ball bearing thrust attenuation here is not usual, I note your confidence in it. A spherical bearing in thrust as here, has two points of contact fore/aft, two per raceway (Four total). Under the load of IPT aft force, a vibration works to squeeze a film to zero, and the phosphating you discuss is left not to lubricate, but armor the Race and the Ball against significant "chatter"? It is not out of the realm of possibilities to suggest that the number of surfaces diminishes as vibration (and imposters, a resonant) can move to unload a number of balls, leaving fewer still to take the load. The Main bearing was reworked due to spalling, what was the remedy? More frequent inspections. Rolls may have been too casual with some results from the test bed prior to introducing this Engine. Too late with the Rumour, but better than never.

Turbine D
29th Dec 2010, 23:55
old engineer
I agree with barit1 that it is unlikely that a compressor stall was the start of this.

I don't think anyone suggested the compressor stall started the chain of events leading to the engine failure. It was primarily a discussion of the two "bangs" heard and reported by the flight deck crew. The reality of it is though, when the compressed airflow of the IP compressor (N2) significantly dropped (no IPT drive), the HP (N3) compressor eventually choked and stalled, especially if it was in a increasing rpm mode to create thrust as demanded by fuel flow to the combustor. This was the situation as I see it. A HP compressor stall was inevitable.
I also see a large, clean ball thrust bearing, with a buckled outer race.

When you look at the views of the engine presented in the ASTB report, I think everything you see is from areas to the rear of the combustor casing. You can still clearly see the complete combustor case with the fuel inputs and electrical igniters, the wires shielded with a reddish insulation, as the engine is being removed from the pylon. I don't believe there was any destruction of the compressors or rupture of the compressor casings (IP or HP), that would release thrust ball bearings. I have seen compressor failures on engines, and the results are really not pretty, even more catastrophic in appearance than on this engine.

bearfoil
30th Dec 2010, 14:42
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?

bearfoil
30th Dec 2010, 16:07
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

Annex14
30th Dec 2010, 16:26
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.

Turbine D
31st Dec 2010, 20:51
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 (http://www.flightglobal.com/page/A380-In-Service-Report/Airbus-A380-In-Service-Technical-issues/)

Happy New Year to all !!!

Turbine D

Brian Abraham
1st Jan 2011, 02:03
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 (http://www.aerosocietychannel.com/aerospace-insight/2010/12/exclusive-qantas-qf32-flight-from-the-cockpit)

Annex14
1st Jan 2011, 09:27
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

bearfoil
1st Jan 2011, 12:45
Annex14

One hopes LHTek will be instrumental in developing a solution to this engine's issues.

May all here prosper and have Peace in the New Year,

Turbine D
1st Jan 2011, 14:19
bearfoil
One hopes LHTek will be instrumental in developing a solution to this engine's issues.
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.

Fabrice691
1st Jan 2011, 14:41
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 (http://www.speedshare.org/download.php?id=BFE46CE611)

SpeedShare - Download Damages_description_wingtopskin.pdf (http://www.speedshare.org/download.php?id=D552208211)

:ok: :ok: :ok:

bearfoil
1st Jan 2011, 15:11
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.

Annex14
1st Jan 2011, 15:54
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

Annex14
1st Jan 2011, 18:13
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

Annex14
1st Jan 2011, 18:30
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 ??

Turbine D
1st Jan 2011, 20:22
Annex14
deposits on IPT fragment

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.

Turbine D
1st Jan 2011, 22:18
bearfoil
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.

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.

What is the nature of the actions taken that now create a reduced possibility of in flight Burst?

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.

Is the Mission of the EASA to protect Corporate proprietaries? Or is its Mission to protect the safety of the Public in Carriage??

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.

bearfoil
1st Jan 2011, 22:36
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)

firstfloor
2nd Jan 2011, 12:23
Qantas A380s to return to US route, Airbus misses delivery target (http://www.smh.com.au/travel/travel-news/qantas-superjumbos-to-return-to-us-route-20101231-19bi1.html)

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.


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.

bearfoil
2nd Jan 2011, 13:05
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.

firstfloor
2nd Jan 2011, 14:28
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).

bearfoil
2nd Jan 2011, 14:57
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.

Turbine D
2nd Jan 2011, 14:57
firstfloor
The connection between the QF32 failure and high takeoff thrust on certain runways remains very mysterious if indeed there is any connection at all.
I wonder about some things relative to the airports and the A380. At LAX, there are two parallel runways, one (25L) is 11,095 ft. X 200 ft, the other 12,091 ft. X 150 ft.
TO on the wider runway is at 250.2° and would generally be into the wind (breeze off the ocean) but at time could be downwind (Santa Ana winds from the mountains to the east of the airport.)

At JFK, the runway (13R) is 14,511 ft. X 200 Ft. TO normally would be at 133.9°.

The LAX runway is 3,416 ft. shorter than that at JFK.

Are A380s limited to 200 ft wide runways for TO & landings?

If so, perhaps a fully loaded and fueled Qantas A380 departing LAX would require maximum thrust on TO (72K) at times, especially with an east wind blowing. TOs are always to the southwest. Full fuel loading would probably be needed to assure sufficient reserves non-stop to Sydney, head winds, etc.

Any thoughts?

Annex14
2nd Jan 2011, 16:40
As you surely know, there are 2 more RWYīs at LAX, 24 L + 24 R. Both shorter than the southern pair and therefore not used, I assume. At least it wouldnīt make no sense at all to use a shorter runway if a longer one is available with these heavy departures.

RWY width of 200 ft. used to be the limit at the very early stage of introduction of A 3800, but a while later the limit was lowered to 150 ft. The much greater limiting factor to runway use are the dimensions and lay out of the attached taxiways. I know of several airports that had to widen taxiways or at least the shoulders. Also curving radii where a case of concern.

Ref. downwind take offs, I thought the general limit to that kind of operation is set at 5 kts.

Annex14
2nd Jan 2011, 16:46
Hope this one works
Aircraft Characteristics (http://www.airbus.com/en/services/customer-services/maintenance-engineering/tech-data/aircraft-characteristics/)
Than select A 380 and the .pdf file with all A 380 data will be downloaded.

bearfoil
3rd Jan 2011, 12:25
Good morning. Looking for some input on Shaft interlinkage via vibration. HP seems to have had the most, and to have caused secondary vibrations. This is not a tri Shaft Isolate machine, Shafts share a common airspace, and at extremely close quarters. What caused the damage to the Stub pipe? Again, the bore/align may have been off, but the wear evident in the pipe's interior bore shows excessive amounts of bore expansion, vibration??

Is vibration the source of damage to the HPIP structure?? Is it also due to insufficient strength causing flex in the diaphragm's field?What about the extra RPM's and Contra rotation?? Is there fatigue here? Are the bearings susceptible to damage and axial drift due wear from vibration and vibration instigated lack of oiling??

CAAAD
3rd Jan 2011, 13:08
Bearfoil - Have we had confirmation that wear was present in the stub pipe? You seem to be pretty convinced but I haven't seen a single supporting opinion.

Was the HP/IP structure damaged prior to disc burst?

Most likely scenario remains oil fire leading to disc release and overspeed to burst.

firstfloor
3rd Jan 2011, 13:47
RR: It was just a stub pipe. It’s fixed, you’re good to go.
Q: Wait a minute. You see our lawyers have said we have to be sure that everything’s ok before we fly again.
RR: It is. Have a nice flight.
Q: Yeah but, the thing is, we grounded the whole fleet you see.
RR: You did what?!
Q: Well, you know, we need to know it’s safe to fly. The lawyers say we gotta know stuff.
RR: What stuff?
Q: About the A, the B and the C mods. Component life times and all that.
RR: Yeah, well, we can’t go into details but we fixed that ages ago. The fleet gets gradually upgraded as we go. Don’t worry about it. Have a nice flight!
Q: Yeah, but, you see, the lawyers are telling us, well, they’re not quite sure why we grounded the fleet, and now we need reasons for doing that and more reasons for flying again.
RR: Right. Erm. Ok, have a nice flight!
Q: Uh!
RR: I’m not sure we can help you with that one sport.
Q: Well, you know, it’s the lawyers; you gotta help us out here.
RR: Look here old fruit, we’ve got lawyers too. It’s like this. It’s a standard defence. You sue us, we shut up. Have a nice flight.
Q: Gulp! ……………. Fire up the engines!

lomapaseo
3rd Jan 2011, 13:51
Bearfoil
Have we had confirmation that wear was present in the stub pipe? You seem to be pretty convinced but I haven't seen a single supporting opinion.

Was the HP/IP structure damaged prior to disc burst?

Most likely scenario remains oil fire leading to disc release and overspeed to burst.

I hesitate to get into speculation about what did happen in a specific incident about which somebody else holds all the cards of evidence knowledge and all I am providing is ignorant speculation.

But from a general sense :)

Parts not meeting design specifications are prone to early wear-out modes from even normal engine operation including temperatures and vibrations.

Fatigue itself is a wear-out mode to me. Left long enough a crack grows to a point where it opens up and squirts oil.

Failure conditions themselves often lead to cascading collateral damage. Thus a disk failure that doesn't clear the engine in a few miliseconds is sure to mess up its rotor drive shaft and bearings.

Chicken and egg questions are the challenge to the investigator and require postulations, experience, and lots of eyeballing of minute damage to confirm. Any one person is sure to get parts of the scenario wrong, so a team approach with pro and cons works best to establish a meaningful corrective action program.

bearfoil
3rd Jan 2011, 14:49
lomapaseo

I have always (three years worth), held utmost respect for you and your work. From the first reading of your TWA800 Paper, I noticed you have a keen grasp of traditional approaches to questions proposed re: Failure mode/chain fail.

If you have read Shakespeare, you might discern the meaning of my internet name. Your style is, well, predictable, if I may say. You are frankly what is known in the old english as a scolde. You never fail to expound on the rather dated approach (IMO), to investigation. There is no disagreement with your post, but for one issue. Ignorance. Ignorance is a straightforward word that has a multitude of definitions. Suffice to say that I do not consider myself ignorant here, in the way you may mean.

Engine failures propagate, they may start small, and perhaps minor, but without attention they involve increasingly the other interrelated systems and components (modules). The Disc Burst did not just "happen". Neither is the Oil Fire the single Bullet theory that so many would have us believe. From the first T/O on the 380 wing, the 972 started to self destruct, as opposed to simply wear down, or out.

So did the 700 Edelweiss incident. Not due to lack of prescribed maintenance, or bad fuel, or Oil. This engine family is a Formula One engine in a Chevrolet. You will excuse the Automotive reference, but in racing, a powerplant has only to excel for a short time, its life is measured in shorter terms, and success is measured in a win, and likely retirement of the entire engine, all of it.

The TRENT is marketed as a lightweight, it is well known to weigh at least a ton less than its competitors. This is eight thousand pounds of increased useful load on a four engine a/c like the A380. Over time, that is a remarkable amount of increased profit, remarkable profit Also the brochures will tout its "Modular design", allowing for shorter turns at checks and strip. Unfortunately, Qantas was told that to retain its advantaged position due light engine weight, Thrust would need to be augmented by that ton to get an additional six tons of hitherto undiscovered weight off the deck from California to Sydney. Still with the advantage, by the mere addition of a keystroke, and not a single change needed on the Engine !!

The Fan is a new design, its shape still being fought over with a competitor. It presents new challenges to an existing design. The Fan has a "fuller" disc and drives more air, more efficiently. How completely was this Fan tested relative to new challenges? Perhaps not as completely as it should have been, with data being misunderstood or even actively ignored?? Please note the vibration reads on the failure of the IP disc on Number two. As N1 and N2 dropped, what was the IPT doing? You should know this, do you?

Finally, there is a format of incident investigation that is being used in rooms across the globe. You could google. First know this: The enemy of the Truth is consensus.

Agreement in and of itself is the enemy of discovery, so I would make reference to your mention of "teamwork". The new deal is confrontational dialogue, not in the sense of rudeness, but in the sense of exploration. It has been in use since I learned of its development at a University in California, well, a long time ago. It does not fail.

Humans think that to collaborate is good. In most things it is. It is an instinct, and like most instincts it has a place. It does not have a place in the Boardroom, or the Investigating table. Confrontation (non-physical, of course) brings to bear (!) a primal clearing of inputs and data (but not exclusively!), while one proponent can excise a nugget of new that has not been entertained because it cannot pierce the traditional paradigm of................consensus. Attacking a problem together can have unwanted results when compliance and social desires trump a good fight.

It is a long and interesting (to me, anyway), discussion. The player in the exercise who forms the wall the Truth can bounce off, is the foil, the one(s) who will fight to keep agreement at bay, and investigation at its highest expression. Please don't do anything differently. and I should not tell you this, but I enjoy greatly when you are at your most righteously snarky.

Turbine D
3rd Jan 2011, 15:42
Annex14
Thanks for the treasure trove of information on the A380, it will keep one busy for quite awhile studying it all.

Re: LAX - I was aware of the 2 northern runways. But, for the A380, they don't work because the taxiway (24L) is too close to the runway and must be cleared of all planes during A380 operations. The first Airbus A380 into LAX actually landed on 24R in 2007.

The airport spent $88M to widen turnoffs and build a new cross taxiway at the western end for A380s landing on 25L from the east. This may be visible from the Google map, if it is up to date.

Also, the 25L/7R runway was widened to 200 feet so that the outboard engines of the A380 didn't overhang in the grassy areas leading to potential FOD damage.

derbyshire
3rd Jan 2011, 16:04
"The player in the exercise who forms the wall the Truth can bounce off, is the foil, the one(s) who will fight to keep agreement at bay, and investigation at its highest expression."

First one to say "Best Practice" gets promoted! :rolleyes:

Turbine D
3rd Jan 2011, 16:05
bearfoil
This is an old article, but, it is the same Qantas A380 that is parked in Singapore awaiting repair disposition. I wonder which engine it was at LAX?

Qantas A380 grounded in Los Angeles - Travel - smh.com.au (http://www.smh.com.au/news/travel/qantas-a380-grounded-in-los-angeles/2009/01/26/1232818350222.html?sssdmh=dm16.357386&from=top5)

firstfloor
3rd Jan 2011, 16:23
The TRENT is marketed as a lightweight, .........

I really must strongly disagree once again. Not formula one, not lightweight in the sense you mean. The difference is three spools, the design goal since the sixties being efficiency and compact design at the expense of greater complexity over the two spool turbofan. It has taken Rolls Royce a long time to achieve the weight advantage it presently has but it is in no sense a fragile piece of equipment. Think robust instead. The technical advantages of the three spool design grow with engine size.



From the first T/O on the 380 wing, the 972 started to self destruct,


Give me strength!!

Bearfoil = wrong, dead wrong and completely and totally wrong.
Truth = start by reading the ATSB preliminary report.

TopBunk
3rd Jan 2011, 16:28
From experience, the runway utilisation at LAX usually has arrivals on the outer pair (24R and 25L) and departures from the inner pair (24L and 25R), so landing 24R would be not unusual.

Maybe a better question is where do the QF A380's normally park at LAX? Do they still use the Tom Bradley international terminal, and if so which stands are A380 suitable?

I understand the taxyway issues with the A380, it could be that the parking location determines both the landing runway and departure runway assignation. For example, if they use Tom Bradley northern end then 24R for landing and 24L for departure probably interferes less with other taxying traffic; conversely the southern runways for parking TB southern end.

The northern pair are, however, shorter in length, and hence may be the cause of the requirement for rated thrust usage rather than some degree of derated thrust.

Annex14
3rd Jan 2011, 16:48
Found the attached message digging in all kind of messages probably containing something called" the light at the end of the tunnel"
Rolls-Royce Bearing Box Blamed in A380 Engine Fire (http://www.bearingtrends.com/bearing-news/skf/2998-rolls-royce-bearing-box-blamed-in-a380-engine-fire)

I am looking foreward to your comments

firstfloor
3rd Jan 2011, 17:08
Annex14:
From the article.

over Indonesia last week

And the date of this report is?

bearfoil
3rd Jan 2011, 17:11
Goodness!! What's a poor ignoramus supposed to do with this?

The bearing failure, slop, flop and buzz, allowed the IP Shaft to "migrate" aft?? Isn't that what AD's are for?? So much for a duff stub pipe. Unless, unless, it was the one lubing the ball bearing thrust snubbers at IPHP. Not the one lubing the Rollers?? Tickle my arse with a feather.

Vibration, vibration, vibration. Location location location.

Question then. What of the bearing boxes in the 900?? How about in the X ?? Highly strung fuss budget? Or Gorilla meant for decades on the wing.?? You make the call.

first floor

The date is important, and more important is the nature of the Failure. When is it not allowable to organize one's thoughts around a year's worth of documents and inspections?? Jump ship because a highly suspect corporation wants to pin this disaster on a piece of tubing??? It was not Ian at the bench with a hangover. My prediction is that RR will regret having tried to mislead, and keep secrets relative to Safety. Power by the Hour is nifty, if both parties are honest, and not bent on protecting their personal hides because they've pushed the Camel over the cliff. The Camel didn't die, and he is quite pissed.

bearfoil

where's old engineer and Turbine D when they are well and truly needed.

Annex14
3rd Jan 2011, 17:52
Sorry, donīt know. Got it via this Home page : Ball Bearing, Roller Bearings & Power Transmission Distributors Manufacturers Community For SKF Timken FAG INA NSK (http://www.bearingtrends.com/)
There it says : News and thereafter one can click on each of the brands named in the list. In that SKF list itīs report Nr. 2

Annex14
3rd Jan 2011, 17:59
Page 31 ATSB Preliminary Report

Other party safety actions >>> Qantas

Quote:
3. Before further flight, carry out a borescope inspection of the bolted joints of the HP/IP [High Pressure/Intermediate Pressure] Support Structure area of each engine per RR NMSB G592.
Any connections to >>>540 Psi at P30 ????

Must admit, only after the probably 6th or 7 th time reading that report I struggled across this statement.

bearfoil
3rd Jan 2011, 20:28
I think probably due vibration due to wear/loose tolerances, or Vibration alone, or a resonant frequency. Wonder how the Ball Thrust box was found and hung on the case post engine removal??

Turbine D
3rd Jan 2011, 21:11
bearfoil - Annex14 - firstfloor
where's old engineer and Turbine D when they are well and truly needed.

Humm, Thinking!

It would appears that we are back to the proposition: A leads to B, B leads to C and C leads to D, C = fire, D = BANG! The questions are: What are A & B, Is there A & B or just B or is it even more complex A1, A2, B1, B2, etc.

The visit of the Airbus CEO to Southeast Asia no doubt was prompted to see first hand and be briefed on the damaged aircraft in Singapore. He then probably went on to Sydney to meet with Qantas leadership to further discuss the matter as a good aircraft supplier would do with a good customer. Now if his interview only took place a week after the event, there wasn't enough time to state with certainty the actual cause of the failure, but maybe only generalities or suspicions, perhaps from technical difficulties plus modifications being made with Trent 900 engines, i.e., SIA and Lufthansa and ongoing mods at Airbus.

Here is the timeline of events as reported by the ATSB:
11/4 The "event" takes place
11/9 Flight crew interviews
11/9 Start of aircraft examination
11/11 Aircraft examination continuing, crew interviews completed.
11/12 Recovered disc section sent to UK/RR for examination.
11/13 Engine successfully removed from the aircraft.
11/17 Engine dismantling at a workshop in Singapore with the LPT module being removed to gain access to IP turbine damage area.
11/22 Parts of interest have been photographed and sent to UK/RR for further examination.
12/2 Stub pipe announcement is made with a photograph of fatigue fracture.

So I think the Airbus CEO "interview" and reporting of the same is not in the right place on the time line for any conclusive cause to have been made.

3. Before further flight, carry out a borescope inspection of the bolted joints of the HP/IP [High Pressure/Intermediate Pressure] Support Structure area of each engine per RR NMSB G592.

Which one? Are there two? The one of suspicion would be the one between the HPT rotor and the IPT rotor which contains the plenum chamber where the oil lines feed and drain the roller bearing box. This is also where I think the stub pipe location is.

The bearing failure, slop, flop and buzz, allowed the IP Shaft to "migrate" aft??

I am having trouble believing the IP shaft could move back hardly at all without scoring the LPT shaft where it flares out going aft. There is not enough room there for this to happen without seeing the effects which are not in evidence in the photo of the removed LPT module.

Obviously, it sure would be nice to see the compressor areas of the engine to know all of this for certain.

Firstfloor - I loved you fictionalized Law vs Machine dissertation,LOL:), but probably not far from reality.

Turbine D
3rd Jan 2011, 22:43
TopBunk

There remains an issue with the TB international terminal and the A380. First the location is extremely tight with all wide bodies having to be towed to the gates due to the crowding. The A380s of Qantas are towed to the west wing annex area for loading and unloading with passengers bussed to the main TB terminal as I understand it. This is to be remedied this year with a complete overhaul of the terminal to accommodate the super-sized A380 and eliminate the bussing among other positive renovations.

The north runways 24R/6L and 24L/6R pose a different problem. They are too close together and too close to the taxiways for multiple operations if one of the aircraft happens to be an A-380. A plan to both widen and relocate one of the runways to balance operations, similar as to what was done on the south side was rejected. So those two runways will no doubt be used more for smaller jets, TOs and landings with the widebodies utilizing the southern runways. The western end of the southern runways was totally rebuilt to give more operational room for the A380 to taxi towards the TB terminal.

I am not a pilot, but as far as runway length goes, If you have a fully loaded, fully fueled Qantas A380 taking off on 25L, do you have enough distance left at or just before V1 to abort the TO safely if you only can use 70K (degraded) maximum thrust? It may depend on day to day changing factors, if at all. The 72K thrust may be the guarantee it is OK.

johdi
3rd Jan 2011, 22:48
Date of that report, see link, was November 12, 2010
Airbus says bearing box failed in Rolls engine Japan Today: Japan News and Discussion (http://www.japantoday.com/category/world/view/airbus-says-bearing-box-failed-in-rolls-engine)

Turbine D
3rd Jan 2011, 23:05
bearfoil

Wonder how the Ball Thrust box was found and hung on the case post engine removal??

Who said this was "hanging" on the case post?

bearfoil
3rd Jan 2011, 23:48
Turbine D

I was referring to old engineer's comments on the bearing case. Re: T/O LAX. It is the availibility of rated thrust that allows a 380 (Gross) to take off at all from LAX?

The area between HP/IP "support structure" seems to mean to most people the diaphragm supporting the roller bearings. It isn't important either way. The roller bearings I believe are victims, not progenitors. Anyway, the bearing box is affixed one assumes with the very bolts the AD demanded be borescoped, though a borescope could not conceivably measure torque. It could present damage to the rolling surfaces and raceways, assumedly this result would give RR the go-ahead to remove the engine, or prevent further use, (grounding).

Now, if the stub pipe entered service looking as it did in the pic, I'm quite surprised. One sees random scoring on the bore's wall, a channel cut into the bore, (the supposed Q/A blunder) and fractured rim with an ugly circular wear deficit on the coupling's face. This is caused by vibration, and I'm taking wagers. The couple may have failed, though it may have stayed attached, and been uncoupled at disassemble.
The OIL FIRE is almost certainly the result of A and B, as you say.

A........High powered vibration of several expressions.

B....... Severe fatigue due Oiling issues and Raceway, ball wear caused by the combination, oil starvation and vibration. Ball bearings are a "seam", and can vibrate at their own rate, driven by vibs on either side of the support. They are not rigid, and are subject to remarkable load that can reverse several times a second. Now if the bearings wear enough, the axial travel expands, and the IPT can contact the Stator inner, and the Vanes Platform, Outer. This is not my text, but a straightforward paraphrase of the AD.

C........loss of Oil line integrity, and fire. There is no evidence of a fire in the LPT cave, and most interpretations of the fire have it in the annulus between the HPT and IPT. This could of course blow the bearings to bits (rollers), but something simpler and more mechanical is likely to have happened. No need for Occam on this one. Follow the AD, the Wear, the concern, the Burst, the Grounding, and the struggle to refit, repair, and replace. Oil Fire is merely the penultimate failure, not the cause.

Look for insidious Fan Vibration, Fan shaft IPC damage, and weakening of the area around the HPT bearing and the IPT bearing. there is a 20,000 RPM net interface between these bearings. Oil fire is patent on test, though not widely known. The fire is of course a primary suspect, but needn't be at all the procuring cause of failure, just as overspeed is unlikely, given the proximate architecture of the IPT/Stator and the almost certain instantaneous loss of IPT Blades due to Axial Drift aftward. The LPT shaft and Turbines are remarkably free of damage, or even discoloration. Had the IPT blades been lost instant, the Massive Pressure in the LPT barrel would have (and seems to have) blown everything out the bolted together LP case and the IP case separation and missing pieces of case.The HPT was intact, and prevented access to any portion of the Gas path forward of its dynamic seal. Hence the exit of everything out the visible holes in the case.

Again, this is not my conclusion, and certainly not unsupported by the history prior to, the damage during, and the spin around the repair/refit/replace. It is what the Authority predicted, and probably with Rolls critical input. But no, we want it to be a duff piece of tube, flying in the face of enormous effort (unsuccessful) to prevent this very thing from occurring. Spline wear-vibration, oil issues. Bearing wear-vibration, oil issues, Fire-vibration-oil feeds.

The EEC, EMU. Next................

BigG22
3rd Jan 2011, 23:57
I have been following this thread with interest, and have to agree with OE that turbomachinery faults can and do propagate through many levels.

QF32 brought to light the T900 issues with regard to spline wear. Helical spline coupling between compressor and turbine appears to me to be simple and ingenious - the torque generated by the turbine naturally closes the spline coupling. It is a solution conducive to modularity.

AD EASA AD 2010-0008 and its revision reveal problems with regard to IP shaft spline wear. To quote the AD, 'The shaft to coupling spline interface provides the means of controlling the turbine axial setting and wear through of the splines would permit the IP turbine to move rearwards. Rearward movement of the IP turbine would enable contact with static turbine components and would result in loss of engine performance with potential for in-flight shut down, oil migration and oil fire below the LP turbine discs prior to sufficient indication resulting in loss of LP turbine disc integrity.'

It seems an unlikely proposition that the AD and the QF32 incident are unrelated, but that is merely my own personal opinion. No matter what our engineering discipline might be, coincidences like this are rare.

From the data reproduced in ATSB preliminary report AO-2010-089, it appears that at time 02:00:22 oil temperature and pressure values begin to diverge from the recorded values for the other engines.

N3 vibrations increased to an extremely high and non-typical value, while N1 and N2 shaft speeds slowed. N3 shaft speed increased - possibly as the EEC increased fuel demand to compensate? Is this perhaps an indication of a bearing in some severe distress?

Here in this forum we can only speculate, however we must note that the AD makes no mention of the impact upon engine bearings in the event of shaft displacement due to spline wear - it only identifies the consequences of IP shaft rearward movement that would 'enable contact with static turbine components and would result in loss of engine performance with potential for in-flight shut down, oil migration and oil fire below the LP turbine discs prior to sufficient indication resulting in loss of LP turbine disc integrity'.

Returning to the ATSB published data, we observe unusual vibrations from the aircraft body lateral accelerometer at the time of 'thrust drop' and which is coincident with N1 and N2 shaft speeds dropping to zero.

Personally, I suspect that this coincides with the time at which bearing overheat (causing increased oil temperature) and mechanical interference with static LP turbine components may have caused the IP drive arm fracture.

Furthermore, and from the data published, I suspect that that the oil fire commenced at this point because this is when EGT commenced its rise. P30 collapse resulted in a fuel shut off - but I suspect the IPT disc was already in the 'departure lounge'. If I am correct, then the oil fire had little to to do with the IPT drive arm fracture. An engine surge possibly contributed more energy to the break-up of the distressed IPT disc than the resulting oil fire that was of short duration. I seem to recall that was already suggested in this forum but I may be incorrect?

I am therefore hypothesising that the stub oil pipe failure may therefore have resulted from HP/IP bearing faliure and a consequential and excessive HP vibration. Of course, the spline wear problem may have contributed to stub pipe fatigue. There seems to be some merit in returning to the IP spline AD issue and in particular to its cause.

Of course this is all speculative hypothesis based upon information and thinking published in the public domain. Please feel free to shout me down - I'm a new guy here and won't be offended. We can only learn.

bearfoil
4th Jan 2011, 00:36
BigG22

Howdy there. Big G. I think I'll have to take responsibility for the comment about the Fire being of insufficient length and ferocity to "Melt" the DA. I also have opined on the surge as the cause (one of) the IPT disc's erratic spin, a contributory factor in its loss, and I thank you for the support. I have held from the beginning that mechanical slip and effaced wheels causing great friction heat did in the Drive Arm, the Stator, and of course ultimately the IPWheel. Ingenious Helical Splineage?? Oh yeah, but remember, what screws in, also screws out. The bearings were not mentioned in the AD because technically they ARE 'Static Turbine Components', and were therefore covered in Rolls' expression of potential catastrophic failure. Not really non disclosure, 'not really'.

My conclusion had everything to do with the AD, a document that was rather suddenly abandoned in favor of a "may have intiated events that caused...." reported by RR through the ATSB.

Pray, what can be said about Vibration, the mother of this blast??

Turbine D
4th Jan 2011, 01:38
Bearfoil & BigG22

I think we are all parked pretty much in the same corner. Although RR avows there is no connection between spline wear and what happened, it may be a brave statement. One of the things that is least predictable is extraneous vibrations that can develop, particularly those that develop in the torque field. The old saying "the best laid plans of mice and men often go astray" happens more often than not when it comes to vibration. You can do all sorts of testing and analysis, but an unpredicted and unanalyzed vibration could creep in over time and affect a component/components somewhere. I don't discount the potential that spline wear could have create vibration somewhere else in the engine, like tubes or fittings, bearings/bearing support structures, the stub pipe, the plenum or even fastening devises in the torque field, including the disc power drive arm to IP shaft flange bolt holes and bolts. For instance, the bolt holes are very critical in a torque field, and generally treated with significant multipliers of stress to deal with vibration and fatigue. What if some unusual vibration or harmonics entered the equation? Is premature spline wear something you anticipate and analyze for in terms of vibrational effects? Was this anticipated in the margins provided? This is the "A leads to B" I've talked about. The experts with all of the pieces and data have to figure this out. "The spline problem has nothing to do with this engine failure" (RR statement), well I say, "Never Say Never" until all the cards are face up on the table. At this point, all the cards aren't face up on the table. Lets hope they will be, because root cause/causes of failures are only fixed by identifying them and not denying they existed at all. Oil fire and BANG are obvious, A and B are not so obvious. I don't have the answers, not seeing all the face up cards, but RR should.

bearfoil
4th Jan 2011, 02:03
I do have access to the answers, as do others. The problem of the splines was identified in test. The characteristics of the vibration that caused this particular event were identified in test. It is a tramp, a harmonic, and not an insignificant one. The LP Shaft impinges through vibration on the IP Shaft. Chronic oil loss was ignored in test. All this plus an oil fire in test was documented. Shaft relationships were identified as troublesome due to proximity and vibration of two of the three shafts relative to the third. There was no "Oh my goodness, what a surprise". This engine was fielded too quickly, and without the customary care and sticklers for Proof that is ordinarily so much a part of RR. This includes all the 9's, not just the 72. I am just about through with this thread, it has been a laborious march, and the answers are dangling on the stage. I am no prophet, but as I have said before, this story has very long legs, and it is far from over. This entire event has no chance of containment, just like the IP Wheel. It has barely begun. It is entering the world of Industrial intrigue, politics and corporate survival, IMO.

Turbine D
4th Jan 2011, 02:21
bearfoil

A very interesting and troubling piece of information, indeed. Things like this can't be ignored. Speed to market is one thing, but ...... Stick around, it will be interesting as the future unfolds.

lomapaseo
4th Jan 2011, 03:03
A very interesting and troubling piece of information, indeed. Things like this can't be ignored. Speed to market is one thing, but ...... Stick around, it will be interesting as the future unfolds.



I suspect a lot of "I told you so" just like the ones that we are still waiting for predicting that all kinds of aircraft would eventually fall out of the sky from eating the icelandic dust of a year ago.

This after market management is what's known as "continued airworthiness" and as such must be perfomed based on data and analysis by the certificate holder to the satisfaction of the regulatory authority.

It is not the intent to satsify the nay-sayers and in many cases the general public can submit their own comments to the docket for consideration. Meanwhile the present course is to satisfy the emergency AD notice

The typical course of problems like this is to tweak the interim corrective action programs as additional data is received and until a closing action is decided upon and effected. There have been far bigger problems than this in aviation including the B747 fuse pin problem and the various uncommanded reverser problems.

bearfoil
4th Jan 2011, 03:26
Sorry, "Far bigger problems than this" ?? I thought no one knew what happened yet. Very odd take on things, and dare I say, Premature??

Turbine D

Yes, I think parked in the same place. Good company, regards.......

Annex14
4th Jan 2011, 18:10
Quite some commotion in progress since my last entry!! However I have meanwhile detected that this report I linked was not the only one, no there is a whole wave of similar sounding news reports. The origin however, seems to be the report issued by associated press on Nov, 12 right after the Airbus CEO spoke in Australia.
So far firstfloor and Turbine D I agree in what you posted, most unlikely the CEO was - knowingly - talking hard facts about the QF 32 failure.
However, have to ask the question: How did he come to the conclusion to mouth something so serious as a cause of failure in public, if not some information about this possible problem area was known to him ???

Turbine D
Those bolted joines that are subject to boroscopic evaluation have to be those connections between the Modules 2, 3 and 4 - s.a. RR-brochure > gasturbines_tcm92-4977.pdf - sorry I have no working link. One of these bolts is visible in that Trent 900 cutaway I posted a while ago just on top of the Nr. 2 ball bearing.

My question about the decolouringf the disk fragment and the obvious lack of wear or damage to the side of the disk that was supposed to have slammed into the rearward structure and the nozzle guide vane ring was triggered by
lomopaseo
quote: However, once again I would urge you to forget about the significance of friction once the failure scenario has started. At the speeds that turbo machinery runs the interface conditions in a contact environment is nothing but molten metal.

Okay if friction is no player in the game and also no obvious marks about a "fluid bearing" neither in the bore nor at the circumferential crack in the drive arm, and also no mark of contact at least on the recovered part of the disk, what is left as explanation for the disk failure?? Overspeed/ overstress and a plain "ductile fracture" as explained in the ATSB report ??? Here the engineers are demanded !! Its just a conclusion !

Assisted by what?? Look at Fig. 13 of the ATSB report, enlarge it a bit and check the visible rear side of the nozzle guide vanes of the IP turbine. Its there well visible, just some shiny or dark marking, probable contact on break up ? and the gas channels at - as I consider it - normal performance colouration. There is no Oil, there is no oil soot, there is just plain metal !! Wasnīt that the side where that feroscious -blowtorch like - oilfire had to have its devastating work done ??
Hard to believe !!
Still I am thinking of the hottest place of that oilfire more foreward, seen the damage from inside outward on the remains of the bottom section aft cowling.Wasnīt there nearby not that Inner Gear Box witha connection to the ring in front of ball bearing Nr. 3 ??

Finally, the "spline wear" AD is still in force, as is the restriction to 75 takeoffs with power settings at 540 Psi at P30!! Why that ??
Obviously the oil tube is a contributing cause but the real problem still excists and is not identified to the public. Looks like someone tries the old game of "sectioned information and selected truth" Okay, Okay, if at the end the case is sober and no one gets hurt, but meanwhile ?? how long will it take to be really back on the safe side of the game ??

bearfoil
4th Jan 2011, 18:41
Annex14

Howdy. The AD is the Gorilla in the living room. Eventually, and ironically, RR and EASA will have to merge reality with prior work. It won't go away, and the liability can never be diminished. Ever.

In the Broad view, time is running out on the program. Fewer and fewer of the principals are adhering to "Let's wait and see". Or, more laughably, "Let's wait for the final report". Any rush to Nirvana will be roundly criticized, but the patience of the entire Aviation landscape will get thin.

There is a reason for intensified scrutiny. There is a reason for the borescope. There is also, like white on rice, the need to strip and bare the insufficencies, which perforce will cost the community untold money. We are witnessing the underside of what is wrong with the too cozy relationships between the Authority and the Manufacturer/Operator.

I think there will be a "fix". The question is obviously, is there room for it inside the confines of the certificate?? The "Back in the Air, what a relief" has to do with a system that hadn't any part in the cascade of cause, the fingered "Stub Pipe", around which there is no AD. There is only an emergency directive. While the audience is fixed on OIL, the "modules" are switched. Presto.

Can this feint be pulled off?? Only if it is not a feint, but as RR and all would have it, merely a duff piece of metal tube.

Hiding in plain sight has gotten orders of magnitude more difficult than days of old. This is a good thing; all the artifacts, fossils and tricks are uncovered to enhance Safety. Disclosure is a very good thing, always. It is sadly predictable that keeping secrets and hiding is getting ever more difficult, bummer............

rottenray
4th Jan 2011, 19:17
Annex writes:
Those bolted joines that are subject to boroscopic evaluation have to be those connections between the Modules 2, 3 and 4 - s.a. RR-brochure > gasturbines_tcm92-4977.pdf - sorry I have no working link. One of these bolts is visible in that Trent 900 cutaway I posted a while ago just on top of the Nr. 2 ball bearing. Try this: www.rolls-royce.com/Images/gasturbines_tcm92-4977.pdf (http://www.rolls-royce.com/Images/gasturbines_tcm92-4977.pdf)

Cheers!

Turbine D
4th Jan 2011, 22:45
lomapaseo
I suspect a lot of "I told you so" just like the ones that we are still waiting for predicting that all kinds of aircraft would eventually fall out of the sky from eating the icelandic dust of a year ago.

Here is another "told you so" to think about....

Joerg Handwerg, a spokesman for the pilots’ union for Lufthansa said that minor problems are routine for any jet engine, but it is possible that the issues were an indication that regulators did not adequately check the engine before approving it for commercial use.

“When you see we have a problem with not just one of these engines but several then it points towards that we have a problem in the certification process,” Handwerg said. Why Lufthansa is check-fly, check-fly, etc.?

So, the Trent 900 engine was certified as being airworthy and then the certification of the Airbus A380 began with the Trent engines. So in this aircraft certification process, how many engines do you think would be acceptable to come of wing due to "technical problems"? 5, 10, 20, 25, 30? I am not referring to planned removals. I think the true number would surprise you. Maybe this is where Airbus Chief Operating Officer, John Leahy had information the general public didn't.

Technical problems with the engines, lets fix them, starting with the ones sitting at Airbus?? What about the ones flying? Humm.

Now the RR lawyers are in charge of the business, settle with Qantas and Airbus as to damages while not admitting to or denying anything was the fault of RR. Isn't that the way business is done these days?? Sure is! Too Bad!!!

bearfoil
5th Jan 2011, 01:08
Turbine D

Lufty has been quiet since the outset, and I hadn't seen Herr Joerg's comment. LuftTek has the marbles, the action they have taken/acceded to will speak volumes when they speak, I'd say. Qantas by now has a thick jacket on the 9 and RR's "unusual" timetable. A shiny newbie gets re-engined prior to one that takes off and dodges a bullet?? I'm watching for action around the AD's. Something is amiss when a flying operator is passed over when the AD's call for such draconian levels of inspections, and repair, rebuild, re-new. Is there anything in the "C" model that stretches the Certificate to fit it?? What can be so attractive about a rebuild when it doesn't satisfy its own Certificate and retains so many limitations?? The DEP/EEC has new programming, and what good is the extra 2000 pounds when all it gets one is trouble and sanctions?? Speaks volumes about what might be wrong with the 900 as well. It isn't the Oil, and it isn't the DEP, Coupled shafts have issues, can RR design/build a new engine to wear the 900 livery, spec sheet and maintain the certificate?? EASA and ROLLS are in a corner. Qantas has some challenges as the result of the Burst, but just because the situation paints them the victim, money is way off, and how to recoup their position?? Haven't heard from Mr. Joyce recently.

Time to break the huddle and line-up??

Turbine D
5th Jan 2011, 02:34
Annex14

Assisted by what?? Look at Fig. 13 of the ATSB report, enlarge it a bit and check the visible rear side of the nozzle guide vanes of the IP turbine. Its there well visible, just some shiny or dark marking, probable contact on break up ? and the gas channels at - as I consider it - normal performance colouration. There is no Oil, there is no oil soot, there is just plain metal !! Wasnīt that the side where that feroscious -blowtorch like - oilfire had to have its devastating work done ??
Hard to believe !!


You are correct, that is the nozzle vane that sits behind the HPT rotor, it is a hot gas path at that point and the vanes are air-cooled. They are no doubt coated to prevent oxidation/sulfidation and the brownish color is the deposit left by the fuel that has been burned in the combustor. There would be no soot from oil burning it would be completely consumed because of the gas path temperature (~ 1800℉). The vanes are not the problem, it is the plenum chamber directly under these vanes that you can not see that is the problem. As you would move down that plenum towards engine centerline, the HPT/HPC rear roller bear sits, supported by the end of the plenum.Just slightly rearward sits the IPT/IPC rear roller bearing. If there was an oil fire in this plenum, it could cause it to rupture exposing the front face of the disc near the bore. The plenum is (or should be) under positive pressure from the cooling air that has passed through the nozzle vanes. the vanes didn't see the oil at all.

Okay if friction is no player in the game and also no obvious marks about a "fluid bearing" neither in the bore nor at the circumferential crack in the drive arm, and also no mark of contact at least on the recovered part of the disk, what is left as explanation for the disk failure?? Overspeed/ over-stress and a plain "ductile fracture" as explained in the ATSB report ??? Here the engineers are demanded !! Its just a conclusion !

In one of the press releases or media briefings by the ASTB, they talked about the disc and the fact that it showed both melting and molten metal splatter on the rear surface of the disc. I think I mentioned that the light grey area next to the bore was just that. When something is spinning at 7-8K rpms, the metal spreads out into a film (usually a combination of metal and metallic oxide). Also, look at the recovered nozzle vane photo in the ASTB report. They note a coating on the surface of the airfoils they intended to examine. That to could be a molten metal deposit film as well. I believe the disc broke free from the bolt holes when the power drive arm broke at that location. Once free, it was able to rotate to whatever speed the HPT gas flow could drive it and remember the N3 was 98% at its peak. At this point it would be stretching. They will be able to determine this by dimensional measurements taken on this recovered section. So it moved back contacting the Stg. 1 LPT nozzle, not blade to vane but blade to the inner nozzle band forward overhang. Look at the vane photo again, the inner forward overhang is gone, not there. The other possibility is what Bearfoil proposes. No matter which, the disc over-sped. It all happened in a couple of seconds. Mostly everything went out including the Stg. 1 nozzle vanes, very little went back through the LPT which is what you would expect if the disc didn't burst.

firstfloor
5th Jan 2011, 10:41
Just so nobody goes away with the idea that Rolls Royce is the only one with engine problems. In the news today is this.

GE says it is working with the carrier, after local reports from Angola said that TAAG grounded its three 777-200ERs after another incident on 23 December involving a GE90.

But back on subject, it seems to me that the only way to know if the C engine still has a design issue is if it comes back on the USA west coast routes with restrictions imposed on 72k takeoffs. This restriction has so far only been mentioned in the infamous Qantas affidavit.

Turbine D
5th Jan 2011, 13:23
DERG
There also seems to be some confusion on market share and market leader when it comes to the Trent 800 & Boeing 777. RR, in the brochure for this engine states that they are the market leader at a 41% market share. In that there are only two engines offered, one being a RR, how can you be the leader at 41% share? I think the same disclaimer is on the back page.

Turbine D

Annex14
5th Jan 2011, 13:56
Thanks for your comments. Those tremendous gas and thermo dynamics inherent in a running jet engine are always good for surprise, I assume.

Ref. that statement of Cpt. Handwerg, VC - the union of the LH pilots - is indeed amazing, Iīve read it too. But knowing their reluctance to go public with company related insider data, this is a clear sighn that the pilots and technicians At DLH see a potential problem.Will have a close watch what else they might release in this case.

firstfloor

There is thread in Rumors & News about that TAAG-incident on Dec, 6 . The flight returned to Lisbon with vibrations in one engine. On its way back parts - engine ?? - fell onto cars in southern Portugal.

Jo

Turbine D
5th Jan 2011, 14:53
firstfloor

This is from Flightglobal/Insight:

Qantas disclosed in an affidavit on 2 December that there are three modification standards - designated A, B and C - for the HP/IP support structure on the Trent 900 series. The document specified the failed engine as an 'A' modification powerplant.
According to Rolls-Royce's engine manual, the life of the 'A' support structure was limited to 2,000 cycles, said the airline. The 'B' modification was issued in December 2007 and its life limit extended to 14,800 cycles. The latest 'C' modification standard was introduced in April 2009 and has unlimited life, says Qantas.
The Australian Transport Safety Bureau declared its investigation was concentrating on 'A' and 'B' standard engines.
Powerplants with the 'C' modification status are not affected, because they do not have the same oil feed stub pipe installation, which is considered central to the engine failure chain.
Investigators believe that the stub pipe developed a fracture in a section with a small wall thickness, which led to an oil leak and fire in the HP/IP structure cavity. This thin wall section has been confirmed as a result of the manufacturing process.
EASA issued the revision of the second emergency directive this week, stating: "Manufacturing and inspection data, and stress analysis performed by Rolls-Royce, now confirm that oil feed tubes with a defined minimum thin wall section feature a higher life and lower risk of fracture." This would allow longer service periods for respective engines before the inspections.

The "A" Mod Qantas #2 engine (677 cycles total) didn't quite make it to the 2000 cycle limitation.:(

Turbine D

Turbine D
5th Jan 2011, 15:06
firstfloor

Re: The GE90 incidents: From Flightglobal

Angolan carrier TAAG is working with General Electric to determine the root cause of two engine events on the airline's Boeing 777-200ERs.
One event, according to the US National Transportation Safety Board, was on 6 December. The board says the GE90-powered aircraft suffered a low-pressure turbine failure in the number two engine after take-off from Portuguese capital Lisbon. The flightcrew performed a turnback and landed without any injuries.
The NTSB says turbine blades were reportedly expelled from the rear of the engine over a populated area.


Turbine D

Annex14
5th Jan 2011, 15:50
Reading that second last entry I stumbled across the quoted report from FlightGlobal/Insight and especially this sentence:
Quote:
Powerplants with the 'C' modification status are not affected, because they do not have the same oil feed stub pipe installation, which is considered central to the engine failure chain.

At once I rembered to have read also somewhere - unfortunately I canīt find it where it was, therefore I ommitted to refer to it - that this special wording "oil feed stub pipe installation" was used. To be correct it was in German language and therefore I thought that this phrasing was just a thought or bad translation that came off some reporters brain, but as it looks it is not. In that information I read it was said that the different trials to correct / change the mounting/ installation of the feed stub pipe was undertaken to overcome constant oil leak problems. The hack with it, that I cannot find it back !!

If they really talk about a change in stub pipe installation - and they do - that means change of one or more parts in the oil feeding system, correct ?? Still the question remains where is the location of that changed installation / bearing chamber ??

bearfoil
5th Jan 2011, 16:16
The Oil Stub Pipe "Installation" was affected directly and profoundly by vibration overlooked in testing.

By reference to the Report, it is "an OIL SUPPLY tube". Not a scavenge, not a vent. The image of the "offending" tube shows damage caused by a poor (read loose) coupling and/or vibration. Whether an atomizer, or a coupling in one of the ten radial struts that support the Bearing Structure between the IPT and the HPT roller bearings. Apparently. No location is reported, but that is ok, the OIL FIRE is almost certainly not the cause of the Destruction, but an effect. There is no apparent evidence of fire in the LPT Drum. There is evidence (soot) at the forward portion of the LP Shaft (the aft stub). Damage was limited to missing Blades from LPT #1.

The IPT Blades efface the "Platform" of the NGV's of the Stator behind it. The Vanes were located at the forward portion (in the 700, Edelweiss) and generally acknowledged as preventing the Burst of the IP Disc, having slowed it in shearing its Blades. In QF32, the slide of the IPT into the platform likely heated the IP Disc Rim, fir trees, and the IPT lost its blades in this manner. It would explain a loss of P30 forward, first through the Gas Path, and then at the Splines at LP and IP Ball Bearing case. The immense reversal of torque would certainly serve to explain the IP (Shaft) sever, the Overspeed of the IPT, and the sequence of sounds reported. The reversal of Gas Path would explain sound #1, and the second sound would of course be the Explosive Burst of the IPT out the case (IP case).

As BigG22 has said, to conclude that the Burst was unrelated to the AD's is a bit of a stretch.

Nothing that has been released to the public, by way of explanation is wrong. Neither is it in any way even partially explanatory of the events on board 32Whale. The releases are beyond cautious, they are misleading in their content. If the Gas Path had reverted to forward of the IPT, it would overwhelm the seals of the bearings, and the Labyrinthines on the shafts. it could have even entered the Plenum and after the IPT exited, the continuing fire would be explained (Note the sooty streaks on the LPC guide Vane Cowl).

bearfoil
5th Jan 2011, 17:08
EASA, FAA, NTSB, ATSB

Relative to the recent release of important info re: Rolls Royce and the scandalous and incestuous relationship they have with EASA, I thought it would be extremely important to engage in technical discussions of failed protocol, a defiance of traditional Mission, and where one thinks the engineering might recapture its former sheen.. Someone named Ben has posted a swell recap of this thread here. Pla ne Talk ing..Give us a read, eh?

bearfoil
5th Jan 2011, 17:13
I think a thread involving all in Aviation who value a commitment to Safety in the Air, and open dialog between the Principal players would serve a good purpose, hopefully to include a recommitment to the values of honesty, straight shooting, and a personal commitment to the Flying Public, and ourselves.

The Rumour is: Rolls is busted, big-time. Qantas and Airbus have some bones, as should we all. Hopefully the Firm will rededicate itself to Quality and leadership instead of Greed and Deceit.

just sayin'

firstfloor
5th Jan 2011, 17:23
Rolls-Royce engines cleared for LA take-off | The Australian (http://www.theaustralian.com.au/business/engines-cleared-for-la-take-off/story-e6frg8zx-1225982631762)

QANTAS has been given the green light by engine-maker Rolls-Royce to operate its A380 aircraft at full payload on the Los Angeles route.

bearfoil
5th Jan 2011, 17:30
Engine maker Rolls Royce is being sued for undisclosed amounts by Qantas, as the airline, keen on re-entering overwater service LA SYD, has a thick file on Rolls' dereliction in modifying the Aircraft in service with new mods. The Airline is not restarting the service as yet, as it is Rolls' statements alone that "CLEAR" the powerplant to re-enter service. Having been screwed on several counts by Rolls, Qantas has said 'it is not up to Rolls, obviously, there is the matter of clearance from the authorities, and for that matter, our own engineers, pilots, and attorney's.........' We'll wait.

firstfloor
5th Jan 2011, 17:43
Obviously, Qantas have dug themselves a very deep hole. But what is fairly clear by now is that there was never at fault anything fundamentally more serious that a badly formed stub pipe connection.

Previous speculation about vibration, splined couplings and the rest have always been unfounded imo and still are.

bearfoil
5th Jan 2011, 17:46
point taken, let's wait, then. I would say, however, that Rolls' decisions have been abominable, and relying on them further is risky. It also should underline the need to put some stones back in the pack at EASA.

Permission to fly at full weight from LAX? Without cycles limit? Don't you at least wish to hear from the regulator?? Qantas might be....

Rolls972/oil pipe

Cold/Aspirin

firstfloor
5th Jan 2011, 18:11
I think the AD inspections and established intervals will remain in force for some time to verify findings if nothing else. The final report is awaited of course but it may be that RR have effectively concluded their investigation.

It looks as though the precautionary high thrust/cycles limitation has been lifted - not that we know much about the restriction directly.

I think that whatever gremlin might be dreamt up by we speculators, RR, their peers and the accademics with whom they collaborate will have most likely written the book on the subject many yeas ago. So I am not a skeptic.

Turbine D
5th Jan 2011, 18:16
bearfoil
In QF32, the slide of the IPT into the platform likely heated the IP Disc Rim, fir trees, and the IPT lost its blades in this manner. It would explain a loss of P30 forward, first through the Gas Path, and then at the Splines at LP and IP Ball Bearing case. The immense reversal of torque would certainly serve to explain the IP (Shaft) sever, the Overspeed of the IPT, and the sequence of sounds reported. The reversal of Gas Path would explain sound #1, and the second sound would of course be the Explosive Burst of the IPT out the case (IP case).

If I understand this correctly, when the IPT rotor went aft (coupling slippage), the blades started to disappear, therefore there was nothing driving the IP compressor and it began to slow. Then, since there is less and less air entering into the HP compressor, which is running at a N3 of 98%, the P30 drops (stall?) and fuel to the combustor is reduced, but maybe not cutoff completely. Now if the high speed HPC stalls for lack of air, what happens? It is running in the opposite direction of the IP spool.

Also, what do you mean by reversal of gas path and reversal of torque? The direction of rotation of the IP spool reverses? If this happened instantaneously, perhaps the shaft would shear, I don't know as I can't envision this complete process at the moment without a clearer explanation.

bearfoil
5th Jan 2011, 18:32
First, I rely on lomapaseo's astute observation that metal to metal at differing RPM is causative of heat sufficient to melt the masses.

If the Blades were leaving the IPT, (obviously at some point they do), then things can go wrong that have disastrous consequences. First, to potentiate a Gas Path Reversal (The Drums loss of pressure due partial IPT blade failure) the Dynamic Seal at the IP needs to be compromised. Ongoing blade loss covers this, and as it proceeds, the IPC would reverse their Stress (not their direction) such that the IPT is now 'Driven', not Driving?? It is at this point the already worn Spline joint scrubs smoothe. Now the IPT has nothing to do but 'coast' down, the HPC has lost pressure from IPC, and it has ceased driving the HPT which speeds on burning fuel the EEC has not had time to halt as yet. Now the IPC, The HPC, and the LPC/LPT are done, they roll stop. The remainder of P30 blows past the Bladeless IPT, (First Bang). The Wheel overspeeds or not, but has sufficient energy to Disintegrate, having lost the Drive Arm due Friction Heat and possibly P30 blowout. The fact that There is no discolouration and very little damage evident in the LPT Drum. suggests that everything that disintegrated, Blades, Vanes, Disc, Platform, etc. was blown forward out the chasm created by the First Bang, the exit of the contents responsible for the second Bang.

Obviously conjecture here. The timetable wants more precision. (Or deletion).

bearfoil
6th Jan 2011, 15:33
DERG

Engine reliability is not only a critical part of ETOPS, it is life and death. No matter the pronouncements of the EASA re: ADs and compliance, the Manufacturer does have the last word. Now that RollsRoyce has bestowed reliability on the 972, we breathe relief and climb aboard ??

QF32 happened to a four engine ship, and it barely escaped a ditch or crash. Keep in mind that N3 continued past Burst, and fed a fire. The EEC may have had problems similar to Number One. Remember Number One was impossible to shut down, and with sound internals, (until swallowing canal mud), it ran on two hours.

If Number Two hadn't ultimately shut down, the engine fire that resulted may have ignited the sloshing puddles of fuel in the wing. One can imagine easily a more tragic outcome than loss of Face, Money, and RepCred. 1000 is not yet certificated for ETOPS, and the Dreamliner can ill afford more doubts and delays. On top of the mechanical issues, serious enough on their own, the absurd and selfish, dare one say criminal and clumsy attempts at keeping things quiet, puts in question three decades of Twin reliability. I like the 757 ETOPS, but the 737 gives me the willies.

The OIL SYSTEM is no doubt deeply involved in this uncontained failure, but unwinding the true cause is inevitable. Given a clean bill of health at this point would not restore Faith in the Firm, IMO.

The EEC has two channels, each one an independent system that is dormant when the other operates. At ignition, the EEC determines randomly which channel to activate, and which to isolate. With certain parameters extant, the EEC switches channels, and recovers control. The random selection exists to alleviate a dormant fault from being unidentified in one channel, allowing the EEC to operate essentially with only one channel reliability. The EEC was removed from the engine's Fan Cowl before the image was taken, noticeable are the fifteen cables wrapped in plastic bags left on the cowl, and the four mounting towers of the EEC. To me, imo, the actual vibratory environment of this unit's area suggests a rather brave decision. The mounts are snubbed with rubber, missing in the picture.

gas path
6th Jan 2011, 15:48
Still showing faith in the RR Trent 900 and 1000 products BA has just signed on the dotted line for both!:ok:

bearfoil
6th Jan 2011, 15:53
gas path

Like I say, the manufacturer, (and the operator) have the last say. No conflicts there!!

The regulators sign off on anything approved by the Manufacturer, the Line has no vested interest in the other?? You are a trifle naive, Sir.

The AD was relaxed on the 900 in August, two months prior to the Burst. Based on what information?? Inspections performed by the Manufacturer's agents!!

Does one have a copy of the contract?? Thought not.

Turbine D
6th Jan 2011, 16:06
DERG

Fumigation melts the plastic? SCARY! I've flown more on 2 engine ETOPs overseas than on 4 engine in recent times, all with good results, fortunate I guess.

But on to the point: All is well with the Trents, problems solved, Total Care works.

Rolls-Royce and British Airways have finally signed a long-awaited contract for Trent 900 and 1000 engines to power the carrier's forthcoming Airbus A380 and Boeing 787 fleets.
It covers Trent 900s to power 12 A380s (plus seven options) and 24 Boeing 787s (plus 18 options) and is worth more than $5 billion at list prices if all the options are exercised. One new aspect of the contract is the inclusion of the powerplant manufacturer's TotalCare long-term support package.
"We are delighted to have concluded these contracts, which position British Airways strongly for the future," says BA CEO Willie Walsh. "We believe the support of the TotalCare package will significantly benefit British Airways' operations."
His opposite number at Rolls-Royce, Sir John Rose, adds: "We are pleased that British Airways continues to put its trust in our world-class Trent engine technology and service provision."
The agreement was originally announced in September 2007 but has only now been completed: "It's a very complex and detailed contract, especially given the fact that the aircraft haven't been in the fleet when they were due to be in the fleet, for a variety of reasons," says a BA spokesman.

I am always reminded of a statement years ago from a large US aircraft customer directed at both US engine suppliers that went something like this: "You guys design the engine, develop it and have it certified as being flightworthy. Then we put it on our aircraft as a fully developed engine, but your development continues, that is to say development that should have been completed before certification that wasn't. This is unacceptable and must be changed."

I guess not much has changed...

bearfoil
6th Jan 2011, 16:34
The discussion becomes one of "Certificate Amendment", a process called "Continuing Airworthiness" (lomapaseo). It is arguably sufficient, but recent events have brought its weaknesses to the fore. We are treated to Press (RR) that certifies that the engine had no unmitigable problems in test, and was worhty of commercial service. That will out as a downright lie, not anything covered under "we'll fix that later". The Locomotive is stuck full throttle, and the bridge is out.

WojtekSz
6th Jan 2011, 22:42
derg:
As regulators they do no more than RUBBER STAMP what the manufacturers tell them. THE DOCUMENTS THEY PRODUCE ARE IMPENETRABLE AND INCORRECT.
They are not independent.
unfortunately i am fully in support for these statements.
So have we reached the point where the globalisation and production concentration has practically killed competition and responsibility towards customers?
Looks like the AT&T antitrust break-up be a good example to follow as with just 2 competing companies which are too big to fall there is no real choice.

bearfoil
6th Jan 2011, 23:00
AT&T? How about Standard Oil?? Or are the collective constraints extra corporeal, and merely a tacit Warfare on the Public in Carriage??

Tech nugget for qualification: Vibration issues are patent on the TRENT 700, The GE90, and now the 900. Can I repair the engine's glaring blunders and call it Airworthiness compliance on the "FLY?" Can I beef up the Shafts and call it recurrent maintenance? Thanks, how about Deferred?

here's some dough, and....Golf next week, James?? Alan?

Bolty McBolt
7th Jan 2011, 01:58
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.


As regulators they do no more than RUBBER STAMP what the manufacturers tell them. THE DOCUMENTS THEY PRODUCE ARE IMPENETRABLE AND INCORRECT.
They are not independent.
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

bearfoil
7th Jan 2011, 06:28
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?

A664
8th Jan 2011, 11:49
bearfoil:
Keep in mind that N3 continued past Burst, and fed a fire. The EEC may have had problems similar to Number One. Remember Number One was impossible to shut down, and with sound internals, (until swallowing canal mud), it ran on two hours.

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.

The EEC has two channels, each one an independent system that is dormant when the other operates. At ignition, the EEC determines randomly which channel to activate, and which to isolate.

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

WojtekSz
8th Jan 2011, 13:40
Derg:
Unless this A-380 accident had happened over central London and that 50kg lump of metal had landed on the Prime Minister there is unlikely to be a quick solution.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!

CAAAD
8th Jan 2011, 14:38
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!

bearfoil
8th Jan 2011, 16:48
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.?

Turbine D
8th Jan 2011, 16:55
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

bearfoil
8th Jan 2011, 17:02
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??

CAAAD
8th Jan 2011, 17:30
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

bearfoil
8th Jan 2011, 17:50
Actually the TRENT 900 isn't really a TRENT. Too fine a Point??

HazelNuts39
8th Jan 2011, 18:22
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??Where does that leave the Regulatory Agencies of, for example, Australia and Canada?

bearfoil
8th Jan 2011, 18:42
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.

35YearPilot
8th Jan 2011, 19:37
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.

35YearPilot
8th Jan 2011, 19:44
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.

Turbine D
8th Jan 2011, 20:11
CAAD

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.

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_turbine_oil_specification_pres_STLE.pdf

bearfoil
8th Jan 2011, 20:55
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

bearfoil
8th Jan 2011, 21:11
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

BigG22
8th Jan 2011, 22:01
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?

Turbine D
8th Jan 2011, 22:04
35Year Pilot

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.

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).

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.

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,

bearfoil
8th Jan 2011, 22:43
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

Turbine D
9th Jan 2011, 02:01
bearfoil

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.

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.

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??

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.

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.

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...

bearfoil
9th Jan 2011, 02:14
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??

CAAAD
9th Jan 2011, 07:18
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.

WojtekSz
9th Jan 2011, 07:55
TurbineD, bearfoil

Quote:
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.
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.
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?

bearfoil
9th Jan 2011, 08:50
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.

Annex14
9th Jan 2011, 10:14
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 ??

WojtekSz
9th Jan 2011, 10:28
Handbook of case histories in failure analysis


Handbook of case histories in ... - Google Ksi??ki (http://books.google.pl/books?id=SG81FlgeSSgC) @ 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?

Fretting wear is surface damage that occurs between two contacting surfaces experiencing cyclic motion (oscillatory tangential displacement) of small amplitude. At the contact areas, lubricant is squeezed out, resulting in metal-to-metal contact. Because the low amplitude motion does not permit the contact area to be relubricated, serious localized wear can occur. This type of wear further promotes two-body abrasion, adhesion and/or fretting fatigue (a form of surface fatigue) wear. source and more info at : Fretting Wear in Lubricated Systems (http://www.machinerylubrication.com/Read/693/fretting-wear) - 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.

lomapaseo
9th Jan 2011, 14:10
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

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)

Turbine D
9th Jan 2011, 14:25
Annex14

That worked by using those RR issued brochures of the Trent 800 and 900 engines cutaways.

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

Thanks,

Turbine D

Turbine D
9th Jan 2011, 14:31
lomapaeso

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)

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.

WojtekSz
9th Jan 2011, 14:34
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) (http://www.youtube.com/watch?v=UazsDDFsS7Q)
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' ?

bearfoil
9th Jan 2011, 15:06
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.

WojtekSz
9th Jan 2011, 15:58
bearfoil
To isolate massive vibratory impetus would more than likely involve strengthening the Shafts by adding metal. Inside Diameter? Outside? Both?
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.

Turbine D
9th Jan 2011, 16:21
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) (http://www.youtube.com/watch?v=WD2I7muBImk&NR=1)

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.

mike-wsm
9th Jan 2011, 16:40
Turbine D

Trent 800 brochure (http://www.2dix.com/pdf-2010/trent-800-pdf.php)

Turbine D
9th Jan 2011, 17:33
mike-wsm

Thanks for the Trent 800 link.

Annex14
9th Jan 2011, 18:22
mike-wsm Thanks for posting the link. I am just back from an event and would have to start the answer to Turbine Dīs request.
Hope it works as it did here.

Annex14
9th Jan 2011, 18:24
I have also this
Large aircraft engines - Rolls-Royce (http://www.rolls-royce.com/civil/products/largeaircraft/)

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

Turbine D
9th Jan 2011, 19:20
DERG
Oil temperatures of 196C max are not acceptable in my view, but you must remember the Trents have three rotors and therefore more heat to disperse than GE products. Another issue that has been over looked is th the fact that the coking (tar like carbon) deposits are flammable.

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.

bearfoil
10th Jan 2011, 14:27
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.

Annex14
14th Jan 2011, 09:58
Although itīs "silent boat" in this thread since 5 days Iīd rather like to "bang" the door one more time. We have worked through the case fairly well, I think. However, why do we stop close to the point where "Pandoras Box" is pulled open ? I like to refer to Turbine Dīs list posted in Nr. 1888

Quote:
One way to look at it is this way: (A) leads to (B), (B) leads to (C), (C) leads to (D) and (E) leads to failure. This is the classical failure methodology of a complex system. Looking at engine #2's failure,

(A) = Unknown
(B) = Unknown
(C) = Unknown
(D) = Stub pipe
(E) = IPT Disc burst/major engine failure/damage to aircraft

The trick is to identify (C), (B) and (A), (A) being the root cause.[/quote]


Rolling down that list reversal way Iīd like to start at

(E) : IPT Disc burst/major engine failure/damage to the aircraft - symptom caused by "D" through "A"
(D) : Stub pipe fracture /oil spill - probable contributional cause ? sympton
caused by "B" or "C" or "A" ??
(C) : vibration - light on LP and IP shaft, severe on HP shaft - sympton caused
by "B" or "A" ??
(B) : rising oil temperature, wear of bearing ?? - sympton caused by "A" ?????
(A) : the real start and cause of the desaster, this one triggered all the other
recorded events.

I believe there is something technically that I can not cover with my knowledge about sophisticated jet engines, but that engineers might know of. There fore this as my last try to get a logical answer to what went wrong in that Qantas engine.

lomapaseo
14th Jan 2011, 13:37
A is caused by the design of the T-900. Too many bearings too close together. :D

Yes, we will not rest until RR goes in and removes one of those bearings ... their pick of which one ;)

Smilin_Ed
14th Jan 2011, 15:04
Is there one less in the T-1000?

Annex14
14th Jan 2011, 17:58
Smilin_ Ed, I doubt that there are less bearings in the T 1000 than in any previous 3 shaft engine.
If you want to check, this link gives access to all the big engines
Large aircraft engines - Rolls-Royce (http://www.rolls-royce.com/civil/products/largeaircraft/)

lomopaseo, how sure can one be that a simple switch to a stronger bearing - or several - will solve the obviously existing problem ??
Do you think itīs just bearing ??

Turbine D
14th Jan 2011, 22:25
Annex14

Here are the cutaway views of the two engines. Although one cannot see the details clearly, the general engine layout and differences can be seen. To see the actual details, one has to view the engine and see all the parts laid out on tables.

http://www.pw.utc.com/StaticFiles/Pratt%20&%20Whitney%20New/Media%20Center/Assets/1%20Static%20Files/Images/gp7000_cutaway_high.jpg

http://www.rolls-royce.com/Images/brochure_Trent900_tcm92-11346.pdf

Several things strike me: If there is any scale at all between the artistic renditions, the thrust ball bearings in the GP7200 look larger than those in the Trent 900. In the turbine area of the GP7200, the emphasis on slowing a speeding turbine rotor can be seen on both rotors where there would be blade on vane contact, there is no spacing concerns. The stage two turbine rotor (similar to the IPT rotor of the Trent 900) sits close to the structural frame behind it and the blade would contact the struts if this turbine disc were to move back.

Both engines deliver the same thrust, both have the same fan diameter, both have 14 compressor stages, the GP7200 has 6 LPT stages verses 5 for the Trent 900. The GP7200 is slightly longer and weighs 956 lbs. more. It has been reported the GP7200 has a 1% better SFC than the Trent 900, but RR disputes this. Both engines appear to be capable of being mounted on a common designed pylon. The maximum HP spool speed of the GP7200 is slightly higher than the Trent 900, but the maximum fan speed is lower on the GP7200.

For those wondering why the Trent 800 couldn't be used, you can't just clip 5" off the fan without rebalancing the rest of the engine, especially if you are being pressed on SFC to meet aircraft range goals. So two things happened on both engines, incorporation of 3-D highly aerodynamic efficient swept fans, higher HP spool speeds, higher pressures and temperatures, all to generate thrust requirements and deliver good SFC.

I do wonder if the counter-rotational feature (new to a commercial high by-pass engine) had any effects on bearings, frequencies or vibration in the Trent 900.

Bolty McBolt
15th Jan 2011, 01:53
I enjoy this thread as it is filled with useful info.
To add to Turbine D input
Several things strike me: If there is any scale at all between the artistic renditions, the thrust ball bearings in the GP7200 look larger than those in the Trent 900

The GP7200 ball thrust bearing carries greater radial loads as well as thrust loads where the T900 has a large roller brg to carry the radial loads with the thrust loads transferred to location bearing adjacent the engine mount. Roller bearings typically have higher load capacity than ball bearings for a given size.

Both engines deliver the same thrust, both have the same fan diameter, both have 14 compressor stages, the GP7200 has 6 LPT stages verses 5 for the Trent 900. The GP7200 is slightly longer and weighs 956 lbs. more. It has been reported the GP7200 has a 1% better SFC than the Trent 900,

The GP7200 has had its fair share of problems, Fan balance issues that have cracked airframe structure and lowered engine mounted accesories life spans. This has generated huge manhour costs and extended ground times but to date has not exploded mid-air. GP7200 1 , RR nil

For those wondering why the Trent 800 couldn't be used, you can't just clip 5" off the fan without rebalancing the rest of the engine, especially if you are being pressed on SFC to meet aircraft range goals. So two things happened on both engines, incorporation of 3-D highly aerodynamic efficient swept fans, higher HP spool speeds, higher pressures and temperatures, all to generate thrust requirements and deliver good SFC.

I see your point except the T800 was a known off the shelf product, now very reliable with the thrust avail to do whats asked plus more. So why the T900 when it requires greater SFC to offset its greater weight before it offers any greater efficiency to the aircraft. So at a glance it does not add up unless huge future promises (SFC) were attached to the T900 model that could not be acheived from current models ?

...--------...Thust...Weight .Thrust to weight...Length.. Fan Dia..Serv Enrty
Trent 892 - 92,000...13,100....---....7.0 ......... 172 .... 110...... 1997
Trent 972 - 76,752...13,842....---....5.5 ......... 179 .... 116...... 2006


I do wonder if the counter-rotational feature (new to a commercial high by-pass engine) had any effects on bearings, frequencies or vibration in the Trent 900.

This is true but RR have been building a contra rotating core for the harrier since the 1960s so I would not call it new to RR and the location IP bearing that supports the fan location bearing turns in the same direction i.e. the ball race speeds have not been a marked increase. This bearing design has been a thorn in RR side since the conception of the RB211 but again is not new technology.
I suspect we will find out once the hype has died down and RR PR machine have massaged and cajoled its customers to accept a modified core engine at a lowered price with the guarantees of increased efficiency ?? (read reliability)
The money will have to come from somewhere and I suspect it will be shared across RR EADS and customers all of whom have committed so much can not afford this to fail. Time will tell.

Annex14
15th Jan 2011, 03:32
Turbine D - Bolty McBolt

Once again a very helpful explanation to a layman in jet engine technology.
Especially I like the comparison of GP 7200 and Trent 900. Within a glance it is clear that the construction of those elements that carry the dynamic loads are much lesser concentrated on one small area in the GP 7200 than in the Trent 900. Wether that has a real influence on the problems we have seen on the QF - Trent I only can imagine / assume. But if this problem exists for so many years - Bolty McBolt says since the beginning of the RB 211 - and the production of that type engines goes on with now and than a "big bang" one must ask the question wether there has been ever an in depth investigation towards possible harmonics???

I remember that there have been aircraft desighns that used a long driving shaft for the propeller. Few of these even had counterrotating props. Some of the types ran into kind of severe shaft failures - as far as I remember - caused by kind of harmonics or resonant frequencies ?? I may be corrected at this, too long ago. Doesnīt know if this is applicable in now a days desighn technologies. But what if, . . . . . the counterrotating HP component generates a harmonics that is transferred via bearings the different shafts to other parts of the engine ?? Is that thinkable ?? I must admit, my confidence in RR - engineers abilities exclude such a scenario.
Again I have to cry for help by the engineers !!

DERG

Is that yellow marking just a gag or is it true ??. I have seen some Harriers - must admit on fly by - but havnīt seen something like that. But I can imagine that it might have been indeed a measure of caution.
Jo

WojtekSz
15th Jan 2011, 10:59
there is also another difference concerning spline location
in GP the spline is located directly 'inside' bearing and in T900 the IP spline is 'outside' of the bearing plane. The difference becomes significant under dynamic load when any radial forces and radial play comes into account.

DozyWannabe
15th Jan 2011, 14:29
Indeed yes...and a yellow warning band was painted around where the engine parts would explode out of.

So this fault is about 50 years old.

Except the Pegasus was originally a Bristol-Siddeley design, whereas the RB211 from which the modern Trents were derived was from Barnoldswick.

Loving the discussion (despite a lot of it going over my head), shame about the RR-bashing though.

lomapaseo
15th Jan 2011, 14:38
I remember that there have been aircraft desighns that used a long driving shaft for the propeller. Few of these even had counterrotating props. Some of the types ran into kind of severe shaft failures - as far as I remember - caused by kind of harmonics or resonant frequencies ?? I may be corrected at this,

All kinds of vibratory modes/harmonics,coincidence, backward whirl, etc. have been with us for a very long time in gas turbines and Props. Today's engineers have computer models that keep track of the forcing functions and the receptors. Design rules exist to maintain margins between RPM-range drivers and receptors both within and outside the allowed operation limits. In one sense the margins consist of limits on measured vibratory stress while in the case of higher speeds than normal a healthy margin in speed between normal operation and a dangerous vibration (GE CF6, National Airlines)

The problem comes in when operation is either abnormal (damaged parts creating unbalance or aerodynamic burbles) or parts which have lower than expected fatigue margin due to manufacturing flaws. And one of the largest corntributors have been misassembled parts which seriously affect the stiffness of joints between parts.

Nothing that RR doesn't already know and adresses

Annex14
15th Jan 2011, 14:55
Thanks thats sure a brief but helpful explanation. As I expressed already, would be hard to understand if the RR engineers had not addressed that problem properly.
Yet, we are chewing on that cause (A) - the root cause.
Jo

Turbine D
15th Jan 2011, 17:03
Bolty McBolt

In my previous post, I erred on the clipped fan and re-balancing scenario. Actually, I should have been referring to the GE90, not the Trent 800. The core of the GP7200 engine comes via the GE90 core. So when the fan diameter was reduced to 116" from the normal ~123" diameter fan used on the GE90, some other things had to be adjusted. The GE90 core evolved out of the "Energy Efficient Engine". A scaled GE90 engine was built to test the concept from which the true GE90 emerged. So GE had good knowledge as to how to scale downward the core to match fan diameter. In fact, the GEnx engine basically uses the scaled GE90 core.

I just think the drive for both the Trent 900 and GP7200 engines was to improve specific fuel consumption (SFC). If you look at the CF6-80C2, the model used on the B-747-400, The sea level SFC is 0.316, at cruise it is 0.605.

If you look at the Trent 800 on the B-777, the sea level SFC is 0.35, at cruise it is 0.56.
If you look at the GE90 on the B-777, the sea level SFC is 0.324, at cruise it is 0.52.
It is estimated the GEnx on the B-747-8, the sea level SFC is 0.27, no figures yet for cruise.
Theere are no SFC published figures out yet for the Trent 900 or the GP7200 engines, except for the comments from the Emirates CEO.

So with the trend of less fuel usage (improved engine efficiency), IMO, the Trent 900 and GP7200 fits somewhere nearer to the GEnx.

Turbine D
16th Jan 2011, 01:42
Some news out of Qantas:

Video: Qantas quashes A380 LA flight rumours (http://video.dailytelegraph.com.au/1721965196/Qantas-quashes-A380-LA-flight-rumours?area=endslate4)

Blow-up grounds Qantas flight bound for LA | The Daily Telegraph (http://www.dailytelegraph.com.au/travel/news/blow-up-grounds-qantas-flight-for-la/story-e6frezi0-1225988730178)

radken
16th Jan 2011, 02:16
Turbine D - DERG

I've been following with great interest the discussion in this thread relative to the several failure scenarios that have been set forth re: Qantas T900 uncontained IPT failure. Back in the conversation (#'s 221 and 223) you briefly brought up the topic of oil and possible coking problems during heat soaking. There was a brief suggestion that inclusion of an external oil circulator unit would have been a sensible part of the overall design for longevity.

Could you discuss from your engineering standpoints, the possible or probable effects of short and long term coking on the actual performance of the hot section bearing(s) in this engine? I've been wondering if it's possible that bearing performance from coking could have degraded to the point where it may have overheated, chattered, and or vibrated itself to the extent that it either partially or even totally disintegrated, whilst also impacting the stub pipe. What I'm asking is, is it possible the bearing itself was causal in the sequence of events ending in the IPT overspeed? Maybe I missed someone discussing this very event in an earlier part of the thread?
Failures of this type are not unknown, of course, in automotive and aircraft turbochargers. The simple solution has always been to, one way or another, make sure the shaft bearings are bathed in circulating oil after shut down. Even old dirty mineral oil is ok to stop most coking, just so long as it keeps coming. If this solution is found necessary for T900 bearings I'd almost bet that it could be done for far less penalty than a 50kg bolt-on accessory.

Thanks everybody for all your great contributions to this thread. What a wonderful resource this forum is.

Annex14
16th Jan 2011, 08:25
Oh NO !!! Not another Trent engine smashed to pieces. Lucky enough this is a contained failure and it happened on the ground.
Guess, finally someone might have to start thinking !!!

Annex14
16th Jan 2011, 08:34
The oil coking problem in pipes was detected and explained on some earlier incidents with other type Trent engines. The pipes involved where bearing chamber vent pipes. It was anticipated in investigation that the coking blocked these pipes leading to heating and failure of the bearings.
It was also in the first segment of this thread once mentioned in conection with the QF 32 engine failure. I didnīt even know that oil coking could become a cause of problems in bearings. But I can see your point.

barit1
16th Jan 2011, 12:21
The coking problem is genuine, and may be influenced by operational techniques.

Tactical aircraft oft perform rapid turnarounds, reloading/refueling as fast as possible. If the engine is shut down soon after high-power ops, and if the engine has an oil-fuel heat exchanger in the high-pressure fuel manifold, the hot oil works on the static fuel mass and may boil the fuel, inducing fuel vapor into the hot combustor, and causing a brief post-shutdown fire. Probably not harmful, because of brief duration, but likely exciting.

In the commercial world, a proper cooldown period is important to prevent coking, especially when T900 "normal" oil temps are as high as 180C. In thinking about A380 ops, since only inboards are equipped with reversers, they are likely to see hotter oil at shutdown than the outboards.

And so it is possible that something in QF shutdown timing technique is aggravating the coking problem. I suspect QF and R-R are already examining this issue. :8

barit1
16th Jan 2011, 12:28
DERG:Of course it is also recorded for analysis later if needed. After this accident one senior mechanical engineer said: "we have an enormous amount of data, and it is going to take some time to plough through it"

The two universal, perennial complaints of the engineering profession:

"To solve the problem, we need more data" - and:

"There's so much data, we need more time to analyze it all" :O

bearfoil
16th Jan 2011, 14:20
DERG

Howdy. Rather than dredge up my old posts, I'll rephrase and update. The "Pipe" is NOT the victim of some inattentive Bench Monkey.

First, notice the "Land", or "Ledge" that supposedly resulted from a "counterbore" gone awry. Look closely at the "corner" enunciated at the transition from ledge to Wall.

It is COVED. It shows no sharp delineation twixt the bore and the "Shoulder". This is 100 per cent the result of wear, and given its locale, almost certainly caused by vibration.

Next, note the Striae on the wall of the inner surface of the "normal" pipe. My opinion is a pulled extrusion process assuredly excluding any secondary operation, or Blunder. Gently Helical signatures from a normal process of machining. Now, look at the area of the Pipe proxima; to the "ledge". There are circumferential grooves, the result of metal/metal wear, as this is undoubtedly the joint locus of two fittings. Look closely and see that the grooves are at bias to the ledge, and irregular, random even, and certainly not the result of any machining process.

There is a great deal more. Suffice that ATSB allowed for a wide open gate for later correction: "....MAY have initiated a sequence of failures that led to burst...."

CAAAD
16th Jan 2011, 15:20
bear

I think you are incorrect in your suppositions, which do not seem to be shared by anyone else.

The 'cove' at the bottom of the incorrect counterbore is the runout radius of the counterbore tool. Radius at this position is essential to avoid a stress concentration factor. Careful design would never tolerate a sharp corner .

The 'bias' in the tooling marks is caused by the feeding in of the tool. It is a shallow angle helix determined by the feed rate of the cutter.

We are all ignorant as to the design surrounding this failed part, but it is probably the female element of an O ring seal. As such, gross frettage of the nature which you assume is unlikely.

Time to move on.

barit1
16th Jan 2011, 15:45
DERG:

I'm not so sure about the labeling on the photo. The region labeled "fatigue cracking" can also be interpreted as a brittle fracture. BUT - The part clearly should have never reached the assembly floor, and should have been a manufacturing engineer's object lesson many months prior.

But the immediate subject of discussion was oil coking, and coking can readily occur without such a manufacturing fubar. :*

bearfoil
16th Jan 2011, 17:37
Keep in mind the Splines are not situate centrally within the boundaries of the Thrust bearings balance points. There is a reason this powerplant is light, and 'efficient'. The two go together and rely on fine balance and gentle transition through the Thrust range.

Derg, in a nutshell, you have it. Within your parameters add Contra Rotation, higher Wheel Speeds, and ineffective EEC at failure boundary. There was a Punch List at introduction that should have undergone remediation prior to Service, IMO.

There were surmountable obstacles to be sure, but the time to address them is prior to On Wing Commercial service. Not cute to allow actual passengers to piggy back a development programme.

Turbine D
16th Jan 2011, 18:33
I agree that the labeling is odd in the photo. I tend to believe the actual slow, but ever progressing fracture surface is in the forefront of the photo, out of focus. The "clean" fracture area does look brittle to me, the final break, so to speak. IMO, this part is a nickel-base alloy, an Inconel or Hastalloy type material. Normally a part like this would be investment cast to a near net shape and subsequently machined as required to final desired tolerances. I am sure vibration played a big role in this component failure besides whatever the configuration and how it got to be that way. I am sure oil was slowly seeping from this fracture into the cavity and one wonders how long and how much was there before the final event took place.

It has been silent as to the progress of the failure investigation, no updates from the ASTB since December 23. It makes one wonder about progress being made in going through the total failure progression scenario, identifying the true root cause or causes.

Turbine D
18th Jan 2011, 18:21
radken

I would both hope and believe that coking on the failed engine was not a related cause given its rather short cyclic life on wing. Coking in the longer engine service life is a problem and with the higher operating oil temperatures, could begin to occur sooner as cyclic life progresses. Everything depends on accurate metal and air temperature predictions for bearings, sumps and surrounding cavities, particularly in hot turbine areas of the engine. Heat transfer analysis is extremely difficult due to the complexity of the oil flow in and around the bearings. Obviously there is prior history to fall back on, but in a new engine design (IMO, the 970 is one), rig testing of the bearing cluster would be performed to determine bearing heat characteristics and instrumented engine test data would be used to determine air and heat in the surrounding areas. Then the heat transfer analysis program would be refined and run to determine if the design is adequate or not. It is important to keep all oil wetted surfaces below 400℉ and that includes anticipated soak back heat generation. If one does not accomplish this, coking can occur in sumps along the walls and in tubing associated with the sump. The big worry in the 970 would be the roller bearings under the IPT rotor.

But, probably the most difficult item to face is to get all the vibrations/harmonics identified and dealt within the oil tube piping system. This usually winds up being iterative process during the engine testing phase, identification and correction.

To give you some ideas on maximum oil temperatures on various engines:

RB211 Series 335℉
Trent 700 374℉
Trent 800 375℉
Trent 900 385℉
Trent 1000 365℉

CF6-50 320℉
CF6-80C2 320℉
PW4000 350℉
GE90 270℉
GEnx 320℉

A main coking generation factor is, what happens when you shutdown a hot engine quickly as barit1 points out and there is no longer oil flow?

Hope this helps...

KBPsen
18th Jan 2011, 19:33
It is pretty meaningless to list oil temperatures and attempt to make some sort of comparison unless also listing where in the system the temperature is measured and how this measurement relates to the highest temperature in the system.

Annex14
18th Jan 2011, 20:59
Hmmm . . . easy speech !! Can you offer a better or more detailed listing ??
Jo

KBPsen
18th Jan 2011, 21:41
Sure it is easy. It is as easy as listing a series of maximum continuous oil temperatures without at the same time listing where these temperatures are measured, how it relates to the maximum temperature experienced in the system and what oil specifications are used for the particular engines.

It's a bit like comparing turbine temperatures without specifying whether you are talking about TIT, ITT, EGT and what material the turbine is made of.

Turbine D
18th Jan 2011, 22:19
KBPsen

All the RR engines, RB211, Trent 700,800,900 and 1000 are combined scavenge temperatures. So are the PW4000, CF6-50, CF6-80C2 and the GP7000. The two I am not sure of would be the GE90 and GEnx. These two engines, particularly the GE90, may have a different measuring location, not sure.

The point is that the three spool engines generally run a higher oil temperature compared to two spool engines. But, none of the reported temperatures may relate to the highest temperature experienced (the hottest bearing sump) although I think the engine manufacturers know the relationship.

Annex14
19th Jan 2011, 15:45
Turbine D
What is the meaning of the 400°F you mention in your post Nr. 257 ? It is too low, as far as I know, for self ignition temperature of oil. Is it than a border temperature for coking ?

In that connection, you mentioned several times the plenum in front of the IPT disk. It is supposed by best knowledge, I assume, to be the space the oil feed tube that finally failed runs through. At the same time it is the supporting structure for the bearing chamber of the IP and HP roller bearings.

How likely would you consider the possibility to be that, although the engine had that bearing problem, was in repair shop from Sept. 2009 untill Dec. 2009, was boroscoped in June 2010, no one had a look into that plenum chamber and detected that cracked feed tube spilling oil into that space ??

If the engine was checked including that section - what I would expect to happen with such a major repair - and there was no oil, it means the leak developed later. If however, this section wasnīt checked at all - means neither in the repair shop nor on the boroscopic inspection - the oil leak and spil could have started quite a long time before there was that oilfire.

The ATSB investigators have come to the conclusion there was an oil fire - so for us thats fact. Question is, when started it and what damage did it ?

If - worst case - the oil leak existed undetected for a longer period of time it appears likely that over the many hours of usage quite a bunch of oil coking has happened. I would expect to have the lower part of that plenum chamber substantially filled with a swamp of coke and oil. For a while the cooling air fed into that chamber might have prevented heating beyond SIT of the coke-oil mixture. It was said that this temperature is substantially lower than plain oil SIT.
So when the fire started that way after engine start at SIN would that fire accomplish a burn through?? or is the material the plenum is made of heat resistant. I think it has to in that hot region of the engine.

So if in fact no burn through occured, just weakening of the lower half of that supporting structure, what consequences would that have on the precise fixture of the bearing chamber ?? Is my assumption correct that the chamber triggered by vibration may have started some kind of motion that made the disk tumble ??

DERG

In your post Nr. 262 you mention now twist, vibration and kinetic energy. So if I understand that post correct, you point to the same causes that I mentioned in my former post about shaft failure with specific engine / propeller installations.
But is that something to consider ??
What I have thought also about several times is balance. I know balancing the plain disk is not the art, mounting several tenth or hundred of vanes on that disk and still keep it in balance is the tricky part.
Probably everyone will say: no impossible ! But yet I would like to ask is it technically possible to balance a compound of pieces so secure that it will run without any imbalance at all possible rpmīs ??? If not ?? If only balanced to bearable amounts of vibration for cruise power ?? Thatīs the power setting longest used on a flight and appears more important than anything else.

Remember lomopaseo said that all kind of vibration and harmonics are common items in engine development and use that normally are covered by computer programs. That should suggest that those sketched possibilities are not existing. Correct ???

I hope this becomes another trigger to push the efforts on this circle closer to the truth behind the engine failure.

A said before, everyone would be wiser if the pictures of the inner parts of the engine would be released. But I am sure ATSB will come along sooner or later with a more profound report than a prelim ever can be.

Turbine D
19th Jan 2011, 17:29
Annex14

What is the meaning of the 400°F you mention in your post Nr. 257 ?
Oil begins to coke at a temperature of 440℉ to 450℉. The 400℉ is what you attempt to design to in the sump oil wetted wall areas to prevent coking as a safety margin, but, also having an idea as to what the maximum soak back temperature would be/could be through a heat transfer analysis program that examines that entire engine area.

In that connection, you mentioned several times the plenum in front of the IPT disk. It is supposed by best knowledge, I assume, to be the space the oil feed tube that finally failed runs through. At the same time it is the supporting structure for the bearing chamber of the IP and HP roller bearings.
Yes, that would be my opinion.

How likely would you consider the possibility to be that, although the engine had that bearing problem, was in repair shop from Sept. 2009 untill Dec. 2009, was boroscoped in June 2010, no one had a look into that plenum chamber and detected that cracked feed tube spilling oil into that space ??
The bearing problem was with a ball bearing cage and race that I assume to be in the fan/IPC area of the engine. To get at that, the engine would have to be torn-down in a modular fashion. It is conceivable the IP Turbine module containing the plenum wasn't looked at from an internal point of view. It is hard to say what happened for sure. It could have been weeping or slightly seeping or not yet leaking at the time of the bearing replacement. The boroscope inspection was for the spline wear, again, in the Fan/IPC/HPC area of the engine.

For a while the cooling air fed into that chamber might have prevented heating beyond SIT of the coke-oil mixture. It was said that this temperature is substantially lower than plain oil SIT.
The cooling air really isn't that cool in the IPT area of the engine. I would suspect sections of the frame, Casing, hot gas path airfoils (including outer and inner bands and the plenum itself would be made of different materials depending on expected temperatures. The plenum material would have to be a medium temperature material capable of being formed (hot forming?) given the very contoured shape fitting in the cavity in that area. It may also have to be a weldable material. In two spool engines, this would be a "turbine mid-frame", something that was finally eliminated as it was such a pain to both make and then subsequently dealing with never ending problems in service.

So when the fire started that way after engine start at SIN would that fire accomplish a burn through??
IMO, the fire was intense enough to burn through the plenum wall, exposing the bore of the IPT disc to temperatures beyond the disc material's load carrying capability. I am sure the bearing structure supported by this frame was adversely affected by all of what was taking place. It is very possible the bearing upset together with the weakened disc (stretching) could cause an uneven spin plane from normal.

Annex14
19th Jan 2011, 19:26
Thanks! That helps a lot in understanding the relations involved.
PM sent

.

Turbine D
20th Jan 2011, 13:51
DERG
The torque discussion is interesting. I read somewhere that the Trent 900 engine series accelerates from ground idle to maximum TO rpm in something like 5.3 seconds. Seems like a lot of twisting/torque going on in a hurry.

All rotors are balanced after blades are inserted into the disc prior to actual assembly into the module build. Each blade has been weighed to the gram and may be inserted into the disc based on weight distributions. The balancing machine is like that experienced in an auto tire shop except it is more sophisticated and goes to higher speeds.

After final assembly of a new engine, it is filled with oil and put on a test stand to run through its paces while being closely monitored. Vibs are examined quite closely as well as EGT margin. The process takes about 3 hours of engine running time to complete. If all is good, the engine has the oil removed and it is packed up for shipment. If it is not good, the engine is returned to dis-assembly to figure out what the problem/problems are. This doesn't happen often but when it does, the engine is known as a "hanger queen".

barit1
20th Jan 2011, 16:58
DERG & bearfoil:

You are drawing a bunch of speculative conclusions based on rather incomplete data. I know that speculation is intrinsic in R&N, and R-R is holding cards close to the vest, but to read ulterior motive into their silence is over the edge IMHO. :ouch:

bearfoil
20th Jan 2011, 17:13
barit1

With respect, my conclusions are based on information from professionals who have/are working for the principals here. Consider what you read speculation or not, it is most definitely not "over the top". No signs of Oil problems were found in these engines for upwards of a year prior to this Burst. Oil Fire is not the cause of the Burst, nor is it due repetitive malfunctioning of ridiculous claims of "Misbored" pipes.

This will all out. It won't go away. If you rely only on long cites of lab work and legal claims to allow posting, you will have to wait.

WojtekSz
20th Jan 2011, 22:03
Derg:

actually both two-spool and three-spool engines have shafts inside shafts

These shafts are subject to TWIST forces and are located by splines. The T-970 series shafts are shorter than the existing shafts in the RR RB-211 seign so far. We also know that this engine is designed to have a MINIMUM MASS for a MAXIMUM THRUST.
Now you can imagine that the twist forces are not constant. As the engine spools up the forces get progressively greater. The shaft seeks to TWIST and moreover the shafts VIBRATE.
I hope now we can see why the splines have been under so much stress. Not only the expected stress from the tube but also the UNEXPECTED self destructive stress from VIBRATION.when discussing different load components acting in any joint it is important to evaluate actual values of these load components. If not possible to measure than standard evaluations are taken assuming that the loads would be of similar type to existing known solutions (trent 800 et al). The twist load is definitely calculated and appropriately taken care of. Even if combustion may not be constant process but the force to the shaft is transferred via hot air which is a lot more compessible than stiff disc so the total torsional shaft load is very much smoothered by this.

So the question now is: How come RR could not mathematiccaly model the variables with computer software? Surely these harmonic, self destructive vibrations could have been easily predicted.not really and for two good reasons:
(1) difficulty to define the vibration characteristic of the vibrating parts - especially when we have to take into account non ideally stiff (so non linear) elements like spline coupling and bearings
(2) difficulty to define the source, type and size of excitation: bearings, other rotating elements and their relative influence

You might say..surely NO! How could this be? How could they have made such a basic fundamental error? That is the question we all want to know. RR has been making this basic design for 50 years, this phenomena is not unknown.yes, the phenomena is well known but the new solutions are being developed using new techniques: instead of making models and improving them RR try to digitally model and improve the digital model. But if it is easy to model the KNOWN forces like thrust and imbalance tolerences than the vibrations and wear are the real problems, especially if they develop into not foreseen way.

Turbine D
21st Jan 2011, 01:10
WojtekSz

Even if combustion may not be constant process but the force to the shaft is transferred via hot air which is a lot more compessible than stiff disc so the total torsional shaft load is very much smoothered by this.

I am not sure I understand what is meant here, could you explain more clearly?

bearfoil
21st Jan 2011, 02:44
Turbine D

I get from Wojtek that he is offering a "Fluid Drive" argument against torque problems that may result in stress wear or fracture. I'm not sure it obtains to this discussion, however, at the cusp of Torque "reversal", there is enormous stress on the rigid coupling, having to translate gobs of torque from components that were at one moment driving in one direction, but quickly changing to "driven" mode. Vibration could mimic this reversal of torque, but in more and shallower "events". Load, Unload, Load, etc. A resonant frequency would cause the same, but even more chaotically. At the "Null" point, where torque is balanced (neutral) any wear or excess tolerance in these bearings would cause chaotic vibration in erratic "Ovoids", a chattering mess of blurred steel balls, raceway and cage. Can you hear the din of bearings "floating" as the result of intense and unplanned for motion?? We've all heard it. Rattle, shriek, and stop.

flying lid
21st Jan 2011, 07:56
A little off the (interesting & enlightening) technical discussion, but what is the current situation with the A380 involved ?.

Is she still in Singapore ?. Will she be fully repaired there, or patched up & flown to France for full repairs ? Or is she unrepairable given the substantial wing damage and machined tapered thickness slab construction of the wing skin ?, - (mentioned & youtube illustrated many threads ago).

I recently read a book entitled "The Somerset & Dorset Railway, Then and Now" by Mac Hawkins. An interesting comment is made regarding Winsor Hill Tunnel (Near Shepton Mallet), which was used, in 1968, after the line was closed and lines lifted, by Rolls Royce for destructive tests on the Olympus engine destined for Concorde.

To quote the book, "Up to the late 1980's the tunnel's portals were obscured by massive steel doors, built a little in front of the stonework and supported by a frame. These where constructed as an anti-blast measure by Rolls Royce in 1968, who used the tunnel for destructive tests on the Olympus engine for Concorde. They ran an engine without oil, expecting it to blow up within 20 minutes or so, but in the event it laster for well over two hours !. The tunnel's use for this purpose was only over a few days, planning permission having been sought from Shepton Mallet RDC as a matter of course, in case an explosion caused a change in the local topography"

WojtekSz
23rd Jan 2011, 09:03
TurbineD:
torsional load on the shaft and on the spline coupling comes form hot gases from burning process. Bearfoil calls it fluid drive but the fluid is still very compressable compared to any real fluid. This has significant smootering efect. The burning process creates vibrations but these are small compared to overall value of forces acting on a blade (and additionally dampened by the dovetail blade fixing). And than we have a relatively heavy disc where this vibrating loads from many blades are totalled into significantly smoother torque on the coupling

WojtekSz
23rd Jan 2011, 22:07
Bearfoil:
i can agree to certain level of vibrations from the burning process but i do belive that it must be very much similar to the very process eqisting in all other aero engines flying all over the world for some time already. We are looking for reasons that are UNIQUE to T900, right?

bearfoil
23rd Jan 2011, 22:25
WojtekSz

No. Not "fluid" drive in the sense of "Hydraulic", where the medium is contained. The Gas Path does have open ends at either end, so technically it does not qualify. In addressing this problem, the "Rigid Coupling", it isn't relevant, imo. The Vibration (causatuve of rupture) had alot of time to act on the weak portion of the design, even at that both Disc fractures occurred on climbout, and one of the Powerplants was a TRENT 700. The identified problem was not embraced by RR at any time, whether inadvertent or some thing more diabolical. They have the benefit of the doubt, as far as I am concerned. That covers the Design, Test, and Certification modes. What the firm did after the Burst/Explosion is inexcusable, keeping a client (QANTAS) in total darkness, while they casually (and cynically) completed newer Airframes for delivery. They allowed the Engines to "Time In" because they had duped EASA into relaxing the Inspex. Even in that, they almost made it.

They will correct, and move on. Hopefully, the fallout from their self sabotage will hurt deeply, suffiicient to caution themselves and others against playing Roulette with the lives of paying innocents.

WojtekSz
23rd Jan 2011, 22:35
Derg:
using the finite element method scientist/engineers can predict mechanical beahviour of any part in known conditions. Actually they can model it according to known and proven cases. Problem starts when we try to predict/calculate mechanical behaviour in the unknown/unpredictable/non-linear situations like worn bearing where actual 'worn' may have very different meanings including radial and/or axial play with different dampening properties. This calculation comes even worse if we get closer to loose spline coupling - i would bet a pint of guiness that there are no actual models for calculating behavoiur of loose spline couplings - simply because these couplings are designed to STAY and not to get LOOSE.

Once i heard a story of an experienced machine-tool designer who used to say: ok, so we have built it. Let's start it and see why it doesn't work.
;)

WojtekSz
23rd Jan 2011, 22:47
Bearfoil:
do i get you right: technically they could have made a mistake but instead of making it clear they kept on selling the stuff hoping to get away with it?
Do you believe RR have already identified the real cause and having it fixed even before the first engine exploded, just wanted the market to stay in the dark for PR or just any other business reason.? The Greed in action?

bearfoil
24th Jan 2011, 01:49
WojtekSz

IMO Rolls had identified the problem prior to the AD. They negotiated a schedule of inspections meant to monitor the wear on the Splines at Abutment Face. Clearly the AD took into account the actual cause of the problem, for goodness' sake, they approved the Fix!! The "C" modification was to have mooted all concern, for the Engines under the AD's demands were to have been pulled from service so the Power was "Exonerated". The Explosive Burst put everything into limbo. It became clear Rolls was furnishing the new engine to Airbus for facilitation of delivery of new aircraft, whilst the 972 was on wing, subjecting each flight to hazards at clearly, (Demonstrably) unacceptable levels.

How could RR not have known the source of the trouble and then claimed the "C" mod was sufficient?? Magic?? Guesswork?? Chicken Guts??

The relaxation of the inspection regimen is on the EASA's shoulders solely. They put their faith in RR and their bluff, as RR cynically advantaged the gullibility of the regulator, and their Prime client for the TRENT 972. (QANTAS).

It turns out the C mod is under the gun, and QANTAS is taking their sweet time approving LAX SYD flights at max thrust (max TOW) Where does this put the TRENT 900?? Do-Overs?? How about, 'once burned, twice shy'.......

BigG22
24th Jan 2011, 02:08
We could all do with a pint of guiness right now I think .. but as yet it is somewhat premature - there is still much to be resolved.

But was there ever a pprune reunion? There's a long way to go yet, but it's a cool thought.

barit1
24th Jan 2011, 12:38
Not only counterfeit parts from bogus suppliers, but substandard parts from "approved" suppliers.

There's been a recurring problem - going back decades - with fasteners that look OK, dimensionally OK, static strength OK, but they don't meet the fatigue strength spec. It's affected all the engine mfrs. and tinknockers at one time or another. It results from cost-reduction shortcuts at the suppliers' shops. :ugh:

FAA has cracked down - even the FBI was involved - and the problem has quieted down from its worst days.

Turbine D
24th Jan 2011, 14:13
DERG

Oil Consumption
For engines that use labyrinth seals, oil consumption is largely dependent on vent air-flows and oil temperatures. As the seals wear, oil consumption rates go up. Depending on the engine design, typical consumption rates would be in the range of 0.05 to 0.30 gallons (0.19 to 1.14 liters) per hour.

SFC - Trent verses GP

One of the things that strikes me on the SFC situation is the difference between a well designed two spool engine verses a three spool design. IMO, a bare two spool engine in a test cell will have better SFC than a three spool RR engine every time. The reason has to do with the more efficent HPT of a two spool engine. It is a different story on wing. The shorter three spool engine in a shorter nacelle makes up the difference of SFC shortfall in the test cell. The reason is less aircraft drag. However, looking at the Trent 900 & the GP7200 on the A-380 wing, a longer nacelle is used for both engines and the shorter engine advantage of a three spool engine is lost. I do believe, at this moment, the GP7200 does have a SFC advantage over the Trent 900 and RR is working the issue. This may also be an issue on the Trent 1000 verses the GEnx on the B787.

Just some thoughts,,,

barit1
24th Jan 2011, 15:17
DERG:
I(t) seems to me that if oil was slopping around in that T-972 then maybe a few more tins than ususual would have been used. What you do you think?

I honestly do not recall any oil consumption figures, other than it might be comparable to a Continental A-65 in my old Taylorcraft.

The vent system design has a lot to do with overboard oil loss. A good centrifugal air-oil separator (sometimes built right into the main shafts) can make a big difference. :)

Certainly excess oil consumption can indicate internal problems that need addressing, and not neglected! But do we know for sure the sequence of events in the present case?

411A
24th Jan 2011, 15:27
FAA has cracked down - even the FBI was involved - and the problem has quieted down from its worst days.
It reached a peak about two-three years ago.
I personally watched the FBI raid an aircraft repair station, haul away many records, two helicopters...and three persons...in cuffs.
The FAA and FBI appeared to mean business, as in...lock 'em up.

lomapaseo
24th Jan 2011, 15:41
Oil consumption is a maintenance issue and rarely a safety issue beyond being an indicator needing other parameters to be considered (vibration, Oil temp, EGT)

Oil leakage can be a flight safety issue if you don't know where the oil is going. I've seen some operators who added quarts of oil at every major turn, figuring that next week they could get the engine changed out. Only they never made it to next week before they blew a turbine out the side of the engine. On the other hand when I was aboard one of these operators on a long haul over water, the pilot got a low oil light and turned back. Sure enough the ground crew pushed a stand up to the engine as we, the passengers watched, and there on top of the stairs was a full case of oil.

Ah but it was good news, they poured in the oil and motored the engine and presto out came the oil from a blown CSD gasket (external from the engine). That confirmed where the oil had gone! So they replaced the gasket and we were off again for our flight. Had they simply replaced the oil, I would have gotten off (I did chat with the capt about this :)

Most of the oil consumption is in fumes out the breather and thankfully the pressure balances do a good job of keeping the oil out of rotor-disk cavities. The problem is when wet oil finds it's way into a rotor disk cavity where it is often hot enough to light it off.