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Qantas A380 uncontained #2 engine failure

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Qantas A380 uncontained #2 engine failure

Old 12th Dec 2010, 06:26
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Old engineer said

"That looks to me like Qantas is planning at the moment not to exceed 72,000 lbs thrust with this engine, in case of losing one engine while climbing above terrain or restriction as at Singapore, whereas before they might have approached 80,000 with one engine out."

This is not the case. QF has a maximum thrust available of 72,000 LB on each available engine. This is the certification that they have purchased from RR & the engine has been "set" accordingly to this maximum output. All the performance data in the TOPA [Takeoff Performance Application] is based on this which is both Operator & Aircraft specific and the aircraft must meet all of it's performance criteria based on this fact, which it does.

QF derate all takeoff thrust levels on ALL fleets to an appropriate level considering both performance and safety. It is true that on the A380, more so than on other fleets, that Takeoff thrust can be less than Climb thrust. As per some earlier posts this is very good for the longevity of the engines & to the best of my knowledge the highest wear and tear factor [stress] on an engine occurs during "Rotate" due to the centrifugal [gyroscopic] forces that occur especially on the "FAN". Thus the more derate on Takeoff the better, within acceptable limits and the longer the engine life will be with less problems. [Manufacturing defects aside]

P B
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Old 12th Dec 2010, 08:57
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Turbine D
I suspect that RR didn't ask for a US certification as there is no current US aircraft application at the moment.
FAA TCDS NUMBER E00075EN

OE
Barit1's interpretation is incorrect re thrust percentage.
0% thrust = Engine not running
100% Thrust = Thrust lever at TOGA and all engine bleeds off.
Each Thrust Mode indicates the thrust rating limit(FLX, CLB, DCLB1, DCLB2 etc., which in normal mode, is a percentage somewhere usually between 70 and 100%
A 15% thrust increase after take-off is quite normal. The climb thrust of 87% indicates the normal use of DCLB2 (derated climb thrust setting 2 - a 10% decrease from maximum climb thrust, which washes out by 30,000ft)
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Old 12th Dec 2010, 12:55
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I don,t understand the hypothesis relative to this A380 thread of a link between thrust or tenperature to the failure causes

That's as much of a stretch as most of the other technical sounding discussions in this Rumors & News forum.

At least one ought to precise RPM and pressure in an exact way as well without just waving a baton over the differences from one rating to the next.

It makes a lot more sense to link a discussion to a fresh news or rumor story so at least the relevance can be seen by the reader. Else why not just take this to the Technical forum.
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Old 12th Dec 2010, 13:46
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Trent 972

Thanks for the certification info. I just couldn't come up with this yesterday.

Turbine D
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Old 12th Dec 2010, 13:51
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Going Boeing:

The departure off Rwy 20C in Singapore has a height requirement of 4000A at position SUDPO. This height is quite challenging for widebody jets and thus it is normal to do a derated takeoff and transition to full Climb thrust to meet that restriction.
SUDPO at or above 2,000.

It seems all to be quite a challenge for the performance engineers, unless they just punt to the flight crew because it is all engines operating.

Note 5% to 400 feet, then 3.3%. Yet, it is only 2.4 miles from the DER of 20C to SUDPO. Seems to me that the 5% limitation to 400 feet would require that takeoff thrust not only account for runway performance requirements but also to meet the 400' restriction. (perhaps the takeoff that is the subject of this thread was accomplished at max rated takeoff thrust.)


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Old 12th Dec 2010, 17:04
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Turbine D - I searched for that TC on the FAA site, and just didn't find it. Thanks. Definitely the actual figures for this engine are needed, as lomopaseo noted. Also noted:

I don,t understand the hypothesis relative to this A380 thread of a link between thrust or tenperature to the failure causes
Assuming the reference in the statement to "failure causes" is disconnection of the oil supply pipe at the bearing housing oil inlet boss, and resultant oil fire, one can say that temperatures elsewhere in the engine are reflected in temporarily high temperatures (due to high engine load) in the area of the proposed* oil fire. *Edit: I meant to say "alleged oil fire."

It is very difficult to say mathematically how much was added to the temperature of the oil fire, or even if the general engine heat penetrated to the area of spilled (or spilling, which is unknown) oil to such an extent that the general engine heat ignited the spilled oil. Heat transfer usually involves non-linear equations, for which solutions have been found in only a limited number of simple cases. We can't put a thermal imaging camera in this location, so we are left only to learn by experience.

It is possible the oil fire evidence (oil sediment?) was left by a previous oil fire that simply burned and went out. The oil feed pipe, socket cracked to be sure, may simply have been dislodged this time by the blowout of the IPT section. Any substantial oil leak would have shut the engine down in short order (in an orderly fashion, I presume) as the oil carried is hardly more than enough to supply a modest consumption rate (less than 2 pints per hour) for less than 24 hours. Yes, I took that figure from a different model of RB211 engine. Actual figures when I find them.

I think Qantas is acting prudently in this situation, which still IMO contains a lot of uncertainty. Qantas has to know more about what they are facing, operationally, than we do. Only in the last two days have the TO challenges at Changi entered into the picture, at least as we here understand it. I can't quarrel with their caution.

OE

Last edited by Old Engineer; 12th Dec 2010 at 18:51. Reason: To clarify what I meant to say, see * above.
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Old 12th Dec 2010, 18:20
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Thus far, I honestly don't 'see' an hypothesis here, of any kind, not one that can be systematically critiqued in any case. There are present several progenitors of a hypothesis or three, but it is too early to criticize "the hypothesis" in this thread, except to perhaps lament the nature of present discussion.

A hypothesis, properly offered, is entitled to more than the vague criticism it seems to be getting, in its absence. Heaven forbid an 'unapproved' theory.

Oil Fire. Contributing unwanted energy to a balanced system at full demand.
Oil Fire. Consuming Lubricating Oil as a Fuel, with precious little on hand.
Oil Fire. A contributing cause of chaotic internal Pressures.
Oil Fire. Produces irregular loads on Discs, and Shafts.
Oil Fire. Greatly increased Friction (bearings), causing extreme Heat of its own.

There is evidence (Photographic) of soot on the forward portion of the aft LP Shaft, this is unusual, and since this area of the Shaft is in the same axial location as the Bearings surrounding it (IP/HP Thrust), some involvement of Fire is assumed here.

Oil Fire. Caused the Uncontained Disintegration of the IPT Wheel. (per RR). This is a Conclusion, from the manufacturers themselves. It is vague enough to withstand any pertinent criticism, and lacking any further data, is unassailable. That is the way I see it.

Have at it.
 
Old 12th Dec 2010, 18:57
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bearfoil:
Oil Fire. Contributing unwanted energy to a balanced system at full demand.
Oil Fire. Consuming Lubricating Oil as a Fuel, with precious little on hand.
Oil Fire. A contributing cause of chaotic internal Pressures.
Oil Fire. Produces irregular loads on Discs, and Shafts.
Oil Fire. Greatly increased Friction (bearings), causing extreme Heat of its own.
Top of my head, and by no means am I expert on the Trent, but considering it only as another gas turbine:

Some pages back I commented on #1 - the additional unmetered BTU's contributed by the oil fire will be compensated by the EEC - it will still do its job of holding its assigned parameter (N1, whatever...) steady, and will reduce metered fuel flow to accomplish this. Possibly noticeable on FF instrument, if you're really paying attention; Not likely to be seen by an unsuspecting crew.

#2 - Of course, and any operator who does not track oil consumption is falling short of minimums. But the fire maybe was of short duration?

#3 - Negative. Unless sump vents are blocked, internal pressures won't change.

#4 - Same as #3. If pressures and rpms are normal, stresses will be also. HOWEVER, a sump fire heats the structures to the point the materials cannot sustain normal stresses. Ergo, the danger of rotor burst, either directly (degraded disc strength), or indirectly (shaft failure, loss of mechanical load, and overspeed).

#5 - Yes, although #4 may occur first.

$0.02 worth.
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Old 12th Dec 2010, 19:45
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aterpster, thanks for posting that chart. I was relying on my poor memory when posting - I should have said waypoint SUSIN for the 4000' requirement. The SUDPO 2000A requirement is only during the nominated hours as I understand it relates to a military jet corridor to the training areas. Most aircraft cannot achieve this but it is normally easy to co-ordinate a dispensation when there is no conflicting military traffic (most heavy departures for Europe are outside the hours). The SUSIN requirement, I believe, is because of the Batam airport (WIDD) CTA so it is more difficult to get a dispensation and this is what requires use of maximum thrust to achieve.

The QF32 was departing to the South-East and would have been on the VENTU ONE BRAVO Departure which tracks initially by the same two waypoints (SUDPO & SUSIN). Cheers GB
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Old 12th Dec 2010, 20:50
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barit1

#1 Unwanted in the sense of being incompatible with the engine's normal operation, not simply a burden on FFC.

#3 Pressures exclusive of Gas Path?? The seals at the Bearing cavity were lost, and the possibility exists that they didn't "burn up", but were blown out (hence chaotic) ??

Also, as I understand it, the scavenge tubes are pressure sensitive, to allow a compensating Pressure to enter the tube "without combustion", if the tube fractures, as is quite common in other types also.

The 2003 Failure of the TRENT 700 IPT was exacerbated by the existence of fire in the Gallery vents. the feed tubes transit the Gas Path, and I am unsure of the position of the Coupling, but a compromised couple would hasten ignition?? Not to mention loss of Oil??

Fuel Flow might be noticeable. My take on this fire is that it was quite rapid after reaching a certain value, and the remedy was past its effective timing?? To mean that it may have been burning, but once the coupling failed (if it did), the loss of the disc may have taken only another ten seconds.

At "Turbine OverHeat" (alert), The First Officer started his 30 seconds of monitoring w/o action until the Fire Warning lit, then the screen went back to OH only, and he re-started the Timer. The Fire Warning may have been the onset of fully Oil fed Fire, unknown as to why it may have relented.

#4 By irregular loads I mean to say the Plastic character of overheated Metals, and the Friction induced disintegration of bearings, perhaps caused by Siezeing, due the Heat of the Oil Fire. I think it possible that there was fire in both sets of bearings, IP/HP, the Ball and Rollers. There is no evidence of fire on the LP shaft in its cavity with the IPT, but the Pressure here was much greater than that in front of the IPT??
I think the 'assumption' of Normal Temps and Pressures maintained by the FFC is difficult to make, given the probability of rapid failure? It certainly is not intended to "normalize stress" during an Oil Fire?? So I think juxtaposing a "Normal" set with an abnormal one has time limited value? I definitely would not reject the idea that FFC action could mitigate abnormals while the Oil Fire was "maintaining" a "steady" burn rate??

I definitely agree that #4, and #5 are either/or, to include pre/post.

Have you had a chance to see the Soot on the LP aftShaft?? It is a slow process for me, to try to grasp the architecure of this engine and entertain a failure such as this, it is a complex machine, to me.

rgds.
 
Old 12th Dec 2010, 21:40
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I have been studying the sequence of events on engine 2 leading to the failure. Using the written data and graphical chart data from the ATSB report AO-2010-089, some things observed are puzzling to me.

First, I am assuming that the engine was in the autothrust mode, being electronically managed as dictated by the FADEC unit with operational data being recorded by the EMU/EEC units. As the aircraft climbed through 4,500 feet, all is well, all engines.

Engine # 2

1. At 0200.22, The oil temperature starts increasing abnormally and this trend continues until the IPT disc burst.

2. At 0200.59, the IP spool N2% begins to drop along with a corresponding increase of the HP spool N3%

3. At 0201.03, the IP spool N2% regains slightly, the HP spool N3% continues to rise.

4. At 0201.05, the IP spool N2% begins a precipitous drop towards zero, the HP spool N3% continues to rise.

5. At 0201.07, the HP spool N3% reaches it maximum point (peak) followed shortly (less than a second) by a turbine overheat and warning to the flight deck. Fuel flow is cut off due to P30 collapse.

6. At 0201.08, The HP spool N3% begins to drop, then slightly rises and steadies at 0201.09.

7. At 0201.11, the IP turbine disc burst occurs.

Total time from the onset of the abnormal rise of oil temperature to disc burst, 49 seconds.

So, not being at all familiar with the Trent 900 engine or the FADEC electronics system, I have some questions to those that are more familiar and knowledgeable about Trent engines.

A. At 0200.59, is the IP spool N2% decreasing resulting from abnormal bearing conditions at the IP compressor (ball bearing) or the IP turbine (roller bearing)? Does the HP spool N3% increase because the electronics detect the IP spool N2% is decreasing and so it commands more fuel flow and does so through 0201.07 to recover thrust?

B. At 0201.05, why does the IP spool N2% drop sharply? Has a disconnect occurred of the IP compressor from the IP turbine rotor that drives the compressor?


c. At 0201.07
, is the turbine overheat condition detected due to the lack of cooling air for the HPT nozzles and HP turbine blades resulting from no IP compressor bleed air being fed to the HP turbine airfoils?

D. At 0201.11, did the IP turbine rotor disc burst because it was freed from the IP compressor (6 seconds prior to this time) and now the disc is driven freely by the increased airflow exiting the HP turbine due to the N3% increase? At what point would the oil catch fire based on temperature, it reached 195 degrees C at 0201.11 before dropping off?

Turbine D

Edited: Correction -Total time of event start to burst
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Old 12th Dec 2010, 21:51
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Turbine D
From your table, there is enough to make some interesting supposes. 49 seconds from first sign to Burst. If a thirty second "wait and see" (monitor only) is included from OverHeat alert, there is no time to act. This is especially true since a short "Fire" warning caused a restart of the monitoring clock. The software rework then becomes the 'failsafe' to prevent uncontained failure and perhaps a far worse outcome than QF32.

I could repeat that ostensibly, the software mod is not a correction of the failChain, but an earlier warning, and still remarkably close to Burst. The replacement of "Module" and poor quality parts then becomes the nuts and bolts of remediation.
Someone like barit1, or you yourself, Turbine D, or old engineer should analyze the chronology. That would help us all to better understand this engine self destructing.

Thanks for this record, cheers

bear

Last edited by bearfoil; 12th Dec 2010 at 22:54.
 
Old 12th Dec 2010, 22:12
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Thanks Bear for pointing this out, made a correction.

Turbine D
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Old 12th Dec 2010, 22:45
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Bearfoil & barit1

Relative to oil, do you think oil quantity might be monitored through the electronics and oil that is lost or added is maintained in this manner? I note the oil quantity information depicted on Figure A-3 Graphical representation of engine oil properties prior to event in the ATSB report near the report end. I am guessing these charts were put together by ATSB personnel for the report, but actual data may be much more detailed. It indicates a slight drop in oil from just under 12 quarts at the disc burst, a quick recovery and then a steady drop off to 2 quarts at 0201.48.
Personally, I don't have an idea if this is true or not.

Turbine D
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Old 12th Dec 2010, 23:05
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Turbine D

200:22
Oil Temps increase. Ordinarily the Oil is supposed to increase in Temperature, but only as a cycle of cooling the Bearings, thence to the FOHE to itself be cooled. I assume the increase, here, is in addition to its normal operating temperature. It is reasonable to assume that something unusual is responsible for this increase, perhaps abnormal friction, or a loss (increase) of the flow? There is a de-aerating tray in the circuit, so one assumes the Oil is supplied as a mist, or air/oil mixture of some ratio. The oil temps are sensed where? I am back to the stub pipe's appearance, worn, and decoupled: rapid loss?

bear
 
Old 12th Dec 2010, 23:18
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Turbine writes:
B. At 0201.05, why does the IP spool N2% drop sharply? Has a disconnect occurred of the IP compressor from the IP turbine rotor that drives the compressor?
This is a good question. Given its mass, one wouldn't expect it to actually physically slow down extremely fast.

The only answer I can think of is that the sensor was beginning to fail.

Typically, such a sensor will be based on magnetic reluctance - a change in the magnetic relationship between a a fixed magnetic reference, a pickup (usually a coil), and a moving piece of which has at least some magnetic characteristics.

Heat and/or vibration can cause a coil to short; also, if you move the reference pieces outside of their area of influence the signal will degrade quickly.


It will be fascinating to learn exactly where the oil fire took place.


Cheers!
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Old 12th Dec 2010, 23:24
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It needn't spool down to lose "Value"? The IPT was oversped, and was putting out zippo. Other mischief was afoot, not just wheel speed, I think. On the other hand, if fire was involved in the forward IP/HP cavity, a bearing siezure can slow a Shaft instantly. Mr. Turbine has said, that IPT may have parted company from its Shaft. This would freespool the IPC module, neutering its purpose re: the HPC. If the Bearing effacement of the IP Wheel was lost, the Shaft would wobble with alarming energy, enough to release the Turbine completely.

Remember from the TRENT 700 failure, the IP Disc had a "Circumferential Fracture" at the Drive Arm?? Had this preceded the 'siezure' on this 972, the wobble would have been enough to liberate the Disc from the casing. IMO. The wobble could possibly explain the loss of IPT blades, against the Casing at first, and then with ungodly wobble, shaken the loose roots out of the dovetails.????? This wobble could also explain the "Folding Over" of the Drive Arm relative to the Disc.

bear

Last edited by bearfoil; 12th Dec 2010 at 23:36.
 
Old 13th Dec 2010, 00:07
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One should not go too far in positing reasons for the parameter changes unless you undertsand and know the contoling parameters in the FADEC relative to N1, N2, N3, RPM,s Pressure and temperatures.

Friction between parts is insignificant. Blade tip clearances are the most significant and temperatures, pressures follow that more closely.

Seeing as how RR have already offered up a FADEDC logic as another temporary means of defense it seem plausible that they know what and why is going on.
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Old 13th Dec 2010, 00:17
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If I go outside the lines, occasionally a brighter bulb will illuminate.

Thank You, lomapaseo. I wish to learn, I don't care who the teacher is, or how he judges me. Anything further? Be warned, I can get far more fantastic than this!!

best,
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Old 13th Dec 2010, 00:31
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Turbine D & rottenray:
4. At 0201.05, the IP spool N2% begins a precipitous drop towards zero, the HP spool N3% continues to rise.
I read this that the N2 shaft has separated, and yes, there's considerable mass in the IPC spool, but it's also doing a LOT of work compressing dense air. Tens of thousands of HP work - maybe hundreds of thousands. That will indeed slow it down in a hurry when undriven.
7. At 0201.11, the IP turbine disc burst occurs.
Thus the time to reach IPT burst rpm is six seconds, right? That is plenty of time for software logic to decide IPC is no longer being driven, and that autoshutdown is indicated.
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