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QANTAS A380 Uncontained failure.

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QANTAS A380 Uncontained failure.

Old 27th Dec 2010, 21:43
  #41 (permalink)  
 
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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
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Old 27th Dec 2010, 22:26
  #42 (permalink)  
 
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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.
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Old 27th Dec 2010, 23:42
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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.
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Old 28th Dec 2010, 04:53
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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.
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Old 28th Dec 2010, 09:27
  #45 (permalink)  
 
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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 wouldn´t cover the requirements in an engine at all I assume. So I went on and found this Schaeffler Technologies | Sectors / Key Industries | Product range
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.
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Old 28th Dec 2010, 13:52
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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.

Last edited by bearfoil; 28th Dec 2010 at 14:28.
 
Old 28th Dec 2010, 15:03
  #47 (permalink)  
 
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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!
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Old 28th Dec 2010, 15:10
  #48 (permalink)  
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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.
 
Old 28th Dec 2010, 15:21
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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.
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Old 28th Dec 2010, 15:30
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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.
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Old 28th Dec 2010, 15:34
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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.
 
Old 28th Dec 2010, 16:10
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bearfoil

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.
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Old 28th Dec 2010, 16:17
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Turbine D

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.
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Old 28th Dec 2010, 16:20
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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.
 
Old 28th Dec 2010, 17:06
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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.
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Old 28th Dec 2010, 19:35
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Turbine D

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.
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Old 28th Dec 2010, 21:30
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Could the second bang have been the disc segment hitting the wing?
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Old 28th Dec 2010, 22:17
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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.
 
Old 28th Dec 2010, 22:42
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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!!

Last edited by bearfoil; 29th Dec 2010 at 00:04.
 
Old 29th Dec 2010, 01:02
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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 135º 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
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