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Qantas A380 uncontained #2 engine failure

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Qantas A380 uncontained #2 engine failure

Old 20th Dec 2010, 05:37
  #1941 (permalink)  
 
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Presuming that the aircraft will have to go home to mother for repair, is it likely that the mainplane can be repaired, or to obtain full service life will it have to be replaced.

Either way I also presume that it will take some time for either option and how will this affect the fleet use age.

Can repairs be done at Singapore that would enable the aircraft to be flown to France and again I presume that all engines would need to be available.

Looks like a long and expensive lay over till the aircraft can return to revenue service.

Regards

Col
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Old 20th Dec 2010, 17:04
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Found this link to description of typical jet engine turbine to compressor coupling. Not meant to represent RB211 technology but may well be quite similar.

YouTube - J79 Main Coupling - Turbine Engines: A Closer Look
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Old 20th Dec 2010, 20:16
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firstfloor

Thanks for your post on the spline coupling!
I would bet the coupling from the fan to LPT is accomplished just as illustrated.

Turbine D
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Old 20th Dec 2010, 20:53
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FT.com / Companies / Aerospace & Defence - Rolls-Royce scrambles to pin down problem
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Old 22nd Dec 2010, 05:27
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Also, in this one, you can see the coupling in a junked engine that appears to have been cut in half with an oxy torch.
YouTube - Dropped into a turbine engine
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Old 22nd Dec 2010, 12:29
  #1946 (permalink)  
 
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FWIW, firstfloor.

Your link requires subsctiption/registration at FT.
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Old 22nd Dec 2010, 12:38
  #1947 (permalink)  
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Does anyone have a vid or diagram of the problem area in the TRENT 972?
The "Rigid Coupling" that failed on QF32 was the IPT/C joint? A question also about the term. If allowing fore and aft movement of the IPT, how Rigid is the coupling to begin with? Wear of the "Rigid" portion of the Coupling is actually quantified in the AD, what is the source of such rapid wear? If the AD is "coupled" to the engine failure, is it plausible to assume that the "Oil Fire" may indeed have been the result and not the cause of this unwanted aft movement?

The AD's language is quite specific relative to this aftward migration, and it appears patent on this specific powerplant. With the obvious wear of the "Stub Pipe", its failure appears also to have been the result of an ongoing and serious issue. So are the oil leaks causative, or are they indicative of problems caused by a coupling that fails over time. If so, How "cross-type" is this design, and does it contribute in any way to the performance and service issues of other models? With aftward migration of the Shaft, wear points are the Roller Bearings, the Thrust Bearings, and other critical areas. Was there Overspeed? Or was the IP Wheel's movement into the Stator the cause of disintegration in and of itself?
 
Old 22nd Dec 2010, 14:17
  #1948 (permalink)  
 
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Bear

The disc burst - this is only likely to happen through overspeed or the disc material loosing it's mechanical properties through e.g heat.

Given the apparent wind down in speed of the front compressor part of the IP just before failure, it seems possible that the back end of the IP had become disconnected & was doing the opposite due to not having to turn the compressor - hence overspeed, and burst.

How did the oil issue & fire contribute to the IP turbine coming away from the IP compressor might be a good question to the experts - if indeed they did separate.
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Old 22nd Dec 2010, 14:26
  #1949 (permalink)  
 
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JFZ90 & Bearfoil

See the latest EASA AD revision that relaxes the time between inspections from 20 hours to 100 hours. The way the failure is described, the location is in the IPT area in the "cavity" around that bearing area. The resulting fire caused the drive arm of the IPT disc to fracture at the 580 bolt holes leading then to disc burst.

EASA Airworthiness Directives Publishing Tool
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Old 22nd Dec 2010, 14:39
  #1950 (permalink)  
 
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I first identified this general scenario - albeit not the same consequences - in this post regarding the RB211 IPT failure on a QF 744 on 31 Aug. out of SFO.

R-R has claimed these two events, plus the T1000 test bench failure, are not related. I have yet to see substantiation for that claim.
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Old 22nd Dec 2010, 15:51
  #1951 (permalink)  
 
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barit1

Also, the event out of Miami involving a Trent 700.

DCA04IA002

Although all the causes leading to a fire in the IPT area are perhaps different, the one thing that is common is failure of the IPT drive arm, probably because the temperature of the disc reached 538°C, or greater, reducing its strength capability.

Turbine D
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Old 22nd Dec 2010, 16:15
  #1952 (permalink)  
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JFZ90

I agree with your opinion that the Burst followed a separation of fore/aft IP Shaft. This is the rigid coupling noted by reports of failure after the accident. If such is the case, the Oil Fire had precisely what to do with Disc disintegration? These are the Splines (failure) the AD referenced from the beginning. At 7500 RPM, a drift into the IP/LP Stator aft the IP Wheel is sufficient, No?

The most recent AD (mod!) has Rolls Royce as the authority for compliance and airworthiness, allowing a deferred inspection schedule of Two Hundred Cycles!!

With failure of the intermediate oil line coupling with the Stub Pipe, the Gas Path should be flooded with hot oil under 60psi. There is no evidence of a Carbon rich combustion on the after portion of the LP Shaft, such as there is in the vicinity of the LP Shaft at the exit of HP/IP cavity....

It is the Splines, not the Stub Pipe. The duff pipe is no doubt contributory, but the signature on the one in the image supplied is of Wear, not tooling. IMO

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Old 22nd Dec 2010, 19:01
  #1953 (permalink)  
 
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I'm confused where the oil fire was. It sounds like it was at the rear ip/lp bearing (rollers only). A fire here would not necessarily mark the lp shaft?
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Old 22nd Dec 2010, 19:25
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bearfoil

I concur in what you write. If one reads in between the lines of the most recent AD it only can be the cavity between IPC and HPC. That ist the supporting structure in severity. And it is to my best estimate the # 2 roller bearing that does it. No doubt the drop of recorded N2 has started with an self demolishing bearing that finally uncoupled IPC-shaft from IPT-shaft.
Look in the posts '' 331 and 337 what Whirlybird1 and DevX wrote as a first comment !!
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Old 22nd Dec 2010, 20:23
  #1955 (permalink)  
 
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JFZ90

Your last post just made me check that picture of the dismantled LPT part of the engine with that green LPT shaft again in Photoshop. I have followed this entire thread from the beginning and worked myself through facts and bits of information like we did in I&A Investigation some 30+ years ago. I believe that you are correct in that there are no oil related marks on the rear end of the shaft. How could it possibly be if the entire shaft is shielded by the IP shaft. If now, as first anticipated by me too, the oil fire started around the housing of the roller bearing, that had to be because of the rupture of that oil tube. However, a rupture so massive would automatically severe the oil flow and lubrication of BOTH the roller bearings of the HPT and IPT. But as shown in the time tabel of events, N3 was up close to max untill the fuelflow was throttled back a fraction ahead of the disintegration of the IPT disk. So I think that part was healthy to such an extend that, if at all, only the roller bearing of the IPT shaft was severed by its backward motion. The only place I think one can speak of oil soot - I think bearfoil said it first - is right behind that area on the shaft that looks like machined - close to foreward end of the LPT shaft.
One item more is visible on the picture I believe, the socalled "machined surface" is nothing else but the receiving part of the helical spline of the LPC and LPT shaft. Amplified as said in Photoshop I donīt think that foreward pointing line of the dark material looks machined. Itīs jagged to some extend and just in front of it on the again green shaft there is a dark mark too, just as if the released parts had contacted each other.
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Old 22nd Dec 2010, 20:29
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bearfoil

Sorry mistake in my post. Itīs of course not the nr. 2 roller bearing but the nr.2 ball bearing. The one that takes care of correct rotation of the IP shaft spline, catches the foreward forces of IPC and HPC. I concluded the involvement of that part of the engine in the entire problem because of the limitation to only 75 cycles at 540 psi at p30. Where else does all the extra pressure, heat and forces in that environment go to ???
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Old 22nd Dec 2010, 21:09
  #1957 (permalink)  
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The aft IP Shaft is not suspended or resisted directly by a bearing, but through its coupling (Splines) to the ForeShaft. Any excess clearance between the two Shafts will work directly on the Thrust Bearing, #2 by way of vibration and Resonance. Spline wear is addressed directly via AD, the weakness is a known quantity. See the AD for exact limits. A failure of the #2 Bearing (not catastrophic, but compromised) sets the Stage for increasing amounts of all that is bad in a Turbine. Heat through friction, Seal Failure, increasing travel axially and Radially of the Affected Shaft, etc.Not to mention metal bits, degraded lubricating oil (coking) etc.

For the soot to have accumulated on the LP aft Shaft (where it did) demands a failure (leakage) of Gas, Oil, and Pressure from the Thrust Bearing case. That N2 dropped is patent, but does not necessarily mean parted Shafts. A hole in the bearing case (via blown seal) would release a great deal of energy also.

That the HPC and T revolve anti clockwise, from the front, imparts a serious strain to the webbing containing the Bearings, and ultimately the Shaft. The vibration produced by a net differential of (hopefully balanced) 20,000 RPM is monumental.

I am saying that the IPT drifted aftward, blew the Stator into an unknown number of bits, and caused the IPT to exit. I am also saying that the Shafts were still together.

Had the IP Shaft parted, the HPC would have blown up along with the IP Disc, and the a/c likely would have been lost. I am saying the Splines were unable to restrain the Shafts from axially widening their Gap, but the Shafts did not separate. I'm working on the Math, but don't think it will be difficult, 72,000 pounds of Thrust.

Good Lord.
 
Old 22nd Dec 2010, 21:20
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JFZ90

I am not a 100% sure which bearing area instigated the fire but have been leaning towards the roller bearings beneath the IPT rotor. In my mind a fire in the cavity here makes more sense to me at this time. If the web of the disc and the bore area gets heated beyond the material strength capability then it could result in the fracture of the power drive arm at the 580 bolt holes, leading to overspeed and rupture of the disc+the blades impacting the stage 1 LPT nozzle ring. The IPC/IPT shaft does not fail and that is why the LPT shaft is shielded in this area. Also, in this process of failure, as soon as the disc is free from the shaft, the IPC rotor spools down in speed (no longer being driven) and this translates into another problem, a HP compressor stall. I do believe one of the "bangs" heard was this as the highly compressed hot gases are blown both forward towards the IPC and back towards where the IPT rotor was. Any time there is a very significant compressor stall due to major component failure, flames come out both ends of the engine. Who knows what this could have done to the IPC ball bearing area.

Also, if the IP shaft severed, The IPC spool would be free to move rearward and there would have been considerable damage to the IP compressor blades/stators with debris going back into the HPC. Damage has not been reported at all to indicate this, at least at this time.

So those are the thought behind my leaning towards the IPT area as the problem area.
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Old 23rd Dec 2010, 09:18
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The aft IP Shaft is not suspended or resisted directly by a bearing, but through its coupling (Splines) to the ForeShaft.
What complete rubbish! Have a look at the diagram on page 70. The HP spool has two bearings, the other spools have three each. Main bearing in the centre and roller bearings at each end.

Forget about the splined coupling, it has nothing to do with QF32!

Please stop the nonsense, you're driving me nuts.
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Old 23rd Dec 2010, 12:00
  #1960 (permalink)  
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firstfloor

I believe you are mistaken. If you look at the diagram, page 70, you will note that the Aft IP Shaft terminates short of what you call the "Third bearing". As a unit, you are correct, but as separate Shafts you are wrong. The terminus of the Wheel (IP) Shaft is short of the #2 Thrust (Ball) bearing. This leaves the Splines to carry the (aft) Shaft's load to the Thrust bearing. Take a look.

I was unclear in former post, The Aft Shaft has Two bearings. I can see where one may think I stated it had none. I can also understand why people would think it had Three. I do think it would be better for Rolls to have people "forget" about the Splines, but the AD's have not been withdrawn.
 

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