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Qantas A380 uncontained #2 engine failure

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Qantas A380 uncontained #2 engine failure

Old 6th Dec 2010, 13:15
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PBL

It seems to me that the flap track damage (not the "major damage" as the manufacturer put it) lies outside of even the 15 region. Since all damage is supposed to be covered by the assumptions, this led to my wondering if the acceptable-means-of-compliance guidance would be revisited.
Fair point, however the divergence angles were derived from statistical data and never considered absolute. Neither is the protection of the aircraft considered absolute. Taken in total the rule is aimed overall at "best practices" that should maintain the fleets within a broadband of historical acceptability.

There probably is some room to find improvement here, but I suspect it will have to be subjectively aimed at the certifying angency since they often decide what trades they will ultimately accept.
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Old 6th Dec 2010, 13:26
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Machinbird:
A witness onboard reported fire in the holes in the wing for several minutes. Does the A380 have a fuel inerting system?
No inerting of the A380 fuel tanks. Further, I would assume that with holing of a tank or tanks, particularly holing above the tank, the airspace within the holed fuel tank would be rather soon filed with atmospheric air, negating inerting.
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Old 6th Dec 2010, 13:44
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If there were flames in the wing....ATF Vapours would have ignited,unless it was restricted to the Dry bay.
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Old 6th Dec 2010, 13:50
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JFZ90 wrote:
Obviously a metal disc doesn't burn under fire like a piece of string, but its mechnical strength can still be significantly changed - even at modest temps well under melting point to the point where it is no longer strong enough to spin at its normal speed of say 7000rpm.
I don't question that, but I have this question: for a material built to withstand the temps and pressures of air that has combusted under pressure at about 1300-1400 deg C, (those numbers from the RR video linked a few pages back) how does one surmise that the material fails when subjected to burning lube oil, (which I think burns at a lower temp than jet fuel )?. From all of the explanations, I am left with the oil fire weakening something else (not quite sure what) which then led to turbine wheel doing X (contact with stator/fixed part) leading to failure.

The other explanation, that oil consumed in an oil fire does not return via scavenge to lube system and eventually lube system is starved, temps rise, and something fails, a something which then leads to turbine wheel/disc failure.

Am I following correctly?

Panzer John:
A wonderful effort by the crew.I wonder why they took so long to disembark the passegers, esp as the No1 engine was still running. And as for using only one exit as they wanted to headcount, did they think they may have lost someone?. I know its a big plane, but?
Mach 2.7
"The passengers commenced disembarking from the aircraft via the No 2 main deck forward door about 55 minutes after the aircraft touched down. The last passengers and cabin crew disembarked the aircraft about 1 hour later."
Meaning 1hr and 55min after touch down ?
Initially, the most likely answer was that they'd wish to shut down the engine, then disembark pax. As each means to shut the engine down didn't produce a secured engine, the worry that they still have pax on board and an uncontrollable engine (and an aircraft fuel system not responding as desired) on their hands, the crew (IMO correctly) decided to get the pax off in the safest and orderly manner possible. The head count rule and strict control reflect legal and regulatory requirements that one keep track of passengers who board, and who disembark, on a one for one basis. If that slightly slowed down disembarkation, they were prepared to speed it up IF Necessary. Speeding up did not become necessary. Controlled and deliberate.
Looks like a good call to me.

Turbine D (Post # 1620)
I would also suspect the IP turbine blade rotor slid aft contacting the LPT stage 1 nozzle ring and then burst due to overspeed as it was no longer coupled to the IP compressor. If you look carefully at the engine being removed from the pylon, you can see the gap (missing casing that held the LP stage one nozzle ring. (and more, some great posts, thanks!)
(More Turbine D)
AD 2010-0008 R1
This AD requires inspection of the IP shaft coupling splines and, depending on the results, requires further repetitive inspections or corrective actions.
Could the spline wear and potential vibrations cause the initiation of the stub pipe fracture? In other words, are there multiple events taking place that lead to the engine failure in a different location (IPT) instead of LPT) as postulated in the AD?
bearfoil:
The possible starvation of oil can create a dynamic wear, over time; it is this wear the EASA wanted a firm grip upon. The splines were allowed a loss of "crest" down to .5mm from 2.65 new. The TRENT is a fire breather, add some hydrocarbons, it is thrilled. The oil fire did not directly affect the thrust values, imo. The oil fire burned up the lubrication, very bad. The ramp up of N2 to 98 when 88 was selected across the wings, may have been coincident with Shaft Coupling loss.
Your estimate, or a summary of a report out at present?
Old Engineer:
Buckling is a difficult concept to explain--
Thanks for that post. Made some things about wing design more clear to me (and recalled what I learned about skyscraper design/three d lattice work, as I read up on NIST conclusions after 9-11).

PBL:
Thanks for the link to your commentary on providing accurate information to the public.
It seems to me that the flap track damage (not the "major damage" as the manufacturer put it) lies outside of even the 15 region. Since all damage is supposed to be covered by the assumptions, this led to my wondering if the acceptable-means-of-compliance guidance would be revisited.
Ricochet? Isn't one somewhat at the mercy of probability and distribution once the catastrophic failure occurs and the various bits, each in his own departure angle, accelerates away from where it is supposed to be ... which is still on the engine?
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Old 6th Dec 2010, 14:00
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Ricochet? Isn't one somewhat at the mercy of probability and distribution once the catastrophic failure occurs and the various bits, each in his own departure angle, accelerates away from where it is supposed to be ... which is still on the engine?
That is certainly part of it

However the highest energy parts having enough energy to pass through multiple metal layers of engine, do not ricochet until/unless they are substaintially slowed (energy removed).

Parts coming out open holes in the case at lower energies are the most likely to ricochet (deflect) off pylons structures etc.
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Old 6th Dec 2010, 14:22
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However the highest energy parts having enough energy to pass through multiple metal layers of engine, do not ricochet until/unless they are substaintially slowed (energy removed).
Roger, point taken.

What had me thinking is that depending on the strength and amount of material hit by that high MV (momentum) parts, the path after collision will be a different vector/direction than the path at point of collision. So, not necessarily a "pure" deflection ricochet, but maybe a "midcourse adjustment" due to the usual reasons of action-reaction.
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Old 6th Dec 2010, 15:00
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LoneWolf 50 That may be the reason for the erroneous representation of the Trajectories of the Projectiles, showing them starting above the axis of (clockwise) Rotation, and yet still exiting to Starboard. If a line of sight was accomplished through the wing, it may well "point" to the "above axis" start point, but didn't allow for deflection through the wing. Yes? I think we should give the wing some credit for "Mass", eh?

Also, re: schematic, above. Each of the Stub pipes show what I take to be a "Quick Couple", short of the Stub's Exit end. If this coupling is what caused wear at the pipe's "end" (Not the exit ), then the image shows a faulty coupling, not a faulty pipe. If the coupling separated , one envisions a "Snake" squirting Oil everywhere, while the Stub pipe is dry, and the fine machinery inside goes South, for want of oiling. A coupling, with its slop tolerances, would be most prone to vibration damage, Yes??

Moderators? Can we combine the two TRENT 900 Threads, they are quite similar??

To ADD: Note the "Fuel-cooled oil cooler" on Ferpe's drawing? As Re: BA038, that should read: "Oil Heated Fuel Heater" Read the AD.

bear

Last edited by bearfoil; 6th Dec 2010 at 16:21.
 
Old 6th Dec 2010, 15:09
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Indeed, bear. As I understand the wingbox (thanks to some brilliant pictures previously posted in this very thread), numerous structural members (as well as eng/ hyd / flight contr systems pieces) were in a cone to be to hit / damaged/ deflected off of, and thus play the role of "trajectory adjustor." ( Sort of like an insurance adjustor, but without the infected soul ... ).

From the earlier discussions regarding the kinetic energy of the turbine disc, perhaps even the strongest structural member was able to deflect high speed bits only slightly. Learning of the 5 deg / 15 deg standards (a few posts up) was most enlightening.

Something about that V^2 term and bits of straw rammed into doors during tornadoes comes to mind.

Last edited by Lonewolf_50; 6th Dec 2010 at 16:50.
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Old 6th Dec 2010, 15:16
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Lompaseo and PLB

I doubt if we will get any more information on the damage sustained to the wing, apart from the already published photos which do give a clear indication of location and approximate sizes of the damage sites.

Regarding calculations of reductions in strength these would be largely academic exercises now; the focus of the repair activity will be designing, justifying and maufacturing repair parts which A) restore full static strength, and B) restore as far as possible the fatigue life.

I imagine such repairs will be a combination of removing and replacing discrete structural parts where possible, and where not, repairing in situ with bolted plates, straps, etc. This will not be easy with structure which has few regular or flat surfaces, and where introducing new bolt positions causes its own problems. They will endeavour to leave the outer wing surfaces undisturbed, for aerodynamic reasons, but this may not be possible. The one benefit they have is accessibility, being such a large aircraft. As always there will be compromises and I imagine there will have to be additional inspections relating to the repaired structure.
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Old 6th Dec 2010, 15:27
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SRMman

Here is an example of where CFRP can truly shine. I venture Patternmakers are unlisting their emails hoping to avoid being part of the Spar repair crew. I see this cantilever as an infinite "Post Tension" system, where web acts as compression and tensile members? Sistering Aluminium won't cut the Moutard; Splints of Poured and baked in place Composite, there we go!!

Subject to old engineer's review..........
 
Old 6th Dec 2010, 18:19
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To ADD: Note the "Fuel-cooled oil cooler" on Ferpe's drawing? As Re: BA038, that should read: "Oil Heated Fuel Heater" Read the AD.

Surely a fuel-cooled oil cooler IS an oil heated fuel-heater!

Have any more funny pipes turned up?
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Old 6th Dec 2010, 18:45
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first floor

You'd think so, but when heated Fuel is most necessary, the FOHE is bypassed in favor of the "air-cooled Oil cooler".

Give it some thought........

Save the Snark, I am immune to 'dismissive' and 'marginalizing'

Besides I never "Inhale"..............

bear

See, when Fuel is at its coldest, at Cruise or long descent, the FOHE doesn't circulate the Oil, besides, it isn't warm enough to need cooling, hence the "Air-cooling". The Fuel 'heating' thing is a 'device', a political one.
 
Old 6th Dec 2010, 19:09
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Bearfoil

I think a better depiction of the 900 architecture is presented in 26/11/10 Post#1375 by No-Hoper. I think it has changed somewhat from the RB-211 526G as to the IP rigid coupling. If you look at this 900 cross section, the rigid coupling (color-pink) is just aft of the number 4 bearing. It is a axial spline coupling, maybe helical in actual design. Just slightly forward of this is the rigid coupling (blue-color) for the Fan - LPT shaft. Upon disconnect, it is the actual spline at the end of the shaft you were questioning in the photo of the pulled LPT module.

As a matter of interest, the IP shaft material would be a high strength steel selected probably based on tensile strength (the higher the better) to handle torque/twisting of the shaft. Typical materials are maraging steel or equivalent. It does not have very high temperature capability nor superior wear resistance, so the splines are probably coated to overcome this deficiency. So it is this IP rigid coupling which is concerning for spline wear as rearward slippage would move the IP rotor towards the stage 1 LPT nozzle ring. Not having any photos of the engine forward of the LPT module, it is difficult to know what exactly permitted the IPT rotor to move rearward. Did it pull out of the rigid coupling or did it fail (softening) because of the fire beneath the IPT rotor where the bearings are located, or without oil, did the shaft get scored and then just broke.

Nevertheless, I do think there is a strong possibility, that spline wear contributed through unexpected vibration or harmonics to the failure of the stub pipe, sooner rather than later.

Just some information & thoughts on my part, cheers!

Turbine D
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Old 6th Dec 2010, 19:50
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The Fan, LPT rigid coupling is within the IPT Shaft, and I see no oiling capability. How would an oiler penetrate the IP Shaft? My assumption is perhaps grease, or no lube for the Long Shaft. The LPT Shaft fits within its forward mate, so the oiling is, what? I think fire, of course, DevX has said so. However, Fire alone? The fire may have plasticized the Shaft, as you say, but I think failing an aft movement, there may have been no "contact" with the Stator (LP). The leak is known to have existed prior to failure, as has the Spline Wear. So whether "Acceptable" or not, the utter failure, imo, has to do with oil starvation after a high effort climb, high temps, and massive vibration.

Without Oil, all manner of chaos would ensue. Consider "Friction Stir". If the bearings, in thrust and carriage, failed utterly, a very quick aft movement, a Disc "Burst" and seizure of the Shaft? Without the IPT all combustion is free to migrate forward, to exit the Low Pressure Stator vanes, and foul the cowling? If the IPT Hub was plastic, perhaps seizure caused the separation, Overspeed is unlikely if the bearings were dry?
 
Old 6th Dec 2010, 20:03
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Save the Snark, I am immune to 'dismissive' and 'marginalizing'
No offence was intended. I do apologise. The main reason for posting was to know if there is any news on the search for other examples of the off-centre counter bore.

By the way, curious about how a splined joint would work I think the helical shape (if that is what it is) serves to screw the joint together by action of shaft torque and so resisting shaft tension.
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Old 6th Dec 2010, 20:09
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first floor

I see reference made to the "abutment" (face?) of the Splines, in the AD, and I take it to mean the Splines termination at what I would call "Ring Boss". Splines cannot defer thrust, to my knowledge, so it occurs elsewhere? The "Ring" may run in a central groove on the inner race of Bearing #2, but without pics, what to do? My feeling for loss of Splines has to do with possible overspeed (had they rubbed "smoothe")? And Thrust has to do with axial movement, but I am very old-fashioned.

It is also possible that the splines are "part of" the inner race, and serve only to add surface area to a very critical Joint. If they are "attached" I haven't a clue how that would work. At some stage, the Engine needs to be disassembled, and the "Slip" of the Spline joint would allow axial travel for strip?

To add: Stub Pipe. Not even an id as to which end of the pipe we are looking at, eh? RR is close to the vest, and until I see some engineering drawings, I'm not stepping foot on a TRENT motivated airframe, unless it is chocked, and I'm near an exit. But that's just me.

bear
 
Old 6th Dec 2010, 21:15
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Originally Posted by bearfoil
To add: Stub Pipe. Not even an id as to which end of the pipe we are looking at, eh? RR is close to the vest,
...and I was just thinking that we'd got a lot of official info pretty early on this one - I would say ATSB doing a good job with it. Not like some countries where you wait years to find out essentially nothing.

and until I see some engineering drawings, I'm not stepping foot on a TRENT motivated airframe, unless it is chocked, and I'm near an exit. But that's just me.

bear
And P&W ? [ http://cdn1.atp.com/ADs/pdf/102409.pdf ]

[...] cracking of No. 3 bearing oil pressure tubes, which could result in
internal oil fire, failure of the high-pressure turbine disks, [...]
Does that not sound spookily similar ?

And GE ? [ SB-10-20 - four actual uncontained failures inside two years ! ]

Any major engine mfrs I've missed ?

Also curious - what did you do after BA038 ? To me, this incident looks a lot more clear cut and fixable / manageable, after comparatively little investigation time. For BA038 there were major unknowns for considerable time (and arguably still are). Uncontained engine failure is survivable, with a little luck. Fuel cutoff to all engines leaves you needing a lot of luck (IMO).
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Old 6th Dec 2010, 21:29
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Subject to old engineer's review..........
My review shows your post (and a few others) contain right amount of "engineer's black humor". Or is there also "pilot's black humor"?

Why did I ever think I was the only one to notice that the air-cooler was conditioning the hot oil so it could heat the fuel...

As for cutting the Moutard, only in England would they not know that it is only the Grey Moutard that will cut it, not the 'poxy patch...

OE

Last edited by Old Engineer; 6th Dec 2010 at 21:49. Reason: Correcting the King's English
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Old 6th Dec 2010, 21:58
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Bearfoil
I think you misunderstood what I was attempting to say, perhaps I wasn't clear.
Indeed, the fan-LPT shaft is inside the IP shaft. The rigid coupling between the two is underneath and between bearings #3 and #4 as a reference point only. I said nothing about oil.
The IP shaft rigid coupling is located just aft of the #4 bearing but forward of the #5 bearing for location reference. It is this coupling that I think is cause for wear concern by the safety folks. Again, I did not mention oil.
Both couplings are axial spline couplings.
The only oil I mentioned is that which came out as a result of the stub pipe which failed and went somewhere it shouldn't have. This oil pertains to the #6 and #7 bearings that reside between the IPT disc ID and the OD of the IP shaft.

Hope this is clearer to you.

Turbine D
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Old 6th Dec 2010, 22:46
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I am indexing the bearings by type, not by numerical position. There are the Three Thrust (Ball) bearings, and the rest, rollers. I think I am located correctly, and that the #2 Thrust bearing is forward of the large Splined sleeve? As to oiling, I think the stub in question sprays the buffer cavity between #2 and #3 Thrust bearings?

Could well be wrong.

cheers, bear
 

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