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Qantas A380 uncontained #2 engine failure

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Qantas A380 uncontained #2 engine failure

Old 12th Nov 2010, 16:35
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This question has probably been asked and answered but would the same engine failure have given the same damage and/or scare on a B747?

Last edited by garp; 12th Nov 2010 at 16:52.
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Old 12th Nov 2010, 16:46
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Originally Posted by garp
This question has probaly been asked and answered but would the same engine failure have given the same damage and/or scare on a B747?
I think the answer is the usual one... "depends".
By the time you're talking about an uncontained engine failure, all bets are off, as they were in this case.
I would say that an uncontained engine failure still does have the potential to bring down any airliner, if enough goes wrong at the wrong time.

CJ
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Old 12th Nov 2010, 17:04
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Saw BA 747 that had a roller let go quite badly many years ago.
The engine was virtually cut in half and bits of blade/disk / whatever was in the fuse and wing.Not as nearly bad as the 380 but so many variables can alter the outcome.
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Old 12th Nov 2010, 17:12
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I question this;

Faulty bearing box, and shrapnel came very close to striking the front spar.

Airbus says bearing box failed in Rolls engine - Yahoo! News
What is their source for this? It sounds like it came from a wild ass guess post on here.

Speaking of wild ass guesses... Now that more facts are in and continue to come in, who is willing to eat crow on their baseless, wild ass guesses and assumptions that have littered this thread? ie- QF maintenance?

Finally, has it been offically determined that there was a fuel leak?
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Old 12th Nov 2010, 17:14
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BBC whoopsie.

I think the answer is the usual one... "depends".
By the time you're talking about an uncontained engine failure, all bets are off, as they were in this case.
I would say that an uncontained engine failure still does have the potential to bring down any airliner, if enough goes wrong at the wrong time.

CJ
I think you're right there Christiaan, but how much more could go wrong? It seems to me - as an engineer from outside aviation, but with great and long term interest - that catastrophic failure of a turbine rotor disc is just about the worst thing that can happen to a modern jet engine. As has been discussed here, there is so much energy wrapped up in the assembly that it is virtually impossible to contain, as such, and thus primary safety - don't let it happen in the first place - is the only realistic answer.

It is true that the aeroplane suffered tremendous insult from all the flying shrapnel, but it has survived what could be considered a maximum credible accident - therefore all credit. Having watched a documentary a few days ago about how the A380 wing is constructed, it is difficult to see how a repair can be effected unless 'body repair' techniques and welding can be employed.

As for the difficulty in stopping the #1 engine, that does seem to be problematic - and endemic if the Ethiad A340 is any guide. Having said that, it does seem logical to have a control system that can detect a command control loss and maintain the last valid commanded power setting. However, since this leads somehow inevitably to the 'pouring tons of water into it to drown the buqqer' scenario, I'd bet a plumber would suggest a big, entirely manual 'gate valve' in the main fuel line of each engine. Accessed, of course, by a key on a long pole. Crude? Certainly, but then isn't waiting for the fire brigade to drown it rather less dignified?

During a Radio 4 news item I heard in the car this morning, the BBC reported that RR had; "established the component that failed which caused the oil fire in the Qantas A380 ...... " To be fair, this was corrected in the body of the item.

Roger.
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Old 12th Nov 2010, 17:32
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I think informed speculation is inevitable, and I post with that a given. The AD itself focuses on "restricted" restrictors. Coking and Carbon were identified. Now this might be a maintenance issue. If failure happens before scheduled work, it is not a maintenance issue, but a problem that escaped design or materials considerations, or specifying a part incorrectly. The important part of the first AD relates to the "return line"

This return line(s) had installed restrictors to control oil flow. These restrictors evidently pack up with combustion and heat byproducts that further restrict the flow of lubricating oil. If the flow "back" stops, the pump continues to supply oil, and the bearing compartment may fill with oil, to overwhelm the seals.

Whether this is what caused the oil fire and loss of IPT is not at all shown, but whether a cynic or an innocent, it provides a very convenient explanation for the entire kerfuffel. For two cents worth of Coke/Carbon, this engine failed, and all we need do is restrict the too big installed restrictors and perhaps pull out the light tube more often. Easy Peasy. Move along then? Were I RR, or all the players, this explanation allows everyone a big "relief". Perhaps a relief (oil) that should have been designed in earlier?

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Old 12th Nov 2010, 17:37
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How difficult would it be to measure input oil flow and output oil flow and look for an excessive difference to indicate an "incipient bearing box filling up" state? Or maybe infer that from existing oil pressure transducers?

Could that work? I note that R-R are saying that software changes are being made as well as hardware changes.
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Old 12th Nov 2010, 17:40
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Question:

How come no alert came on in the cockpit indicating a fire?
It's already very hot inside the engine. This is due to the inside of a turbine engine in operation having a fire continuously lit, and the increase in energy, and thus temperature, that compressing air creates as it feeds that fire to create thrust.

The failure happened inside an operating engine. Most fire detectors are IR detectors. Do you have an innovative design for a fire detector, versus an overtemperature detector (typically a thermocouple), that can distinguish between the fire and hot air that is supposed to be inside of it, and the fire/hot air that isn't?
Their early warning system is when a piece of blown rotor hits you in the head. That's not good.
No, it hit a wing.

See rest of thread on what some design and risk considerations are in re turbine wheels and failure prevention.
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Old 12th Nov 2010, 17:42
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Trent 700 : 2003

http://www.ntsb.gov/recs/letters/2006/a06_85_87.pdf

...The airplane sustained impact damage and holes in the left wing and in the fuselage (the airplane’s pressure vessel was not breached). Both thrust reverser halves of the No. 1 engine experienced ballistic impact damage and large pieces of the reversers departed the airplane. Examination of the No. 1 engine revealed that the intermediate pressure (IP) turbine case was ruptured 360° circumferentially and that the IP turbine disk had fractured from its drive arm and had liberated all of its blades. Further inspection revealed that the high pressure/intermediate pressure (HP/IP) turbine bearing chamber external vent tube had two burn-through holes.
Disassembly of the No. 1 engine revealed evidence of heat damage and distress in the HP/IP turbine bearing chamber consistent with the presence of an oil fire...
...National Transportation Safety Board’s investigation determined that the fire in the No. 1 engine was caused by carbon build up in the internal vent tube of the HP/IP turbine bearing compartment, which led to the liberation of the IP turbine blades...
Some similarity.

-0-
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Old 12th Nov 2010, 17:47
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@kristofera

pprune is possibly the most technically incisive forum on the internet, particularly where fault tree analysis is concerned. Therefore, any journalist researching such, would have to be 'clinically thick' not to reference the insight provided!

sAx
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Old 12th Nov 2010, 17:55
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Feathers McGraw:
How difficult would it be to measure input oil flow and output oil flow and look for an excessive difference to indicate an "incipient bearing box filling up" state? Or maybe infer that from existing oil pressure transducers?
Nice concept, and maybe do-able. Measuring oil flow into the sump is straightforward, a simple volumetric meter will give you litres/minute or whatever units are desired.

Output (or scavenge) flow is a different matter, much more volume, because it's perhaps 20% oil and 80% air. The air is the result of pressurized sump seals, intended to prevent oil leaking out. Don't know how you'd reduce this to liquid oil flow rate.

Another simpler approach is to monitor scavenge oil temperature. If there's a fire in the sump, it will soon be obvious on the gage.
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Old 12th Nov 2010, 18:11
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Just been looking at the ATSB site showing the aircraft flight path on google earth and the locations of the engine parts. Very interesting that the 'Turbine disc segment' was found by my calculations around 2.8 km from the position where the engine failed! Shows the extraordinary energies involved, and perhaps provides the answer to those who question why containment shields aren't designed for every part of the engine. I guess the recovered segment would have left the engine initially at some positive angle to the lateral axis; around 45 degrees would have given the longest 'lob'. So it begs the question, how far did the rest of the disc travel? Assuming a similar piece was ejected in more or less the opposite direction it seems to me that it will be much closer to the flight path. To avoid the aircraft structure it would have had a low or very high trajectory. In fact there seems to be evidence from the published photos that at least one major part of the disc went through the wingbox, thus absorbing some of the energy and reducing the distance travelled.
Incidentally, I don't like the look of what appears to be dense jungle just where they will be searching!
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Old 12th Nov 2010, 18:19
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All these people foretelling gloom and doom for RR are obviously too young to remember the first B747's sitting on the ramp in Seattle with concrete blocks tied to the nacelles waiting for P&W to sort out the ovalating problem
No I'm not, nor the gear coming up through the wing of one of the pre-production 707's !

" Those who ignore history are doomed to repeat it "
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Old 12th Nov 2010, 18:48
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Originally Posted by SRMman
Just been looking at the ATSB site showing the aircraft flight path on google earth and the locations of the engine parts. Very interesting that the 'Turbine disc segment' was found by my calculations around 2.8 km from the position where the engine failed!
I'd like to know why they reckon the parts yet to be located will be on the right-hand side of the track whereas every piece so far located is on the left-hand side

I know, maybe they haven't looked on the left-hand side eh?
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Old 12th Nov 2010, 19:06
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I'd like to know why they reckon the parts yet to be located will be on the right-hand side of the track whereas every piece so far located is on the left-hand side.
It's because a burst turbine disc will typically split in three segments, going three different directions. If two have been found on the left side, the third will be on the _____ (fill in the blank) side.
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Old 12th Nov 2010, 19:09
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The failure happened inside an operating engine. Most fire detectors are IR detectors. Do you have an innovative design for a fire detector, versus an overtemperature detector (typically a thermocouple), that can distinguish between the fire and hot air that is supposed to be inside of it, and the fire/hot air that isn't?
Usually a car engine which is burning oil is pretty obvious to the naked eye - there is blue smoke coming out of the tailpipe.
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Old 12th Nov 2010, 19:13
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Originally Posted by barit1
It's because a burst turbine disc will typically split in three segments, going three different directions. If two have been found on the left side, the third will be on the _____ (fill in the blank) side.
If that is correct and the disc split into 3 segments, then wouldn't one expect them to go off 120 degrees from each other?

Clearly 1 went Up and through the wing, so did one go off to port, but downwards (missing the outboard engine) and the other to starboard again downwards but thankfully missing the fuselage?
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Old 12th Nov 2010, 19:32
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Missing pieces

There looks to be quite a bit of low lying and likely boggy ground, maybe even mangrove swamp, in the area the ATSB plans to search for the IPT remnants. The missing pieces may be several feet underground/water. Perhaps there might be a mud spray pattern about the entry hole -- until washed off by rain.
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Old 12th Nov 2010, 19:40
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Metal detectors (think glorified beachcombers) sometimes work well.
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Old 12th Nov 2010, 19:42
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Thanks for your first post, SRMman - interesting deductions.

Also, without it, I wouldn't have found those excellent continuing updates on the ATSB site - which, I have to say, is slightly difficult to find one's way around!

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