Qantas A380 uncontained #2 engine failure
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GenDeveloper, You are about spot on with your statement: ''....... That leakage can lead to a fire, and a softened disk, which then maybe lets its blades go, and departs from the engine.''
What must not be forgotten is the fact that the shafts and bearings are also affected by the extra heat from oil firing which is also a contributory factor to the release of the disc.
With the T1000 disc failure, oil was the culprit again and I believe Boeing have been issued with new guidlines for engine cranking and subsequent running to avoid a repeat performance, but the press release concerning the test cell incident was, from an insider's point of view, interesting to say the least!
What must not be forgotten is the fact that the shafts and bearings are also affected by the extra heat from oil firing which is also a contributory factor to the release of the disc.
With the T1000 disc failure, oil was the culprit again and I believe Boeing have been issued with new guidlines for engine cranking and subsequent running to avoid a repeat performance, but the press release concerning the test cell incident was, from an insider's point of view, interesting to say the least!
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Gem Developer
Hello. My picture of turbine wheels has the accelerated gas passing through their chamber at the perimeter, not "through them". The gas passes through the "Blades"?
pedantic?
Blade Loss, timing.
The incipient failure I think was the IPT migrating aft and "nesting" on the face of the stator, which severed all the wheel's Blades, and quite likely rapidly. While an Oil fire is hot, and may have caused some shaft and wheel distortion problems, the heat produced in a mating of two wheels with a dramatic difference in RPM may suggest alarming Heat also. The heat signature on the IPT rotor, which is under discussion ( as a "shape" ) , looks from my experience to be 23-25hundred degrees.
I think it's been mentioned that the first AD referenced "Oil Relief" circuits that needed inspection for clogging vanes, that could over-pressure the bearing race, and cause a fire. (Coking and Carbon, as above). In addition, as GD reports, the drag on the wheel "could force" the turbine wheel aft. After losing blades, and opening its well to Stall, a reversal in airflow would force the IPT forward, Bladeless, to allow Combustion products to blow into the LP well, then out the Thrust Stator, depositing the telltale "Soot" on the nacelle. The forward migration followed by a reversal to aftward, could produce some impressive loads on the shaft, from elliptical stress (unbalanced). These reversals, depending on number, (if any), would hasten the failure at the interface with Shaft two.
It starts to come into view where the little bits had the energy to "shot Peen" the IPT.
bear
Hello. My picture of turbine wheels has the accelerated gas passing through their chamber at the perimeter, not "through them". The gas passes through the "Blades"?
pedantic?
Blade Loss, timing.
The incipient failure I think was the IPT migrating aft and "nesting" on the face of the stator, which severed all the wheel's Blades, and quite likely rapidly. While an Oil fire is hot, and may have caused some shaft and wheel distortion problems, the heat produced in a mating of two wheels with a dramatic difference in RPM may suggest alarming Heat also. The heat signature on the IPT rotor, which is under discussion ( as a "shape" ) , looks from my experience to be 23-25hundred degrees.
I think it's been mentioned that the first AD referenced "Oil Relief" circuits that needed inspection for clogging vanes, that could over-pressure the bearing race, and cause a fire. (Coking and Carbon, as above). In addition, as GD reports, the drag on the wheel "could force" the turbine wheel aft. After losing blades, and opening its well to Stall, a reversal in airflow would force the IPT forward, Bladeless, to allow Combustion products to blow into the LP well, then out the Thrust Stator, depositing the telltale "Soot" on the nacelle. The forward migration followed by a reversal to aftward, could produce some impressive loads on the shaft, from elliptical stress (unbalanced). These reversals, depending on number, (if any), would hasten the failure at the interface with Shaft two.
It starts to come into view where the little bits had the energy to "shot Peen" the IPT.
bear
Last edited by bearfoil; 11th Nov 2010 at 17:13.
There are many possible scenarios to this, and all well known and understood by the manufacturer. The evidence is in the remaining parts both the disk and the engine.
Friction is not enough to fail the disk, an oil fire is
The B747 QF that occured out of LAX failed in the same area but tangled the blades and vanes together adding both a braking action as well reducing the driving torque.
Other features at play would be the stretch of the disk either being absorbed partially by the case or releasing the blades from their slots and significantly reducing the load on the disk.
Taken together in light of the well demonstrated tolerance of the Rolls design in the earlier QF incident the loss of the disk in the A380 was a surprise. The rotor hardware is not easy to change so my bet is that the final fix will be on keeping the oil where it belongs.
Friction is not enough to fail the disk, an oil fire is
The B747 QF that occured out of LAX failed in the same area but tangled the blades and vanes together adding both a braking action as well reducing the driving torque.
Other features at play would be the stretch of the disk either being absorbed partially by the case or releasing the blades from their slots and significantly reducing the load on the disk.
Taken together in light of the well demonstrated tolerance of the Rolls design in the earlier QF incident the loss of the disk in the A380 was a surprise. The rotor hardware is not easy to change so my bet is that the final fix will be on keeping the oil where it belongs.
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I disagree, though with a caveat. Friction as heat won't melt the disc, (nor would much). Friction is my candidate for the instantaneous lock, IPT to Shaft, that loosed the wedges of Wheel we see (actually just one that was found thus far) through the engine's casing. I say this because I notice an "undamaged Perimeter" of the "Wheel". Without Blades, its makes no thrust, and is not affected by airstream reversals. The loss of the wheel was concentrated on the Hub, and Shaft face, it's where the Wheel "Broke Apart". So Heat, Oxidation, and Humungous Centrifugal force at the Hub/Shaft, Bearing Seal, Etc.
Think "Friction Stir". Focal Temps at the join of two dissimilar metals can be quite alarming.
Your comment re: "Keeping the Oil in its place". Natch. Please let's don't entertain a fix that involves placing drums under the 2nd Stage at each Gate, not like the "earlier" 'Pratts'
. Beyond my pay Grade, but if the fix is a mitigation composed of "Seal, Relief, Return and Oil Delivery" Mods, then nothing of grave concern presents. RR makes Primo Power, always has, always will. If SIA is only swapping three, where did the spares come from? Assuming that if it is the same glitch (as the 972), the repair may be 'simple' and 'straightforward'.
cheers,
bear
I disagree, though with a caveat. Friction as heat won't melt the disc, (nor would much). Friction is my candidate for the instantaneous lock, IPT to Shaft, that loosed the wedges of Wheel we see (actually just one that was found thus far) through the engine's casing. I say this because I notice an "undamaged Perimeter" of the "Wheel". Without Blades, its makes no thrust, and is not affected by airstream reversals. The loss of the wheel was concentrated on the Hub, and Shaft face, it's where the Wheel "Broke Apart". So Heat, Oxidation, and Humungous Centrifugal force at the Hub/Shaft, Bearing Seal, Etc.
Think "Friction Stir". Focal Temps at the join of two dissimilar metals can be quite alarming.
Your comment re: "Keeping the Oil in its place". Natch. Please let's don't entertain a fix that involves placing drums under the 2nd Stage at each Gate, not like the "earlier" 'Pratts'
. Beyond my pay Grade, but if the fix is a mitigation composed of "Seal, Relief, Return and Oil Delivery" Mods, then nothing of grave concern presents. RR makes Primo Power, always has, always will. If SIA is only swapping three, where did the spares come from? Assuming that if it is the same glitch (as the 972), the repair may be 'simple' and 'straightforward'.cheers,
bear
Last edited by bearfoil; 11th Nov 2010 at 17:30.
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Replacement Engines
I've seen comments on this thread suggesting a "shortage" of replacement engines and multiple aircraft out of service, but I assume that with cannibalization only one aircraft need be grounded per 4 "pulled" engines? If this is the case, would a cannibalized pool be shared between the operators to keep the maximum number of aircraft in operation regardless of operator?
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lomapaseo
... so my bet is that the final fix will be on keeping the oil where it belongs.
Two things that no-one seems to have commented on. Am I right that the HP spool of the Trent revolves in the opposite direction to the IP and LP stages, au Pegasus? Does that mean that there are any intershaft bearings and seals that are really having to whizz around, as they have the combined relative speed? Nice to think that the Trent core could be the basis of a re-engined Harrier... my, would that go...
And no-one has commented on my question on whether the operators all are using the same synthetic turbine oil... or whether QF is on one company's and SQ and LH on another’s. Despite the similarity in base fluids, the differences in final formulation can make a difference in propensity to form deposits and carbon up seals, I seem to recall. And carboned-up seals usually don't seal very well, they leak.
Last edited by GemDeveloper; 11th Nov 2010 at 18:54.
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For a start there are 3 spare engines (presumably undamaged) on the airframe that suffered the failure
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Originally Posted by SandyW
For a start there are 3 spare engines (presumably undamaged) on the airframe that suffered the failure
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GemDeveloper, you are correct in your assumption about the HP system being contra rotating, and the recommended oil is BP 2197. Whether or not operators decide to use that oil is of course up to them with the relevant caveat applied.
http://www.hascooil.com/images/pdfs/...o_oil_2197.pdf
http://www.hascooil.com/images/pdfs/...o_oil_2197.pdf
Re Herald Sun article
"The crew also had to rely on gravity for the undercarriage to drop and lock into place".
"The crew also had to rely on gravity for the undercarriage to drop and lock into place".
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"The crew also had to rely on gravity for the undercarriage to drop and lock into place".
Throughout my long career, I've never heard of "gravity" failing so I guess that the Journo worded it this way just to make it sound more sensational. They no longer appear to have any respect for their profession.
What's wrong with what the journalist said?
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"Had to rely on gravity"..... seems a proper and probably accurate phrase in this instance since apparently the crew could not rely on normal hydraulics to lower the rollers.
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Re: ATSB is THE source.
I want to second NOTanAM's post (#772 - http://www.pprune.org/rumours-news/4...ml#post6053931) recommending the ATSB site. For those interested, updates are provided here and all investigation information and links are at the investigation page.
In my view the ATSB are very professional. While I'd usually be concerned about a national body investigating an incident involving their own nation's airline, in the case of the ATSB I've never had cause for that concern. There are a number of things I like about their process. Firstly they are reasonably open with updates being provided before official reports. Secondly, they are not about apportioning blame. Rather they are looking for all the holes in the "swiss cheese model". They will report on all the factors. Thirdly their reports are comprehensive. There is no lack of detail. So even if someone was concerned about national interests influencing the investigation, the detailed facts allow other commentary.
Their factual report is due by 3 Dec and that ought to be good reading. Keep an eye on the website.
In my view the ATSB are very professional. While I'd usually be concerned about a national body investigating an incident involving their own nation's airline, in the case of the ATSB I've never had cause for that concern. There are a number of things I like about their process. Firstly they are reasonably open with updates being provided before official reports. Secondly, they are not about apportioning blame. Rather they are looking for all the holes in the "swiss cheese model". They will report on all the factors. Thirdly their reports are comprehensive. There is no lack of detail. So even if someone was concerned about national interests influencing the investigation, the detailed facts allow other commentary.
Their factual report is due by 3 Dec and that ought to be good reading. Keep an eye on the website.
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Note that the crew also "had to rely on gravity" to bring the plane down out of the sky and onto the ground, and, once stopped, they had to rely on gravity to keep the plane on the ground while everyone got off it. Somehow these didn't get a mention...
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"The way it's written implies that gravity is in some way unreliable..."
Well, in a sense it is. Though certainly Airbus is perfectly able to design gear that lock down if "manually" extended, a less well-designed airplane can have gear that free-falls but, because of excess airspeed, fails to engage the downlocks. If that happens--it's a consideration on certain GA aircraft--you don't have hydraulics or electric jackscrews to push the gear into the downlocks once you've slowed adequately. And no, they sometimes won't simply click into place as you slow, because the downlocks require something of a thump--free fall under gravity--to engage.
You're being too hard on the journalist.
Well, in a sense it is. Though certainly Airbus is perfectly able to design gear that lock down if "manually" extended, a less well-designed airplane can have gear that free-falls but, because of excess airspeed, fails to engage the downlocks. If that happens--it's a consideration on certain GA aircraft--you don't have hydraulics or electric jackscrews to push the gear into the downlocks once you've slowed adequately. And no, they sometimes won't simply click into place as you slow, because the downlocks require something of a thump--free fall under gravity--to engage.
You're being too hard on the journalist.
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Note that the crew also "had to rely on gravity" to bring the plane down out of the sky and onto the ground, and, once stopped, they had to rely on gravity to keep the plane on the ground while everyone got off it. Somehow these didn't get a mention...