Qantas A380 uncontained #2 engine failure
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They should have plenty of time to borescope the Trents. Just schedule the flights to time out passing thru the U.S. While TSA gropes 450 or so pasajeros, send the mechs to grope the engines
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Especially this Wednesday, what a cf to be!
JFZ90, CAAAD, Lonewolf50
Fellas. I will try my best to develop another approach, it is not my intent to frighten anyone. Sometimes I can't help thinking of the Black Knight, though.......
"Merely a flesh wound, nothing more". If others showed a little concern in public here, I could let go of a little 'canary in the mine.'
salud, 1700 hours, happy hour.
bear
JFZ90, CAAAD, Lonewolf50
Fellas. I will try my best to develop another approach, it is not my intent to frighten anyone. Sometimes I can't help thinking of the Black Knight, though.......
"Merely a flesh wound, nothing more". If others showed a little concern in public here, I could let go of a little 'canary in the mine.'
salud, 1700 hours, happy hour.
bear
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Titanuim is certainly NOT used in hot areas - and by hot I mean probably the whole HPC and aft. It's a very desirable material within its temperature limits, but not beyond. I could tell you of several "teething" problems with titanium circa 1966-1980 wherein service experience taught a harsh lesson.
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they won't be flying to and from LA for a while yet.
"The airline has imposed thrust limitations on the aircraft's troubled Trent 900 engines, so as to keep them well within safe operating parameters. This means that they won't be operating on the Los Angeles route in the immediate future."
Qantas A380 superjumbos to resume service | QF32 engine failure
"The airline has imposed thrust limitations on the aircraft's troubled Trent 900 engines, so as to keep them well within safe operating parameters. This means that they won't be operating on the Los Angeles route in the immediate future."
Qantas A380 superjumbos to resume service | QF32 engine failure
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QF Returns
Qantas will resume with the 380 flights to UK via singapore only.The trents will operate on reduced thrust as LH and SIN operate sowillnot do the Pacific route yet .You also should note that QF dont own the RR engines but rather RR have a complete supply and mtce package thru LH in frankfurt
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End of panic, then. The cause is identified as an oil fire and the AD checks imply an 'easy' fix. The conclusion must be that the turbine discs themselves are sound.
Time to buy some RR shares before they go up again (although the Chinese order has already achieved some of that).
Time to buy some RR shares before they go up again (although the Chinese order has already achieved some of that).
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This A380 will be returned to service
Mr Joyce apparently said of the plane:
Regarding the damaged Nancy-Bird Walton, it's repairable and would be returned to service, though the timing of its return was in the "medium term".
Regarding the damaged Nancy-Bird Walton, it's repairable and would be returned to service, though the timing of its return was in the "medium term".
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acbus1
Howdy. I cannot recall a single entry (here) that referenced a "defect" in the disc itself. Failure, yes, but not at its own behest. DevX suggested a fire in the location near the disc' mount on the shaft, hot enough to cause damage sufficient to precipitate the loss of IP. The AD (both of them) reference Oil Supply and Scavenge problems, which needed closely scheduled inspections. So is your 'relief' (lack of panic?) a result of the exoneration of a problem not entertained by the Authority?
re: disc. The actual metallic composition of the disc would be interesting. It was a surprise to me that some here hold Titanium as 'weak' in the face of fire (a relative thing to be sure). The IP doesn't normally get exposed to fire. If this disc is of insufficient design to bear an oil fire, the question becomes, should it be of other construction? My opinion is no. Prevent the fire, solve the problem?
cheers, bear
Howdy. I cannot recall a single entry (here) that referenced a "defect" in the disc itself. Failure, yes, but not at its own behest. DevX suggested a fire in the location near the disc' mount on the shaft, hot enough to cause damage sufficient to precipitate the loss of IP. The AD (both of them) reference Oil Supply and Scavenge problems, which needed closely scheduled inspections. So is your 'relief' (lack of panic?) a result of the exoneration of a problem not entertained by the Authority?
re: disc. The actual metallic composition of the disc would be interesting. It was a surprise to me that some here hold Titanium as 'weak' in the face of fire (a relative thing to be sure). The IP doesn't normally get exposed to fire. If this disc is of insufficient design to bear an oil fire, the question becomes, should it be of other construction? My opinion is no. Prevent the fire, solve the problem?
cheers, bear
barit1:
Thank you for restoring my vague memory. From what I looked up, my surmise is that compressor rotors are before the hot section and thus in a suitable zone for using Ti to take advantage of its many desirable material properties, to include str-to-weight advantage over steel, and greater corrosion resistance.
bear:
bear:
I don't think anyone holds Ti "weak in the face of fire," that's a nebulous phrasing at best. I think we are all aware that thermal conditions just aft of the explosive fuel and air mixture require materials that can stand those temperature extremes for sustained periods, as well as the expansion and contraction of "engine on / engine off" cycles without significant creep, strain, etcetera.
As I understand three spool engines, the IP turbine is being spun by hot gases (aft of the combustion can) that have just passed through the HP turbine, which is where combusted fuel/air mixture first hits blades and turns things. Next turbine stage to get hot gases would be the IP turbine wheel, and then the five stages of LP turbine.
That flow places the IP turbine in a section of the engine where the temps are likely higher than Ti normally sustains without some change to material properties. See barit1's comment above.
Perhaps I misunderstand the diagram and flow.
Fire prevention in that zone/area of the engine would be the way ahead for remedy ... which appears to be the direction the fix is headed, from what I can glean from some pages of this discussion.
Cheers, and very sorry I was unable to join you for happy hour. The sun is over the yardarm somewhere, though at the moment it's a bit past sunrise here.
Titanuim is certainly NOT used in hot areas - and by hot I mean probably the whole HPC and aft. It's a very desirable material within its temperature limits, but not beyond. I could tell you of several "teething" problems with titanium circa 1966-1980 wherein service experience taught a harsh lesson.
bear:
re: disc. The actual metallic composition of the disc would be interesting. It was a surprise to me that some here hold Titanium as 'weak' in the face of fire (a relative thing to be sure). The IP doesn't normally get exposed to fire.
I don't think anyone holds Ti "weak in the face of fire," that's a nebulous phrasing at best. I think we are all aware that thermal conditions just aft of the explosive fuel and air mixture require materials that can stand those temperature extremes for sustained periods, as well as the expansion and contraction of "engine on / engine off" cycles without significant creep, strain, etcetera.
As I understand three spool engines, the IP turbine is being spun by hot gases (aft of the combustion can) that have just passed through the HP turbine, which is where combusted fuel/air mixture first hits blades and turns things. Next turbine stage to get hot gases would be the IP turbine wheel, and then the five stages of LP turbine.
That flow places the IP turbine in a section of the engine where the temps are likely higher than Ti normally sustains without some change to material properties. See barit1's comment above.
Perhaps I misunderstand the diagram and flow.
If this disc is of insufficient design to bear an oil fire, the question becomes, should it be of other construction? My opinion is no. Prevent the fire, solve the problem?
Cheers, and very sorry I was unable to join you for happy hour. The sun is over the yardarm somewhere, though at the moment it's a bit past sunrise here.
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I'm not entirely sure why people are discussing the strength and durability of titanium. I'm pretty much 100% sure it will be a Ti alloy, with some interesting additions, maybe Mo, Mn, Ge, C even, to make it alpha stable. I don't know the actual "recipe" that RR use, but I am sure it has been well studied and well tested.
Any metallurgists onboard to help me with this?
Any metallurgists onboard to help me with this?
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Once upon a time there was a thread in Tech Log discussing the aspects of this engine failure, but that thread seems dormant now. Allow me a cross-post:
The present accident might lie somewhere between the first and second above. An oil fire in the bearing area could substantially weaken the IP shaft, leading to its failure and an IP disc decoupling/overspeed. At the same time, the hot IP shaft, being firmly coupled to the bore of the disc, will heat the mass of the disc above its normal operating temperature, degrading its strength and making it more vulnerable.
... There are several possible causes, which the metallurgical people are adept at sorting out.
First - most obvious - is overspeed. In that case, the reason for the overspeed must be nailed down, and/or an overlay control system installed to provide redundancy. Think of a helicopter engine encountering a geartrain failure in the helo transmission. Without such loss-of-load protection, the gear failure induces a overspeed in the engine.
Second - overtemperature operation can degrade the material properties to the point that the disc (or shaft) cannot sustain normal operating loads. (This is what happened in the collapse of the WTC towers on 9/11).
Third - a material defect in the disc may not be detected for a few hundred (or many thousands) of start/stop cycles - until it finally lets go. This is called Low Cycle Fatigue or LCF. A huge amount of quality inspection and process control goes into disc manufacturing, and the state of the art improves year-by-year. Even so, the predicted safe life (in cycles) becomes part of the certification standards; once a highly-stressed prime-reliable part reaches its LCF limit, it must be scrapped and replaced.
First - most obvious - is overspeed. In that case, the reason for the overspeed must be nailed down, and/or an overlay control system installed to provide redundancy. Think of a helicopter engine encountering a geartrain failure in the helo transmission. Without such loss-of-load protection, the gear failure induces a overspeed in the engine.
Second - overtemperature operation can degrade the material properties to the point that the disc (or shaft) cannot sustain normal operating loads. (This is what happened in the collapse of the WTC towers on 9/11).
Third - a material defect in the disc may not be detected for a few hundred (or many thousands) of start/stop cycles - until it finally lets go. This is called Low Cycle Fatigue or LCF. A huge amount of quality inspection and process control goes into disc manufacturing, and the state of the art improves year-by-year. Even so, the predicted safe life (in cycles) becomes part of the certification standards; once a highly-stressed prime-reliable part reaches its LCF limit, it must be scrapped and replaced.
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Thank you for restoring my vague memory. From what I looked up, my surmise is that compressor rotors are before the hot section and thus in a suitable zone for using Ti
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It occurs to me that differential heating might play a role in such a failure. This is purely speculation - I have no experience of aero engine design, nor any inside knowledge.
Under normal operation, the disk will be under severe tensile stress in a radial direction (from centripetal acceleration), and obviously it's designed to cope with that load. And the outer edge of the disk, exposed to hot gases will expand more than the centre. This would increase tensile forces in the radial direction, but compress the disk around the circumference. Thus normal heating would serve to somewhat mitigate cracking that might start at the outside edge and propogate inwards.
If you now heat the centre of the disk, as the oil fire might do, this will serve to expand the centre of the disk relative to the outside. This would put the outside of the disk under less compression (or greater tension) around the circumference. Just the sort of force that might allow a crack to start at the outer edge and propogate inwards towards the centre.
I don't know how strong this effect would be, but it might be one way the disk could fail, even if a fire was not hot enough to actually weaken the metal itself.
Under normal operation, the disk will be under severe tensile stress in a radial direction (from centripetal acceleration), and obviously it's designed to cope with that load. And the outer edge of the disk, exposed to hot gases will expand more than the centre. This would increase tensile forces in the radial direction, but compress the disk around the circumference. Thus normal heating would serve to somewhat mitigate cracking that might start at the outside edge and propogate inwards.
If you now heat the centre of the disk, as the oil fire might do, this will serve to expand the centre of the disk relative to the outside. This would put the outside of the disk under less compression (or greater tension) around the circumference. Just the sort of force that might allow a crack to start at the outer edge and propogate inwards towards the centre.
I don't know how strong this effect would be, but it might be one way the disk could fail, even if a fire was not hot enough to actually weaken the metal itself.
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In normal operation, the IP disc loads incoming air from LP into a smaller area, thus increasing the energy by compression, and a concomitant rise in T. My view of overspeed in this case, would be a "normalizing" event that reduced the load behind the IP. The LP overpowers the flow behind the IP, forcing it aft, and increasing its rate of rotation, since the mitigating Pressure of normal flow has diminished. (Proper airflow keeps all rotating mass in designed-for relative velocity limits)
The migration aft can force the Wheel into the Stator separating IP from HP. This causes increased friction, with the heat of the oil fire, the wheel fails in its mount, whilst shedding blades (at this point, probably through the Stator into the HP, rather than centrifugally out the Titanium case). The damage to Hub shows a possibility of such migration.
Any Turbine (or propellor for that matter) which 'falls behind' airflow, Windmills; without a variable Blade AoA, a "flat Pitch" starts an overspeeding event. What causes the loss of Pressure in the IP cavity? Fire? With fuel, (The Oil), compression, (patent), where is the ignition? Possibly failing bearings, with unlubricated metal/metal causing a flurry of sparks? If the ensuing Fire "Blew out" the normal fires behind, there is a source of low compression behind the IP.
Fzz: Most interesting. Puts a grip on the stresses in the wheel.
The migration aft can force the Wheel into the Stator separating IP from HP. This causes increased friction, with the heat of the oil fire, the wheel fails in its mount, whilst shedding blades (at this point, probably through the Stator into the HP, rather than centrifugally out the Titanium case). The damage to Hub shows a possibility of such migration.
Any Turbine (or propellor for that matter) which 'falls behind' airflow, Windmills; without a variable Blade AoA, a "flat Pitch" starts an overspeeding event. What causes the loss of Pressure in the IP cavity? Fire? With fuel, (The Oil), compression, (patent), where is the ignition? Possibly failing bearings, with unlubricated metal/metal causing a flurry of sparks? If the ensuing Fire "Blew out" the normal fires behind, there is a source of low compression behind the IP.
Fzz: Most interesting. Puts a grip on the stresses in the wheel.
barit1, roger the energy added to input air. My head is a bit sore figuring out how about six and a half tons of Ti end up in the Trent ... but it's not that important.
Thanks again.
Thanks again.