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Qantas A380 uncontained #2 engine failure

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Qantas A380 uncontained #2 engine failure

Old 9th Dec 2010, 11:00
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There is a great interview with the Qantas Senior Check on the Royal Aeronautical Society website giving a blow by blow account of what it was like on the flightdeck. You have to be a member to sign in to read it. Join up now!
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Old 9th Dec 2010, 11:10
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EXCLUSIVE - Qantas QF32 flight from the cockpit | Aerospace Insight | The Royal Aeronautical Society

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Old 9th Dec 2010, 12:32
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Originally Posted by NigelOnDraft

I am open to suggestions, but cannot see what help this is? It would be a very subjective decision making process... but above all, in my simpleton pilot view, if a fragment has gone through my main spar either the wing is strong enough to continue flying or it is not. If not, it will have fallen off, so no decision necessary If it is strong enough, we are only getting lighter as we burn fuel, and us airline types tend to manoeuvre gently all the time, so "limiting 'g'" is not really necessary advice.
I agree that it will be hard to evaluate properly the extent of the damages just by looking at the wing, and this is the weak point, and it will be different every time. However, I think we can go a bit more in depth than a one or zero analysis..
OK the wing hasn't come off but for how long ? You of course will fly at VA and be gentle on the controls, but what about other factors like the atmosphere : what about loads induced by thermals, wind shifts, orographical turbulence, wake turbulence?..., what about the loads induced by any degraded flying controls?,... I think all of this has to be taken into account and without information, I personnally would feel more confident to stay not too long in the air, if possible (and depending on what's ahead of the runway, accept an eventual slight runway overshoot)
ps : also, without fuel jettison, are we really getting much lighter in a short timeframe ?
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Old 9th Dec 2010, 12:48
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Re: Spline Wear AD. The document references accelerated wear at the "Abutment" Face. From the drawing, the "Trough" cut for the Spline shows a lazy exit for tooling at the aft, sharp end of the feature. Is this then the "Abutment" (Terminus) for Spline Travel? The "Crest" of the Spline is to be measured as often as every third Flight. Is the Spline subject to "sharpening" against the stop? Does this allow the Shaft to wander aft? It is of course far more difficult to make a "Pocket" of the Trough end, and expensive, yet a squared stop would absorb more energy, longer? What do you think?
 
Old 9th Dec 2010, 14:46
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Engine 4 also non-normal

One thing that came out of the interview that I was not aware of was that Engine 4 was also in a degraded mode.
The Engine 2 was shut down. Part of the damage caused Engines 1 & 4 to go into a ‘degraded’ mode. The engines were still operating and Engine 3 was the only engine that was operating normally.
So number 2 burst, chunks cut some wiring to number 1 which goes in to a degraded mode. Number 3 is running fine, but number 4 seems to have gone into a similar degraded mode as number 1. Anyone understand why this might have happened? Could it have been due to the loss of the electric busses or one of the other systems? Or did the autothrottle hold number 4 back to balance the reduced thrust on the other side given that one engine was gone and the other not working 100% in which case I'm seeing similarities to Kegworth on this bit?
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Old 9th Dec 2010, 14:53
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engine degraded mode on 1 & 4

I think it is to prevent thrust asymmetry between 1 & 4.

But what I would liked to know is what does "engine degraded mode" mean?

What cant be done with the engines when in degraded mode that could be done in normal mode?
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Old 9th Dec 2010, 15:02
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I think from the interview, AutoThrust was inop. So if manual thrust only, AB would call it "degraded". "Less than optimum", but perhaps not a very serious consideration?
 
Old 9th Dec 2010, 15:13
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If autothrust not being available was the case then why was #3 not in degraded mode?
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Old 9th Dec 2010, 15:18
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I think from the interview, AutoThrust was inop. So if manual thrust only, AB would call it "degraded"
Likely not quite correct. A320 etc. have a "degraded mode", used when some sensors / systems are lost. Loss of ATHR is likely a consequence of degraded mode, not the cause. Suspect A380 similar.

In fact, some of the iPhone cockpit pics show the different displays for #1 / #4 to #3.

"Less than optimum", but perhaps not a very serious consideration?
Again, if like A320, true.

Noteworthy the crew elected not to use #1/#4 more than necessary i.e. they left them at 1 fixed power setting, and controlled thrust via #3. Will be interesting if this is trained for technique, or one that was just found/judged to most appropriate on the day.

NoD
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Old 9th Dec 2010, 15:36
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Cant verify this;

"Engines 1 and 4 indicating ‘degraded mode’ – which means no N1 rating limit. Requires all engines to be switched to ‘Alternate’ mode with a 4% maximum thrust loss."
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Old 9th Dec 2010, 15:45
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Poor syntax. Meant "Degraded Mode" leading to no ATHR. yep.
 
Old 9th Dec 2010, 18:46
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The FADEC has three modes. Normal, alternate and degraded. If two engines go into degraded mode, then the auto thrust is lost.

Correction. 3 engines degraded, no a/thr.

Last edited by mrdeux; 10th Dec 2010 at 19:37.
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Old 9th Dec 2010, 19:44
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Bearfoil

There is a final report out regarding the Trent 700 uncontained engine failure on an aircraft departing Miami, FL (7 yrs. ago if you can believe). However the content is an interesting read, particularly concerning the IPT rotor disc and failure mode. In this incident the disc stayed in the engine, although all the turbine blade exited the disc.

DCA04IA002

A summary of this incident is on the Aviation Herald and the writer references the A-380 incident by mentioning the location of the fire is the same on both; Writer's conjecture, or actual knowledge?

At any rate, I have been leaning towards the bearing area beneath the IPT disc as the start of the event, rather than the IP shaft forward bearing complex.

Regards,

Turbine D
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Old 9th Dec 2010, 20:01
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Bearfoil


old engineer

Re: Spline Wear AD. The document references accelerated wear at the "Abutment" Face. From the drawing, the "Trough" cut for the Spline shows a lazy exit for tooling at the aft, sharp end of the feature. Is this then the "Abutment" (Terminus) for Spline Travel? The "Crest" of the Spline is to be measured as often as every third Flight. Is the Spline subject to "sharpening" against the stop? Does this allow the Shaft to wander aft? It is of course far more difficult to make a "Pocket" of the Trough end, and expensive, yet a squared stop would absorb more energy, longer? What do you think?
What I'm thinking right now is that perhaps the source of the "oil fire" can be approached by considering the energy that the splined/geared coupling might have absorbed, and when and why it might have done so. (I'm deliberately using "splined" and "geared" interchangeably. It would take a full post to say why; but briefly a patent for AC application of such a coupling makes the same comment-- the GE patent?)

I'm now looking at there being a distinct possibility that the energy dissipated at the point of spline damage could well have caused the coupling to have ignited its own lubrication. For example, a spur gear running in a case containing an oil bath will often require an arrangement to cool the oil. This is true even though involute spur gears are 98% efficient. The other 2% can be a real problem. Our coupling has involute gear teeth/splines (again it is correct to equate the terms); the helical form of about 30 degree lead is just a twisted form of a spur gear.

If we lose the spline/gear teeth (say the oil fire they lit starts to soften them), and suppose we take at face value the AD comment that the IPT may then move rearwards (ruckwarts gegen, perhaps-- German is the language to discribe such events... fewer softening words), then the sequence of events is: Spline/gear overheats; its lubrication ignites, weakening splines-- mild steel would lose 1/4 its strength in a hot kitchen oven; splines are sheared completely off; IPT moves rearwards into LPT inlet vanes; IPT section explodes, oops bursts; in the burst the stub oil line to the IPT aft bearing is dislodged, breaking the already fatigue- cracked oil-inlet boss.

Post hoc, ergo propter hoc, eh? I think I've got all the events of the official communiques, just in a different order. Alright, I did add loss of the splines/gears. But the official preliminary ATSB report does show them missing, doesn't it? At least, posters are saying they can't see the splines. So the question remains, what event is post hoc, and what is propter hoc? (For those without a misspent youth, "came after, therefore was because of".) Not to mention, are the splines there, or not?

I did discover a few things about the Trent 1000 as used on the B787, in 6 US-certified versions, presumably those used on the test airframe. Some of this may shed some light on the 972 engine which failed:

0. L & dia of engine 15'-6" & just under 12'-6" dia.
1. The wt of all versions is 12,710.
2. The thrust of all versions is different, range about 20%.
3. The original version thrust is near but not at the top of that range.
4. Max thrust is permitted for 5 min; 10 if one engine out. Data ff w/aux's:
5. Max thrust TO is 74511; max cont 69523 lbs-- most powerful version.
6. Max thrust TO is 69194; max cont 64722 lbs-- original version engine.
7. Max temp TO, at entrance vanes to LPT, is 900-C (5/10 min as above).
8. Max continuous temp is 850-C.
9. Max overtemp 920-C, limit 20 seconds. Ascertain why and correct.
(Suggests to me 20 sec to see trend, decide, & shut down).
10. LPT shaft 100% rpm's = 2683. Max permissable rpm's follow:
11. LPT max setting N1 = 98% (or 2629 rpm), rpm's not reported to pilot.
12. LPT max setting N1 = 96.5% (or 2589 rpm) if fwd speed below 60 kts.
13. LP stages: compressor, 1; turbine, 6.
14. Fan diameter: 112 inches.
15. Shafts: LP and IP rotate CCW; HP rotates CW; looking from rear.
16. Engine is fitted with vibration sensor; sends to AC (then pilot, or HQ?)
17. Oil pressure 30-75 psi.
18. There is a list of lifetime-limited parts.
19. Engine does not supply compressed air for airframe ventilation.
20. Engine not rated for thrust reverser operation.
21. Engine not eligible for ETOPS.
22. Engine not rated for operation with faults present in the control sys.
23. Fuel inlet (@engine) min temp: minus 25-C. (I infer FOHE now OFHE)
24. TC holder is RR plc, Derby.
25. Use is: OI-Trent 1000-B787.

I'm going to try to answer your specific questions ASAP. I don't know exactly where and in what form the stops are, and have been trying to find that out. I do think that on disassembly the LPT section is simply unbolted, and the shaft just pulls rearward with it, without any restraint except drag or slight friction. This would not be true of the splined/geared collar (of the coupling) into which its spline/gears fit; the collar must be restrained in some way, either to the forward shaft, or locally to some other element or structure. The collar being restrained by the forward shaft would however re-raise the same question you asked.

That is why I introduced the conventional geared coupling idea. These are so ancient and so not under a lid of trade-secrecy that the answer to the stops might be found there. The problem is the same; the solution might be similar.

I do now know (I didn't at my last post) that this shaft coupling is not a "curvic" coupling. Curvic couplings do occur in this engine (I assume, because it is so common in the ff use), but are used to join the centers of the disks (that carry the vanes) within a stage. They are like cups with gear teeth on their rim. Yes, gear teeth, although of a special form that would (possibly) permit the whole stack to curve without losing concentricity (ie, if my idea of the whole engine casing, LPT shaft and all, flexing into an arc under a max thrust TO, is at all true). They are a kind of bevel gear laid out flat as a pancake-- invented by Gleason Gear 60 years ago for keeping the tool posts on big lathes lined up true when taking a heavy cut, or somesuch.

Joined together, these "curvix" widgets also form a tunnel of sorts over the shafting. Then, perhaps, the hollow shafts can be more effectively be air-cooled. But I'm sure the shaft coupling is more on the idea of the GE-patent coupling with the parabolic gears/splines. That'll take a whole post, too. Well, a long post but I wanted to throw out some grist for ideas.

OE

Last edited by Old Engineer; 9th Dec 2010 at 22:03. Reason: #11,12-fwd spd below 60 kts; grammar para 3.
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Old 9th Dec 2010, 20:09
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The FADEC has three modes. Normal, alternate and degraded. If two engines go into degraded mode, then the auto thrust is lost.
But when the wiring from one engine/between engines is severed, how is one FADEC to know which other engines/components are working or failed?
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Old 9th Dec 2010, 21:43
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The gear comment (gear/spline) I take to mean that the two shafts rotate slightly as the axial movement "screws" one shaft into the other, dependent on "Drive/Driven" mode.

It is a parse, and the "ratio" is Linear/Radial related? This I assume accomplishes a constant effacement, to prevent "Clash". (Take up of slop expressed as "Clearance").

The Max Temp. Timing is in the Manual. I assume when this a/c ECAMMED "Turbine Overheat", there is a 30 second interval for monitoring, and action. The Screen then alerted Engine #2 FIRE, briefly, and returned to "OH". How can the RR1000 be "ETOPS U/A" on a Massive Twin (787)? Stumper, that.

There are no Public records of the IPT Shaft splines, only reference that the parts (with photographs) were sent to Derby.

The splines that are in public view are at the front of the aft LP Shaft, just in front of the "Soot" deposit? (If any).

From Ferpe's diagram, the offending Oiler is located at Rollers 6, 7. We have no discussion of a relationship between aft HP/IP, and forward HP/IP cavities (re Fire?). From the sooty deposit (Howdy!), I take evidence of combustion at HP/IP forward bearing Buffer. Due to my unfortunate hyperfocus on the IP Wheel, I haven't delved too far into Oil Fire at IP Wheel only, as the cause of "Burst". The AD and the Oiling to me seem quite likely linked, Spline wear accomodating aft drift into the Stator ring (Mount). If the Spline issue is separate in this case, then an Oil Fire at the front of the IP Disc at the Hub, causing plasticity and drift as the Drive Arm folded "Over" itself, from Turbine D. If there was a similar "Circumferential Crack" at Drive Arm (from the '03 incident) then it would be fair to assume a fold back of Drive Arm remnants as the Turbine separated at that location? It is clear from Rolls' statements that they are "leaning" toward "single component Failure", at least so far?

cheers bear

Last edited by bearfoil; 9th Dec 2010 at 22:01.
 
Old 9th Dec 2010, 21:54
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Turbine D

From your reference, both incidents happened soon after TO. The "Coking" problem appears to have been seen before, then. The passengers claim of White and Orange Flames remind of an earlier post stating "Titanium burns White"? I'm looking intently at the "JFZ90" image (page 70) to see if an IPT (locale) Fire can travel forward along the Shaft to involve the forward bearing assembly, and Splines. (Or ViceVersa).

cheers bear

Last edited by bearfoil; 9th Dec 2010 at 22:56.
 
Old 9th Dec 2010, 22:53
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Thrust Control on Finals and Wing Strength

The quality of this topic is very impressive - particularly from the engineers. Thank you. Here are a few insights.

Thrust Control on Finals

Thrust Control - Good guessing but lots of noise here ...

Eng 3 in ALTN Mode (N1 with -4% thrust protection) (Due EEC having insufficient valid signals to calculate TPR)

1+4 EEC errors logged. Degraded mode is purely due to loss of sensor inputs/EEC errors. Think of it as the engine in Direct Law (no thrust protections!) (Due EEC not able to calc TPR demand. So N1 commanded as a function of TRA and altitude)

One engine in a degraded mode does not cause another symmetrical engine into degrade mode. Airbus never matches thrust - it's against their philosophy "manual thrust is manual thrust!" - not like pseudo Boeing "manual thrust".

So 1 & 4 in Degraded (think Direct Law) Mode (no protections)
3 in ALTN mode (think Alternate Law with protections)
2 was in Degraded mode (not surprising given there were so few sensors left)

NO engines were in a normal mode.

This is why 1,2,4 had N1 centric displays (Degraded) and 3 had an TPR centric display (ALTN) (though thrust set via N1 with 4% pad).

Thrust control on 1,3,4 all 100% correct (but differing protections)

Auto Thrust inop due to MORE THAN 2 eng in Degraded Mode

1+4 thrust levers held constant to: (not in any manuals)
  1. permit very accurate (vernier) total thrust -> speed control on finals
  2. minimise thrust missmatch->yaw->roll->flight control demand on finals with thrust changes (ESSENTIAL when little excess roll control available)

1+4 WAS NOT held at constant thrust due to them being in Degraded Mode (illogical).

Conclusion: The three level 380s thrust system has incredible fail operational capability.

WING STRENGTH
  1. Not a problem. Wing loaded ~23% to ultimate limit (1.1/2.5 X 440/569 X 1/1.5) (Max 20 deg AOB/MaxG, Wt/MTOW, Ultimate Load factor)
  2. Airbus supercritical wings are VERY aft-loaded.
  3. Leading spar only contributes 5% strength - it's more scaffolding for the leading edge

Last edited by 35YearPilot; 18th Dec 2010 at 21:43.
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Old 9th Dec 2010, 23:00
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1+4 WAS NOT held at constant thrust due to them being in Degraded Mode (illogical).
According to one of the pilots of the flight;

With Engine 1 and 4 being in degraded mode it was discussed whether or not to really use those actively and the decision was made to leave them in a particular power setting and control the aircraft’s speed with Engine 3 only – the one engine that was in a normal mode.
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Old 10th Dec 2010, 07:08
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Massive crisis mismanagement at Qantas, they seem to be waiting for 11 perfectly good engines to be modified to latest build standard or replaced. Idiots! I would not think for one minute that they are entitled to the special treatment they are demanding. As far as the airline is concerned the engine is a black box – just put the oil in here and push this lever to go forwards – you don’t need to know the build standard, just check the certificate.

All this nonsense to cover their back sides after their really stupid decision to ground everything.
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