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Qantas A380 uncontained #2 engine failure

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Qantas A380 uncontained #2 engine failure

Old 4th Dec 2010, 09:46
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Originally Posted by rottenray
I hate when people do this... But is there a source for this?

I haven't heard anything solid about the IP turbine going overspeed - if you have, please share!



Cheers!
I don't think there is an official source - yet, but if any such driven disk becomes disconnected from its load it will accelerate rapidly, and will break sooner or later. The better made, well balanced and strong will fail at a higher speed. So just apply Occam's razor and dismiss this with difficulty - but those specialists with access to the parts found will know for sure.

See the Sioux City DC-10 crash for an example how a fan disk can fail due to old material defects. I wonder if the A380 has hydraulic fuses as recommended in the report of that 20 year old accident?

Last edited by sensor_validation; 4th Dec 2010 at 10:01.
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Old 4th Dec 2010, 11:16
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I think he passed his check to line.

. . . and I suspect that every simulator ride until he retires will be a walk in the park.

As I posted earlier, almost certainly the newbie 380 Capt was being checked to the line by the newbie A-380 check captain, who was possibly being checked out by the equally newbie A-380 line manager, or whatever terminology is in use today.

What a fantastic crew to exercise team management (CRM) with!

OK. Itís time to switch off the non-aviator's ceaseless hypothetical-ising (sic), and read the ATSB's initial report, via those fine journoís at Flight, and reports following. This is how it is done. Slowly. Carefully. Getting the facts straight.

It's here:
Multiple systems failures on QF32 after engine blow-out , et al.

Now be quiet, and be glad it wasn't you on your check-to-line.

Bloody magnificent effort.
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Old 4th Dec 2010, 12:28
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Rottenray .. re IP overspeed

You are correct re IP overspeed. Refer to ATSB preliminary investigation report AO-2010-089 figure A-2 on page 48. Note that it was the HP shaft (N3) that exhibited an overspeed condition. In addition, this was preceeded by an exceptional increase in N3 first order vibration. Those flight deck indications would undoubtedly have prompted a precautionary shutdown had there been sufficient time in which to respond.

Sensor Validation makes a valid point however!
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Old 4th Dec 2010, 14:34
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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???
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Old 4th Dec 2010, 15:52
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Blade Master:
In Post 1375, the ball bearing carrying the fan load, is shown underneath the IPC. How are the stationary races anchored to the engine case? Is there a rearward traveling extension shaft coming from the 2 roller bearings near the fan? Any one have a diagram or links to other web pages showing more detailed drawings or photos of this engine type? thanks.
Please refer to my post #1447.
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Old 4th Dec 2010, 16:56
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As I posted earlier, almost certainly the newbie 380 Capt was being checked to the line by the newbie A-380 check captain
hmmm
The PIC had a total experience of 15104 hours thereof 570 on the A380
The second quote says to me that the PIC was undergoing an annual line/route check, rather than being 'checked to line'.
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Old 4th Dec 2010, 16:59
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To attempt to put some things into perspective:


From the Australian TSB

Following a normal takeoff, the crew retracted the landing gear and flaps. The crew reported that, while maintaining 250 kts in the climb and passing 7,000 ft above mean sea level, they heard two almost coincident 'loud bangs', followed shortly after by indications of a failure of the No 2 engine.

The report identifies an overspeed-related failure in the intermediate pressure turbine disc in the aircraft's No 2 engine. Sections of the fractured disc and other engine components penetrated the aircraft's left wing and a number of other areas on the aircraft, resulting in significant structural and systems damage to the aircraft.


I would suspect the first bang was a compressor stall (HPC) followed quickly by the disintegration of the IPT disk and surrounding structure. If you look closely at the pulled LPT module, you are looking at the LPT first stage blades. I think in a normal engine, you would be looking at the LPT first stage nozzle ring, but in the failed engine, all the vanes are gone including the section of casing that held them in place. The LPT stage one blades are fractured at various points, some airfoils completely missing, others partially missing. I suspect some of the nozzle vanes went into these blades. 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.

If you look at the photo of a section of the recovered IPT rotor disk, I think you are viewing the side that faces the HPT. I say that because there are 8 turbine blade dovetails still in the slots and I think you can detect the protrusion on the dovetails that keep the blades from moving aft. There are 47 empty slots, but no broken posts, at least in this section. I don't see any evidence of molten metal splatter, but some slots show evidence of brick or masonry debris embedded as the disk crashed through a brick wall. It is a classic example of a bore failure from overspeed.

From the Australian TSB

While the analysis of the engine failure is ongoing, it has been identified that the leakage of oil into the HP/IP bearing structure buffer space (and a subsequent oil fire within that area) was central to the engine failure and IP turbine disc liberation event.

No doubt there was an oil fire around the IP bearing area and there was a manufacturing problem with the stub pipe. But there are questions. If it is a fatigue failure, was it high cycle fatigue or low cycle fatigue that initiated the failure? Were there striations on the fatigue surface that gives a clue to the time duration from start of cracking to separation? Is this the part that RR stated as being the single part causing the failure or was it a different part? Recall RR had started to replace a part or parts on engines in the Airbus factory believed to be causing oil leakage and apparently verified in flight engines based on oil staining noted on turbine blades. Knowing that oil leakage and accumulation outside of the IP bearing box could cause an oil fire, wouldn't you think the flight engines containing the believed to be causing part/parts be serviced first, then the factory engines next? This leads back to the AD regarding spline wear.

AD 2010-0008 R1

Wear, beyond Engine Manual limits, has been identified on the abutment
faces of the splines on the Trent 900 Intermediate Pressure (IP) shaft rigid
coupling on several engines during strip. The shaft to coupling spline
interface provides the means of controlling the turbine axial setting and
wear through of the splines would permit the IP turbine to move
rearwards.
Rearward movement of the IP turbine would enable contact with static
turbine components and would result in loss of engine performance with
potential for in-flight shut down, oil migration and oil fire below the LP
turbine discs prior to sufficient indication resulting in loss of LP turbine disc
integrity. Some of these conditions present a potential unsafe condition to
the aeroplane.
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?
It is an interesting puzzle with all the pieces yet to be put into place.
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Old 4th Dec 2010, 17:05
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Oil Fire. Not so much to do with Thrust, if at all. Has a lot to do with interrupting oil flow and recovery from bearings (and splines) that need lubrication. No Lube, no run. No run, we sieze, or worse. The splines are helically ground and appear on the outer rim of the IP Shaft. These splines run inside the inner race of bearing #2. If these splines wear smoothe, or seize, there will be noise. The presence of these splines suggest a need for direct coupling (Rigid Coupling), and axial movement. If the rigid couple fails, the Shaft is free to move (axially) aft, as mentioned in the AD. Either way, it looks like a tough catch even with a borescope. 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.

Post #1347. The front of the LP shaft shows a "Machined" surface. It is possible this is where its Splines were.

This is of course, conjecture.

Last edited by bearfoil; 4th Dec 2010 at 18:56.
 
Old 4th Dec 2010, 17:07
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I wonder why they took so long to disembark the passegers, esp as the No1 engine was still running.
Maybe in part because the #1 was running.

However, in general, using emergency chutes (even if only on one side), is not a decision undertaken lightly on a big aircraft - there will be injuries.

I'm pretty sure that the situation will have been fully evaluated (whilst retaining emergency options). The crew obviously came to the conclusion that there was no immediate danger that required the passengers to be thrown down the slides, and that an orderly disembarkation was the best option, and that the passengers would be more comfortable in seats than in 30degC humidity outside with vehicles driving around.

Deciding on what to do, then the mechanism and then getting the wherewithall (steps/marshalls/vehicles etc) all takes time. Validating the numbers is probably a bit of a red herring, but complete evacuation is a requirement, so using 1 exit is an additional crosscheck.
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Old 4th Dec 2010, 18:29
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I expect using 1 exit ensures the others are free from steps and can be used with slides at short notice. I assume slides are the quickest way to evacuate, noting they are not free of injury risk. This is an option you want to keep open if e.g. The left wing suddenly caught fire etc.
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Old 4th Dec 2010, 19:49
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The ATSB full media release stated the report identifies an overspeed-related failure in the intermediate pressure turbine disc in the aircraft's No 2 engine. I don't think the actual preliminary report AO 2010-089 gets into this other than to say the IP turbine disc failed.
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Old 4th Dec 2010, 19:59
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Bearfoil

My thought of the bang- bang, heard by the flight crew, would be: The first bang was a compressor stall, probably the HPC and the second bang was the catastrophic failure in the IP turbine area.
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Old 4th Dec 2010, 20:11
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JenCluse
As I posted earlier, almost certainly the newbie 380 Capt was being checked to the line by the newbie A-380 check captain, who was possibly being checked out by the equally newbie A-380 line manager, or whatever terminology is in use today.
RdC is a line pilot, and if memory serves correctly, was the second QF pilot actually endorsed on the 380.

The reason for the disparity in hours is that there has been very little 380 flying to go around, and training takes a major part of what there is.
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Old 4th Dec 2010, 20:33
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Bearfoil
The forward end of the LPT shaft that looks machined is the coupling to the fan shaft. It is hard to tell if the spline coupling is there or not. The silver colored area just behind this is where the bearing is located that separates the IP shaft from the LP shaft. What is interesting in this photo is: You are looking at the stage 1 LPT rotor that has varying damage to the turbine blades. I think what you should be looking at in a normal engine would be the stage 1 LPT nozzle ring forward of the stage 1 turbine rotor. However it is totally gone along with the casing that supported the nozzle ring. If you look at the photo of the engine being removed from the pylon, you will see the missing space where this nozzle use to be. This is why I think the IP rotor was free to move aft (in overspeed mode) into the the LP nozzle and then burst. Part of the freed nozzles went into the stage 1 turbine blades, hence the broken blades and some went overboard with the casing.
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Old 4th Dec 2010, 20:58
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The more you read about it, the more you appreciate the incredible work of the crew getting that sorry mess on the ground in one piece.
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Old 4th Dec 2010, 21:39
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Page 9 of ATSB Preliminary Report

"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 ?
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Old 4th Dec 2010, 22:07
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This was made for a lay audience but may be of interest: Australia's public broadcaster ABC Radio National has just broadcast a measured one-hour analysis piece, Background Briefing. Will be available for download and a transcript will be on the site in a few days. It goes into some detail about cost-cutting in the industry, various machinations and the "not enough sets of eyes" situation brought about by third-party maintenance. (And of course it includes high praise for the crew). Also refers to 2006 and 2008 warnings published in the relevant industry magazines, and pulls together several threads.

Background Briefing

The airline, the engine maker, the 500 passengers and their lucky escape
"It's what keeps aeronautical engineers awake at night - an engine explosion at 30,000 feet. They are rare but the Qantas A380 incident has triggered a fierce debate about the design, maintenance and safety of engines that power the new super jumbos. Reporter, Stan Correy."
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Old 4th Dec 2010, 22:46
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mrdeux,

So you are saying that despite being one of the first on type and in about 2.5 years the PIC only got 570 odd hours?

What is the average sector length? Ten or eleven or twelve hours?

Did the SCC check out much earlier than the PIC? How come he has so many more hours?

I think the PIC did a remarkable job given he was doing very little flying.

H & H
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Old 4th Dec 2010, 23:06
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All kinds of variables with flight schedules and as mentioned so much training going on , I assume pilots are taken off their trips regularly and often for other pilots to get required training onto the A380 fleet.


To the folks wondering about the seemingly long time from landing to getting off the dumbojet.... with the successful resolution of the flight, no injured ANYONE on the aircraft, and a mostly intact aircraft safely delivered to near the end of the runway, I am in no way ready to be anything other than awe struck at the judgement and skills of the crew in the pointy end of the beast.
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Old 4th Dec 2010, 23:31
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Turbine D

The stationery ring that is missing is what the EASA explained was the contact when the IPT migrated aft. If the IPT went aft, it stopped because of the cavity Pressure. The damage to LPT1 is irregular, suggesting that what got eaten were pieces of the Stator, forced to the perimeter by gas flow. The interior of all the stages of the LPT look pristine, as does #1's gathering ring. I think the IPT was blown forward and out, with its blades more or less nested in until exiting the Case. Without the IPT, any combusted gases would linger and lose pressure, in synchrony with reported N values.

The Report mentions small molten bits peening the Aft face of the IPT. Bearing bits?

All guesswork, not intended for conclusions.

bear
 

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