A380 engine failure - Qantas

[DERG]

Trent 972

This engine is only used on the Qantas machines. So over the four units an extra 8,000lbs of thrust is available. Reason: 15 hr flight to Melbourne at max weights.

Would suggest a harmonic vibration has stress fractured the oil lines. This takes us back to 1950s failures. Just why this could not be modelled is a mystery.

[Bizman]

Why is QF still grounded while LH & SQ are flying?

Derg:

"This engine is only used on the Qantas machines. So over the four units an extra 8,000lbs of thrust is available. Reason: 15 hr flight to Melbourne at max weights."

I get that, but surely this only applies for takeoff and the 25 minutes or so to climb to initial cruise altitude. Thereafter, won't almost the same thrust be required to maintain same LRC or higher as it would for SQ or LH with the 970 Trent?

Okay, a little higher weight, so a little more thrust required initially to maintain same altitude at same speed, but at cruise altitude, the thrust difference isn't 2,000 lbs per engine, more likely only 200 lbs per engine for the next 14 and half hours.

I understand the opportunity for harmonic vibration, both mechanical and aerodynamic through the engine, at higher thrust ratings, but again, I don't see how SQ could assume all these factors after the initial failure in QF32. Surely, initially, no-one knew why #2 in QF32 let go. So how come SQ was back in the air after 12 reluctant hours of checks, while QF was still grounded?

What is even more disturbing for me, is that SQ had already had one total IFSD of a Trent 900 on their A380 and is believed to have prematurely removed from wing and changed over a dozen engines on their fleet. They must know the engine is far from mature, particularly in the hot section, and there are still design issues in the hot section that are far from reaching the "bucket" level of a mature MTBF. Every new event like QF32's must surely be cause to sit back and ask yourself what is it that we don't know about what we don't know?

[DERG]

Bizman

At the outset i have to say that I have watched Qantas and this 380 saga closely and at times my heart went out to them. Australia has had rotten luck. Of course Qantas is not that big an outfit and ferrying the machines upto Lufthansa cannot be logistically easy for a C check.

"What is even more disturbing for me, is that SQ had already had one total IFSD of a Trent 900 on their A380 and is believed to have prematurely removed from wing and changed over a dozen engines on their fleet."

My God..that tells a tale. News to me. RR has just announced a £750 million deal to supply China with engines and back up. This is 12 noon zulu Tues Nov 9th 2010.

This accident happened on the climb out so that is the first clue. Of course I agree with you and see clearly your reasoning. You know these failures happened regularly back in the 50s and 60s and for the life of me I cannot work this out.

We are a hell of along way past slide rules and log tables in 2010 and this failure ..? Either the volcanic dust has shot blasted some mass away from the internals or RR have completely screwed up some specs on materials. God only knows.

In some way the turbine oil has got loose, union failure, stress fracture to lines? Now as far as the public is concerned SQ and Lufthansa are immaculate and of course Qantas has been kicked in the balls yet again.

If you note the wear on the splines that also suggests some chattering. I just don't know if these engines had telemetry on them as do say JetBlues do in KJFK. Of course the guarantees JetBlue got were phenomenal. They can not loose. Even Bird strikes are covered.

Then you lost an engine in your one of your 74s. You push 'em hard and thats what they were built for but I have to say that the 380 was/is not fit for the purpose. I would seriously consider sending them back to Toulose. Let them tie them down run up to 98% and see what happens load em up to full, move around the freight.

Even the friggen sea seals have radio collars fitted to them with a satellite telemetry link. Annoying.

[awblain]

Energy of disk?

The question was asked what's equivalent to the energy of the blade disk?

Give or take -

Energy ~ 0.5 * number * mass * (radius)**2 * (omega)**2

number - relates moment of inertia to a hoop of same mass - say 0.6
omega = rotational velocity = assumed 600 radians/s ~ 6000 rpm (?)
mass = 50Kg (maybe a bit low?)
radius = 0.5m (?) - maybe OK including the blades.

Energy ~ 1.4 MJ.

At 70 mph (30 m/s) this is the same as the kinetic energy of a 2.6 ton truck.

So, a car at highway speeds is not going to be too far off the mark.

At 300 m/s, the same energy as a 30kg cannonball. At a radius of 0.5m and omega of 600 radians/s, the circumference moves at 300 m/s, so it's also very like three 10Kg cannonballs being fired straight out of the engine.

[yotty]

Just a small comment here... if the shaft connecting the compressor and turbine breaks, the turbine is designed to move forward to self destruct on the NGVs and stators to prevent an uncontained failure ..least ways it's like that on the 895...

[barit1]

That would be hard to do. If you break down all the static and dynamic air forces on a turbine, they sum to a large AFT component. In other words, the shaft is in tension, and if it ever fails, the turbine rotor shifts aft.

In a multistage LPT, it's generally possible to contrive a system in which the rotor and stator airfoils will clash and thus destroy the driving torque; ergo the rotor grinds safely to a stop.

In the case of the HPT, as soon as the shaft separates, there is no torque driving the HPC, so it soon quits supplying air to the cycle, and the HPT coasts down.

The IPT is another animal. If the core HPC/HPT keeps running, why wouldn't the IPT overspeed? I don't think I'd want to be anywhere in the same county!

[robertbartsch]

I have not read much at all about the airframe design. Are investigators leaning towards a concluson that it is a RR engine only problem?

[lomapaseo]

In the case of the HPT, as soon as the shaft separates, there is no torque driving the HPC, so it soon quits supplying air to the cycle, and the HPT coasts down.

Of course the timing of the HPC quitting is quite critical, but methinks that the low enertia of the High turbine will be long gone out the side of the engine as it eats the air still left coming out of the combustor

[DERG]

Volcano Dust

If this fault turns out that it is volcano dust related it is bonanza time for technicians, loads of $$!

[Bizman]

Volcanic Dust

Extremely unlikely.

If any volcanic dust were present there would glazed pellets in the combustion areas, and pitting of compressor blades. None of this has been reported.

Besides LH has not been near volcanoes of late, yet swapped an engine as result of latest AD

I think RR now has a pretty clear bead on cause & wud be beavering away on a long term rectification

[Bolty McBolt]

awblain Energy of disk ?

I would put the diameter of the HP disc closer 1.1 meter and the weight(mass) around 75 kgs + with blades fitted

The IP disc is larger again but not as thick but I suspect a similar mass.
I remember as an apprentice building up modules that the turbines discs were light enough for 2 people to lift but we didn't as they needed to be put down very gently to protect knife edge seals on the faces

Now the RR G2 N3 spins at approx 12,000 at 100% at climb thrust the N3 would still be above 90%.

Using "awblain" formula above. As "barit" said you don't want to be anywhere near it if either let go. I

Would suggest a harmonic vibration has stress fractured the oil lines. This takes us back to 1950s failures

From what I am hearing its not fractured tubes or oil supply issues. Think along the lines of the hot area bearing fire. RR use labyrinth seals and looks like the high temp air could be getting into the HP/IP Turb bearing compartment cooking the oil causing bearing seize or failure.
This could explain why RR have asked to look at turb blades because if the oil is getting out perhaps the hot air is getting in where it should not.

Just my interpretation of the AD

[fruitloop]

Quote....Just a small comment here... if the shaft connecting the compressor and turbine breaks, the turbine is designed to move forward to self destruct on the NGVs and stators to prevent an uncontained failure ..least ways it's like that on the 895...
WOW never heard of this before !!!

[Hobo]

Sydney Morning Herald 12/11/10


QANTAS has signalled that its flagship A380 aircraft could be out of service during the lucrative summer holidays, as preliminary investigations pin the blame for the midair emergency last week on an ''oil fire''.

[DERG]

Hiya Bolty

See if you can dig up something on a Shell turbine oil called ASTO 560.

This oil coked up another RR Trent around 2002.
see:

http://www.ntsb.gov/ntsb/brief2.asp?ev_id=20040528X00693&ntsbno=DCA04IA002&akey=1

It was withdrawn by RR. the oil that is..

I checked and this oil is still widely available, maybe Qantas are still using it. Who knows?

Anyway the bottom line is it was coking the vent tubes from the bearing.

[Flash2001]

Please give all quantities of energy in stone-barleycorns. Velocity and speed should be given in furlongs per fortnight.

The Qantas landing qualifies as excellent!

[lomapaseo]

See if you can dig up something on a Shell turbine oil called ASTO 560.

This oil coked up another RR Trent around 2002.
see:

http://www.ntsb.gov/ntsb/brief2.asp?ev_id=20040528X00693&ntsbno=DCA04IA002& akey=1

It was withdrawn by RR. the oil that is..

I checked and this oil is still widely available, maybe Qantas are still using it. Who knows?

Anyway the bottom line is it was coking the vent tubes from the bearing.

The most significant part of coking in a jet engine is hot air mixing with the oil. Leaking hot air into a bearing compartment through the seals leads to coking in the scavenge system which leads to higher pressure in the bearing compartment which leads to oil blowing out through the bearing compartment seals and possible light off around a spinning disk.

There is also the possibility that seals worn badly enough could leak oil out of the bearing compartment even though no excessive pressure rise within the compartment has been caused by coking in the scavenge lines.

Other possibilities exist so perhaps when the full details of the RR fix become known we can better understand.

[rmm]

Qantas use BP turbo 2197 oil in the 380

[DERG]

Now we are getting somewhere...

Thanks for the repiles

[barit1]

We still have the QF RB211/747 SFO "explosion" and return to SFO (31 Aug), involving the IPT - it shed its blades, and thus the disc did not burst. I've heard claims of "no connection to the Trent events", but no detailed or convincing substantiation of that claim.

Further, it would be pretty hard for QF #2 Trent to encounter volcanic ash when #1, #3 & #4 and the airframe itself show no such distress signature. (I say no distress, because if ash HAD BEEN a factor, R-R would have immediately posited this for whatever commercial value could be gained).

[DERG]

No connection to 74 engines. Qantas push 'em hard because of the route lengths and TO weights. Always were hard on engines.

RR knew of a fault with T970s back in summer 2009. They made a modification to engines on the line at Toulouse. They notifed Euro Cert Authority and they decided to monitor and not to stop operation.

Of the 80 T970 units in service over half already had the newer design. Qantas was left out of the information loop.

The rest is now history.