QANTAS A380 Uncontained failure.

[Lyman]

Hi Turbine D

Here... As the stress limits begin to be exceeded, the power drive arm fails, releasing the disk and the disk is free to rotate with no control over rotational speed. As the rotational speed increases with no impediment to slow it, it bursts. That, I believe, is what happened on this engine.

I think you are missing something, and it is key to my description of the failure. Using your own description, above, when the Disk is released, it has not the time to increase in rotational velocity. None.

The very instant it is released, it wobbles wildly out of control,, no longer restrained by a symmetric join. It contacts the case, wobbles forward and aftward, and begins immediately to SLOW. It is converting what was controlled and productive rotation into chaotic and catastrophic disintegration of the IPT cave, bursting the case.This is the mechanical Bang. The second bang is the release of P30 gases into the atmosphere, possibly.

Again, once released, it goes non planar and is free to eccentrically smash everything in its path, for a VERY short time, constrained in a Titanium "Barrrel".


There is no overspeed. Out of control rotation, along with the eccentric "orbit" of the disc, shears the blades, and initiates the tri-partite decomposition of the Disc. Failure at the IPT/Drive Arm it was, as reported by Rolls.

What say you, my friend?

[Lyman]

barit1

To continue, is it possible that the six seconds of N2 spool drop are connected to the loss of the rigid joint at IPT/Drive ARM? Is the IPT slowing, and converting its energy into a disruption of the contents of the IPT cave? Without the obstacle of the Turbine, is the pressure stage increasing rapidly in pressure, since there is no mechanism to transmit it to the LPT? The HP is still functional (and gains rpm, and 'added' fuel, sent by the ECM, to make up for the loss of the IPT 'barrier').

I don't think it happened that way, the IPT, in circling the case, cannot have stayed for six seconds?

[Turbine D]

What say you, my friend?

I have given you my thoughts, there is nothing more to add....

TD

[Lyman]

I should have asked my question more directly. Once separated from the Power Arm, how can the Disk possibly retain stability sufficient to gain rpm? Won't it start going bs on its cramped environs?

Sorry for the obtuseness, Turbine D.

respect

[barit1]

Wobbling? What is the source of the force required to start it wobbling? Have you ever contemplated the magnitude of force required to accomplish this with a 100kg disc turning 7000 rpm?

Or have you been reading too much Velikowsky?

[Turbine D]

Lyman,

I should have asked my question more directly. Once separated from the Power Arm, how can the Disk possibly retain stability sufficient to gain rpm? Won't it start going bs on its cramped environs?

Do you realize that if you stand in front of a turbofan engine and grasp one of the fan blades with your little finger you can, with very, very little effort at all, turn the fan over, which in turn, turns the LP compressor and the LP turbine? It is a jewel and the same is true with a triple spool engine. So when you think about that, think of what happens in the IP turbine on the Trent 900 when the disk separates from the shaft holding it. We are talking here no more than a couple of seconds. Your talking as if we are in slow motion. The turbine wheel, once the power drive arm fractured, over sped very, very quickly. The thing driving it was the highly hot compressed air that was expanding, but passing through its turbine blades, still attached to the disk. Remember the aircraft was in the climb mode. The rotational inertia for the given mass is unbelievable in this situation, The turbine wheel was driving nothing, a free turbine is a nightmare. Additionally, there was nothing in the way to stop it, it just proceeded to burst and that is what the photos of the found disk fragment depicted.

I would suggest you, once again, look at the engine cross section and note if it moved rearward, there was no substantial material to decrease it rotational speed except for the inner flow path band of the stage 1 LPT nozzle. Whether it wobbled or not is immaterial, in fact it may have gained enough rotational speed while still in place over the IP shaft, but free of the shaft to initiate the speed leading to final failure. Remember, there was little damage to the LP turbine except for the stage 1 LPT nozzle. The majority of debris went outward in a radial direction, not rearward.

Think real time, not slow motion time which is only recorded by high speed cameras.

TD

[barit1]

There is another aspect to this, and that is the rate of heat transfer from the oil fire. Lightweight components heat up very quickly, but massive structures much more slowly. The IP rotor disc is a composite of massive areas (the disc bore) and much thinner areas (the drive arm). Therefore I suspect the drive arm overheated much more quickly than the disc proper.

This reinforces the scenario in which the drive arm failed first (after the oil fire escaped the sump). This released the disc assembly, blades included, and since it was subject to a big gas pressure load on the front face, it was immediately blown aft until it was seated on some static parts, establishing a "false bearing". It's still turning 7000 rpm, and the false bearing is quickly friction-heated producing liquid metal, which has some lubricating properties.

And it's still being driven by core turbine exhaust airflow, and it has lost the normal torque load of the IP compressor.

Guaranteed overspeed, as previously stated.

[Lyman]

TD: " The rotational inertia for the given mass is unbelievable in this situation, The turbine wheel was driving nothing, a free turbine is a nightmare. Additionally, there was nothing in the way to stop it, it just proceeded to burst and that is what the photos of the found disk fragment depicted."

That is my point. I think from Edelweiss, and evidence at LPT#1, there was no time for the debris to blow aft. It exited out the opening created by the departing blades, followed immediately by the three main, and hundreds of minor, bits of the disintegrated wheel. If we consider that the wheel, to gain rpm, needed time on shaft (or, 'false bearing'), then debris would have exited back through the LPT proper, making a proper mess. As the wheel was blown instantly back against the Stator vanes platform, the IP blades were shorn, and blew out the case, co-planar with rotational orbit. This is what happened to Edelweiss; in that case, the IPT remained attached (though 'fractured', circumferentially).

Consider, the IPT is not attached to the shaft, per se, and a loss of the drive arm leaves a discrepancy bore diameter/shaft of many centimeters. The bearing is ad hoc, and unable to support rotation. The IPT orbit is instantly eccentric, and the disintegration is likewise instantaneous. It is the relatively undamaged condition of the LP turbine that gives this away; all debris blew out simultaneous loss of drive arm, imho. Similarly, the IPT blades were lost instantly, nothing remained to transmit the gas flow into additional rotation. This is Edelweiss, redux, save IPT loss out the case. Only in Edelweiss, the fracture of the drive arm was not complete, and the wheel was luckily retained.

I know you are convinced of oversped wheel; without blades, and time, I cannot agree. 7000 rpm is well sufficient to blow up the IP system. Is there a conclusion in the report? The initial used the word "may" re: overspeed.

add; [B][Remember, there was little damage to the LP turbine except for the stage 1 LPT nozzle. The majority of debris went outward in a radial direction, not rearward. /B]

Yes, again, my point. Even two seconds would have seen a substantial flow of debris out the tail pipe. Radial exit of virtually all the debris drives my conclusion that the disintegration/exit was instantaneous, not lingering.

For N2 to spool down whilst the IPT was spinning up for seconds, and there is light damage to aft rotational mass, is a reach, imo. What is more likely is a damage trail suggested by the actual AD on this engine. Aft drift of the IP shaft, metal/metal contact, superheated Drive arm, and disintegration, causing aircraft damage and parts on the ground, endangering people below. The AD was written with climb out in mind, hence the reference to population underneath. The 380 serves airports in populated regions, and catastrophic failure puts those below it at risk.

The source of the wear on the rigid coupling is published, and the damage pursuant is also. Drifted shaft, and oil fire are two results of the cause of the AD in the first place. Loss of oil is reported on many a/c, along with oil pressure problems, and preceding incidents.

If the cause of the problem was overspeed, fine; it is not necessary to the explosion, however, and that is my point. I don't see evidence of any kind that isolates this uncontained failure from one predicted by the regulator. For some reason, it has become necessary to propose a new, and unrelated anomaly. Why is that? (Rhetorical). The oil pipe problem was not new, it was not unrelated, and it is not logical to separate the "Oil Fire" from the AD. The wear was caused by vibration of the the Rotating Mass. imho

Thanks

[barit1]

Lyman, I wish you would consider the fact that turbine discs don't just fail at near-normal rpms, absent some significant manufacturing defect. I point to the eight engines intentionally crashed on 9/11. All the turbine discs, from (I believe) three different manufacturers, remained in one piece after the dust had settled. There are plenty of other accidents available for study in which the impact forces failed to break the turbine discs.

Consider also that the IPT on this engine generates (I'm estimating here) 50,000 shaft horsepower, all of which is delivered to the IPC. If the shafting (drive arm in this case) lets go, it's like tromping on the clutch and accelerator at the same time.

No, the only things that I'm aware to cause disc failure are overspeed, overtemperature, or a fault in the disc (either during forging, machining, or some repair process). For you to propose otherwise for QF32 will take some very serious analysis.

[Lyman]

Hi barit1, thanks for the reply. I think there is merit to what you say, without doubt, these rotors are phenomenally strong. The design consideration is strictly that to which you allude, resistant to overspeed and overtemp, to a point. We do not need to look past the existing data to find failure. In fact, the failure was foretold by no less than the regulating authority, to which the engine manufacturer is entirely responsible for proof of quality. So I do not feel the need to go beyond, the failure is in front of us.

Let's assume that some combination of above limit rpm and ambient temp caused failure, fair enough?

My purpose from the outset is to frame the evidence within the data provided in the AD as enforced. If some mechanism failed the connection other than high heat, or overspeed, let's agree it is not present in the analysis? I think the metallic spatter is the product of friction stir at the arm/engine frame, as predicted by EASA. Only one quart of oil was missing, the fire was in front of the wheel, and the prediction via EASA tend to override a lingering spin up whilst the core is melting. The Drive Arm, logically was the last failure before disintegration, and the decomposition happened instantly. For the spatter to appear on the aft face of the wheel speaks against the heat migrating from its front? Yet with a shaft transiting aft, the friction can create instant molten metal, whilst the shaft retains integrity. You cite the N2 loss of rpm, I think that was a result of metal/metal from shaft, case, as predicted. I would say the shaft slowed whilst joined to the Turbine, and EEC poured extra fuel in to compensate for the reduction in power applied to the melting metal in the core.

These are informed from the AD, directly. How can N2 unwind for seconds, as a result of separation of IPT? Again, the IPT without the Drive Arm connection is a sizable herd of horses loose in the barrel. The Orbit would have to remain precisely free of obstruction for the Wheel to accelerate. The Drive Arm/IPT resemble a Bell on a bearing at the small end. If the connection is lost, the mass is not only free to wander, chaotically, but the rim of the Bell is quite distant from the bearing attach, any imbalance would instantaneously throw the entire asembly into an extreme eccentric.

I am not arguing for its own sake, but am trying to fit the results into the predictive regulation published by the engineers before the fact.

See you in JB?

take care, and thanks again, I appreciate your patience with my stubborn streak.

[Bergerie1]

Kucing,

You sent me a private message, but unfortunately the website won't let me reply to you. If you send me another private message with your email address I will try to answer your queries.

[Turbine D]

Lyman,

My purpose from the outset is to frame the evidence within the data provided in the AD as enforced. If some mechanism failed the connection other than high heat, or overspeed, let's agree it is not present in the analysis? I think the metallic spatter is the product of friction stir at the arm/engine frame, as predicted by EASA.

Lets go through some facts again.

From the latest ATSB Interim-factual Report:

"The investigation has found that the intermediate pressure (IP) turbine disc failed as a result of an overspeed condition, liberating sections of the IP turbine disc that then penetrated the engine case and wing structure. The disc failure was initiated by a manufacturing defect in an oil feed pipe that resulted in a wall thickness reduction in an area that is machined to receive a coarse filter. That section of the oil feed pipe sustained a fatigue crack during engine operations that lead to an internal engine oil fire that weakened the IP turbine disc. In turn, a circumferential fracture was induced around the disc, allowing it to separate from the IP turbine shaft. The unrestrained disc accelerated to critical burst speed. This lead to the No 2 engine failure and subsequent significant penetration damage to the airframe structure and systems."

Your quotes directed to barit1:

You cite the N2 loss of rpm, I think that was a result of metal/metal from shaft, case, as predicted. I would say the shaft slowed whilst joined to the Turbine, and EEC poured extra fuel in to compensate for the reduction in power applied to the melting metal in the core.

These are informed from the AD, directly. How can N2 unwind for seconds, as a result of separation of IPT? Again, the IPT without the Drive Arm connection is a sizable herd of horses loose in the barrel. The Orbit would have to remain precisely free of obstruction for the Wheel to accelerate.

The way a three spool turbine engine works is this:

1. The low pressure turbine (LPT) drives the fan and low pressure compressor.
2. The intermediate turbine (IP) drives the intermediate compressor.
3. The high pressure turbine (HPT) drives the high pressure compressor.

So, if the IP turbine disconnects from the shaft resulting from a circumferential fracture of the power drive arm, it is no longer driving the intermediate compressor. Therefore, N2, that is measured at the intermediate compressor begins to decrease, in this case from 94.5% to 93.2% at UTC 0201:00. A 100% speed for the IP turbine rotor means it was rotating at 8,300 RPMs. At 94.5% speed it is rotating at 7844 RPMs. Burst speed would be approximately 10,375 RPMs, assuming a 25% margin above maximum operating RPMs. It didn't have to speed up (overspeed) very far to get to the burst point. The rate of speed up would be determined by the expanding air passing through the IP turbine blades received from the HPT blades. It was probably less than 7 seconds from normal operation to burst.

The Drive Arm/IPT resemble a Bell on a bearing at the small end. If the connection is lost, the mass is not only free to wander, chaotically, but the rim of the Bell is quite distant from the bearing attach, any imbalance would instantaneously throw the entire asembly into an extreme eccentric.

No it doesn't. It only resembles that way on the disc after the failure. Prior to failure, it is a bent downward plate (towards the engine centerline), parallel to the disc face, a circumferential feature that attaches to the end of the shaft by means of a series of bolts that pass through bolt holes in the power drive arm.

If the connection is lost, the mass is not only free to wander, chaotically, but the rim of the Bell is quite distant from the bearing attach, any imbalance would instantaneously throw the entire asembly into an extreme eccentric.

The mass you suggest, the IP turbine rotor disc and blades attached is free to very rapidly accelerate until such time the disc bore stretches which is indicative of pending failure and then moves back. At that point, IMO, the only contact would be near the base of the turbine blades embedded in the disc slots contacting the stage 1 LPT nozzle. That rubbing would create metal splatter observed on the aft surfaces of the disc, similar to what happens during an inertia welding process, an initial false bearing without adequate pressure to slow the rotation of the disc. It was not chaotic at all until the burst occurred. Again, IMO, eccentric motion had little effect on what was about to happen.

[lomapaseo]

about as chaotic as a freely spinning bicycle wheel being dropped from a window ledge or ladder

Try it some time and film it before it hits the ground

[Lyman]

I suggest that once the circumferential fracture separated the wheel from the power arm, the disc was already exceeding a (somewhat lower) burst speed.

Are we looking at the same schematic? The turbine disc has "return" (sleeve) feature that is the drive arm. The circumferential fracture separated the wheel from the arm, therefore the wheel is no longer restrained in a circular orbit. Show me where the wheel has any interest whatsoever in accelerating? The massive pressure of the exiting HPC gases thrusts the wheel instantly into the LPT Stator. The turbine blades are sheared, and the wheel performs a very rapid eccentric dance out the case, post disintegration. Attached to nothing, how do you say the wheel remains stable to resist the flow of gas, and thus accel? It has no axle. No stability.

Lomapaseo. A rapidly spinning bicycle wheel illustrates exactly my point, its gyro expression of high energy slams it into the stationery parts of the core.

I still suggest that the slowing of the IPC demonstrates the axial migration of the IShaft aft ward into the "stationery parts of the engine" (AD). Integrity of the shaft is required until disintegration of the I Turbine, IMO. I suggest that this slowing of N2 (evidence from phonic wheel, and diminished pressure), is what precipitated the introduction of extra fuel into the burners, and caused N3 to increase, perhaps even introducing unburned Fuel into the IP cavity. That can't be a good thing...

How did one quart of oil incinerate this engine?

[barit1]

Show me where the wheel has any interest whatsoever in accelerating? The massive pressure of the exiting HPC gases thrusts the wheel instantly into the LPT Stator. The turbine blades are sheared, and the wheel performs a very rapid eccentric dance out the case, post disintegration.

Sorry, but in the T900 series, the space downstream of the IPT is vacant for quite some distance; The LPT stator (if any **) is well downstream. The IPT blades remained largely intact, providing the "unbalanced torque" (i.e. freewheeling, unloaded) to accelerate the disc to burst speed.

NOTE ** One aerodynamic improvement in the Trent engine is the use of contra-rotating spools. I do not recall positively which ones rotate opposite to others, but I think the IP and LP are opposite. IF this is the case, R-R had the opportunity to ELIMINATE the first stage LPT stator, because the swirl flow upon leaving the IPT accomplishes the same thing. Less weight, less pressure drop, better efficiency, but also the increased opportunity for an IPT overspeed per the present discussion.

[Turbine D]

Lyman,

Your quote:

I still suggest that the slowing of the IPC demonstrates the axial migration of the IShaft aft ward into the "stationery parts of the engine" (AD). Integrity of the shaft is required until disintegration of the I Turbine, IMO.

Again, from the ATSB Interim Factual Report

The investigation has found that the intermediate pressure (IP) turbine disc failed as a result of an overspeed condition, liberating sections of the IP turbine disc that then penetrated the engine case and wing structure. The disc failure was initiated by a manufacturing defect in an oil feed pipe that resulted in a wall thickness reduction in an area that is machined to receive a coarse filter. That section of the oil feed pipe sustained a fatigue crack during engine operations that lead to an internal engine oil fire that weakened the IP turbine disc. In turn, a circumferential fracture was induced around the disc, allowing it to separate from the IP turbine shaft. The unrestrained disc accelerated to critical burst speed. This lead to the No 2 engine failure and subsequent significant penetration damage to the airframe structure and systems.

Quite honestly, I never saw this report until yesterday. It describes what I have thought and tried to express to you all along. However, you believe differently with no evidence to support your theories. So it remains a standoff, your theories verses factual information and some turbine engine experiences on my part. No sense in continuation of this discussion.

How did one quart of oil incinerate this engine?

Simple, it started a fire in a very sensitive area of the engine that generated heat on top of what was already present, which when combined, exceeded the disc material capability for the temperature experienced.

[Turbine D]

Hi barit1,

On the Trent 900 engine, the LP & IP rotors turn counter clockwise with the HP rotor turning clockwise. This enables elimination of the stationary nozzle between the HPT blade wheel and the IPT blade wheel. The only thing between the two is a sheet metal frame structure that contained the failed oil feed pipe that started the fire. The stage 1 LPT nozzle is still there, but has a significantly larger diameter due to the conical nature of the LPT.

[Lyman]

Hi barit1 I think it is HPC that spins contra. The HP shaft is nested inside the well of the IP shaft and the bearings for each have a ~20000 rpm differential due rotation opposition.

TD: From the schematic, the bearings for the aft terminus of the IP shaft are on the shaft side, the Power Arm is outboard of the shaft's end, as it returns foreward, surrounding the bearings. Thus any separation of the Power Arm from the wheel eliminates the cvarriage for the Turbine Disc, via separation, The Disc has no structure left, it is not as if the wheel is inboard, and merely spins on, without bearings.

I have read the report, and it can be read in at least two ways, leaving unclear some of the evidence/conclusion chain of thought.

I have spent hours reviewing the schematic, and to me, it is simple. I might be missing some element, or the drawing may be incomplete or inaccurate. The mate for the Power Arm, Wheel, Shaft, and bearing is in the three lam sandwich at the most aft end of the shaft. If these retaining bolts sheared, the entire Arm/assembly is lost, there is no possibility for any retention of the Wheel's mass for any length of time.

Could you post the Drawing? I have limited computer skill, and perhaps if addressing the same drawing, we could meet in our thoughts? I don't doubt either of you gents, and am in deep water with you two, my mechanical skill is better than my theoretical, and I stand to be corrected, always....

[Turbine D]

Lyman,

The innermost shaft is the LP, the outermost is the HP and IP shaft is between the HP & LP. The bearing supporting the HP rotors are separate (independent) from the IP rotors.

The IP disc accelerated to burst while still over at least part of the two rear roller bearings.

I don't see how you can read the ATSB Report two ways...

[barit1]

Lyman & Turbine D:

On the Trent 900 engine, the LP & IP rotors turn counter clockwise with the HP rotor turning clockwise.

Thank you for reconnecting my aging neurons! My argument stands amended.