While there seems to be much conversation the cause of "bangs" heard.
How about HP/IP bearing fire, bearing seizure and IP turbine wheel on end of said shaft shearing off could be BANG #1

Bang #2 is when IP turbine disc of huge mass bursts its way out of the turbine case travels upwards and hits the nacelles thankfully overdesigned "firewall" and shatters sending disc segments blades thru the wing, wing to body fairings thru air-conditioning bays, fuselage, fin leading edge etc.
That is the Bangs covered. Much of the gas path theory being discussed with a giant slit in the turbine section to describe the bangs heard is beyond the scope of my experience.

( Please see the above comments with tongue firmly in cheek.)

IP coupling failure. ?? There is an inspection of the IP shaft coupling for wear (trent 900). It is a laborious and tedious task and was being scheduled as per requirements but it is unrelated to this failure.


This does look to be the case but who else is qualified with large engine and metallurgical technology, GE or P&W ? I don't think that will happen.

To look at the root cause of this incident, if it were as simple as quality control issue and poor manufacturing of an oil pipe. RR would have said check your engines and if no fault found fly on. But this did not happen.
RR said fly on but don't use (no de-rate) high thrust even thou "high" thrust was NOT being used at time of the incident SIN - SYD.

The Trent 900 was developed for A380 when there was a perfectly acceptable Trent 800 with 110 inch fan producing more thrust than was required of the new T900 116 inch fan.
What was changed in the core engine? Why was it changed? The T900 is heavier, larger and produces less thrust.

IMHO I think I will be seeing a modification program mandated by RR to replace the turbine bearing section with a module that will look incredibly like the same fixture fitted to a T800 to take the stresses of the engine at the top end of the design thrusts.

As someone has already said “As regulators they do no more than RUBBER STAMP what the manufacturers tell them”
A setback or design flaw, I guess it depends if you are an accountant or an engineer.
2 cents

Bolty McBolt

If you read back, you will find bearing seizure is addressed. Also Stall/Surge. In my opinion, whether the HP/IP Roller bearings failed (I think they did) or not, the problem is at the Rigid coupling, the IP/HP thrust (Ball Bearing) locale. This "Module" is insufficient in service to withstand not only great Thrust, but its own idiosyncracies that disqualify it as TRENT anyway. The weaknesses are not my imagination, they are documented and described by the regulator, and stingily by the Actions of the Manufacturer in attempting to design a new engine whilst it (the 'current' iteration de jour) labors on wing in Public Carriage. The "C" mod is not capable of solving the teething problems to satisfy the parameters of the original certificate. It is a Stop Gap, an attempt to keep the engine viable. The alternative is to admit the engine is not ready for service, and face economic failure, and potential criminal prosecution. Will we see this circuitous fraud in the light of day?? Perhaps. Are you a betting man??

Will the "C" last to the expected service life? I think not, another newer module will replace it, and on, and on. What do you think?

bearfoil:
A commanded engine shutdown is only possible through direct connections from the engine master switch to the HP fuel shutoff valve or from the fire push button to the HP and LP fuel shutoff valves. The EEC's authority to close the HP shutoff valve is limited to a few specific cases (e.g., aborted start sequence or certain protections). The fact that engine 1 could not be shut down indicates defective wiring between the switches and these valves but does not imply that the EEC had any problems in controlling its engine as designed.

Independently of this, I still wonder why exactly engines 1 and 4 went into degraded mode, i.e., what led to the loss of internal and external(?) data (certain pressure and temperature measurements were mentioned in an older post) that is supposed to cause this degredation.

Not randomly. Under normal conditions the active channel is changed with each engine start.

Derg:
if it only would have been so simple - we have had in Poland a case last April when in the plane crash some 96 people died including a President and practically all top brass people (for the sake of this we can assume it should equal to IPT landing at 10 Downing Str). And within a short time what do we have - business (+politics) as usual. Moral issues are treated as tools for reaching the targets. Even the Church has stepped into this minefiled and lost its moral credibility.
Some say it is a sign of stable democracy (true) - but we can also say that politics are just the changing curtain covering ever greedy corporations and ever greedy shareholders - does it mean that We (people) are the problem?

I do also have trust in Australians - they do have to care for safety as their land is kind of really empty inside and surrounded by big waters on the outside ;) - their planes do have to fly safely!

DERG - Oils are approved for use by brand name, not spec. A new brand will need to be extensively tested before clearance including lab tests and endurance running. Testing is the responsibility of the Type Certificate holder, results need to be approved by Certificating Authority.

RB211-535 uses 180deg oil, for many years, with no probs.

Eureka!

A664

My mistake, yes the EEC Channel A/B selection at start is normally alternated.

This prevents the accumulation of dormant faults, normally.

However, between starter cut-out and Idle, the EEC may select a channel change. If one Channel has defects, the other channel will be selected for control. Also, if both channels have defects, the channel in control at identification of defects gets (retains) control.

As to degradation, (#1, #4). The EEC monitors/controls the Engine through motors, solenoids, and relays, while transmitting data to the a/c (Cockpit).

The Channel that is in control can make use of the standby channels logic, inputs and outputs. If a like output is faulted in both, the control Channel is the one that remains in operation. So the EEC communicates with the a/c. It maintains and supplies data for fault analysis to other systems on the aircraft. To what extent each of the other EECs is contingent on the failure (or failure reads) of one or both Channels of #2 I am unclear. Can you help with that??

RE: Fuel cutoff. One assumes that the "protections" limiting EEC authority to halt fuel supply include Overheat, and Fire. At the Burst, N3 was over limit. The Fuel is supplied by the HP Pump, which is driven by the Gearbox shaft, which in turn is connected to N3. Prior to 'shutdown' of #2, one assumes the HP was operating overlimits as well, and for a brief time may have been flooding the nozzles with fuel. Since the assumption is made that N3 at 98% was caused by fuel supply continuing past N1 N2 failure to turn, one also assumes the supply had continued, the supply may have been too "plentiful", and that EEC and or cockpit controls had lagged in protecting the engine from burst. Back to DEP, boosted thrust logic, etc.?

Oil Approval Guide
 

CAAD & DERG

Here is the process:

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/0f6f86064c839816862572c60065ba18/$FILE/ANE-2006-33.7-3A.pdf

Turbine D

Are we agreed then that Regulatory Agencies depend fully on the suppliers for specs and tests? (Manufacturers). ??

Does this require a mission that includes considerations other than Money?

Because at the end of the Day, Rolls, Airbus, and Operators will skate on their responsibilities. That is known. How much can we trust a system that is proved beyond doubt incapable of controlling its turf?? I have no patience or trust in the State of Regulation. They are known to be sycophants of the Firms whose actions they are required by Law to regulate. Is there another way to see it??

Turbine D

The Trent is not a US engine. It is from the UK and is therefore certicated by EASA. So the FAA process you quoted does not strictly speaking apply.

However the FAA process appears to be broadly in line with my summary.

Specifications are not usually tight enough. Hence brand names and careful control of oil suppliers is required

Actually the TRENT 900 isn't really a TRENT. Too fine a Point??

Where does that leave the Regulatory Agencies of, for example, Australia and Canada?

Broad Brush?? If the shoe fits......?? In general, if. after an incident, the immediate divulgence of fact and insult, counter insult diminishes...one is left with What, Exactly? The sure and certain notion that mitigation of reputation, money protection, and market is being "massaged"? Yes, I think. Who remembers how many "A"s came off wing, how many were (still are) subject to sanction?? Thought so. The diminution of actual data in favor of spin is instructive of the lack of concern for safety of ALL the players.

Turbine D
 

Thanks for your considered and very rational views over the past few pages. I think your processes are valid but am curious why the IPT blades were not "cookie cutted" away unpowering the IPT when the IPT migrated rearwards.

For your info, the two bangs were separated by about 1/2 second, so the two bangs were from very different processes. I like your thoughts of an HPC stall (boom) followed by the disc burst (boom). A time plot P30 would be of great help.

Less Hyperbole Please
 

For the contributors who make accusations against LU and RR ethics, I would suggest you look at the current long haul industry engine reliability statistics (6 x better than 180 ETOPS requirements), the failure rates of the 747-400 engines from 1989-1992 (I had two), and the current notices concerning PW and GE engines. The conclusions are clear.

BTW: The RR 972 max oil temp is 196 deg C, measured just before the scavenge filter, so an oil temp of 180 deg C is not uncommon.

CAAD

YES, the engine was originally certified by the EASA, but, it was subsequently certified by the US FAA. As to the oil, this presentation may give you better insight into EASA/FAA relationships.

http://isoclean.net/uploads/GE_turbi..._pres_STLE.pdf

35 Year Pilot

FAA Notice of Proposed Rule Making.

Request for Public comment: Under the existing Rule of 51, Hyperbole Reduction Act, Comment is requested.

I'll do my part, I realize I am a titch over the top. Thank you for noticing in a civil manner.

39 year pilot

TW IMC

The FAA is subject to all Laws of the United States. One of these is the Freedom of Information Act, better known as FOIA.

Under this Act, virtually all information owned by the people is subject to petition to disclose. The FAA will certainly receive all pertinent data from EASA. This makes it Public. There is not a single databit that is immune. I do not know the EU's rules, but I am familiar with FAA's. Whatever Secrecy Foreign firms rely on outside of the USA is nonexistent in this country. Every part, purpose and process utilized in compliance mode and timeline will be incorporated by reference in the FAA's decisions. So in a very real way, the EASA and the FAA are one, though the FAA has marginally bigger stones.

under the top

QF 32
 

Guys,

May I remind us all that the value of this forum is a place for discusion amongst professionals. In particular, the QF32 thread has revealed an enormous amount of experience and very genuine concern in our community.

There is information regarding the QF32 incident that has not been released into the public domain. That much is clear.

Please let us retain a civil attitude and respect towards one another, and an open minded and constructive attitude towards the various views being expressed.

The QF 32 outcome could have been much worse. I think we all wish to prevent such a recurrence?

35Year Pilot

Good question... My thoughts on this would be that the rotor sped up as soon as the power drive arm fractured at the 580 bolts, given the N3 speed at 98% and then it moved aft, with the blades contacting the smooth leading edge of the Stage 1 LPT nozzle inner band forward overhang. Now when this happened, there may have been enough force to shear the blades off, just above the blade platform, depending on some features I will discuss below. There was no contact with the Stage 1 nozzle vane airfoils as they are "recessed" too far aft. Obviously, this is not what you want to have happen from a design point of view to slow the rotor down. You would like blade on vane contact. In the failed engine, it is hard to tell some things relative to the blades. If you look at the recovered portion of the disc photo in the ASTB report, Figure 14, Page 21, you can see distinctly two blade dovetails in the corresponding disc slots (maybe a third, not sure). All the others are missing completely. The thing I wonder about is the fastening method used to keep the blades in the disc, forward and aft. I am pretty sure the mechanism to keep the blades from moving aft is a tang that protrudes downward at the blade dovetail (leading edge side and part of the blade casting) that keeps it from moving aft. The blades are inserted in the disc from the forward side during assembly. To keep the blades from coming out of the disc forward, a retainer clip is inserted in the space under the dovetail of the blade (you can see the open area in the photo) from the aft side of the disc, and it is then bent upward both forward and aft sides, thus locking both blade and clip in place. However, there is no evidence of any clips in the Figure 14 photo. Another important feature that I can't tell is if the blades are shrouded at the tip or un-shrouded. If they are un-shrouded, the blades (some) could be pushed out of the disc slots (whole blades) when contacting the nozzle inner band with some being fractured off as the retainers would fail from the stress/heat. If they are shrouded, I would think all blades would fracture off. We just don't see enough and I am not familiar enough with the Trent 900 blades to know for sure. But, either way, I think it was too late as the rotor was already speeding towards burst point before any contact of the stator behind it. Then there is the possibility the disc/rotor was wobbling as it moved back (uneven contact).

I would agree. If the cockpit voice data recorder could have saved the sounds, it could be overlaid with the rest of the engine data to determine the exact points of the bangs in the failure sequence. Now it will be a guess.
Regards and thanks for your comments,

Turbine D

I do believe there was wobble instantly as the Drive Arm Fractured (circumferentially). The seperation, Disc from Arm, would not be in any way orderly, and an imbalance (a certainty) would impart an elliptical and irregular orbit to the Wheel. My drawings show the IPT Blades (Roots) as below ('within the perimeter') of the Stator Vane "Platform". "Cookie Cutter"** shear off of the Roots would force the Blades through and out the front of the fir tree dovetails. Given the "Shake" of the disc (wobble) in its new orbit, the roots would endure a constant force forward, while being mercilessly vibrated, a suitable explanation for their loss from the Wheel??

I've posted this prior, I don't keep track of things, and I regret if this is but repetition. Naturally, any failure description needs to be indexed with a timeline.

Now as to Boom, a Compressor Stall is possible, but so is explosive loss of LPT Drum (Gas) contents. A loss of this highly energetic gas forward and through the lost dynamic seal of the IPT would explain also the rupture of the case, pehaps in concert with exit of high energy debris. If there is a one half second lag, do you think it possible that flowing fuel from the nozzles, Oil fed fire, and loss of IPT blades could explain events in this manner?? IOW, a gas explosion out the weakened case, holed by the IPT?? This might put the Burst in front of the "Stall", so help would be needed to explain this divergent view as to timeline.

**Acknowledgments to 35 Year Pilot