"Wobble"
 

I've looked at the recent posts and informative sites regarding vibrations and what can result. I think Bear gives some good information regarding support structures and what may be going on in these newer engines.

First, if you think about the fan and all related rotating airfoils attached to one end of a cylinder, and the LPT rotor attached to the other end, 7 feet away, you have a dumb bell in a static sense. If you pick up the dumb bell at one point near the center, both ends will sag downward, the LPT end more so as it will generally be heavier. So then, to prevent this from happening in reality, a series of static structures are designed and placed to provide the backbone of the engine. These structures must maintain alignment between rotors and stators and their design is dictated by the need for stiffness, more so than strength. The major sources of load for an engine translates into forces on the structures such as maneuver loads (turning), CAT (clear air turbulence), acceleration/deceleration, gyroscopic forces, moments through the bearings into the frame hubs that support the bearings, unbalance in the rotors, internal variable pressures in the engine flowpath and lastly, thermal differences induced by the airfoils compressing the air and then the hot gasses flowing from the combustor through the turbine components. There is also the dynamic behavior of the engine and interactions with the airframe to which it is affixed. All of these features must be combined with design features and analysis to enable the static structure components to handle different types of loads.

For the designer, there are all kinds of analysis programs to assist in determining the adequacy of the structure design, redundant structural model, finite analysis model and a complete engine structural model and a first engine bending model. In addition,designs are verified by static load testing that can include built-in defects to test design robustness. Extreme engine testing can test for structural capability under extreme vibration. Low cycle and high cycle fatigue capabilities must be examined. Based on all of this, limit conditions can be determined and set so that a well designed structure will not show any sign of deformation or contribute to a loss of performance even if the limit is exceeded in a one time event. So as you can see, the engine structures are key to having successful engine capable of meeting the mission advertised to the customers.

Good structures must be capable of absorbing vibrations and not amplifying them and there are many techniques that can be incorporated to accomplish this. I used the word "robust". Care must be taken to not reduce weight of structures that could compromise long term structural integrity although this is often looked at during weight reduction/saving campaigns to improve performance.

Vibrations and rotor unbalances are always present in an engine and they change as the total engine cycles grow over time. So the engine backbone must be capable of handling all of these variables as they occur.

Turbine D:
thanks - it is a pure pleasure to read such posts :)

could you pls tell a little more on techniques to absorb vibrations? The lower the weight and stiffer the shape the higher is the supporting structure natural frequency but doest is solve the vibration problem?
Looks like multiplatform optimization (technical characteristics vs unit costs vs weight vs project time etc) :)

Turbine D

On the money. A good argument that the 900 is not in the same family as the prior iterations of TRENT would be that the destructive issue at the heart of the dilemma does not affect the others. In using this, RR suggests that the 900 is in fact substantially different from the others.

The problem is distilled as usual into likely courses of action. The question is this..... Will for once the authorities demand a revocation, or will they succumb to pressure to keep the troubled engine in service, although it has obvious service life issues? These issues cause an accelerated loss of dependability, such that mere inspections beg the question!!

Have you searched for the specs on the "C" Modification? Given the reported limits on service, the obvious conclusion is that this powerplant is a "work in Progress". Odd that no one will address the issue, but merely defend the indefensible. I only have the "B1" manual, so my limits are strict. I do know from sources that virtually no oil issues were found in the eighteen months prior to the Burst. I also know from sources what the precise issue is. If so, the fix has some pretty lofty obstacles to a simple cure.

DERG

The seventy cycle limit was required by EASA, not "reported" by RR. No doubt there was a consult, there always is. The consult in August produced the relaxed (lax) inspection cycle amendment in September to allow Spline Wear per se to be "averaged" or normed, using each pair as a contributor instead of the "worst worn" disqualification. It was this very relaxation that allowed the Burst to happen, clearly the wear had proceeded such that certain "pairs" were not even functioning.

It is not an easy question to answer as each engine is different and solutions are different. Some examples might be the type and design of seals used in the bearing box area (seals can be good dampeners), perhaps the number of struts used or even their orientation relative to engine centerline could be another solution. But the finite element analysis program gives good indications as to which technique or techniques might be most advantageous to use if a problem is apparent. One other thing, you can raise the vibrational frequency of a frame without reducing weight by use of a stiffener ring on the OD of the frame so the frame is not resonant with most vibrational modes in the operating range of the engine. A separate item that affects vibrations is the distance separating the engine mounts that attach to the pylon. The further they are apart, the vibrations become larger should an unbalance condition exist in the rotor system of the engine. All these things must be considered in the frame structure design and analysis.

Vibration control
 

One technique I have seen is to de-tune the bearing mounting by a combination of viscous damping with spring centering. The viscous part can be accomplished by a squeeze-film clearance between the outer race and static frame hub, pressurized by the oil supply.

Similar in principle to the suspension in your automobile or aircraft, but tuned to a much higher frequency.

The Cost of Safety for The Public
 

Turbine D, Barit1
thanks for good examples - it really is a case by case operation then ;) like fine tunung relative natural frequencies so they would not happen together. Does this tuning also include the frequencies induces but burning chambers? These seem to be a source of (possibly the most) significant energy vibrations within the engine case.

Derg, Bearfoil
to me the way chosen by EASA is to FORCE the RR to act faster, even if by now they have realized that the class action would cost them a fortune and lost contracts, is asking for painfully frequent maintenance. This way RR has a chance to improve the solution (especially that the exact reason is known) while still statistically safe and without loosing the face.
After all changes to internal engine structures are difficult to prepare, make and implement fleet wide. New seals would not be able to absorb the energy emitted during TO/GA

The solution - advice to public to stop flying A380 with RR engines for a while - the question is how public can be sure the replacements program have been completed?

Excellent case of raison d'etat...

The only hope we have is the ATSB. They are the only ones that do not have a political or economic interest to consider. I guess the only thing they could do is bannish the engine altogther from use on Australian registered aircraft. I dare say off the record a few would agree with that.

There is no question that this mistake has cost RR a lot of money. They will be very carefully attending to these T900s. If another one goes bang they basically have lost all reputation. I would ride on the A388 with the RR Trent because I know that it is safe....well the probabilities are that it is safe..cannot see another novel event happening.

There is a saying about accidents, very much used on this thread; "when all the holes in the cheese line up" Yeah....we had a new engine design using an inexperienced supplier (FAG) and a duff bunch of academics advising the usual bag of dull crayons in management.

It really has been the way NOT to do things. RR made every mistake in the book. As always the general public will be mostly unaware of the background hustle. The deals will be made out of court and business will go on as usual. As Bear says:

"Will for once the authorities demand a revocation, or will they succumb to pressure to keep the troubled engine in service?"

GE will be watching all this in total disbelief. Of course the Schaeffer/FAG bearing manufacturer has opened a plant in Canada specifically to supply GE with bearings for their aerospace gas turbines. I don't think the USA or Canada will be as trusting as RR was.

The unbelievable part to me in ALL this is how RR were led to believe that the telemetry would give them " one and a half hour warning" of a serious engine problem. Just how a bunch of spophistic academics can lead a company like RR to the depths of total incompetence is truly amazing.

DERG (In 12 weeks!)

DERG Am I the only one who finds these claims a little incompatible. :confused:

That's why they hire us to head up projects, we take no prisoners. We can add up too. :E

It has probably been mentioned somwhre - ... can anyone let know which of the A380 carriers are using RR and which are GE ?
Thanks

Hiya
 

RR trents used by Lufthansa, Singapore, Qantas.
Rest are Engine Alliance (GE)

Those on the ground who have not sold off the Titanium are using hundreds of TRENT bits as paperweights.

Tell you what Bear..
 

Turbine D has been a hell of a help on here. Generally the "nay sayers" and "meddlers" have stayed well clear. We did a GOOD JOB on unravelling this mess..:ok:

WojtekSz

I think you will be surprised to learn that this is not a major concern in the combustor, and that is not to say vibrations are not created by the mixing and burning of the fuel. Vibration responses are looked at during the design phase using a sophisticated analysis program but, the major concern is that of LCF (eventual crack initiation) due to the thermal gradients throughout the engine cycle, i.e., cold to hot to cold. The reason vibration is not such a problem is the unique way it is handled. The "flame" is contained inside the combustor liner. The liner is "free floating" inside the combustor pressure vessel meaning it is not firmly attached to the pressure vessel in any way. The liner itself is cantilevered by bolting it to the stage 1 HPT nozzle ring. At the turbine nozzle attachment point, a 360° leaf seal is used to prevent hot gas leakage, but it also provides dampening. The actual liner is constructed from several individual pieces. The dome (front end where the fuel nozzles inject fuel) is one piece. It is bolted to the inner and outer liner walls with a series of self locking bolts. The bolts serve as dampers and prevent vibration from transferring to the fuel nozzles that are attached to the main fuel supply tube ring. So there is vibration but it is dealt with by unique design mechanisms to prevent it from being a problem.

Turbine D:
thanks - your clear explanation + some web search produced much better understanding that the combustor tech can be very simple (available to enthusiasts) or complicated (professional big power aeroturbines). But the vibrations may be contained and to certain extent controlled.
http://www.users.zetnet.co.uk/gas/cutway2.jpg

Is LCF based on using cooling airflow, protective coutings, disposabe elements to prevent temp buildup or polishing and rounding the edges to prevent cracks? Most probalbe a mix of the above but are there any other interesting techniques?

WojtekSz

In answer to your combustor question concerning LCF, just about everything you mentioned is done to improve combustor life. Primarily, I am more familiar with combustors that are not lined, meaning nothing is disposable, but other combustor designs use tiles that can be replaced. The liner walls are cooled with air through a series of small holes to provide a film of cooled air. The flame side of the liners are thermal barrier coated to reduce the magnitude of thermal gradient, e.g. cold - hot - cold. Attention is paid to rounding all edges to minimize potential crack initiation sites. Regardless of the extremes this component sees, they last a long time. Life is very good on engines that fly long distance routes, 10-14 hours in the air, fewer cycles and long hours. There are set periods of time/cycles where boroscope inspection of the combustor is done on wing. If an engine comes off wing regardless of cause, the combustor is inspected. At a specific set time, the combustor is removed and weld repaired as necessary and reassembled with time starting as if it were new. This can typically be done 4 times before it is scrapped.

I should add, the newer combustors utilize twin swirlers that perform better to mix the air with the fuel creating a leaner burn, lower temperatures, improved fuel burn and longer combustor life.

Basic Designs
 

TURBINE D

"I should add, the newer combustors utilize twin swirlers that perform better to mix the air with the fuel creating a leaner burn, lower temperatures, improved fuel burn and longer combustor life."

So we have a cool end where the big intake fan is, and a hot end where the exhaust gas is released. We have your analogy of the central shaft running from fornt to back...about 7 feet..in the case of the T900 upon which all of the various twirlers and compressors are affixed. Then we have the ancillaries the power take off shaft down to the gearbox and another shaft to start the engine. Much appreciate your input..thank you!

OPEN FORUM

Deduction 1.

Looking at the latest GE design we see that the big intake fan is made from carbon fibre. GE also use a fibre case to house the engine. So I think I am correct is assuming the GE products are using carbon fibre technology where as RR are using advanced metallurgy for the blades and old technology for the case.

Deduction 2.
Because the intake fan is lighter in the GE engine it is easier to balance and has inherently less kinetic energy to be lost in vibration. So the big mass at the front end is now "tamed".

Deduction 3.
Running temps. The 180C and 196C max temp of the T972 that failed is higher than other civil aviation engines to date. We have read the data in the Oxford University document and it is noted that 10% or more of RR engines fail the final passing out test due to imbalance. And a higher rejection rate is detected when the engines are overhauled at the RR appointed agents. The high running temps are cause by vibration inherent to this design.

Deduction 4.
Manufacturing tolerances. The RR design is difficult to manufacture beacuse of the nature of the concentricity of the drive shafts and the fact that is has three distinct compression stages. GE, I believe, use two stages.

Deduction 5
Given that the RR product is inherently difficult to balance it is clear that the existing in service methods of detecting an inbalance are inadequate.
On one drawing I see only one vibe detector noted but this was a schematic and there may be more than one.

Deduction 6
RR agents themselves cannot detect vibration or allow engines that are outside the norms back into service.

Deduction 7
RR are aware that the 3 spool design has inherent flaws but are unwilling to adopt a new design because the costs would be to high.

Deduction 8
As we see the fractured oil feed pipe as published in the ATSB report we must assume that the quality checks on parts from outside suppliers is poor.

Deduction 9
Communication failure. As the fractured oil pipe is clearly of poor manufacture we must deduce that the department which does the invigilation does not realise the importance of that part. In other words they have no concept about the vibrations inherent within the machine.

Deduction 10
Management Character. The commercial managers were easily persuaded that the monitoring system using the probablility model was robust. Because the work was done by assumed experts they did not apply rigour in seeking confirmed evidence. As far as we know they did not hire MIT for instance.

We know that a company called Schaeffer with the brand names FAG and INA were given the contract to build the entire bearing set and support structure. This was the first time this company had built this..the entire assemble with supports... a complex and critical part for a civil avaition aerospace gas turbine.

Deduction 11
The failure to be able to shut down the #1 engine on the stricken Qantas A388 was unforseen.

All repiles most welcome.

its been suggested that previous RR design errors have been caused by the RR legend of mechanical perfection influencing RR engineers

Yeah I can believe that.

Derg:
have you invented a new Deduction Generator ;) ?
Looks like too much of a guesswork at play, why don't we stick to facts pls

1. Fan - carbon fibre is lighter but more expensive. Companies do gamble with new technologies sometimes.
2. Balance - lighter does not easier to balance - depends on quality of machining, and the rotational speed also and this is low speed ...
3. Oil Temp: are you sure we can use the data from such article to make such bold statement about 10% engines not passing final tests? Any wise manager would make a fortune by properly implementing 6sigma methodology there to squeeze it down to 1% in 24 months. High oil temp may be caused by vibration but these are caused by 3 shaft design principle. It is a strategic gamble by RR to pursue this road.
4. Manufacturing tolerances: OK, see point 3.
5. Vibration detection: usually small vibrations are more dificult to detect ;)
6. Vibration allowance: as far as i understand, one cannot use the maintenance stand to measure vibrations during engine operation
7. 3 spool design: it has own advantages thou, simply something was not ready in Trent 900 version when started selling it
8. Oil feed pipe: ever heard scape pipe? (sometimes referred to as scapegoat)
9. Communication failure: another reason why kaizen principles should be implemented in RR.
10. Management Character: You have assumed sth based on an univ paper so why shouldn't they? Roller bearings and managers must have tough b..s. Univ papers are seldom treated as robust. At least here... And MIT is from USA, right? For scientists there are two models: coach them or buy them - if you want to get govt support better coach them... Recently Barcelona home grown team plays much better team than Real Galacticostly stars (search for Spanish soccer results) :) Selecting new suppliers in tough times is usually caused by search for economic solutions. Takes time to gain experience.
11. The failure to be able to shut down the #1 engine on the stricken Qantas A388 was unforseen: a big lesson that i am sure has been properly thought over.I do not know the results but from the discassion over here it is not a simple problem.

:}:}:}

The Facts
 

My Facts are as good as YOUR Facts..:cool:

yeah, you're right but would you build anything valuable (say: a 0,1M$ house or a 10M$ bridge or a 10M$ turbine engine) based on such facts as we have here ;)
I would say these are good for discussion or creating opinions but too weak for making real decisions.

Basic Designs
 

WojtekSz

I couldn't let this pass without some comments:

1. The composite material may be more expensive, but the end product isn't. You have to look at the bigger picture. Here is a site that gives you a picture of the machining that is required (none). Also, think about what is all required to produce a hollow titanium fan blade and inspect it for all the things that could present a problem.

GE to Auction GE90 Fan Blade at Oshkosh

The GE90 composite fan blade was not a gamble, the technology was there to do it and it was done.

2. Balancing of the GE90 fan is easier, remember, no machining of the fan blade, only the simple disc and attachment slots.

3. Read the Oxford/Rolls Royce study again. From 4/9/02 - 9/30/03, 11 Trent 500 production engines failed pass-off testing for abnormal vibrations. These are known in the business as "hanger queens". In 17 months, you can barely afford to have one hanger queen, let alone 11. This is indicative of systemic problem that requires lots of attention.

4. The best phrase here is an acronym: K.I.S.S. It means "keep it simple, stupid".

5. Small vibrations are not as hard to detect as unknown vibrations.

6. Vibrations can be measured on an instrumented engine in a test cell. The problem is they may not be the same vibrations encountered in flight on the wing of the aircraft, but, it is a good start.

7. The advantage of a three spool engine is shorter length. Therefore a shorter nacelle can be used that normally produces less drag and better aerodynamic performance for most aircraft. However, the disadvantage is the SFC of a three spool engine is generally less than a longer two spool engine and it could turn out to be a wash. It has been reported the GP7200 engine has better SFC than the Trent 900 in the same nacelle, not a surprise.

8. Only the weak link in the chain.

9. Continuous improvement is important in any business and every organization making up the business including top management. This starts at the very top, water always flows down the staircase and rarely up.

10. Maybe going back to the Trent 500 days, there was some handwriting on the wall there, that was missed as the technology envelope was pushed.

11. A lesson learned on the A-340 that hit the wall on the ground in which they couldn't shut off the engine for 5 hours was thought to be a not repeatable incident.:ooh:

Turbine D, Derg:
hey, you are both right !- there are basic problems somewhere within RR design and business but being an European i am a little biased towards trying to understand RR problems while not being British i do also understand that US has made flying a huge business not without merit. Certain competition is always good for us customers - for me it is good that Boeing has Airbus and GE+PW has RR to watch at. Problem starts when established leader looses the edge over its followers or the followers take shortcuts to try to overcome the leader.
But actually the biggest threat comes from what has been defined as 'innovate downwards' movement that has been started long time ago by certain Sam Walton and transferred into aviation by SouthWest Airlines later. So instead of 'citus-altus-fortus' we have 'everyday low prices'. And people got used to this: all of us! And this attitude has deep consequences - american car producers are just recovering, nike is not making any shoes in US, a new stealth plane was recently presented in China ;)
Cheaper is fine as long as customers allow for lower quality because without profits there is no development and no quality. Just look how many more customers want to fly A380!
Unfortunately times of Apollo and Concorde are gone...

Would I build?
 

"would you build anything valuable (say: a 0,1M$ house or a 10M$ bridge or a 10M$ turbine engine) based on such facts as we have here http://images.ibsrv.net/ibsrv/res/sr...lies/wink2.gif
I would say these are good for discussion or creating opinions but too weak for making real decisions."

Civil Engineers are involved in many projects which are multi disciplinary and the most recent failure was the BP, Trans Ocean and Halliburton accident in the Gulf of Mexico. I was not involved.

Unlike building an engine to a set pattern each job is different so we are familiar in using first principal methods to achieve the result. And all the time we have the finished project in view while building. Safety is paramount.

The value of the project in terms of money is important to the accounts but our job is to build the structure "on schedule, on quality, and on budget". This is often impossible.:suspect:

I have to say that building a gas turbine is relatively less stressful because you have total control of the variables. In that sense mechanical engineering is easier because you know the materials, the environment and loads and temperatures it will have to endure.

The designers, the architects, are often ambitious in what they want to build. "Walt Disney" concepts in perfect world where the sun always shines and the ground never moves.

The facts we have here are abstract ideas based on what we have seen and read. Would I build on them? Or maybe you should ask would I invest in the product or the company using facts we have uncovered. No, I would not.

Although being a little off subject, in the USA, Southwest Airlines is a real good thing, not a innovate downward business at all. They developed a business model long ago that has withstood the pressures of the aviation business in both good times and bad. They adhere to the K.I.S.S. philosophy, point to point flying, no expensive hubs, one airplane model (Boeing 737's) and reservations only through their site. You can fly anywhere in their system for $120 one way and at times, $59. There are no extra fees, add ons, no charges for checked luggage. While the US majors were all filing for bankruptcy, Southwest was making a good profit. Why? Because they had money to hedge fuel and recognized the need to do so when others didn't or couldn't. I can fly to Florida for $198 on Southwest verses $425 on Delta, roundtrip. The seats are the same or better, the airplanes may be better, 737 verses a regional jet on Delta, and the service is great. It's not the same as Walmart.

I just came off reading a book "How Boeing Defied the Airbus Challenge" written by a retired Boeing executive Mohan R. Pandey and my head is full of ETOPS. The book implies that the additional ETOPS rigor in design/testing enhances the overall safety. Does anyone know or have the expertize to say if RR would have probably found the problems if the engines were required to undergo the additional rigor required for ETOPS certification?

ETOPS and the T900?
 

Yeah...excellent question! :ouch:

Radken
 

DERG

As to no. 11 in your list - the “unforeseen”, I know this 380 thread is primarily concerned with the engine event itself, rather than the effects of its shrapnel on other systems/structures. However, it does seem that in PPRune it’s the only thread to use right now to point up and discuss the matter that it is Airbus itself, and not RR, which has also let down the flying public v/v the No. 1 fuel cut-off issue. But they’re not alone.

It’s quite discomforting and significant to know, without any doubt whatsoever, that the QF32 crew would have had absolutely no control (except fire bottles- if they would have worked) over a fuel fed engine/pylon fire at #1 at any point after the #2 burst. What a way to discover a long existent “unforeseen” engineering oversight, to be forced into the full realization that lack of well designed redundancy in this critical system truly endangered everyone on board. The truth is, though (I believe), no cmcl jets have redundancy in this area.

So, we get to learn from QF32... and we get to learn it without loss of life. How wonderful and fortunate is this unusual opportunity for EADS/Airbus to sit back, take a deep breath, clear the mind, and begin thinking about obligations to others besides their “bean counters.”

Trent 972 pointed out that the A380 FCOM shows “fire” is not one of the sensed FADEC parameters. That makes total sense. I’m sure it’s this way for a very good reason. An engine shut-down decision based on supposed fire is much more in the purview of the skipper than it should ever be as the purview of some remote device, which itself may have been instructed erroneously by any number of other devices, themselves of dubious reliability.... such as fire detect loops. But when called for it'd better work!

I can only add that the re-exposure of a previously demonstrated (Turbine D - A340 versus the wall) weak link in what should be an “infallible” engine/pylon fuel cut-off system should be addressed by Airbus (Boeing, etc.) ASAP. Redundancy in hydraulics, electrics, tank plumbing? Why not in fuel shut-off, too? It apparently could be real handy at times. It may not be “Rocket Science,” but it sure sounds like good “Jet Science.”

Radken
 

"Trent 972 pointed out that the A380 FCOM shows “fire” is not one of the sensed FADEC parameters. That makes total sense. I’m sure it’s this way for a very good reason. An engine shut-down decision based on supposed fire is much more in the purview of the skipper than it should ever be as the purview of some remote device, which itself may have been instructed erroneously by any number of other devices, themselves of dubious reliability.... such as fire detect loops. But when called for it'd better work!"

I know Airbus made a statement that they had made changes to the software so this issue was addressed. Just how or what they did they did I don't know. I agree entirely about automation and I have argued a for big red "master off" button elsewhere on this site. I know Airbus have issued statements to encourage a return "to basic flying skills", to always keep up the skill, because I think they too are scared at how much crews rely on the machine.

I don't view Airbus as a culprit in this event. Structurally the wing structure took the missiles very well and there was clearly enough redundancy in the design. The Qantas crew was very confident that the aircraft was doing OK-ish until they could not shut down #1. To me this was the most dangerous part of the event until the passengers were off.

As to the loss of the controls by the missiles: the electrical loom did not cause a fire and there was a circuit some where that could energise the motors that drive the hydraulics. There were five qualified people on the flight deck to work out what the machine was telling them and they were able to sift the chaf from the wheat. They all had previous Airbus experience so knew the basic systems well.

If the escaping fluids had caught fire it would have been a total loss and I would be nowhere near this thread passing opinions. I am not sure it was good fortune though. There is a concept called "the unforseen point load" which will be familiar to civil engineers. Basically this means that at any point on the structure it is subject to improbable events or abuse. I am sure that Airbus had considered and addressed this possibility.

The fact that sparks from the broken wheels did not ignite the fuel was again luck perhaps..but maybe they had chosen a certain alloy for the wheel construction that did not spark so easily. The brakes must have been red hot too.

Looking back, the first thing that came to mind was the way the emergency fire crews dealt with the still running engine, fuel on the floor, hot brakes and rims and 469 souls still on board. It was then that I saw a need for an external stop control. An emergency panel that rescuers could access to shut down the fuel flow.

I agree with the pylon failure yes. That should be easy enough to do. This A380 was designed as a load carrier and as such made some compromises.

Would ETOPS Have Made A Difference?
 

avgenie

I am not sure. If the 900's were on a two engine aircraft, they probably would not have ETOPS approval beyond the lowest level at this point in time. But, they would still be flying.

ETOPS certification involves assessment of aircraft and engine reliability and enhanced training requirements of the aircraft operator's flight crews, mantenence personnel for both aircraft and engines and even the personnel that do the route planning.

The current approval standard for 180-minute ETOPS is 0.02 shutdowns per 1,000 hours of engine operation. That’s amounts to an in-flight shutdown rate of one every 50,000 hours. Many of the world’s 92 ETOPS operators are achieving 0.01 shutdowns per 1,000 hours or, for twinjets on eight-hour ETOPS flights (accumulating 16 hours of total engine time per flight), an average IFSD of one every 6,200 flights. This level of demonstrated safety has prompted many operators and authorites to opt for longer planned diversion times, from 240 minutes to virtually "unrestricted" ETOPS. Statistically, twin engine planes have a lower likelyhood of a diversion compared to 3 or four engine planes.

ETOPS REGULATORY REQUIREMENTS

a. All two-engine airplanes and three- and four-engine passenger-carrying airplanes operated under part 121 are required to comply with 14 CFR 121.161. This regulation imposes special requirements for ETOPS for these airplanes. These operations are defined as:

(1) Two-Engine Airplanes. These are flights whose planned routing contains a point farther than 60 minutes flying time from an adequate airport at an approved one-engine inoperative cruise speed under standard conditions in still air.

(2) Passenger-Carrying Airplanes with More Than Two Engines. These are flights whose planned routing contains a point farther than 180 minutes flying time from an adequate airport at an approved one-engine inoperative cruise speed under standard conditions in still air.

If you would like detailed information to the requirements and how they must be satisfied, copy and paste the address into your browser for the the FAA site below:

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/2e0f31985abd83ef8625746b0057fd06/$FILE/AC%20120-42B.pdf

Turbine D

The TRENT 700 has two documented cases of dual engine failure in ETOPS service.

Extended-range Twin-engine Operational Performance Standards.

Wouldn't that cause a problem?

It did. One Hull Loss and one anxious relight.

What sort of engine failure allows a successful re-light?

Poor choice of words, forget. The engines kept running, but at idle thrust. The Flight had to descend to 13k AGL before regaining climb thrust. Over the Rockies.

OPS: Oscillating Pucker Syndrome.

Poor choice of words! I'll say. You claimed two Trent airborne failures which weren't failures at all. What about the other claim?

fuel starvation requiring an emergency (ENGINE) AD qualifies as a failure to me. One a/c was lost due lack of thrust, another came within 13k feet of impacting remote Mountains. Our give and take could get arcane and adversarial; I'll stipulate that we have an impasse.

With this caveat. The FOHE in these incidents/accidents is also under suspicion in the QF32 Burst, along with the EEC's inability to shut down the QF32's #1 and #2. The FOHE is the only oil cooler on board both iterations of these variants. The OIL in 972 is a known issue, as to temps, and service life at poured specs.

The fact that some believe the 972 has no FADEC fire point is not relevant, the panel showed FIRE (via EEC) on the ECAM, interposed between two alerts for "OVERHEAT", yet the Engine (S) both were allowed to run on. And ON. The Architecture in TRENT installs is borderline AD worthy at any given moment. Emirates over the wall Hull Loss, BA038's Crash, and QF32's Serious Incident.


edit. To others. Isn't it a matter of concern that the loss of #2 and the runon of #1 are indicative of a common fault?? To me it is obvious; am I alone in noting the original lack of shut down of #2 and the run on of #1 ?? The EEC technically caused the Burst AND the Loss of #1 via mud ingestion?? The High Oil Temp may not have been the result of Bearing overheat, but the lack of Cooling at the FOHE, which then allowed the bearings to O/H, and Fail?? There is a great deal more to this than meets the eye. EG "OIL Aeration, Misting, OverTemping," etc.

Trent-700 ETOPS Failure
 

Forget

Bearfoil didn't mention this one.

DCA04IA002

It was eerily similar in results to the Qantas QF32 except for the fact the IPT disc didn't burst because it moved back into the stator behind it with the rotor blades contacting the nozzle vanes slowing the disc rotational speed below the burst point. The problem on this engine was coking that clogged the oil venting system and with surrounding heat, caught on fire. The aircraft was on an ETOPS route after departing Miami, Florida.

Fuel starvation, if the cause of starvation can be corrected; Compressor stall, if there is enough time and altitude to preform an air start. Just two examples, there are probably more.
Here is an example of a successful fuel starvation re-light, Boeing 767 with GE-CF6-80 engines:

On June 30, 1987, shortly after a Delta 767 took off from Los Angeles with 205 passengers on board, Capt. John Gilfoil mistakenly moved the fuel-control knobs to the "cut off" position while intending to move other switches on a nearby engine-control panel.

With both engines shut down, the 767 dropped from 2,000 feet to 500 feet above the Pacific Ocean, before Gilfoil restarted the engines and flew on to Cincinnati.:ok: