This is not a conspiracy to undermine safety. It's the fact that the overriding concern is to master new techniques to keep weight down. All the companies involved have modelled everything to the Nth degree before a single piece of metal is struck, but it's impossible to get right first time.

Lyman,
Are you a metallurgist by background? The problem is complex. There are many processing steps from the time the alloy produced until the final part arrives at engine assembly. Each step must be accomplished within the defined parameters. You make it seem like it is simplistic, it is not. I did post graduate metallurgical failure work on the sudden failures of huge oil storage tanks which turned out to be hydrogen embrittlement, not what was expected at the time. I know how complex these thing can be. Don't lecture me on being in the dark or in the shadows... Good failure analysis and failure problem solutions depends on good first hand data, not on outsider speculation or imagination...

TD

The last thing I want is to take this discussion into the adversarial. 'Complex' is a highly subjective term; there is an element of 'proprietary' all too often in the realm of investigation which does not serve the public.

People do not fly on 'secrecy' or should not. I should simply have asked where to find more detailed evidence. I will try to be less sensitive to the process of failure analysis as it is practiced.

I would suspect that there is very little "proprietary" in the whole issue, given that the root cause (suspect hydrogen embrittlement) is a well-recognized and long-standing metallurgical phenomenon.

Factors unique to the GEnx (geometry, alloy, design unit stress ...) are the unknowns you and I can only ponder. The exact manufacturing process for this set of factors can only be guessed at by us, even though we probably know the basics.

I for one am content for GE and their FAA colleagues to ferret out the problem (without our help), and complete required inspections on-wing and off-wing. And if outside help is needed, there is a long tradition of consultancy between competing OEM's - to maintain the industry's safety reputation. (I am reminded of Douglas & Boeing helping audit the Lockheed L188 design during its whirl-mode problems fifty years ago).

I flew on a Holiday Airline Electra into South Lake Tahoe years ago.

The approach was a long straight in, of course, and the turbulence in the basin was extreme. Power was all over the map, and on one sink, the Captain firewalled all four. I was sitting F1' just ahead of the left wing.

I don't know from whirl mode, but One and Two were describing circles in the air two feet in diameter at the spinners. I was convinced both would come off the wing. The extension forward of engine and prop on this aircraft is remarkable, and made for some exciting wobble.

Lost at the casinos, naturally.

Hi barit1

By proprietary I do mean 'ownership', but not of processes or formulas.

I address ownership of the investigation. It should be the property, in its entirety, of the people, all of them, who have an interest in commercial flight.

Not the owners of the equipment, or the operators, or even the regulatory entity. Everybody.

You are comfortable with GE and FAA. OK by me. Those of us who remember pencil whipped inspections 737 skin, avoidance of AD 447 pitot, and other forms of deceit, what do we do? Were the Thales AA even certified properly?

Some one should care...

The final reports of incidents and accidents in the West *are* published by independent government agencies. The presence of the manufacturers is simply to take advantage of their expertise - contrary to popular opinion they have no say in the output. And at least since the '80s, whenever a manufacturer tried to, they were told in no uncertain terms it wasn't going to happen.

DozyWannabe "...published by independent government agencies. Manufacturers have no say in the output."

What is an "independent government agency"?

Manufacturers and their reps are frequently given draft product to edit.

But they don't have final say on the end product.

An independent agency is just that - separate from the regulator and restricted to publishing proven facts. The industry has experienced two major catastrophes when aircraft were prematurely given the go-ahead to return to service and neither De Havilland nor McDonnell-Douglas exist as separate entities anymore. The lesson taken from those cases is that trying to sweep things under the carpet is more trouble than it's worth.

Lyman,
They were according to the requirements that existed at the time.

Wrong! They are often given draft proposals to comment on, not edit. When all the responses are received, the Agency publishes a complete listing of proposed changes or objections received and then either agrees to or denies each change or objection, giving the reason/reasons why or why not...

TD

Usually, yes. BEA does not appear to do so in 447 report at least (and I cannot believe neither mfr or airline commented). Unless someone can point me at the comments I've missed ?

Doesnt this kind of thing almost always happen with new engine types? Thats a rhetorical question... yes it does.

TurbineD, But not aircraft specific, I believe. They were "sistered" onto the A330.

TurbineD "Wrong! They are often given draft proposals to comment on, not edit"

Goodness, I hope I am not WRONG. Shall we devolve into parsing words, and furnishing examples of how the Agency has been prevailed upon to erm "issue a MEMO" ? How a request to review has resulted in paragraphs omitted, and Airframers pleased with a lessening of the "Load" ?

It is a long and unproductive tit for tat, and you are at least as stubborn as I am annoying?

Lyman,
Lets be clear here:
In the instance of the EASA or the FAA initiating an AD for a problem or event such as the subject of this thread, these agencies may "consult" with the manufacturing folks involved or the airline for factual information, but decide the appropriate action to be taken independently of either party. A recommendation from the NTSB is not required for an AD to be issued, but because of the Charleston event, the NTSB initiated an investigation concerning the GEnx engine problem.

In the instance of either agency proposing changes to certification requirement, aircraft, engines, pitot tubes, avionic equipment, onboard weather radar, you name it, they issue draft proposals and ask for comments and recommendations. Then they decide on each one as I previously noted. For an example, you should read this and then Google to find the detailed response that Airbus gave...

Airbus backs overhaul of pitot icing certification standards

Private Jet,
You gave the right answer to your question. Unexpected issues seem to always emerge regardless of all the testing and certification steps that are taken and all the lessons learned from previous engines. For the GEnx, it would seem to be an inadequacy of a manufacturing process or processes for the component involved, not necessarily a general design problem of this component.

TD

Infrequent,
The BEA like the NTSB only recommends to EASA or FAA. It is then up to the EASA or FAA to decide to or not incorporate recommendations made. They generally do this through draft proposals and ask the parties involved for comments and recommendation before reaching a final decision.

TD

Turbine D has it right.

It's one thing for interested parties to review a draft and comment privately. It's an entirely different view when the subsequent comments are material enough in nature to result in a disagreement that need be publisized.

Yes the investigating agency has the final say in their opinions to what gets published. However the regulatory agency has the final say in what corrective action is accepted.

Typically the designer/manufacturer/operator is the one that must propose such continued airworthiness actions. If these in themselves are not deemed adequate the regulator may alter them and modify the certificate to the point where the product can not be flown until ....

It's shame that all this what-ifs get burried in a specific incident thread, Like others have said the identification of causal factors in this case are generally agreed between parties the corrective action has been proposed by compentent people and now that the implementation is under way even then the issue remains open to any new data (like more cracks)

Fear not if this becomes a bigger issue then such modification of the certificate will be published for wider expert comment. I do say expert, because most of the coments made by non-experts are disposed in a general sense during publication. If no certificate modification is published than all the questions by those on the sidelines will likely not be furthur addressed than by News releases.

I beg to differ.

For what it's worth: Here's an accident report with a remarkably similar root cause. It happens to be a skipped manufacturing step in a helical-splined piston, in an established propeller product (not a new design).

barit1,
I think Private Jet was referring to teething problems in general on new engines going into service, not just the GEnx. The most recent serious was the RR Trent 900, A-380 incident. But, others that come to mind include the GE90 introduction on British Airways' B-777 where gearbox bearing wear caused BA to terminate long range service for nearly a year. CFM56 introduction on the DC-8's where the starter shafts sheared due to too tight of geometric tolerances, also, HPT blades clogging with fine sand dust due (blades burned up eventually) to dust holes not being big enough, and I am sure there are P&W examples as well. Annoying but also disruptive problems to the airlines during initial introductions into service...

TD

Looking for "Teething Problems" in the curriculae....

The TRENT's problem was a lack of (proper) material in the IPT shaft, it is memorialized in the AD. That is not a teething issue, that is a spec/engineering mistake/blunder.

The "misaligned Stub Pipe" likewise is a blunder in machining and QA. I will continue to consider these facts and be sceptical of marketing/promotion issues that fly in the face of quality, and attempts to downplay the seriousness of these issues.

Which Trent? The 972/A380? The 1000 test bench oops?

And don't forget the RB211/747 IPT @ SFO...

There was an oil fire in a 9, in Australia, in the test cell. All the Trents have (had) the susceptibility to vibration/harmonics, and poor resistance due to coupling weakness. Too light by several kilograms...

Weight is profit lost, migrating shafts are a potential loss of life.

There's a bit more to it than that. Lighter and more efficient propulsion is not simply a question of maximising profits, it is also (IMO more importantly) a necessity if aviation is going to be able to keep up with demand in a world where oil is becoming scarcer.

Every introduction of new technology brings with it some risk, but most people are fairly sanguine about that if the long-term benefits are worth it.

I don't think I need add that none of the problems with newer engines have resulted in a fatality.

The FAA's airworthiness directive orders

(Excerpts from the AD)

"We are issuing this AD to prevent failure of the FMS resulting in one or more engine failure(s) and possible loss of the airplane."


How does one say "crapshoot" in technese?

As with the EASA AD before it (TRENT 972), the potential for loss of an aircraft is heightened....

Statistician?

Selective emphasis. The key word is "possibly" - you can have an AD which allows the aircraft to fly while being closely monitored if the chance of hull-loss is relatively remote. Compare that to the Applegate DC-10 memorandum, which stated clearly that "in most cases [this would be likely to] result in the loss of the aircraft". That is the point at which grounding until the AD is applied becomes imperative.

All transportation, from walking across the street to going into orbit, involves a degree of risk management, and everyone who takes an interest is - or at least should be - well aware of that.

Qantas dodged a shrapnel bomb, and landed successfully. The RR AD had recently been relaxed, and taken advantage of. if the plea to relax the ADhad not been granted, no explosion, by demonstration.

Risk Management? You are heating your seat.

That's a little melodramatic. If anything, the existence of the AD proves that the system has improved. Compare this to Kegworth, where the engines on the 734 were grandfathered from the 733 design despite having to handle more stress. In that case there was no AD until after the report was published, and another 734 suffered the same problem (although thankfully with no loss of life).

Your reference to certs piled on existing, are you referring to the TRENT FAMILY?

Sistering specs and expectations for a functionally different powerplant? Gads, not again?

Your reference though intended I suppose to point to an aberration, is evocative of the fallacy that caused the TRENT failure.

Scaling up thrust by scaling up dimensions is a fool's erand, as you eloquently point out, though perhaps inadvertently.

chee ahz...

There's a lot more to the differences in the RR Trent family than simply "scaling up" - there are significant design differences between them in order to suit their application better. The GP7000 series (the alternative A380 engine) was not a from-scratch design, it was developed from the GE90 and PW4000.

I'm prepared to bet that when the A380-800 series lands for the last time, there won't be a significant difference in reliability or incident between the engine types.

Engines let go sometimes, always have. Because of this, designs are refined during the time they are made. For example, the original RB211 was considered something of a nightmare in terms of reliability initially, but by the time the -535 variant was installed on the B757, they had achieved a level of reliability so good that even the Americans had to take notice.

There's a lot more to the differences in the RR Trent family than simply "scaling up" - there are significant design differences between them in order to suit their application better.

And that is why some of their certs should not have been "borrowed" from earlier designs,


:ugh:

Lyman

Which bit of GE do you work for?

A thread about three unusual failures of a GenX engine and you've dominated the last couple of pages with ill-informed mush about the alternative engine choice. Good job!

A cursory Google search doesn't seem to uncover any evidence of this - can you point me to yours?

Covered extensively in the thread, search there. Briefly, "A three spool is a three spool"

See also why the 700, with blade stator clash, contained the IPT in 'Edelweiss' ex Miami.

The 900 substituted a Stator 'platform', the IPT oversped, and the Islanders collected Titanium. same certificate....

I know, lets eliminate the variables, and model the differentials....

Oncemore....sorry, followed the bunny hole. I'll clean it up..

Actually, the failures are quite similar in nature. 100k thrust cannot be gained by inventing a brand new platform. There was more room in GE's device, but that does not exonerate them from shortcuts to the grail.

Oversimplification. If this were the case then the entire Trent series could be grandfathered from the RB211. We know this isn't the case and that each series of the Trent had to undergo most if not all of the certification tests individually.

The overriding feature of the Trent series was to minimise the requirement for variable stators - there's a nice overview here : Rolls-Royce Engines: Trent

All new and derived designs have kinks that require ironing out - this is accepted fact.

None of this is specific to the Trent series though - it's just a feature of progress in jet engine design. The "two-spool vs. three-spool" argument is a fallacy as unnecessary as the old "A vs. B" chestnut.

For example, a two-spool CF6-80 notoriously let go during a test at LAX:
FAA to Tighten Inspections on Some GE Jet Engines - Los Angeles Times

I must apologize, Dozy...

I thought for the longest time you were purposely avoiding the point made.

I am convinced you miss it on the natch...

No idea - what's "the point" as you see it?

The fact is that modern engines are statistically a hell of a lot more reliable than their forebears were when they were new...

Well, it seems the thread has morphed from the very well defined topic of discussion into a US vs UK point -counterpoint debate. Lyman, on one hand, is looking for 110% perfection on jet engines introductions. OTOH, Dozy is attempting to point out that problems with jet engines go beyond national boundaries, i.e. the RR vs GE debate, a revived but standing debate. So lets look at this.

Under Lyman theory, all aircraft would be grounded tomorrow at dawn because an unexpected event, just might be a possibility, one that doesn't meet the 110% margin of safety. Sorry, the world doesn't work that way. Next time you descend into the "grassy valley" on that winding road, worry about if your car brakes will control the descent or not. It is about the same as if a modern jet engine will perform its task or not. Despite legalistic thinking, nothing is assured to 110%.

Now Dozy brings up an interesting experience at American Airlines regarding an engine that had an unusual engine vibration as reported by the crew bringing the B-767 into LAX. The amateur test theory, as applied to your car engine experiencing the same problem, would be to back it out of the garage into your driveway, and rev it up to red line, at which point, boom! That is exactly what happened at AA. They took the aircraft to a remote area, rev'd it up to red line and boom! The correct procedure was to remove the engine from the wing and perform a look-see to find a HPT disc that had a significant crack out of the dovetail slot region after all those cycles and years. This would be a cost
reduction/elimination decision to the reduce the cost of quality that went amok at AA. The result of the amok was a loss of an airplane, not to worry, the insurance folks picked up the tab.

So lets get back to the original purpose of the thread, should any new information develop...

@TD

I hope that nothing I've said points to a tit-for-tat international debate!

All I care about is that wherever the donks come from they are designed, tested and built as well as possible...

Dozy,
Not at all! Nothing you said is a problem in my mind. All the engine folks do the best they can, always have...

So the SHA event is different !

I asked way back for any pictures since there had been a post that stated that there were some.

It's hard to afix blame without the facts

carry on