Cheeses
 

The latest advisory has deflected thinking on this thread into the mechanics of the Trent powerplant. But in reality its another cheese situation all over again, and the three relevant Cheeses are: temperature profile, fuel quality, and powerplant design. Only two of these, realistically/sensibly, can we change.

FE Hoppy and I, and one or two others way back at the beginning of 2008 said that the fuel will have had a role, and in the last few days Airfoil Mod and Spilko have reiterated that thought.

Blocking at least one hole in the cheese (Trent 800 FOHE redesign) takes care of the issue at least on the surface. But I would be more comfortable if someone could compare the performance with the current Trent powerplant flying the same temperature profile with fuels from from, say a European or a US refinery, compared to RP-3. (Jet Fuel #3, even when on spec and meeting Jet A-1 spec, can sometimes be, like Russian fuel, different compositionally to 'traditional' Jet A/A-1, if there can be said to be such a thing).

There was a statement in this thread some time ago referring to the fact that the behaviour of Jet fuel under extreme low temperature conditions was being shown to throw up some surprises in the testing following the incident, indicating that our knowledge may not be as good as we thought. Well, yes. I have said in an earlier thread why the recovered fuel may not be fully representative of the loaded fuel and in the final report I would like to see the GC/MS curves of the retention sample vs the recovered sample as well as the usual tests that define on-spec Jet fuel so we can have an educated guess at understanding the role that the fuel played - or not.

One thing I dont understand is a constant lack of reference to the retention sample. The AAIB report says that "It was estimated that the fuel uplifted in Beijing at the start of the accident flight might have contained up to 70 ppm of dissolved and entrained (suspended) water". Why estimate? Use the value that was in the retention sample which you will have analysed... or do you not actually have a valid retention sample?"

But, more generally, why should we bother? Surely if we block one cheese hole by fixing the Trent issue we can pack up and go home because the issue is fixed whether there is loads of water in the fuel or not?

The answer is we should bother because over the next five years we will see a proliferation in biofuel-based and Gas-to-liquids (GTL) based Jet A/A-1 blends some of which have known issues related to low temperature performance. The kinds of research that is now being conducted following the BA 038 incident is badly needed to ensure we can reliably predict performance and compatibility issues with, and better testing for, drop-in biojet blends which will prevent a similar incident. We need to confirm that the current testing regime - which has been in place with only a few modifications since before most of us were born - is sufficiently protective in current operational situations and with the diverse range of fuels that are about to enter the mainstream.

Can we afford not to block the second hole in the cheese by fully understanding the role that fuel played in the incident and the implications for different fuels that will be with us within a decade? That is why we must fully support the establishment of a joint FAA-EASA research and testing program that is a recommendation of Interim report 2.

Pinkman

There is a very real difference between twins and quads and that is the surplus of power available on twins which together with efficient wing design allows higher cruise altitudes than quads and with it lower temperatures.

You are correct of course AFM. :ok:

Then there are the people in a quiet room somewhere at Mega-Corp Airlines' home office that crunch such numbers regularly. Our regulators also play this game, something I find the NTSB and the FAA at 'odds' on constantly.

vapilot
 

Agreed, would have the oddsmaker a more conservative sort.

Some people confuse Warranty with Guaranty, Eh?

AF

Airfoilmod, yes you are correct about fuel heating, the temperature issue was addressed in the AAIB report however there is a need for fuel heating if and when the FOHE becomes blocked. An earlier suggestion in the thread drew attention to a similar problem on the DC8 that was solved by reversing the flow of oil to have the hottest oil near the inlet face.

It might be a useful addition to the OH panel to have a differential pressure light activated by sensors either side pf the FOHE, I quick cheap mod that would alert crews to a potential problem.

An alternative solution could be to have air/oilHE.

Unexpected ice formation in areas of restricted flow has caused problems in the past, viz. the loss of the nuclear powered attack submarine USS Thresher (SSN-593) in 1963.

"Thresher had probably suffered the failure of a join in a salt water piping system, which relied heavily on silver brazing instead of welding; earlier tests using ultrasound equipment found potential problems with about 14% of the tested brazed joints, most of which were determined not to pose a risk significant enough to require a repair. High-pressure water spraying from a broken pipe joint may have shorted out one of the many electrical panels, which in turn caused a shutdown ("scram") of the reactor, with a subsequent loss of propulsion. The inability to blow the ballast tanks was later attributed to excessive moisture in the ship's high-pressure air flasks, which froze and plugged the flasks' flowpaths while passing through the valves. This was later simulated in dock-side tests on Thresher’s sister ship, USS Tinosa (SSN-606). During a test to simulate blowing ballast at or near test depth, ice formed on strainers installed in valves; the flow of air lasted only a few seconds. Air driers were later retrofitted to the high pressure air compressors, beginning with Tinosa, to permit the emergency blow system to operate properly."

:ooh:

As people seem to be taking the NTSB press release a little bit too far, I will repeat what I wrote in post 2282 :-

======================
======================


From the NTSB press release posted above :-

"......... These recommendations are being issued in response to the findings in two investigations - an accident and an incident - involving engine thrust rollbacks on Boeing 777-200ER airplanes powered by Rolls-Royce RB211 Trent 800 Series engines. In both cases a build-up of ice (from water normally present in all jet fuel) on the fuel/oil heat
exchanger (FOHE) restricted the flow of fuel to the engine, resulting in an uncommanded engine rollback. ............" (my bold)


Fascinating.

According to this, the two investigations have been completed (at least they have specific "findings" and are factually known) as opposed to theories or speculation !

Likewise, they have supposedly explained where the additional water came to cause the problem.

Unforunately they haven't bothered to highlight other engine installations in other planes which need similar flight restrictions.

.

=====================
=====================


The AAIB interim report number 2 only indicates the possibility of the FOHE being the problem. Its experients were with fuel with 90 ppm rather than the expected maximum 70 ppm of the actual accident plane which had tested remains of 40 ppm and of which the expected maximum of 70 ppm would have been reduced by ice forming at the bottom surface of the tanks.

For the cause of the accident to be properly explained the fault must be properly explained - it is not good enough to guestimate it.

Likewise, other aircraft with various other enginge/fuel installations should be examined for possible similar problems with the new phenomomen of fuel/ice slush (or whatever they are going to call it.

People seem to think the work is over and the aviation world has the problem put to bed - there could be masses more work to come.

As for the near simultaneous fasilure in two separate systems and its effect on ETOPS I will ignore that due to total ignorance.

.

how to make a million.
 

Some one needs to come up with an inline water extractor for fuel that can be retro-fitted the aircraft fuel systems upstream of where the ice may become a problem.

ETOPS
 

Phil - the concurrent rollbacks are not mysterious, neither are they complicated. Nearer the engines, the Fuel systems "rejoin" in their critical attributes. The Plumbing, Fuel, and Fuel delivery systems are virtually identical, close in. Given they burn the same Fuel, stored identically, in identical ambient temps, I think I can explain why #2 quit seven seconds before #1. The #1 engine (Port) was fed from a tank in a wing that had been in the Sun flying West. The Starboard wing tank was in the shade of the Fuselage, on the North side of the a/c.

Right or wrong, ETOPS isn't perfect. Facetiously I suggested in a post way long ago, that true isolation would be served by mounting a Trent on #1 pylon and a GE on #2. "Designed Anomalous Systems" - DAS. What Else could I call it?

What I think would be fascinating is a hard copy made available of this thread. Warts and All. Informal Hangar Talk with the odd expert poking in now and again, a year long exercise in the new format of the "Pilot Lounge"

AF

FE Hoppy
 

Cool the Fuel at the Refinery and filter it, removing the Ice before it gets into the a/c. You think Jet is expensive now, wow. If an a/c can separate the water in flight (Ice), I think it could be done on the ground.

"Sticky Ice" ?? Teflon Pipes.

sky9 GE "Heats the Fuel" with a second pass through the FOHE.

bernd What of the GE architecture ? (HP) in front of their FOHE instead of downstream of it?

Phil Depending on who can make the better case, "It's the Fuel", "No it's the Trent", some compromise may involve all other types. But it's a hard sell, without a record of at least an "Incident" on another non 777-200ER a/c

I also think there are folks in China hoping for another incident that doesn't involve Chinese Fuel. (Consider the foul-up outcome in China?)

Bypass, Bypass, Bypass. (Blender included, no extra charge)

AF

AirFoil Mod
 

AirfoilMod

I told you before...stick to what you know (clearly not fuel systems)! Take the water out at the refinery (they do - there are filters and coalescers) and it will be back again by the time the fuel reaches the aircraft.

Water is removed and checked for again and again. But the nature of the fuelling supply chain and the fact that heating and cooling of fuel takes dissolved water and condenses and re-entrains it as free/suspended water means it will ALWAYS be present at low levels in aircraft tanks.

The point that I agree with you is that there are lots of other fuel related questions that havent been asked, let alone answered. Chinese Jet fuel has an incredibly low (better) freeze point than Jet (-40C) or Jet A-1 (-47C). At THAT temperature (better than - 50C) how would the GE system perform?

Pinkman

Thanks for the reminder
 

Pinkman. What is your input on the type of Ice reported by Boeing? What about the GE architecture? Alcohol or other solutions?

I'll reel meself in if you open up a bit. Deal?

AF

One other thing before you cry Uncle at H2O in Fuel. Nitrogen transporters? Closed system pumping. May be time to build Fuels for ETOPS in water free enviros?

Apologies if this question has been asked before.

I am a very frequent non-pilot flyer, and always assumed that safety was in part my responsibility. I listen to briefings, check for exits and scan this forum from time to time for news on flight safety.

I had never felt great about flying the atlantic with twin engine planes, but had taken some comfort from ETOPS certification, understanding that the chance of failure was extremely low given the testing and modelling of systems in ETOPS certified planes.

In the face of the documented problems and NTSB warnings, how is the 777 able to maintain its ETOPS rating?

andy
 

It's been asked, but perhaps not quite so well or succinctly.

First of all, it isn't 777. It is one iteration, the 777-200-ER (Extended Range). The one with the Trent RB211-800 engine fit. There are 228 of these flying.

As for your question, no one can or will say. The FAA (EASA's counterpart in America), has issued an Airworthiness Directive (AD) regarding prevention/mitigation of the problem of Ice plugging the FOHE. It is assumed that this step is sufficient to make safe this fleet of a/c for now, anticipating the development and certification of a replacement for the challenged system. When that fix is available, the a/c will be refit in some sequence deemed appropriate to the specific fleet. This is my understanding, and since an error in this forum is immediately pounced upon, I am reasonably confident of its accuracy.

AF

Statistics
 

airfoilmod says in #2341:

The statistics just don't mean that. The implication is that on analysis of several million trips (or tens of millions - I don't have my statistics textbooks to hand and my maths degree is getting a little rusty) it will turn out that the event will have occurred in about one in a hundred thousand. The statistic does not mean that there will definitely be one occurrence, and only one occurrence, in every sample of 100,000 trips. Without presence of a common causal factor, any two trips are equally likely (or unlikely) to hit the problem.

Dairyground
 

Noted. In my job long ago as a croupier, I was taught that each roll of the dice is independent of all others. Without drifting into chaos theory, or Quanta, the odds on rolling a seven are six in thirty six. I once saw eleven straight passes at the table, the "odds" are very long. Would you place a wager on such a thing. For a pax, the odds are almost nil that a rollback will occur. A frequent pax not so nil. Pilots less so, the Carrier has the most exposure of all, except the Authority has all of it.

AF

Please note I said NOT to rely on statistics. And include the Flip of your assertion to wit: It may happen more often than one in 100,000. That it happened once is startling (look at the length of this thread), twice is astonishing, absent your "Common Cause".

No less an authority than NTSB claims a recurrence is "likely". Read the report..... Less Faeries on a pin, more on the conclusion of the lab coats.

AFM

I will reply in a PM to avoid thread clog.

Pinkman

ETOPs is based on the assumption of independent failures of the engines.like a turbine and a FADEC

EROPs includes all engine combinations including Quads and dependent failures like ice

I'm far more concerned abot fleet statistics impacting EROPs than ETOPs
but I'll leave that to the statiticians to ponder

GE matters aside, it is interesting that both roll back aircraft (Delta and British Airways) were uplifted in China.

During the NTSB testing, they discovered that ice is stickier and more troublesome not at the lowest fuel operating temps, but in the bottom third of the typical range for the flight profile. The lower freeze formulation of that particular fuel moved the range into the area of concern.

I remain perplexed as to how this was missed during the airframe fuel system & engine certification and design paths and why the problem has remained hidden until now.

The 777, as the biggest twin, is exploring new territory wrt operating higher (and colder) for longer. So rather than making the fuel more expensive for everyone, why not identify a solution specifically for this type of operation? A new system requirement for extreme cold exposure is implied. That RR are now urgently taking this on board is a given. Other systems designers (certainly not just engine designers) should be equally diligent.

I don't suppose anyone has the additives that the Chinese add to the fuel to drop the freezing point ???

I have a feeling there is something there that shouldn't be there.

Failing that, anyone who comes ex-PEK, can you get a cupful of fuel and I will do a decent NMR on it, I have a suspicious feeling about all of this.

So, anyone know the RR Vs GE ratio - 777 flights out of China?

Perhaps there is a specific molecule in the fuel that acts as a nucleus that collects several water molecules about it. This wax/water blob would then freeze to cold surfaces and subsequently collect its fellows.

I think the fact that it has only affected the Trent 800 power plant is of more interest and significance. I have operated in and out of Beijing for many years in various types but not on B777, as have thousands and thousands more over many years. This problem has not and is not occuring on other engines.

Why can't people accept the Boeing and RR findings and recommendations?:confused:

Airfoilmod :


.............. What I think would be fascinating is a hard copy made available of this thread. Warts and All. Informal Hangar Talk with the odd expert poking in now and again, a year long exercise in the new format of the "Pilot Lounge"


Remember this is the second thread on the accident, the first one was pretty huge as well.

.

Why can't people accept the Boeing and RR findings and recommendations?

They are no more than interim.

They used non-representative fuel, and unless they are being very odd haven't managed to recreate the problem using representative fuel (anyone know ?)

-----------

In addition, the new fuel/ice behaviour needs examination and new rules written - AND all engine/fuel installations need to be examined against the [future] new rules. There may be more aircraft at risk than we know.

.

.

Phil,
Low freezing point Chinese or Russian fuel has been in use since Adam was a little boy. I am talking about exposure of this fuel for some 30 odd years before my retirement. Can you tell me why this problem has only affected the Trent800.:confused:

Additives (again)
 

Several of us discussed this matter waaay back. I brought up some issues -- as did airfoilmod and several others -- related to FSII. As was mentioned a few posts previously, these additives work by attracting water molecules to attach themselves to the additive molecules. It may well be that the properties of the resultant "stuff" are just not well known in long lasting low temp conditions.

Excerpt from a post from last June (18th):

“I am certainly no subject matter expert when it comes to fuels and fuel properties but several previous incidents (and a couple of accidents) keep worming their way into my thoughts when I think of this occurrence. The cases I’m talking about have this in common: Unpredicted or unexpected changes to the behaviour, consistency, lubricity, viscosity or dispersal characteristics of fuel – caused by FSII. (Contrary to what some have written FSII is not one specific chemical formulation but can be one of several compositions, including dipropylene glycol, glycerol formal, and DiEGME.) As many of you know, the amount (if any) of FSII in the fuel loaded in China could fall into a fairly wide spectrum and still be within specs. In serving this ball into the PPRuNe court, I expect (and would appreciate) comments and critique on the possibility of FSII being a factor.”

Grizz

I say again, why has it only affected the Trent800.:confused:

Hot Dog...
 

You are asking the wrong question... the question is not "why only RR" but rather "at what point, as the temperature decreases in a given fuel will it also affect other engine/airframe combinations"?

That is the point inherent in Phil's and Grizz's excellent replies.

Read http://www.pristaerospace.co/hi-flas...ils/index.html on how dissolved water comes out of solution as avaition fuel is cooled. This explains where the water came from initially. (AAIB reports 70ppm dissolved water in the fuel) The resultant ice and supercooled water then adheres to pipework in the fuel delivery system, including the small bore tubing in the inlet to the FOHE. (anyone know the ID of these tubes as they appear to be very small bore to me? ) In tests the delta P across the FOHE was observed at levels in excess of 9 barg suggesting tube blockage. (in the NTSB pic of the FOHE tube sheet, after recent testing, many of the tubes are plugged) If the fuel is heated the water remains dissolved and is not problematic in the fuel delivery system.
If you click on "history" on the above website the first instance of this type of failure is reported in a B52 in 1958, where 5 of the eight engines stopped.
Re anti icing additives the Shell Avaition website declares that anti icing additive is mandatory on all military aircraft fuel but is not necessary on commercial aircraft where the fuel is heated.
Was the fuel on the aircraft in question too cold for too long? Does cold unheated fuel on shorter flights deposit ice in the fuel system pipework and is not a problem because not enough of it has formed before the flight ends safely? If the fuel is heated what is the lowest safe temperature before the dissolved water starts to leave the fuel and become an operational problem?
As a retired engineer I am interested in this problem as I flew the same route as a passenger 8 hours behind BA038. I was in a 747 and the OAT west of the Urals was -76 C for hours. My flight was uneventful. I keep asking myself why?

Nothing unusual there!!

There have been much worse incidents concerning things left in aircraft!

1. Inspection Engineers chair.

2. Flow pack in the tanks discovered on fuelling the aircraft.

I could go on point is to learn by our mistakes and in this case a basic design flaw may have been over looked!

luckily only a dented pride, a rather expensive insurance bill, but no lives lost!

No lives lost is the important bit!

Unfortunately as humans we a prone to Human error!

:(

and to poor grammer :E

Oilandgasman:

Thanks for the link to Prist Aero (it is missing an M):Cheers, M

Thanks M for that timely correction, some very interesting info there on water saturated fuel behaviour as the temperature falls.
O&Gman

With all due respect to Prist
 

And I've used it, the first paragraph is deceptive. It's claim, The Water cannot be removed......(on production) is false, because it then describes how supercooled water comes out of solution in the Fuel line, to clog filters and bends, (Something I posted at the beginning of this thread).

If, on Board, the water is "removed", it could just as easily be taken out on the ground, after cooling the Fuel.

Without irritating Pinkman too much, it is eminently possible to produce and transport water free Fuel. Expensive? Oh Yeah.

But it isn't necessary.

The 777/Trent, with new architecture and a mod for its FOHE will be most welcome back into the High and Frigid Land of ETOPS. My posit......

AF

Perhaps, but we've gone from BC to AD and have come up with some new myrrhs for the lamp oils since then. :p

Seriously Rev, I think the Trent might be the canary in the coal mine and there are broader issues at work that we've yet to divine.

You ask why only the Roller, I ask how did this get past the design and certification process, and, the entire fleet of airplanes all of these years and flight hours.

The Rev and vapilot
 

Peace. It isn't one question or the other, it's both. One is pressing, mitigation of a duplicable Fault in one specific a/c, and the other, prevention of unknown problems possible with other types. Also, what other "discrepancies" does Chinese Fuel exhibit besides low FP, if any.

Could the build up of ice in the line upstream of the FOHE in both GE and Trent meet a different obstacle (resolution) closer in? The HP in GE is "in front" of the FOHE, which also has a two pass profile for the oil, heating the Fuel more than a one pass design (Trent).

Boeing has addressed, and NTSB reviewed, the mechanism thus far. NTSB claims another incident is likely without a change in the 777-200ER. FAA has yet to speak since its AD modification. The language of the resulting Interim has "exonerated" other types, so far. Wiser, and sounder minds than mine are comfortable with the pace, what else to say??

AF

Airfoilmod ;

Boeing has addressed, and NTSB reviewed, the mechanism thus far. NTSB claims another incident is likely without a change in the 777-200ER. FAA has yet to speak since its AD modification. The language of the resulting Interim has "exonerated" other types, so far. Wiser, and sounder minds than mine are comfortable with the pace, what else to say??


NO. The tests, as far as can be ascertained, have been carried out using unrepresentative fuel. The mechanism is indicated, but NOT confirmed, and DEFINATELY NOT understood. The mechanism needs to be explained with representative fuel and a real understanding of the mechanism obtained so that new operating and design rules implemented.

The AD has NOT "exonerated" other types whether "so far" or not - have they managed representative tests on ALL other aircraft and engine installations ?

The pace may be as fast as it is possible, but it is nowhere near complete, and if the fuel/ice behaviour is as odd as the AAIB report indicates it may be many years before the whole problem is sorted out.

Is it time to panic - obviously not.

Is it time to relax - no, there is much work still to be done.

.

Whoa
 

Thus Far, I said. I don't claim the mechanism is understood or that anything is in concrete. I am paraphrasing the results from the report.
Rolls is designing a new FOHE, (For the Trent RB211-800 ONLY). Where have I misinterpreted the report? Who claims this situation is resolved?

No AD "exonerates" any a/c, ever. It is written and enforced to address a specific deficiency. It does not address other a/c but the 777-200ER.

It is the Trent fit 777's that are the focus here, if you want others investigated, well, you are allowed to have input to the Authority, it is encouraged. The reports claim no other type is suspect.

AF

I have not read this thread but I wonder if this feedback is interesting for you....

Sir, I am concerned at the decision to allow Boeing 777 aircraft with Rolls-Royce engines to continue flying after the crash landing at Heathrow in January 2008 (report, Mar 14). I cannot help comparing the response to this accident with that after the loss of an Air France Concorde at Paris in 2000. The latter aircraft was brought down after a collision with a metal object on the runway, that should never have been there in the first place. Yet despite the aircraft being relatively blameless, the entire Concorde fleet was grounded within days pending hugely expensive modifications to the fuel tanks.
Within a very short time of the Heathrow crash landing in January 2008 it was apparent that there was a potentially serious design problem affecting this aircraft. The temporary operating procedures for these Boeing 777s, pending modifications, appear to be no more than window dressing to deflect public opinion. I have read internet forums where Boeing 777 pilots have resorted to exchanging informal ideas about what best to do if faced with unresponsive engines at the critical moments on the approach to land. This should not be happening in 21st-century aviation.
It is a letter to your Times newspaper of today. I took the guys name out just in case he-you know-offednded someone?