HotDog

Pinkman,So you are convinced that no other aircraft departing China with Chinese fuel on a long haul sector to Europe or US has ever experienced the range of temperatures that has affected the 777s with TRENT 800 powerplants?

Pinkman

Again you ask the wrong question

YES! I am saying that that particular set of circumstances has not happened before:

THAT batch of fuel
THAT powerplant/airframe combination
THAT temperature for
THAT duration

and THAT is why I keep saying stop focussing on THAT powerplant and look at the entire set of circumstances including the fuel.

You are obviously intelligent... why are you thinking in such a one-dimensional way?

Pinkman

HotDog

Ok Pinkman, the answer to the question is: It will not affect other engine/airframe combinations.

Aren't you glad it has no effect on your glider.

Pinkman

But you dont know that, do you? You don't know because there is no evidence to support it either way except in hot-dog land where if something hasn't happend yet, it can't happen in the future.

How did you know I glide?

HotDog

Dear Pinkman, I have lived in hot-dog land exactly 20 years longer than you have and amassed 20,000 hours in various jet aircraft and flight simulators as a check and training airman. I think you'll agree that after a while in this industry, with the evidence and history at hand; one can arrive at a fairly intelligent assumption on the subject at hand. However, I will not scuttle your theories any further as I consider this conversation terminated. Happy gliding, a great sport! Cheers,HD.

OverRun

Umm, girls, wind back the fingernails. Vapilot2004 (link 2361) said . Good point. Missable perhaps because the certification and design used familiar and well-accepted principles, and the BA038 flight probably strayed into new territory.

I wonder if we were previously on the edge of an (as-yet undefined and only just realised) envelope and have stepped outside that envelope with this combination of aircraft, route, cold soak, fuel, testing, and specification. Not just an issue specific to the manufacturer or supplier, but rather a global issue with global consequences for the present system. Which includes engine and airframe manufacturers, and certification authorities (and not to forget the operators and crew).

Don’t Hang Up hinted at the new territory. I think it is wider than BA038 and similar operations. The new territory encompasses specifications, design and test methods, and presenting the biggest challenge of all - it questions how we will deal with the much bigger issue of the new bio-fuels. There is much work to be done (as PG said). And I think we are only at the start.

PS - Pinkman picked fuel as the cause of BA038 about a year ago, and Hotdog (The Reverend) has been contributing wisdom here for many years.

deltayankee

Everyone knows. If it's supposed to be secret don't put it in your public profile!

Pinkman

Doh!

John Farley

I went to fly a Canberra PR9 prototype back in 1964 and on looking round the cockpit I noticed a switch labelled Fuel Filter Heater. I asked "Wot's that for?" "To stop ice bunging up the works" "When should I put it on?" "When you fly high" "OK" I said.

airfoilmod

From 19 Feb, '08 Posts #126 and #127. See if I got close. I didn't accept the "in spec." from the beginning, so far as it eliminated the Fuel as a cause here. Always be sceptical of reports, or conclusions from any source.

Then there was that off type 777 at LAX with its rollback. Fifty feet of ice making Fuel Line is too much. Interesting read, the "Beginning". The military have been flying at 50,000 feet for fifty years, and higher, this "new" behaviour of systems, Fuel, and Ice is sounding like a red herring.

A simple consideration of the simplest causes leaves, Chinese Fuel, and/or the way the 777Trent reacts as built and engineered to conditions extant for all the history of flight; and oh yes, to Chinese Fuel.

The Lear, a Twin, is certified to 51,000 feet. They fly to China. They also have Fuel line architecture much smaller in cross-section than the 777.
Can we scale back the handwringing regarding the state of ETOPS as impacted by "mysterious new forces?" Thanks in advance.

AF

Dak Man

Some clarification.

T800 is not likely to have a heater matrix bypass installed as part of the FOHE, the modification concerns creating a flush fitting matrix where ice cannot accrete to the protruding ends of the matrix.

Where T800 is different, is FMU spill return. It does not recirculate back around the FCOC whereas the GE, P&W and all RR architectures (except T800) recirc spill back through FCOC.

OverRun

John Farley and airfoilmod – you are of course both right in your facts.

What got me was ethereal and not facts – call it gut feel, call it smelling something, call it vibrations in the ether, call it ‘away with the fairies’. I have no facts. I have no analysis. I have no scientific dissertation. If I told you the background to my concern, most people would laugh out loud - to avoid my further embarrassment, I’ll say that it is based on an “organic chemical”, as are jet fuel and biofuel blends.

I still think that there is a global issue coming with global consequences for the present fuels system. It's not just Chinese fuel. Arguable and dismissible. My only defence is that I sometimes have a disconcerting ability to see this sort of change. That sounds a bit arrogant, so let me apologise and offer Ernest Gann’s defence (as in the loose elevator bolt over California AFAIR) – blind dumb luck leads me to my conclusions.

airfoilmod

Taking note of your clarification, I would question the efficacy of shortening the tubes to terminate flush with the tubesheet. As it is, migrating Ice, when encountering the current design, has the ability to pass by the openings of the tubes and collect between them, for a time, held out of harm's way. The mod may have the advantage of collecting the tube openings closer to the Oil, (the Heat source), but the volume of Ice has nowhere to go but collect at the respective openings into the cannister. From a manufacturing standpoint, it appears a less complicated termination, (the Fix), simply with better access for the welder.

John Farley's anecdote about the Canberra is most instructive, a simple solution provided by a straightforward anticipation of the problem. A filter to remove solids (Ice) from the Fuel Flow, combined with a Heater to melt the Ice and return it? The Canberra was a very high flier; one should question the approach by Boeing/RR about the 777 design.

Over Run - I admit to the same experience. One who ignores any of his senses in flight is not using all his skills.

AF

sooty655

I would guess that the intention is to provide a smooth rapid flow into the tubes to hasten the icy slurry through. The pockets around the protruding tube ends will be stagnant areas and encourage the stuff to stick.

I have been revisiting the fuel system diagram posted by Jet II at post 467, and it shows the LP fuel filter after the FCOC, which also seems to me to be an unusual arrangement.

Anyone out there know why the T800 is like that??

Sooty

airfoilmod

Without adding pressure by placing the HP in front of the FOHE, there will be no real change in Ice migration at the Face, as I see it. Clipping the tubes flush seems an improvement, but hardly a solution. As the migrating Ice hits the entry, it still has the same cross section to contend with, and I still think of the interstices between tubes as a plus for temporary "storage" of the slurry. The closer proximity to the Oil entry in the cannister is a plus, though.

The HP pump is a geared, or lobed mechanism, a positive contact type that would certainly serve to crunch solids or gels into a pumpable mass.

Placing this unit in Front of the FOHE would prevent solids from accessing the Face, as GE does. It was the Plug at the Face that caused cavitation, the HP has no flow/fault relief valve to relieve pressure when draw is prevented. Including the products of spill to cycle through the HP feed would be an alternate supply, or direct connect to HP from FOHE Face bypass would prevent cavitation also. But this would preclude using check valves in the spill return, otherwise cavitation could occur.

spannerz20

Airfoilmod

I was allways under the impression that having the HP fuel downstream of the FOHE was a failsafe design. The theory being that if a pipe within the exchanger ruptures the oil is at a higher pressure than the fuel. This leads to the oil contaminating the fuel system but the engine can combust this. Conversely If the fuel were to contaminate the oil system the lubricating properties of the oil would quickly be lost causing damage to the engine.

I Can't remeber the architecture of the GE system so I don't know how they get round this ?

airfoilmod

What I'm after is the masticating ability of the gears in the HP to blend the Ice back into the Fuel. Bernd posted a while back that GE's HP is upstream of the FOHE.

If it takes different metallurgy for the pipes in the FOHE, or a pressure sensor in the oil portion of the cannister, or a bypass around the FOHE downstream the HP and directly to the nozzles, these are design considerations. It seems to me, though, that if the Oil gets into the Fuel system, it will deplete and cause engine damage anyway. One way round this HP FOHE is a partial bypass. Why direct 100% of the Fuel through the FOHE? Why not a portion of it, enough to cool the oil only.

The FOHE has been shown to be the weak link. Are there others? The Ice picture from the Reports is daunting, no doubt. There remain two issues:
Refitting the Trent/777 immediately, and an intense program of Fuel Research.

spannerz20

I would have to dig the notes out again but I think with oil contaminating LP fuel the rate of oil depletion is much less than HP fuel contaminating the oil thus buying valuable time with the engine still running.

Like you the I found the picture of the Ice accretion very worrying and the modified FOHE can't come soon enough. Practically the retro-fitting of the new units won't happen overnight, with 500+ Trent 800's on wing manufacturing and supplying the units post certification is a logistical challenge in its self.

More research into fuel will definitely be a good thing. The fact that a lot of the design regulations are based on 50 year old research indicates to me that this is long overdue !

Pinkman

I'll admit upfront that I am not an engineer - I am a refining & fuels guy with the oil industry. But I was struck by the fact that AAIB interim report 2 clearly reported that ice accumulated on the face of the FOHE and melted fairly rapidly until the test rig became too cloudy to see what was going on. Surely the idea must be to increase the transfer of heat between oil & fuel. How does remachining the physical face of the FOHE achieve that? Surely you either have to increase the recirculation rate of the oil or elongate the matrix to improve heat transfer. As I am clueless here I am happy to be abused on this!

Pinkman

airfoilmod

As I see it, the extension of the tubes past the Face into a 100% Fuel (cold) environment allowed Ice to accumulate and prevented it from reaching the hotter portions of the HE, the Face. As Sooty says, the goal seems to be to expedite the Ice's migration directly to the Face itself. The schematic I have seems to show the From Engine Oil entering the FOHE at the Fuel exit. The FOHE Away Oil (cooled) seems to be exiting at the Face FOHE. I'd like to be wrong, since I think the Hottest Oil should be at the FOHE's Face.

My question is the region between all the tubes can accomodate some volume of Ice, and trap it out of Harm's way (theoretically), unless the slug of Ice is too large for this and then plugs the 1080 openings. In any case, though helpful, I don't think the foreshortening of the tubes to the Face accomplishes enough to solve the problem.

BA038 Rolled Back after an increase in Fuel was commanded, and the Thrust increased. Did the vibration of added thrust shake loose a quantity of Ice that then occluded the FOHE's? If so, what purpose does the AD's call for occasional max thrust solve? Then return to Idle to melt whatever accumulation has presented? The AD seems insufficient. The GE and Pratt engines, not having had a rollback (seemingly) does not mean they won't or that they haven't and weren't diagnosed properly. The RR fix seems short of the mark. If the AD is used, should it coincide to proximity to an alternate?

AF