Will Fraser

So much of what we see from the authority seems to depend on blind faith. A "tiny sample" can NOT be relied upon to exclude a growing and more pervasive problem. It is shortsighted to assume it is only Trent, based on information in the public domain. It is as you say, sooty.

Without a complete audit of every possibility, this AD rings hollow. A "Patch". An expensive patch, but a patch nonetheless.

Will

lomapaseo

Agree

reminds me of the uncommanded thrust reverser problem. A Boeing specified, requirement but at first unique to only some PW models. An AD appropriately addressed the known. Then more data arrived (Airbus, Douglas, RR, GE) and additional ADs addressing the knowns in a specific fashion.

So I'll watch this space for additional knowns that can be addressed in a specific fashion.

Some may feel that this is guessing at the location of the bullet in the chamber, but then again throwing a design change at something that currently works just adds more bullets.

Will Fraser

The FOHE (Trent) was not specifically designed as a fuel heater/ice melter.

I can't stress this enough. Modifying an existing component to mitigate a problem its overall design was never meant to address is unusual, to say the least. In the absence of further work on fuel/fueling issues, (is there any?), the actual cause of the icing induced rollbacks is being neglected?

The ICE is not the cause, it is what causes the ICE.

falconer1

100+ on that...

wonder, whether that situation IS in fact causing some nailbiting, especially in regards to the ultra ETOPS qualification of the B777..??

not that a common denominator like water / ice contaminated fuel ( for whatever reasons, i.e bad supplier quality and/or bad draining routines, sometimes caused by that fact that during the short downtimes of long range flights you cannot possibly drain all condensation out etc etc) could not down a quad either, BUT the statistical probabilities for a twin to be affected on both motors would be considerably more severe..

so, anybody know?? were there any discussions to at least consider temp withdrawal of ETOPS qualifications????

dont get me wrong, still very impressed with the 777 in general, but that accident shook me up a bit...

and it may point to a far wider reaching problem, and that is fuel quality in general..and maybe insufficient means to get the water out of it..

and that again may not have much to do with the type of aircraft..

Pinkman

Will, As a fuel guy, this is the way I see it:
They cant use the fuel recovered from the aircraft (would be gone very quickly) but they have tried VERY HARD to bung as much water as possible into the test fuel and STILL they have not been able to replicate the fault although they have seen icing. So while I still believe it was fuel related I havent seen anything yet that leads me to believe it was simply water in fuel. I want to know why the fuel FP was elevated over typical RP-3 even though it met the spec for Jet A-1. Do I believe the Trent before the mod was more susceptible? Yes. Do I think that other powerplants would suffer the same problems as the environmental conditions became more severe? Of course.

Regarding your question on handling, it doesnt really matter - if the fuel was on spec and was badly handled and became unfit for purpose despite being on-spec it is no different to it being unfit for purpose and well handled.

Cast your mind back to the Australian avgas incident which caused a plane to fall out of the sky and grounded the Victoria GA fleet. Trace amounts (parts per billion) of Di Ethyl Amine - a chemical that is used widely in refining to remove Sulfur, and something you wouldnt expect to be an issue - caused a wierd reaction with the metal piping / braze in some aircraft fuel lines. The fuel met spec. In this sort of incident it is simply not enough to say "the fuel met Defstan 91-91" or whatever. You have to take it apart molecule by molecule and look for things that you "dont know that you don't know".

vapilot2004

The fix is not melting the ice as much as it is mitigating ice on the move, en masse. According to what I've heard, the FOHE design has been modified for reasons of flow, not heat transfer.

Reliable fuel delivery is something we should have mastered by now. Perhaps after the introduction of new fuel formulations, certification was not thorough enough on this particular aircraft and engine combination.

Will Fraser

vapilot2004

To now, the fix is an operational workaround, a cycling of thrust to heat the engine, melting the Ice.

Until AD compliance, that is the 'fix'.

After fleet wide compliance, a combination of operational and mechanical defense against Ice? There is an assumption here that Trent/777 is an isolated example of inability to resist ICE in FUEL. Absent a broader approach, it has all the appearance of a 'Patch'. The passage of time dulls some of the attention paid to this problem.

Given the nature of design, the workaround will have what effective measure of performance? Unknown, is my guess. Until the Fuel is understood better.

Will

vapilot2004

Will,

I think the interim recommendation addressed two areas of concern. The power increases not only add heat to the FOHE but also cause the fuel flow to increase dramatically above idle rates, forcing accretions to break up and move on down the pipe.

My comment earlier was referencing the Trent's new FOHEs, so I may have mis-quoted your meaning. Apologies.

I agree that there is something odd about what has happened here and once again am left wondering out loud how this could have been missed by Boeing, Rolls and the regulatory bodies during certification. I think something changed and it smells like kerosene to me.

Will Fraser

I haven't smelled Chinese Fuel from China. What drops an FP 20 degrees below 'spec'. If its expensive, why bother ? If it's cheaper, why ?

chris weston

Will,

You can lower the FPt (i) by branching the hydrocarbon chain (use more of a catalytically cracked high Mr feed stock) or (ii) by shortening the chain length (use more of a more petrol/naptha like cut). Its a Van der Waals / London dispersion forces argument.

I would guess that either of these routes would push up costs but the fuel guys will answer that better than I can, I'm just a chemist....and yes yes I appreciate the possible use of (non hydrocarbon) additives.

CW

Pinkman

Would be interesting to take a sample of RP 3 / JF #3 NOW and compare with the recovered sample via GC MS as well as distillation range... and scouting for all those ex-PEK retention samples that will be hanging around from the last 5 years. There are only a few general possibilities for lowering the FP and they include, firstly, changes in the relative proportion of hydrocarbon components that SHOULD be there (eg wider than normal wide cut fuel) and secondly, the addition, either deliberately or accidentally, of hydrocarbon components that SHOULDNT be there (e.g. FAME). Then of course, there's the non - hydrocarbon components.

It would help if we knew which tests were done. If the material was on spec, what is the harm in releasing the data?

Mariner9

FAME can't improve FP in Jet, and is of course tested for nowadays in the standard spec.

Pinkman, I know you keep harping on about GCMS but do you really think it wasn't done? I agree however that there would have been no harm in releasing the data or even add a simple line to the report that nothing unusual was noted on the GCMS profile.

Personally, I would be interested in a comparison of profiles between the fuel samples from the aircraft and the retention samples. A "depressed" FP (if it was in fact depressed) for the aircraft fuel could have arisen from a reduction in the heavy HC components present (wax dropout? - though no wax deposition was apparently found doesn't mean it didn't happen)

M9 (who investigates Jet A-1 contaminations for a living)

sky9

Are we all not in danger of "examining the molecules" while forgetting the big picture.

What needs to be done to avoid the engine stopping again? The FOHE is not a fuel heater but an oil cooler and is designed as such. Presumably the engine is capable of taking a reasonable amount of water or ice in the fuel so does the revised FOHE allow slush ice to go through if not should there be a by-pass?

chris weston

In common with many others, I've read every post made on this venerable and informative thread and it’s good to see their quality and thought-provoking nature being maintained. (Until this one…….)

The issue of bypassing the FOHE has been covered in detail already. If memory serves, one contributor, presumably with tongue firmly in cheek, even claimed a pat pending on his particular solution.

But I'm with you sky9, how can we actually deal with the rollback problem is the key. As we don't know what the problem actually is, that makes things really tough.

Presumably the question is how much ice in the injectors can be handled before blockage and presumably flameout never mind rollback, occurs?

I have the greatest of respect for the quality of the engineers working for RR and I'm quite sure that this will already have been looked at exhaustively by RR. I'm also naïve enough to take on trust that if it was just a matter of putting in a simple bypass system, RR would've done it long ago.

CW

Will Fraser

chris

I have no naive trust, at least not relative to that which I had years ago.
I think a 'simple bypass system', may have been looked at prior to original design vis a vis Trent8, but frankly, I think it is being actively avoided at this point. Retro isn't simple, it isn't cheap, and it isn't logistically benign to any of the principals.

As read, the AD focuses solely on the FOHE. airfoil was the first to point out its design purpose did not include Fuel heating. If it did, Oil would not bypass its chamber as a designed mechanism (oil bypasses now only when it itself does not need cooling). This also raises questions about your faith in an a priori engineered look-see at the potential for Fuel Ice.

Since there is no provision for Fuel supply to the powerplants if for any reason the FOHE is clogged, one doubts the thoroughness of the investigation for potential Fuel starvation due to such a problem.

One could make the compelling claim that in the absence of an alternate path for fuel bypassing the FOHE, the sacrifice of FLOW (fuel) was not deemed to present a critical path, ipso facto; there was a determination made to exclude such a safety implementation. To think that it was excluded by accident, is beyond even my cynical approach and suggests our shared faith in the engineering, though from different perspectives.

Will

Smilin_Ed

Chris:
I'm not being facetious here, but we really do know what the problem is/was. In it's simplest form, some of the "stuff" in the fuel tank froze and blocked path of the fuel to the engines. There may well be a number of scenarios in which this could happen so what we have to do is to prevent freezing during all of them. That means heating the fuel near the in-tank pumps. Is there a source of heat, now wasted, that could be put to good use?

Will, I share your concern about the cost of retro-fitting a change like I propose above, but how does that compare to the cost of losing a plane, not to mention crew and passengers? Fortunately, this time it was only the plane.

Will Fraser

Smilin'Ed

You may have missed the irony in my post, I suggested that a retrofit of a full on bypass for fuel was being actively avoided.

If you think something more than 'converting' a cooler to a heater is necessary here, we are in complete agreement. I also agree with the conclusion that we know precisely what happened to 038 and Delta. The 'mystery' of 'unknown' characteristics of Fuel is a dodge, simply put.

Will

chris weston

Will, Ed, thank you both.

I very much take the point that we know that it was solid phase water that triggered the roll back, my point was a little wider and not well made.

Without going over old ground too much and with due caveats ........

What we don't know is why, if the fuel was shall we say "well within spec" (neutral language) and the flight path and temperature profile not that statistically unusual, the problem has not occurred in something close to this form in many other flights too.

After all I've read, I'm still mostly in the "it's the fuel" camp. Was it made right, was it handled right, was the water drainage right etc ad nauseum.

CW

Cloud1

Question - has BA or Boeing changed anything on the B777 to avoid this happening again? I will be honest, I have not read through the 125+ pages to see if this has been answered so apologies, but hopefully someone will either be able to say yes or no.

lomapaseo

Cloud1

The answer is yes the details are all in the thread including the past week.