Vapilot2004

Agree

No doubt all the manufacturers and regulatory agencies are reviewing their specific systems.

I doubt that there will be a regulatory wording change but a "special condition" might be applied to new installations.

There seems to be some parsing going on. No axe here, the Fuel/Powerplant interface certainly must be rigorously examined. Boeing built a freestanding Tank/Supply mock-up/test-bed, and then concluded that the Trent has issues. Can the Plumbing be re-designed to accomodate the Trent's shortcomings? Add fine screen filters and robust bypass systems, and fuel pre-heat? For good measure refit PW and GE equipped frames so the Trent doesn't feel picked on? I may be missing something, it wouldn't be the first time or the last; Isolating the architecture of the RR F/OHE for criticism appears to be Boeing's conclusion.

AF

I don't think so. The system controls only on the oil temperature. When the oil doesn't need cooling, there is no oil flow through the exchanger, and no fuel heating. The (very small) efficiency gain when the fuel is being (slightly) heated is a bonus, not a design consideration.

Sooty

Quote:
(Actually, increased fuel temperature would incrementally improve thermal efficiency.)
No. Remember, I said incrementally. I doubt if it would even be measurable. But, any heat that you recover from the oil and feed back into the fuel means more heat to be released when the fuel burns. Just basic thermodynamics.

Yet again.

People seem to be reading too much into Boeing's leaks/announcements.

a: They still doesn't explain where the water came from.

b: They don't SEEM to explain the almost simultaneous and near-enough exactly similar problem in two separate systems

c: There is no scientific explanation

d: There are no proposed new rules for fuel and/or engine installations which shall apply to ALL aircraft.


Keep things in perspective.

.

On the Trent the FOHE is always on. There are no controls at all on the fuel flow side, and there is only a bypass on the oil flow side to enable to oil to bypass at very low temp (when the oil is below zero when starting)
The oil temp control system controls the AOHE which is normally closed, and opens at high oil temps to pass fan air through a heat exchanger to cool the oil.

Phil:

Same as always. Nothing new to explain.

Near-enough identical separate systems in same environment produced almost simultaneous results. What more is there to explain?

When it is fully sussed out it will appear in the appropriate peer-reviewed journals.

Sweeping changes require specific knowledge - see item C above. In the meanwhile, making changes to anything other than the affected airframe/powerplant will not improve safety by a warrantable amount.

So Machaca, you are willing to go off thinking there is a solution to an unknown problem (where did the water come from), with an unknown process (the near-enough simultaneous timing and effect on two separate systems) without any scientific explanation or idea how many other aircrat instalations are involved.

You've just demonstrated that however worthy any small action is, it is not a proper solution, merely a palative.

.

Afaik the bypass on the oil side is thermostatic, and diverts oil flow through or around the FOHE to maintain oil temperature. It is designed to cope with a wide range of fuel temperatures from freshly loaded ambient to altitude-soaked cold. With very cold fuel, most oil will bypass the cooler with only a bare minimum passing through to maintain oil temperature. The heating effect on the fuel will be minimal.

Sooty

Why all the emphasis on
?
With respect, we knows where the water in fuel tanks (ground based or airborne) comes from - it comes from the atmosphere - either warm wet air being cooled, or suspended moisture AKA cloud.
Descending through cloud with a large empty centre tank for instance will introduce water in some form. If the tank is cold, the moisture will condense as frost all over the inner surface.
The question is not where does the water (or ice) come from, but how and where does so much manage to successfully accumulate, and yet be suddenly released in such volume that it can bring an aircraft down?
The sudden release looks like melting. The ability to bring the aircraft down looks like refreezing. The path from warm(?) centre tank to engine passes through the (cold?) main tanks.
Other possibilities may exist - that is simply one obvious sequence along the fuel path.
The question is which possibility actually became a reality?

Anyone got any information on number (if any) of following aircraft that had to execute missed approach immediately after the accident? Have been following the thread since early on and don't recollect if it ever was mentioned.

I think a few went around, about 2-4, and a few sidestepped onto 27R.

I think it was 2 sidesteps and 2 go arounds, but not sure. Someone from EGLL Tower shall be able to give the exact.

Thank you Heathrow' for your quick response, just wondering if aircraft was being vectored in the middle of usual heavy traffic (as we all assume) or if perhaps had a pseudo-CDA of sorts from LAM @ FL90 on the day.....Not much info in the interim report regarding time/length of transition onto final and the ILS. You'd expect fuel flows to have been higher than those recorded with aircraft clean in the hold @ 90, if level flight ensued at some point with flap extended later on at lower altitudes.

By the way, I'm not reading too much into this, like all drivers who've been around the block, am having a hard time accepting some of the theories being put forward as intuitively, they go against the grain a bit.

Sorry sooty but the AMM doesn't agree with you
AMM 79-20
* Oil pressure relief bypass valve
If the engine oil is too cold or the heat exchanger oil core is
clogged, the pressure relief bypass valve opens.

The fuel temp does not affect the operation at all. Only oil temp. And by too cold RR mean around zero deg C.

Swedish Steve you are right.

Btw
For Trent 895's the restriction for Take Off is that the OIL temp has to be above 50Deg Centigrade ai out of the amber band.
This is not the case on GE90's.
I still dont know why there is this distinction

A few days ago I asked if the "final" report was out yet on this accident. I have not seen any reply. So.....I am wondering why a malfunctioning FADEC seemingly has been ruled out. I only see discussion on water in the fuel.

Ruled out by whom

The AAIB who hasn't published their final report detailing all considerations? or by Pprune who have discussed it to death?

I really am in favor of having a quiz scattered within these Pprune threads. If you flunk the quiz on discussion subjects than you shall be banned from posting for one week in the thread.

Rumours and News is just that. If it was worthy of quizzes and credential checks, it would cost money. One gets what one pays for, silk purse, sow's ear, etc. I don't want to redo groundschool.

I think we are saying the same thing with different words. I agree the fuel temperature has no direct effect on the bypass. However, the continuous flow of cold fuel would grossly overcool the oil unless the bypass diverted oil around the FOHE to maintain the bulk oil temperature.

All the fuel flow always goes through the FOHE, but at low fuel temperatures, most of the oil goes around the FOHE via the bypass.

Sooty

I'm with you on this.

Although I think the money is on the "ice bullets' theory.

JO