There are new procedures in place for flight crew during flight and engineering prior to flight, to ensure fuel moves!

Smilin_Ed posted:-
I have also read all posts on this and other disasters - though I must enter pleading at being most confused at times by disjointed thread creep - I think I've stayed on track and the one overiding factor common to all is that despite many "experts" on aircraft systems and engineering there seems to be a plethora of "conclusively proved" items that turn out to be absolutely wrong and "impossibilities" that turn out to be anything but.

I am reminded of the expert poster with years of experience in oxygen bottles saying that one had never let go in an aircraft and people suggesting they should be sectioned - yet a large part of one had come through the floor to embed itself in the doorframe - visible to all who looked. We also had explosive experts saying that the viewable photos were not of an explosion and other guys confidently pronouncing metal fatigue - all wrong.

In this particular case it certainly seems that the fuel pumps were fighting against something but ice to me is just a convenient answer when nothing else seems to fit. Just how easy is it for some valves to be closed against the pumps? Does anyone know ? Of course, if the actual temperature of the fuel was known we wouldn't be arguing.

FlyGooseFly

In threads like this you have to read much deeper than individual posts. While I'll admit that the obvious hunches do vary and are discarded along the way as available evidence surfaces, only as ignorance would one profess a conclusively proven point before the final report of facts and analysis is presented. In almost al cases, portions of the postulations of causes have arguments of pro and cons in their consideration, and it is those arguments that become the basis for the support of readership of these threads.

I suggest that you do not assign words like "conclusively proven", "absolutely wrong" or "impossibility" to postulations within these type of discussion threads.

Photographic evidence posted earlier shows the fuel was cold enough to cause frost on the lower wing surface.

Rightbase,
That's an everyday occurrence following high alt coldsoak as is also frost on upper surface.

Frost on the lower wing surface.

In 30 years or more it is only on very short sectors (i.e. less than 3 hours) that I haven't experienced that. With TAT's on the nippy side of comfortable what can anybody expect?


Regards
Exeng

Perhaps an engineer could confirm this....
There is a difference between the Trent and the GE90 in terms of fuel piping layout. If I interpret correctly the various photos I have googled the GE engine has all the fuel pipery and pumps around the core. On the Trent the fuel starts outside the fan casing and then goes through pipes which pass through the fan airflow on their way to the core.
True or false?

The Trent certainly has some fuel system components mounted on the outside of the fan case. I'm not certain but afaik the GE90 has all the system mounted on the core.

However, both engines have to get the fuel through the fan airflow. The only difference is which components are outside and which are inside.

Where Is The Fuel Heater?
 

I had envisioned the fuel heater in the wing. From reading this, I gather that it is in the engine nacelle. It looks to me like they needed one in the wing before the pipes enter the engine pylon.

There are hydraulic oil-to-fuel heat exchangers.
- 1 heat exchanger in the left main tank for the left hydraulic system,
- 2 heat exchangers in the right main tank for the center and right hydraulic systems.

Through the heat exchangers fuel cools the hydraulic oil but due to the large volume of fuel, heating of the fuel is negligeble.

Regards,
Green-dot

Same applies to the Fuel Oil Heat Exchanger (also known as a fuel-cooled oil cooler). It is controlled only on oil temperature. Any heating of the fuel is co-incidental and uncontrolled.

something else....
 

sorry, gentlemen and ladies,

there's abit about fuel management...centre tank runs to x -thousand
lbs./kgs and then stays off until main tanks reduce to y-thousand, then
centre tank pumps run again. could this have been shortly before the approach commenced ? possibly bringing very cold fuel into the situation?

been following thread for some time....

well done all crew, especially the f/o!

Not quite, to be more precise the centre tank override jettison (OJ) pumps are switched off manually at approx. 800kg of fuel remaining in the centre tank. Float-operated shutoff valves prevent fuel scavenge when the main tanks are full. When the main tanks reduce to y-thousand the float-operated shutoff valves open and the fuel scavenge jet pumps will start scavenging (operated by motive flow from the boost pumps) the remaining fuel from the centre tank. The centre tank OJ pumps remain switched off.

Centre tank fuel is relatively warmer than main tank fuel because most of the centre tank is situated above the airconditioning system which radiates heat, it is between forward and aft cargo compartments, and the passenger cabin is above it. Hence, main tank fuel is relatively colder than centre tank fuel.


Green-dot

Was any impact damage to the impeller blades found in the wing tank(s) pump(s) ?

To answer one of Sooty655's previous postings:

You are correct in the understanding that Rolls-Royce RB211 and it's Trent derivatives have the Fuel Control System mounted on the outside of the Fan case where General Electric have generally favoured mounting much of it's systems around the core.

There are pros and cons for both design philosophies. Whilst at first glance it seems a good plan to keep all the fuel system nice and warm by keeping it close to the core, the transient extremes of temperature encountered during flight in such circumstances impose design issues regarding valve tolerances/clearances. There can also be problems with fuel laquering of metering and control valves that operate in fuel luricated systems caused by higher fuel temperatures.

To answer your question though, the RB211-Trent 895 (and all it's RB211 predecessors way back to the original -22B variant of the late 60s/70s) have the following mounted on the fan case:

Low Pressure Fuel Pump
Low Pressure Fuel filter
Fuel Oil Heat Exchanger
High Pressure Fuel Pump
Fuel Metering Unit (and it's constituent control system)
Fuel Manifold Drains Tank and it's ejector pump.


As an aside, the Main Engine Fuel pump designed and fitted to the R-R Trent 895 may well have demonstrated evidence of bearing face cavitation upon strip, however on such pump designs there is no escaping cavitation and it is more a case of designing the pump to minimise what cavitation there is and to encourage the cavitation to take place in the least problematic areas of the unit - more akin to 'managing' the cavitation than anything else . It is the degree and agressiveness of the cavitation scarring that tell the story of the unit's unhappy existence up to it's untimely death and from what information I have seen, the unit was in good health up until a short time before the incident.

The manufacturer of the pump are very well respected in the Industry and were selected by Rolls-Royce for designing a product with a good pedigree and having an extremely good record for dealing with cavitation issues. The pump itself has a delivery capacity that far exceeds the requirements of the 95,000 lb thrust variant fitted to the R-R powered BA 777 as it was targeted for a much higher thrust Trent variant that didn't make it into production for reasons other than design viability or reliability. Having been closely involved in the project's design, I can say with a high degree of confidence that even in the pump's post cavitation degraded state I can not imagine a situation where the pump was incapable of delivering the required fuel other than through starvation/blockage.

I realise that I have probably re-iterated some points previously made and for that I apologise.

GFYA

Thanks, GFYA,

How clear and illuminating. 2035 (+) posts on this thread, and many on its predecessor, since 17th January. How forbearing of you not to comment until now.

Guess you must have been occupied elsewhere... Welcome back.

Any comment on the theoretical relative susceptibility (to icing blockage) of large cross-section plumbing - versus smaller?

GFYA

I may have been reading more into this than intended but should I interpret that the unit did suffer some ill health shortly before the accident?

Guys,
Be reasonable, and read GFYA's post properly.
He is saying cavitation damage may be pointing a finger, but is not unique to this case, if I read it properly.

lomapaseo, I agree he should explain what he means with "I have seen, the unit was in good health up until a short time before the incident."

Chris Scott, We're not all frequent PPRuNe readers.....
It's true nobody really answered your post about "large cross-section plumbing" either....which I thought made sense.

CJ

Fascinating, helpful, and VERY THOUGHT PROVOKING.
 

Thank-you GFYA, very informative.

I would highlight SOME of your post, for others who have posted since - although it should be read as a whole :

".............. the Main Engine Fuel pump ........... may well have demonstrated evidence of bearing face cavitation upon strip, however on such pump designs there is no escaping cavitation .......... and from what information I have seen, the unit was in good health up until a short time before the incident.

............ The pump itself has a delivery capacity that far exceeds the requirements of the 95,000 lb thrust variant fitted ............. I can say with a high degree of confidence that even in the pump's post cavitation degraded state I can not imagine a situation where the pump was incapable of delivering the required fuel other than through starvation/blockage."


Very Thought provoking.

.

Hey.My first post here so please go easy.
Just wondering,any particular (minimum) amount fuel quantity in the centre tanks before you manually switch them off? Or is it procedure to just put the pumps off when the "fuel low centre" message pops up?
Thx in advance.