Will Fraser

The Pump is driven by the engine gearbox, which in GE has its own heat exchanger interface with fuel. The HP doesn't pump a great deal more than the engine requires, and the spill is a fairly closely calculated flow that is more a safety consideration than a potential Gross Tankage circulator. EPR is Fuel reliant directly; the 'Safety' factor not even a critical one, if the fuel isn't enough, the engine keeps running, but at a rate that is flow dependent, as BA038 demonstrates. What's critical is to keep the Flame lit, and not add too much fuel.

All I can do is repeat that Water needs to be out of the Fuel. Including the mystery water that comes from secret places that are mysterious and cause unknown boffins to build imaginary 'test beds' that keep the public distracted until they lose interest. Why heat fuel when sumping and caution are enough ? I say we make them choose; frankly I'd choose better Fuel supervision, but that's me.

Rightbase

No water in the fuel at cruise - too cold, it is all ice.
Descent to a surface still below freezing - atmospheric ingestion contains water vapour which at lower altitudes condenses as frost on the cold tank surface.
If ambient stays below freezing, frost stays on the tank walls. Nothing to sump.
On the return journey, same story except that at lower levels the ambient is above freezing and the frost melts.
The melt water from the centre tank is sent into the still cold fuel in the two main tanks where it freezes again...

Will Fraser

Rightbase

I would acknowledge all your conclusions. I don't see anywhere that you think it is ok, this water in fuel. That leaves sumping after melt at a suitable location. Because something is difficult should not mean it gets a box checked, because to eliminate the water isn't 'easy' ...

It is the tolerance of water build up in 038 over time that is the problem; Boeing had to inject water into the fuel to reproduce the accident conditions.

Will

Rightbase

... warm refuelling.

Water in fuel tanks is inevitable and you are right - sumping is the answer - but it only works above freezing point.

Will Fraser

There's already hot hydrant, but in any case the infrastructure exists, it just takes money and the will.

Smilin_Ed

Assuming that you do pump warm fuel into the tanks, how long will it take for any water, frost, or whatever to condense and settle at the sump drains? If the next flight is only an hour or two away, is that enough time?

Will Fraser

BA038 was on stand overnight....afaik

if it was five hours, that's 40 million an hour and a fractured leg.

Rightbase

is what happens after the frost in the centre tank melts, when the fuel purge pumps get hold of the melt water.
A bit of clever redesign might make the refreezing of this melt water in the cold main tanks slow the purge process rather than the engines.

barit1

Will F:
Not quite true, except at SL. But you gotta consider the whole envelope.

Think about this: The HP pump flow rate is directly proportional to core RPM, and is independent of altitude. Thus if there's a small flow margin at SL, there's a big excess at altitude.

Further: If idle speed is 70% (for discussion purposes...), then the HP flow rate at idle is 70%, where the actual engine burn rate is maybe 10% (or less). Therefore the extra 60% has gotta be bypassed.

STILL further: Idle at top of descent combines the altitude bypass AND the idle bypass, meaning there's a potential local overheating (through recirculation).

It's this significant excess, or bypass, fuel flow that is the question. If it's not gainfully employed, you get hot spots & cold spots in the fuel system.

WhyIsThereAir

Even ignoring the heat, there is significant fuel flow, several times the idle and cruise requirements. Ice has a fairly hard time sticking to reasonably smooth tube in high flow conditions. So the flow itself would likely prevent ice buidup. The heat would also help, even if a fair amount of it was lost by the time the recirculation got back to the tank inlet.

etsd0001

BA038 may well have been on the ground overnight, but what was the ambient temp overnight? What time was it refuelled? I bet about 3 Hrs before dept, as is standard. Not enough time after the refuel to allow any melting & settling for a meaningful water drain

I have been unable to do the sumps on a DC10 after it has been in a hangar for 12 hrs on a UK winters day because they were still frozen.

Will Fraser

Maybe when the Glacier starts to impact Fuel capacity this problem will get attention. Was what was frozen solid in the tanks what was left ? Was the a/c actually totally OOF ??

chris weston

Just when you need it Global Warming lets you down! Yes yes extreme weather etc ad naueum .

More seriously I very much take Wills glacier point, hyperbole in action but he's right to pose the question.

How many fueling cycles, cold soaks, limited efficiency sumpings does it take to build a glacier I wonder?

And .........of course we lost the contents of the centre tank on impact.

CW

Rightbase

Good question for the general case, Chris, but IIRC BA038 was pretty well water and ice free before starting the 2-way trip to Beijing and back.

So irrespective of where it collected, where did it come from?

ChristiaanJ

I followed most of the thread, so my remark is not meant to be fatuous, just very summary...

Says who?
Or was this the icicle that broke off the glacier and broke the camel's back?
Or the slush puppy that finally choked the FOHE?

CJ

Edit: see Rightbase's post below. I concur. Back to base one, largely! Post #1805 is on page 91, to avoid anybody doing a tedious search.

Rightbase

Post #1805 refers .....

PS - it is a real pity they didn't find melt water in the FOHE in their first inspection after the episode. They will know where to look next time.

Pinkman

I just dont buy the simple water theories. The water-carrying capacity of a fuel is finite and varies with temperature. AFAIK the tests have not been able to reproduce the fault without direct injection of water, a situation that would not occur in real life. I am not a conspiracy theorist but I am convinced there is something else fuel related going on.

PS "hot hydrant" doesnt mean "hot" or "warm" in the temperature sense. It simply means that the fuel is continually under positive pressure in the fuel trunk line to the apron service points, in the same way that your house electricty sockets /outlets are "hot" or "live" all the time. Keeping it this way prevents water and dirt entering the fuel line although it does mean that there is an increased risk of fuel leakage which is why there are (or should be) leak detection systems running along the pipe conduit.

Smilin_Ed

I have read the whole thread but most of it was several months back so I'm vague on some of it.

As I recall, the fuel from the aircraft which was tested after the crash was within specifications with regard to water content, but that would not have revealed the water present before the flight. Any water uploaded with the fuel or present in the tanks would have begun to migrate to the drain sumps and the sumps for the in-tank pumps before and during the flight. Some of it would even have been pumped through the engines. Therefore, was it in spec, as far as water is concerned, when it was loaded aboard? While we can test the fuel in the tanks in Beijing, how we can tell what the water content of the fuel in the aircraft was before or during much of the flight. Does anyone really know? I don't think so.

Were the tests conducted with actual fuel from the aircraft or with fuel obtained from some other source? Presumably, fuel from any other source would be more or less water-free, so it would be mandatory to inject some water to get any icing in the pipes and FOHE.

Pinkman

The current arrangements represent a fairly good balance between cost, complexity, and specification. Thats not my opinion, its the opinion of almost everyone in the business. There are over 20 steps in the supply chain for managing quality and checking specifications (including centrifugal (coalescing) separators and microfiltration that you all are going on about). The important thing to understand is that the supply chain QC checks take place in a controlled environment. Aircraft already have filter screens against gross physical contamination. Moving water filtration systems to a aircraft is a complete non-starter because:

1) it moves the quality control operation to an uncontrolled environment
2) it adds weight and fuel burn to the aircraft (have you ever SEEN the kit that is used? weighs about half a tonne) Facet vertical coalescer separators, API-1581, Category C, Type S, Fifth Edition, aviation fuel filtration applications | CLARCOR
3) You would have difficulty inspecting and changing filters safely and inevitably it would get forgotten until, oops
4) The cost of miniaturizing the components would be astronomical

Forget it.

And yes water in fuel systems is inevitable because of the continual ingress of air through the vent which has moisture in it and no its not just a problem at sea level, all air has moisture in it which then freezes and condenses on the inside skin and forms free water which then dribbles down to the bootom of the tank and gets reabsorbed into the fuel in an free water:dissolved water equilibrium situation depending on temperature / density of the bulk fuel .

And in any case who said water was the issue?

Smilin_Ed no, the tests were not done with the actual samples (there is not enough of it) so they faked up a test batch. That didnt reproduce the problems. So they actually injected water into the fuel and eventually managed to get ice rime buiding up on the inside of hoses and on the FOHE plate.

Smilin_Ed

Pinkman, do I understand it correctly that they injected more water than was found in the fuel in the plane?