Gravity cross feeding -A320 family
 

I was wondering whether anybody has ever tried to gravity cross feed fuel in an A320.

As in crossfeed with the tank pumps off?

Yes Amadis, there is a QRH procedure for it but it only appears to apply if you only have one engine running.
In my scenario the tank pumps have failed on the heavy (fuller) side and a large imbalance has developed, greater than allowed in the fcom.

If the on-side engine is running, I don't see such an imbalance developing.

Amadis -dual pump failure on an inner tank after only being in the cruise for a short time.The scenario continues with maintaining the level whilst waiting for the fuel to deareate and feeding both engines from the tank with the working pumps.Following deareation going back to gravity feeding on the affected side. This will lead to an imbalance and if you are unlucky you would be out of the fcom limit.
This is currently a discussion point at work. I am really interested how you would gravity cross feed

Can you explain what do you mean by waiting for fuel to deareate? If you are asking how to gravity cross feed on two engines the answer would be you can't. With fuel pumps on one side failing you would apply FUEL L (R) TANK PUMP1+2 LOW PRESSURE procedure. Much before you create such an imbalance you should be applying WHEN TK(affected) FUEL RQRD: which would lead you to gravity feed on that side.

The gravity fuel feed ceiling is based upon whether the fuel in the tanks has deaerated and this is related to flight time above FL300.If you have been above FL300 for ten minutes and both pumps fail, you could maintain your level and feed from the tank that has working pumps. Whilst this is taking place the fuel is deaerating . You can then use the entry in the gravity feed procedure >30 mins and maintain your level rather than have to descend to a lower level and burn more fuel. The problem wil be that you have created a fuel imbalance by doing so, and if it was excessive how do you correct it.

It is an odd scenario and not of my making!

About imbalance, it is stated by airbus if required you can land with one tank full and other empty. It presents no handling problem. When you consider options it may be better to descend to 300 rather than cross feed. The last option of suitable diversion is always there.

The worst scenario is surely if it happens in the climb and you can't return to your POD (for whatever reason). Passing FL150, you must put the X-Feed on and start timing for 30 mins when you get above FL300 after which time you can put the X-Feed off again. But what is the imbalance when you put the X-Feed OFF after 30 mins. FL150 to FL300 - 500kgs? 30 mins in climb and then cruise at, say, FL350 - 1.5T? So by the time the fuel is aerated you are 2T OOB. In itself, that's ok, but you cannot restore the balance, so have you enough in the lower fuel wing to complete the flight? It could be embarrassing. It's probably best to land somewhere you can get it fixed. You can only dispatch with 1 pump inop.
Food for thought.
I haven't yet thought about the implication of the new A320 fuel system where the CTR TK fuel is transferred by jet pumps!

Note: In exceptional conditions (i.e., fuel system failures) the above-mentioned maximum fuel
imbalance values may be exceeded without significantly affecting the aircraft handling
qualities. The aircraft remains fully controllable in all phases of the flight.


LIM-28 P 1/2 FCOM A to D 15 FEB 13

tubby Linton: just brainstorming here and I know "it's not in the FCOM" but in your scenario, since you still have both engines running, you could if really pushed, use less than equal thrust on the two engines to reduce your fuel imbalance once the cross feed is closed and the gravity feeding is fully established! Very inefficient way of flying but you should be able to retain normal cruise levels. Difficult to see how in real life this scenario would be an operationL issue.

Tin hat on for incoming.............

I had thought of that Meikleour but Vilas's reference negates the need to. I remember being told by an Airbus factory pilot that you could fly the A332 with one wing empty and the other full but I have never looked for any similar information for the 320 family until this came up recently.
With the new fuel system a flow of fuel is forced through the jet nozzle creating a suction effect forcing centre tank fuel into the wingtank. If you lose the initial flow there will be no transfer on the affected side.

Sounds like a group of sim instructors sitting around the breakroom trying to see who can come up with the most cockamamie scenario.

Not that there's anything wrong with that.

To restore the balance you would have to turn off the serviceable fuel pumps and fly with bank on. Approved procedure?
Might be possible with manual asymmetric thrust.... AP must remain engaged in RVSM airspace..
To answer the OQ I am sure the test pilots have done it...

And would you really empty the tank with working pumps? Limitations are for the obedience of fools...

Sorry but as a mere engineer, can someone explain to me how fuel aereates, and what controls it? Is it that the air pressure on the fuel in the tank decreases with altitude?. Never heard this before.

Gravity cross feeding -A320 family
 

For air in the fuel, an analogy might be a diver and the bends.

As for disregarding the specifics of the QRH drill, think of a steaming pile of horse sh1t.

Hi Steve,

Like when you open a bottle of fizzy drink, the gases absorbed in the fuel will form bubbles in the liquid as an aircraft climbs into lower pressure air. The tank pumps repressurise the fuel and deliver it to the engine fuel pumps in a gasless state.

When gravity feeding, this repressurisation will not occur and the engine pumps could ingest air as well as fuel which could cause fuel pressure fluctuations into the engine.

Hence the maximum gravity feed altitude, and the time delay to allow the fuel to deaerate.


PS, don't apologise for being an engineer. We need you guys !

In other words, if you experience R tank pump1+2 Low pressure followed by no.1 engine failure, the only usable fuel that you have is the fuel in the L tank, since gravity fuel is not possible using cross-feed.

CMpilot1:read your QRH again- this situation is covered!

Meiklour: I have already gone through QRH before posting my observations. The excerpts of the QRH given under 'GRAVITY FUEL FEEDING'are given below.

 If no fuel leak and for aircraft handling:
If no fuel leak, and for flight with only one engine running (this engine being fed by gravity), apply the
following:
FUEL X FEED........................................................ ............................................ON
BANK ANGLE...................................... 1 ° WING DOWN ON LIVE ENGINE SIDE
RUDDER TRIM........................................................ ........................................ USE


As you may know, gravity fuel feeding is required when you experience FUEL 1+2 LO PR.

Now, literally reading between the lines from the above checklist...'flight with only one engine running (this engine being fed by gravity)'

INFERENCE: LIVE ENGINE -- DEAD FUEL PUMPS(fuel pumps are dead on the same side as the live engine)


My understanding:

CASE1)The above procedure is assuming that the live engine is fed by gravity from the onside wingtank due to fuel 1+2 LO PR on the onside wingtank and for aircraft handling, the x-feed is opened to use the fuel from the other wing tank whose wing tank pumps are perfectly alright.
Hence, my previous observation about the usable fuel in post #18.

CASE2) This checklist is meant for a highly improbable scenario of having fuel L TNK 1+2 LO PR combined with fuel R TNK 1+2 LO PR(CENTER TANK EMPTY) snags and then opening the x-feed for reasons mentioned above. In that case, my post #18 would be in error..

Hi CMpilot1,
I disagree. See FCOM, PRO-ABN-28 Fuel, Gravity Fuel Feeding.

"F NO FUEL LEAK AND FOR AIRCRAFT HANDLING:
If no fuel leak, and for flight with only one engine running (this engine being fed by gravity), apply the following :
FUEL X FEED...... ON
BANK ANGLE...... 1° WING DOWN ON LIVE ENGINE SIDE
The fuel from the wing tank on the engine running side is used.
RUDDER TRIM USE
Use rudder trim to maintain constant course and neutral stick.
WHEN FUEL IMBALANCE REACHES 1 000 kg (2 200 lb):
BANK ANGLE...... 2° or 3° WING DOWN ON LIVE ENG SIDE
Use fuel from the opposite wing tank, until fuel imbalance is reduced to 0."

Hi Goldenrivett!

I can see that you have quoted my statement from post #18. Please go through my post #20 also. Whatever you have mentioned in your post #21, I have quoted exactly the same thing in my post#20 along with my interpretation. Please go through it once again and offer your comments...

CMpilot1: Airbus write checklists to cover multiple scenarios.

In your case 1 why do you think they would require 1 degree of bank if the offside pumps were still functional? The answer is you wouldn't need any bank if the pumps were working.
The QRH has been written to also cover your case 2 - improbable as it may be!
Thus the bank angle introduces a pressure "head" difference between the two wing tanks and allows the fuel to transfer via the cross feed valve. The QRH goes on to say increase the bank to 2-3 degrees if the imbalance is getting worse.
Airbus have a variation on this cross wing fuel transfer using bank angle on the A330 to get around the failure closed of the cross feed valve. Slightly different plumbing but same principle.

As others have pointed out - this is a very unlikely scenario on a A320 operation.

Hi CMpilot1!
What don't you understand about "Use fuel from the opposite wing tank, until fuel imbalance is reduced to 0."?

Meikleour and goldenrivett. Thanks for your inputs..will keep them in mind while trying it out in the sim..

I posted once about this issue.

Basically I was wondering what did "WHEN TK FUEL RQRD" exactly means.

If you stay at high level to deaereate the fuel, the problem you have is that, although the total fuel on board is usable, an amount of it would have to be used on one engine only, as the wing with pumps on would deplete at some point before the pumpless wing.

This would be a problem only if the imbalance is high and the flight has to divert and/or use part of the final reserve.

So I guess that a way to handle this problem would be: to recalculate a minimum diversion fuel so that losing the pumps-on wing engine due to fuel starvation would not occur. If you estimate to have more than that on arrival, you can continue to destination. If you don't, you could still proceed, if a landing is assured and all that.

Microburst2002: Surely, if the fuel is fully de-aerated then it is not necessary to use the pumps at all and the QRH procedure for imbalance can be used. In other words you would only restrict your range if you continued to use pumps on one side only.

If you have 2 t in the left side and reaching 0 in the right hand side due to the fact that you developed a large imbalance and have been forced to divert and hold, how do you crossfeed? Left side pumps failed, so right hand pumps pumped for a while and now you have the imbalance. When the wing with the pumps, which is the lighter wing, depletes the remaining fuel before the left wing does. How do you use the other wing fuel by gravity now?

You apply the QRH procedure as has been mentioned before in the postings!

Ok, ok

So we would have to accept that one engine would starve if you had to use all the fuel on board when you still had fuel. Not a good situation.

So I would manage it like I said: a revised minimum diversion fuel and end of the story.

I don't think you can develop too large an imbalance in that scenario anyway, but it could happen (being very unlucky) that you needed all of your fuel that very same day.

Microburst2002: You still seem incapable of grasping that you would not necessarily "lose an engine" whilst still having fuel available. Several postings have tried to explain this to you to no avail. What more can one say?

Dear Meikleour

If this thread clarifies anything at all about the matter, I am a transexual who worships Satan.

Now, back to the matter:

QRH lines regarding a bank angle are exclusively dedicated to the one-engine case (they refer to the "live" engine).

Exclusively is exclusively. Not a coincidence!

I mean: Imagine that you have a large fuel imbalance, and now the left side is too low on fuel because you diverted and had just the minimum legal on arrival and then suffered a subsequent delay, and you are now in a mayday fuel situation and then you open the crossfeed valve and bank the airplane to perform a "gravity fuel xfeed" to prevent the left engine from starving, and then… The right engine flames out because it is on gravity and that bank doesn't help with the X FEED open. Just imagine...

Could that happen? I don't know, personally!

But I know that the procedure is very clear that: FUEL XFEED….OFF
I would not open it and bank the airplane, thus totally inventing a new procedure.

What I would do is just to revise my minimum diversion fuel and then to decide if either to continue or divert so as to land with at least the revised final reserve.

Microburst
You have a point. Most posts take it for granted that you must continue your FL and the flight to destination. Maintaining cross feed till impossible situation develops and then try to find a solution does not fit in any decision making tools. Initially when the failure occurs do the ECAM but after that a situational decision needs to be taken from your options. As Tubby elaborated the scenario if you were above FL300 then you can descend to FL300 and stop cross feed. That is the point you were asking WHEN TANK FUEL RQRD. Failed one side pumps and low fuel on the good side due to cross feed is definitely not an option. A diversion needs to be considered. As you rightly pointed out there is no cross feed procedure on two engines. If your company can accept a flame out on good pump side due to starvation and gravity feed on the live engine side then you can try all these methods.

If you have to be careful with your maneuvering (AVOID NEGATIVE G FACTOR) I don't think it is a good idea to bank the airplane and open the X FEED. That might reduce the pressure in the engine LP pump. If the X FEED is closed I guess the bank angle would be OK, but who knows…

The point is that I would minimize procedure invention. QRH "over interpretation" is also a bad thing, but that's a sin we all commit from time to time

OK, what I think:

Before any gravity feed, you will have FUEL L (R) TK PUMP 1 + 2 LO PR. You select cross feed and ignition and the affected pumps OFF. And then…

WHEN TK (affected) FUEL RQRD: TK(AFFECTED)FEED.......................................GRVTY ONLY
L2 Apply GRVTY FUEL FEED procedure, (Refer to PRO-ABN-28 GRVTY FUEL FEEDING). Fuel from the affected tank may be used immediately if there is no ceiling limitation for gravity fuel feeding.

When is required? This is your decision!

Is fuel in the center tank available with operative C. T. Booster pumps? How much?
Taking into consideration the center tank fuel availability and the time above FL300, for how long will you have to maintain what level to be able to star the gravity feed procedure?
How much imbalance will develop in the cross feed configuration for that time?
What will be the final conditions when in gravity feed and the same fuel flow is demanded from both wing tank? Total usable fuel, imbalance, final altitude, position, other aircraft systems, range, etc?

Maybe you have to descend immediately to FL 150, maybe you can maintain FL370, maybe you can maintain FL370 if you cross feed for 5 min and you will develop just 200kg imbalance, maybe…who knows.

Then, standard decision making.

Only in the very unlikely situation that you have dual fuel pumps failure + both on the same tank + one engine inop + the failed pumps on the live engine side:

Just for aircraft handling when imbalance reaches 1000 kg (and no fuel leak), you could use the bank technique (even you can fly the A320 with any imbalance).

IMHO.

Gryphon, I think it's safe to say that I will win the lottery four times in a row before that admittedly dire scenario is ever observed in real life.

As I said the discussion is based on at all cost maintaining the current FL by cross feeding to deareate and then how to deal with the resultant imbalance. This is known as conformity bias where you look for data that conforms your decision rather than for information that would contradict it. Nobody is willing to take the option of descending to FL300 and stop the cross feed. If any one cares to look in the manual he will find that the difference in LRC FF at ISA+10 for a GW of 60 Tons between 370 and 300 is 8kg/HR/Eng. Just use gravity feed on failed side at FL 300.

Yes Amadis. I'm very happy to fully agree with you. :ok:

Yes, just follow the procedures (avoiding unnecessary or premature descents to any gravity feeding level, perhaps avoiding it at all).

Then, for the fuel management question I would take into account that if there is a significant imbalance, some of the fuel would be usable only after one engine starved, so I would consider increasing my final reserve in that amount. THen I would make my decisions based on that. If I have enough to continue, go on, other wise go somewhere else.

Hi Microburst2002,
If I anticipated that I might starve one of my engines of fuel, despite having sufficient fuel on board, then I'd attempt to fuel balance whilst gravity feeding both engines using the one wing low technique. I couldn't make matters any worse and might avoid shutting an engine down.