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..