Airbus GRVTY FUEL FEEDING procedure and WHEN L(R) TK FUEL REQRD

[Microburst2002]

In case all pumps in an inner tank failed the procedure is to switch them off and open the X FEED. Therefore, there is no need to apply the GRVTY FUEL FEEDING procedure just yet, since the fuel lines are still pressurized. This also gives more time to fly at cruising level and possibly to deaereate the fuel, which in turn increases the GRVTY FEED CEILING.

Now: How long can we prolong this situation? How long can we fly feeding both engines from one tank?

Gravity fuel feeding can only take place from the respective tank, right? (or wrong?!) So if we depleted the tank with good pumps, then not only would we be in need for gravity feeding, we would also have an engine shut down due to fuel starvation.

Also, there is no possibility of correcting the fuel imbalance.

there seems to be no guidelines for that, in the FCOMs nor QRH

Only the line WHEN L(R) TK FUEL REQRD

[TyroPicard]

MB2002
Why would you have an engine shut down due to fuel starvation? Think about that first.....

EDIT: A better question is... How can you avoid shutting down an engine due to fuel starvation?

[Goldenrivett]

Hi MB2002,
Also, there is no possibility of correcting the fuel imbalance.
By flying one wing low and gravity feeding both engines, you'd be able to use the fuel from the higher tank.

"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.

// END"

Edit to Lancer in #4
that section only applies to OEI, but yes you can gravity transfer from one tank to the other
That's the only reference I can find to fuel balancing whilst gravity feeding, but if it works OEI - then it should work with both running.

[*Lancer*]

Fuel imbalance is an FCOM limitation, so that is the latest point to initiate GRAVITY FUEL FEEDING.

When the tank with the live pumps reaches 750kg (3000kg FOB), you'll get FUEL L(R) WING TK LO LVL. ECAM asks for FUEL X FEED ON, TK PUMP 1+2 (ON SIDE WITH LO LVL) OFF and will result in GRAVITY FUEL FEEDING from both tanks to both engines.

Obviously not ideal..


[Goldenrivet that section only applies to OEI, but yes you can gravity transfer from one tank to the other]

[vilas]

Lancer
There is no fuel transfer from one tank to another. Only you can use fuel from one side preferentially to other side to balance. Only transfer that takes place is from outer wing tanks to inner tanks

[Microburst2002]

Hi Tyro

That is what I wonder. If I kept indefinitely using only one tank to feed both engines, this tank would deplete. Then we would have a gravity feeding in the full tank with no pumps (which is not the end of the world) and an imbalance (neither is this) but also the engine in the opposite side would starve because there is no fuel in its associated tank and the line can't be pressurized from the other side.

In the 320, the OEI case of gravity feed permits feeding an engine from the opposite tank. There is something similar in the 330. I guess it could work, as it's been suggested. But it is not in the Airbus published procedures… And it seems too complicated anyway.

What intrigues me is: What does the "WHEN L(R) TK FUEL REQRD" line exactly mean in a pumps lost ECAM actions?

I wouldn't desire to deplete a tank only to delay gravity feeding. I would start the gravity feeding well before that. My question is: When is the best moment to do it?

[Goldenrivett]

Hi MB2002,
When is the best moment to do it?
I'd suggest 30 mins after being above FL 300.

"Flight conditions at time of gravity feeding [Gravity feed ceiling]
Flight time above ​FL 300 more than ​30 min [Current FL ]
(Fuel deaerated)"

[TyroPicard]

As I see it, tank fuel is required if you want to reach your destination. As soon as you can, apply Gravity Fuel Feed procedure with the X-Feed OFF. You then get even fuel burn from each wing.
If you get stuck down at FL 150 because of your FL when the pumps fail, you will have to land somewhere and get it fixed.

Or would you climb above FL 300 using one wing tank and X-FEED ON, wait 30 minutes, and then Gravity feed on the failed side? Imbalance might be 1500 kg?
Depends on planned landing fuel... Because it would be irresponsible to deliberately run a tank dry.

[Microburst2002]

Yes, that makes sense. Thanks for your contributions. I guess that once you are in the situation it is a rather straightforward.
I was thinking of a critical situation, like flying in a A330 (deaereated grvty ceiling is FL200) to an isolated airport or something similar, where the nearest en route alternate is quite far.
I thought that, somehow, delaying the procedure by using the X FEED was equivalent to turning some fuel into unusable fuel.

After this thread I undestand the whole thing better now. As a matter of fact, when there is a fuel imbalance, the A330 has a curious way to transfer fuel between inners via the refueling gallery when the X FEED is inop or closed. It also requires banking to the lighter side. This would permit full use of the fuel and maximum delay in the execution of the gravity feed.

The banking method is part of an IMBALANCE procedure in the 330, while it is part of the GRVTY FEED procedure (OEI) in the 320.

As a last note, the A320 procedure for feeding an engine by gravity by the opposite engine, I don't think it would be advisable on a two engines case, since we could starve the other one.

[Goldenrivett]

Hi Microburst2002,
the A320 procedure for feeding an engine by gravity by the opposite engine, I don't think it would be advisable on a two engines case, since we could starve the other one.
Sorry, please could you explain that?

I would have thought that having fuel covering the inlet pipe (which then feeds the cross feed plumbing) must also feed any engine connected to the same plumbing. Even with 5° bank, both engines must still be below the fuel level.

[Microburst2002]

Maybe, but I wouldn't rely on that, if Airbus does not say we can.

I am familiar with the schematic system, only, I don´t know how the real piping is. From the schematics, it seems difficult to me that there would be the same fuel pressure in the high wing than in the low one, even if both are below the level of the tank.

Anyway in the 320 it would be like you said. Wait until fuel is deaereated, then do the procedure.

cheers

[TyroPicard]

MB
What? You still have to turn the aeroplane! I am not aware of any bank angle limit with Gravity Fuel Feed! Only need that technique OEI.

[Microburst2002]

Tyro, I see your point.

However, in a coordinated turn gravity stays normal to the lateral axis. In the gravity feed procedure you have to fly with a sideslip.