A320 gravity fuel feeding ...
Thread Starter
Joined: Apr 2022
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From: Greece
A320 gravity fuel feeding ...
Hi, I am trying to understand the sequence of the events to be unfolded into a given situation.
The first failure that will come into play is:
FUEL L(R) TK PUMP 1+2 LO PR
-If NO FUEL LEAK:
FUEL X FEED (IF ABOVE FL150)....ON
1) Why specific FL150? If we are below why we keep it OFF?
ENG MODE SEL...IGN
TK PUMP 1 (AFFECTED)....OFF
TK PUMP 2 (AFFECTED)....OFF
Let's assume that left hand pumps are the ones inoperative.
At this point, left hand fuel pumps are off, the xfeed is open, so both engine consuming from the right hand engine. From now on we have some other sub cases, like where the failure happened. Let's assume again that the failure happen at FL 350 and we were there for 35 minutes, so the GRAVITY FEED CEILING is current FL.
The procedure continues:
WHEN TK (AFFECTED) FUEL RQRD:
TK (AFFECTED) FEED....GRVTY ONLY
If at this point we go to the procedure of the feeding it says:
ENG MODE SEL...IGN
AVOID NEG G FACTOR
MAX FL:GRAVITY FEED CEILING which is FL350 for us.
When reaching gravity feed ceiling:
FUEL X FEED...OFF
2) So in the beginning we had the x feed ON and the right hand side was supplying. Now the procedure asks us to put it OFF. So from what I understand, the right hand engine will continue to consume the inner/outer tank fuel, xfeed seperated the two sides, and the Left hand pumps are off due low pressure. From what I get is that the left hand engine will shut down from fuel starvation.
3) At this point if we lose one engine, we can't maintain FL350, so we have to pick another Gravity fuel ceiling?!
Then we continue.
If no fuel leak and with one engine running (fed by gravity): which in my mind translates us first part no fuel leak (check) AND this one engine running (we have only one because the other one shut down) is fed by gravity.
FUEL X FEED...ON, so again put it on
BANK ANGLE...1 degree down on the live eng side
RUDDER TRIM...USE
When fuel imbalanve reaches 1000kg:
BANK ANGLE...2or3 degrees on the live eng side.
Now if we continue the FUEL L (R) TK PUMP 1+2 LO PR procedure from the place we left it goes as follows:
WHEN TK (AFFECTED FUEL RQRD:
TK (AFFECTED) FEED .... GRVTY ONLY
Let's assume we diverted and one engine could supply us to the diversion airport.
FUEL X FEED (IF BELOW FL150)...OFF
4) This question probably is the same with the first. Why it asks to switch it off again and specific below FL150?
and then again
If FUEL X FEED off:
PROC: GRVTY FUEL FEEDING (here is has a note saying: As long as the fuel x feed is closed, associated engine is fed by gravity only).
AVOID NEGATIVE G FACTOR
I really don't know if I have burnt myself up, or if I am missing something system wised and I can't get the whole concept, but it seems a bit difficult to me to understand it.
I haven't seen it in the simulator to be honest, maybe it would have been more clear that way, but you work with what you have.
Thanks in advance anyone who will try to explain it to me.
The first failure that will come into play is:
FUEL L(R) TK PUMP 1+2 LO PR
-If NO FUEL LEAK:
FUEL X FEED (IF ABOVE FL150)....ON
1) Why specific FL150? If we are below why we keep it OFF?
ENG MODE SEL...IGN
TK PUMP 1 (AFFECTED)....OFF
TK PUMP 2 (AFFECTED)....OFF
Let's assume that left hand pumps are the ones inoperative.
At this point, left hand fuel pumps are off, the xfeed is open, so both engine consuming from the right hand engine. From now on we have some other sub cases, like where the failure happened. Let's assume again that the failure happen at FL 350 and we were there for 35 minutes, so the GRAVITY FEED CEILING is current FL.
The procedure continues:
WHEN TK (AFFECTED) FUEL RQRD:
TK (AFFECTED) FEED....GRVTY ONLY
If at this point we go to the procedure of the feeding it says:
ENG MODE SEL...IGN
AVOID NEG G FACTOR
MAX FL:GRAVITY FEED CEILING which is FL350 for us.
When reaching gravity feed ceiling:
FUEL X FEED...OFF
2) So in the beginning we had the x feed ON and the right hand side was supplying. Now the procedure asks us to put it OFF. So from what I understand, the right hand engine will continue to consume the inner/outer tank fuel, xfeed seperated the two sides, and the Left hand pumps are off due low pressure. From what I get is that the left hand engine will shut down from fuel starvation.
3) At this point if we lose one engine, we can't maintain FL350, so we have to pick another Gravity fuel ceiling?!
Then we continue.
If no fuel leak and with one engine running (fed by gravity): which in my mind translates us first part no fuel leak (check) AND this one engine running (we have only one because the other one shut down) is fed by gravity.
FUEL X FEED...ON, so again put it on
BANK ANGLE...1 degree down on the live eng side
RUDDER TRIM...USE
When fuel imbalanve reaches 1000kg:
BANK ANGLE...2or3 degrees on the live eng side.
Now if we continue the FUEL L (R) TK PUMP 1+2 LO PR procedure from the place we left it goes as follows:
WHEN TK (AFFECTED FUEL RQRD:
TK (AFFECTED) FEED .... GRVTY ONLY
Let's assume we diverted and one engine could supply us to the diversion airport.
FUEL X FEED (IF BELOW FL150)...OFF
4) This question probably is the same with the first. Why it asks to switch it off again and specific below FL150?
and then again
If FUEL X FEED off:
PROC: GRVTY FUEL FEEDING (here is has a note saying: As long as the fuel x feed is closed, associated engine is fed by gravity only).
AVOID NEGATIVE G FACTOR
I really don't know if I have burnt myself up, or if I am missing something system wised and I can't get the whole concept, but it seems a bit difficult to me to understand it.
I haven't seen it in the simulator to be honest, maybe it would have been more clear that way, but you work with what you have.
Thanks in advance anyone who will try to explain it to me.
Joined: Mar 2012
Posts: 1,714
Likes: 602
From: Dark Side of the Moon
Just think of it this way, when you depart and climb your tank fuel is aerated (contains air), during a rapid climb the air within the fuel will expand and if the fuel is not delivered under pressure then the expanding air can disrupt flow and cause engine flameouts. Below FL150 the expanding air is not sufficient to cause issues. If you have been in a stabilised cruise for more than 30 minutes then the fuel has had a chance to settle and is considered de-aerated. If you are already above FL300 but not for 30 minutes then back to FL300 gives best protection against flameout. So if your two wing tank pumps fail and you are above FL150 then the concern is that the engine will flameout so the ECAM calls for Xfeed open and fuel be delivered to both engines under pressure from the functioning pumps. Once you have established if you have been in cruise above FL300 for more than 30 minutes the fuel,is de-aerated as long as you don’t continue to climb, and you can rely on gravity low pressure feed so xfeed closed. If you are above FL300 but less than 30 minutes then use xfeed open and hi pressure feed until back at FL300, once back at FL300 then Airbus considers the fuel de-aerated so you can close the xfeed and rely on low pressure gravity feed. If you never got to FL300 then back to FL150 for you. The whole point of the procedure is to reduce the risk of flame out when using aerated low pressure fuel, to eliminate that risk you use the high pressure fuel from the good tank using the xfeed. Once you establish the fuel in the low pressure tank is safe to use then you use it by closing the xfeed.
Thread Starter
Joined: Apr 2022
Posts: 7
Likes: 0
From: Greece
Ollie I have understood this and how the deaerated fuel works and so on. Your answer covers the first question about FL150 and thanks for that. The main issue was the sequence of events because I haven't seen the actual failure in the sim, so I have to visualize it. I slept in the night thinking about it and I have found some answers. For the sake of the conversation I will go will the visualization process.You are climbing, at FL200 you have an ECAM for Left tank pumps low pressure. The procedure states, xfeed on and pumps off. So you do that, you make a fordec and you say I have the fuel to continue to my destination because it's tankering, so I can easily climb at FL350 stay there for 30 minutes and still have plenty of fuel in the right hand side of the wing. So you do that.
The procedure states, that WHEN FUEL OF THE AFFECTED WING NEEDED go for the gravity fuel feeding procedure. So you open the QRH and you do the checklist. You put the XFEED OFF because it states when reaching gravity fuel feed ceiling put it off, so at that moment the right hand engine is taking fuel from the right hand from the pumps, the center tank is empty and the left hand engine (the one without pumps) takes fuel through gravity forces so it continue to run.
Then, you go to the next line which says, If no fuel leak and with one engine running (fed by gravity) - which is our case - :
xfeed on, bank angle .. 1degree wing down on the live eng side - this is the right side on our example -
rudder trim ... use.
So bottom, line both of your engines continue to run since both are supplied with fuel somehow. If the left tank depletes a lot you may lose the left hand engine on the approach in case you dont or you cant open the xfeed again.
Am I correct?
Now the questions for the things that aren't clear to me.
1) This sentence: If no fuel leak and with one engine running (fed by gravity), assumes that you may have have 1 engine live (fuel pumps working) and the other fed by gravity - so in general 2 engines working, which is our case - or scenario 2, no engine working through the fuel pumps and you have to make one engine working through the gravity feeding process correct? Like if in cruise you put all pumps off, at some point the engines will go off. Assuming you dont put them on again, you have to bank 1 degree to the right to make your left hand engine take fuel by the left hand side, but this means your right hand engine will not have enough pressure and gravity to take fuel from the right hand side, so this engine will remain off. Do I get it correct?
2) Also, the FCOM/QRH has a gray zone about the deaeration of the fuel. If you search by your own, you know why the limitations are there, you learn about Henry's law and etc. But it doesn't specify at any point if the deaeration needs the fuel pumps to work in order for it to happen or not. So, this is a process that happens once the pumps are working on take off because the initial force has been given and it continues by itself OR you need the fuel pumps to work in order for the pressure and all that to be supplied and the air to deaerate?
The procedure states, that WHEN FUEL OF THE AFFECTED WING NEEDED go for the gravity fuel feeding procedure. So you open the QRH and you do the checklist. You put the XFEED OFF because it states when reaching gravity fuel feed ceiling put it off, so at that moment the right hand engine is taking fuel from the right hand from the pumps, the center tank is empty and the left hand engine (the one without pumps) takes fuel through gravity forces so it continue to run.
Then, you go to the next line which says, If no fuel leak and with one engine running (fed by gravity) - which is our case - :
xfeed on, bank angle .. 1degree wing down on the live eng side - this is the right side on our example -
rudder trim ... use.
So bottom, line both of your engines continue to run since both are supplied with fuel somehow. If the left tank depletes a lot you may lose the left hand engine on the approach in case you dont or you cant open the xfeed again.
Am I correct?
Now the questions for the things that aren't clear to me.
1) This sentence: If no fuel leak and with one engine running (fed by gravity), assumes that you may have have 1 engine live (fuel pumps working) and the other fed by gravity - so in general 2 engines working, which is our case - or scenario 2, no engine working through the fuel pumps and you have to make one engine working through the gravity feeding process correct? Like if in cruise you put all pumps off, at some point the engines will go off. Assuming you dont put them on again, you have to bank 1 degree to the right to make your left hand engine take fuel by the left hand side, but this means your right hand engine will not have enough pressure and gravity to take fuel from the right hand side, so this engine will remain off. Do I get it correct?
2) Also, the FCOM/QRH has a gray zone about the deaeration of the fuel. If you search by your own, you know why the limitations are there, you learn about Henry's law and etc. But it doesn't specify at any point if the deaeration needs the fuel pumps to work in order for it to happen or not. So, this is a process that happens once the pumps are working on take off because the initial force has been given and it continues by itself OR you need the fuel pumps to work in order for the pressure and all that to be supplied and the air to deaerate?
Joined: Mar 2012
Posts: 2,605
Likes: 154
From: Having a margarita on the beach
You are climbing, at FL200 you have an ECAM for Left tank pumps low pressure. The procedure states, xfeed on and pumps off. So you do that, you make a fordec and you say I have the fuel to continue to my destination because it's tankering, so I can easily climb at FL350 stay there for 30 minutes and still have plenty of fuel in the right hand side of the wing. So you do that.
Yes, but make sure You take into consideration negative Gs and the unbalance you will eventually create as a result of burning fuel only from one side. Have a look at This answer.
The procedure states, that WHEN FUEL OF THE AFFECTED WING NEEDED go for the gravity fuel feeding procedure. So you open the QRH and you do the checklist. You put the XFEED OFF because it states when reaching gravity fuel feed ceiling put it off, so at that moment the right hand engine is taking fuel from the right hand from the pumps, the center tank is empty and the left hand engine (the one without pumps) takes fuel through gravity forces so it continue to run.
Then, you go to the next line which says, If no fuel leak and with one engine running (fed by gravity) - which is our case - :
Then, you go to the next line which says, If no fuel leak and with one engine running (fed by gravity) - which is our case - :
Airbus wants to ensure that if you end up single engine without fuel pumps on the live engine side, you maximize the chances of feeding that engine.
If you have both engines running, happy days, your checklist is finished.2) Also, the FCOM/QRH has a gray zone about the deaeration of the fuel. If you search by your own, you know why the limitations are there, you learn about Henry's law and etc. But it doesn't specify at any point if the deaeration needs the fuel pumps to work in order for it to happen or not. So, this is a process that happens once the pumps are working on take off because the initial force has been given and it continues by itself OR you need the fuel pumps to work in order for the pressure and all that to be supplied and the air to deaerate?
Post
Thread Starter
Joined: Apr 2022
Posts: 7
Likes: 0
From: Greece
At FL 300 +30 Minutes ( which is 44 minutes of EET ) you will switch OFF the X Feed and apply the gravity fuel feeding procedure . You can stay at FL 390 and the left tank will be on gravity. Which is in the middle of the paragraph and the way he writes it down, I think that he assumes 2 engine running at this point too.
fuel xfeed on, bank angle 1 wing down, rudder trim use. So the right hand engine will go off in a matter of minutes if not seconds and then you have only one engine left which is fed by gravity. correct?
Let me quote you a very good explanation from vilas that uses the 2 things that as a pilot I like the most: fuel and beer!
PS: I am not allowed to use links, so I deleted them.
Joined: Jun 2007
Posts: 3,443
Likes: 39
From: Wanderlust
The following is from the text:
At FL 300 +30 Minutes ( which is 44 minutes of EET ) you will switch OFF the X Feed and apply the gravity fuel feeding procedure . You can stay at FL 390 and the left tank will be on gravity. Which is in the middle of the paragraph and the way he writes it down, I think that he assumes 2 engine running at this point too.
Ok, so I will make another scenario from the beginning to tell me if now I have it correct in my mind. You climb and at FL200 you have the LO PR on the left hand side again. In a ceo 320 your gravity ceiling is FL150. So you put your xfeed on, eng mode sel..ign, tk pump 1+2 off (the left ones). And on the right hand side we have 2000 kg. When the right hand engine has 100kg, you jump into the gravity fuel feeding, which states. If no fuel leak and with one engine running (fed by gravity):
fuel xfeed on, bank angle 1 wing down, rudder trim use. So the right hand engine will go off in a matter of minutes if not seconds and then you have only one engine left which is fed by gravity. correct?
Yes, I get the whole explanation, my question is something else? You need to have pumps working constantly for the deaeration to happen? Or if they even work for 1 minute and they give the initial force the whole process continue automatically because it only needs a trigger action.
PS: I am not allowed to use links, so I deleted them.
At FL 300 +30 Minutes ( which is 44 minutes of EET ) you will switch OFF the X Feed and apply the gravity fuel feeding procedure . You can stay at FL 390 and the left tank will be on gravity. Which is in the middle of the paragraph and the way he writes it down, I think that he assumes 2 engine running at this point too.
Ok, so I will make another scenario from the beginning to tell me if now I have it correct in my mind. You climb and at FL200 you have the LO PR on the left hand side again. In a ceo 320 your gravity ceiling is FL150. So you put your xfeed on, eng mode sel..ign, tk pump 1+2 off (the left ones). And on the right hand side we have 2000 kg. When the right hand engine has 100kg, you jump into the gravity fuel feeding, which states. If no fuel leak and with one engine running (fed by gravity):
fuel xfeed on, bank angle 1 wing down, rudder trim use. So the right hand engine will go off in a matter of minutes if not seconds and then you have only one engine left which is fed by gravity. correct?
Yes, I get the whole explanation, my question is something else? You need to have pumps working constantly for the deaeration to happen? Or if they even work for 1 minute and they give the initial force the whole process continue automatically because it only needs a trigger action.
PS: I am not allowed to use links, so I deleted them.
Thread Starter
Joined: Apr 2022
Posts: 7
Likes: 0
From: Greece
Fuel pumps have nothing to do with deaeration. Air will keep bubbling as atmospheric pressure keeps dropping. But pumps keep supplying fuel under pressure despite that. You need fuel pumps all the time atleast in one main tank which if required can provide fuel to other side via cross feed. If both tanks pump fail below 30000 then go to 15000ft. If you stayed above 30000ft for 30mts before pumps failed then you can stay there.
Last edited by A320giorgosgreece; 17th September 2024 at 19:38.
