Gravity cross feeding -A320 family
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Goldenrivett
It is not one of the engines but it will be the engine on the good fuel pumps side will starve and you will have to use the failed pump side to cross feed that. You think it is a good idea? what happens if in the process both quite? What are the circumstances that will make you do all this?
It is not one of the engines but it will be the engine on the good fuel pumps side will starve and you will have to use the failed pump side to cross feed that. You think it is a good idea? what happens if in the process both quite? What are the circumstances that will make you do all this?
Villas:Surely, if the imbalance (for whatever reason) is not too large, AND the subsequent flight is forced to fly for a long time - then would not it be prudent to be more proactive and reduce the imbalance with differential thrust. Once the wings are balanced then the flight can be continued with the cross feed closed and each engine operating normally. ie. one on gravity and the other using the pumps. That way you don't lose significant range. And yes, I am aware that you will not find this in the FCOM.
This thread has shown signs of the old arguments that you used to get in the sim. about when to fuel balance. One school saying never do it until told to by an ECAM!
However the original scenario is so unlikely that it is almost not worth considering! I also appreciate that instructors can not be seen to advocate procedures that are not "in the book" however this is a discussion board and we may have lost sight of the original query. I personally have experienced multiple spurious ECAMs and loss of FADEC thrust control. Neither situation was covered in the FCOMs.
This thread has shown signs of the old arguments that you used to get in the sim. about when to fuel balance. One school saying never do it until told to by an ECAM!
However the original scenario is so unlikely that it is almost not worth considering! I also appreciate that instructors can not be seen to advocate procedures that are not "in the book" however this is a discussion board and we may have lost sight of the original query. I personally have experienced multiple spurious ECAMs and loss of FADEC thrust control. Neither situation was covered in the FCOMs.
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Meikleour
My point is what is the compulsion to continue by doing non standard things. As I suggested before if it is a case of 370 you straight descend to 300 and don't allow the imbalance to develop. If it is the case of below 300 then you will have to reassess EFOB to keep some fuel in good pump side and you will have treat it as unusable fuel. If that doesn't take you to destination then why not divert?
My point is what is the compulsion to continue by doing non standard things. As I suggested before if it is a case of 370 you straight descend to 300 and don't allow the imbalance to develop. If it is the case of below 300 then you will have to reassess EFOB to keep some fuel in good pump side and you will have treat it as unusable fuel. If that doesn't take you to destination then why not divert?
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vilas
I don't understand what you are trying to say in post #41.
But if I received ECAM "FUEL IMBALANCE" or "FUEL L (R) WING TK LO LVL"
Then I would:
"Applicable to: ALL
.........
IF NO FUEL LEAK AND FUEL IMBALANCE:
FUEL X FEED ON
TK PUMP 1 (on side with LO LVL) OFF
TK PUMP 2 (on side with LO LVL) OFF
Note:
TK PUMP 1+2 (on side with LO LVL) LO PR warning will be triggered."
In order to use fuel from the tank with more fuel, then I would bank the aircraft by 3 degs towards the lower level tank.
Why do you think either engine would quit? The only warning is to avoid -ve g. In steady level flight all the fuel will experience 1g, but there will be a bigger pressure head from the higher fuel tank.
I don't understand what you are trying to say in post #41.
But if I received ECAM "FUEL IMBALANCE" or "FUEL L (R) WING TK LO LVL"
Then I would:
"Applicable to: ALL
.........
IF NO FUEL LEAK AND FUEL IMBALANCE:
FUEL X FEED ON
TK PUMP 1 (on side with LO LVL) OFF
TK PUMP 2 (on side with LO LVL) OFF
Note:
TK PUMP 1+2 (on side with LO LVL) LO PR warning will be triggered."
In order to use fuel from the tank with more fuel, then I would bank the aircraft by 3 degs towards the lower level tank.
Why do you think either engine would quit? The only warning is to avoid -ve g. In steady level flight all the fuel will experience 1g, but there will be a bigger pressure head from the higher fuel tank.
Last edited by Goldenrivett; 17th Jun 2015 at 06:57. Reason: typo
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Goldenrivett
We are discussing two different aspects of this case. One is practical real life decision making the other is theoretical possibilities. SOP wise there is no gravity feed cross feed with AEO. So situational decision should have been taken whether to continue at same level or descend or to continue to destination at all or divert. Our decision cannot be based on inventing a procedure that is not supported by SOP. What you are suggesting is OEI procedure. In that situation you do not have up wing engine. So in AEO scenario with gravity feed on the up wing engine what will happen to that engine is only a guess work. If you landed up in that situation(which you should not) then you can take your chances. There is an incident in safety magazine where A320 climbed to FL380 with fuel pumps off before both engines flame out. So nothing may happen but no guarantees.
We are discussing two different aspects of this case. One is practical real life decision making the other is theoretical possibilities. SOP wise there is no gravity feed cross feed with AEO. So situational decision should have been taken whether to continue at same level or descend or to continue to destination at all or divert. Our decision cannot be based on inventing a procedure that is not supported by SOP. What you are suggesting is OEI procedure. In that situation you do not have up wing engine. So in AEO scenario with gravity feed on the up wing engine what will happen to that engine is only a guess work. If you landed up in that situation(which you should not) then you can take your chances. There is an incident in safety magazine where A320 climbed to FL380 with fuel pumps off before both engines flame out. So nothing may happen but no guarantees.
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vilas,
If you are concerned that an aircraft, when below its gravity fuel ceiling, and with all fuel pumps off but with 3 degs of slide slip would cause an engine to flame out, then what will you do during mild turbulence?
Do you think such a sensitive fuel system would be approved?
Wouldn't you think that there would be an FCOM reference to maintain perfectly balanced flight during all turns?
As a practical real life decision making exercise, if during the IMBALANCE / FUEL L (R) WING TK LO LVL ECAM procedure I was unable to balance fuel with wings level or with one wing low, then I would consider diversion before an engine failed due fuel starvation.
However, I would not just sit there with wings level, refusing to attempt to balance fuel and repeatedly quote LIM-28 P 1/2 FCOM A to D 15 FEB 13 as in post #10.
If you are concerned that an aircraft, when below its gravity fuel ceiling, and with all fuel pumps off but with 3 degs of slide slip would cause an engine to flame out, then what will you do during mild turbulence?
Do you think such a sensitive fuel system would be approved?
Wouldn't you think that there would be an FCOM reference to maintain perfectly balanced flight during all turns?
As a practical real life decision making exercise, if during the IMBALANCE / FUEL L (R) WING TK LO LVL ECAM procedure I was unable to balance fuel with wings level or with one wing low, then I would consider diversion before an engine failed due fuel starvation.
However, I would not just sit there with wings level, refusing to attempt to balance fuel and repeatedly quote LIM-28 P 1/2 FCOM A to D 15 FEB 13 as in post #10.
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Golden
Let me put it all together. You had ECAM fuel pump 1+2 fail. You opened the cross feed to feed the engines from active fuel pump side. ECAM actions complete. Now are you supposed to sit there and watch fuel imbalance develop? Or start a non standard balancing procedure? No. You take a situational assessment decision. Facts of the case? fuel imbalance is developing and there is no procedure to address that if we need that fuel. Options? we can descend to FL300 and use gravity feed on the failed side and stop the imbalance. Risks? Fuel flow at FL300 is 8kg/H/ENG higher which is within our FOB.(This scenario is given by the poster). In any other situation the decision to divert has to come before the need for non standard procedures. The fuel imbalance procedure you yourself quoted by lowering the wing is for OEI. Fuel system may be sensitive or not I don't care to find out, we are not paid for that we just land and give the job of explaining what to do in that case to airbus.The limitation I quoted is in the context of if you happen to have fuel leak one side and loose all fuel on that side and engine not a big deal landing the plane.
Let me put it all together. You had ECAM fuel pump 1+2 fail. You opened the cross feed to feed the engines from active fuel pump side. ECAM actions complete. Now are you supposed to sit there and watch fuel imbalance develop? Or start a non standard balancing procedure? No. You take a situational assessment decision. Facts of the case? fuel imbalance is developing and there is no procedure to address that if we need that fuel. Options? we can descend to FL300 and use gravity feed on the failed side and stop the imbalance. Risks? Fuel flow at FL300 is 8kg/H/ENG higher which is within our FOB.(This scenario is given by the poster). In any other situation the decision to divert has to come before the need for non standard procedures. The fuel imbalance procedure you yourself quoted by lowering the wing is for OEI. Fuel system may be sensitive or not I don't care to find out, we are not paid for that we just land and give the job of explaining what to do in that case to airbus.The limitation I quoted is in the context of if you happen to have fuel leak one side and loose all fuel on that side and engine not a big deal landing the plane.
Last edited by vilas; 18th Jun 2015 at 06:20.
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I would say that the key factor in all this discussion about either xfeeding or not is the XFEED valve itself.
What happens when it is open and you have a bank (which has to be with crossed controls, otherwise gravity will still be vertical)?
I would say that it makes a big difference, in the sense that with the valve closed, gravity shifts due to bank angles will not result in the head pressure on the engine LP fuel valves. With the valve open, however, it might be otherwise. Since the up wing would be the pumpless wing, that might lead to a flame out. Hence, the procedure tells you how to do that only after the engine is already lost.
What happens when it is open and you have a bank (which has to be with crossed controls, otherwise gravity will still be vertical)?
I would say that it makes a big difference, in the sense that with the valve closed, gravity shifts due to bank angles will not result in the head pressure on the engine LP fuel valves. With the valve open, however, it might be otherwise. Since the up wing would be the pumpless wing, that might lead to a flame out. Hence, the procedure tells you how to do that only after the engine is already lost.
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Hi Microburst2002 & vilas,
Since the suction valve is in the same part of the fuel tank as the main fuel pumps, please explain the scientific physical reason why you think the suction valve would uncover when the crossfeed valve is open and the aircraft has 3 degs of side slip.
See "Suction Valves" DSC-28-10-Engine Feed, General, Main Components.
(N.B. The main fuel pumps don't uncover with full side slip deflection.)
Since the suction valve is in the same part of the fuel tank as the main fuel pumps, please explain the scientific physical reason why you think the suction valve would uncover when the crossfeed valve is open and the aircraft has 3 degs of side slip.
See "Suction Valves" DSC-28-10-Engine Feed, General, Main Components.
(N.B. The main fuel pumps don't uncover with full side slip deflection.)
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This is not my point, it may or may not but I would not like to find out by an accident. There is no approved procedure, so I would simply not allow myself to get into that situation, that is my point. I believe in that old adage of operating the aircraft in a manner which does not require any extra ordinary skill leave alone requires being inventive.
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Suction doesn't really exist. Higher pressure in one side than the other does exist though, and sometimes we refer it to suction.
Those suction valves, honestly I don't know how they work, exactly.
"Closed by pumps pressure in normal operation, they allow the engines to be fed by gravity if the inner tank pumps fail"
I believe, or my guess is, that the suction valves are closed whenever the pumps are on, because of the suction these create. Then, in the absence of pump pressure when the pumps fail, there is no more suction and the valves will open, thus allowing the feeding of the engine by gravity. Does that make sense? any engineer or someone with first hand knowledge of these suction valves?
As I understand it, fuel cannot just flow through the pump by gravity. It needs an alternate path to the engine feed line, which would be via the suction pumps.
So, according to the above, only gravity pushes the fuel into the engines. Not suction. More precisely, weight does push the fuel. Gravity is a field, but what pushes the fuel is a force, or a pressure in the line, if you like.
Gravity feeds the fuel into the engine, and the more the weight of fuel above the valve, the more the pressure in the line. if gravity shifts away and some fuel goes to the other side, it doesn't exert its weight on the fuel covering the valve any longer, and therefore there is less pressure on that point, now. That could lead to a flame out.
Even if the pumps do not uncover, which I agree with you: they will not uncover in any conditions the pumps would not.
Those suction valves, honestly I don't know how they work, exactly.
"Closed by pumps pressure in normal operation, they allow the engines to be fed by gravity if the inner tank pumps fail"
I believe, or my guess is, that the suction valves are closed whenever the pumps are on, because of the suction these create. Then, in the absence of pump pressure when the pumps fail, there is no more suction and the valves will open, thus allowing the feeding of the engine by gravity. Does that make sense? any engineer or someone with first hand knowledge of these suction valves?
As I understand it, fuel cannot just flow through the pump by gravity. It needs an alternate path to the engine feed line, which would be via the suction pumps.
So, according to the above, only gravity pushes the fuel into the engines. Not suction. More precisely, weight does push the fuel. Gravity is a field, but what pushes the fuel is a force, or a pressure in the line, if you like.
Gravity feeds the fuel into the engine, and the more the weight of fuel above the valve, the more the pressure in the line. if gravity shifts away and some fuel goes to the other side, it doesn't exert its weight on the fuel covering the valve any longer, and therefore there is less pressure on that point, now. That could lead to a flame out.
Even if the pumps do not uncover, which I agree with you: they will not uncover in any conditions the pumps would not.
Eureka
I was cleaning the bottom of my pool this afternoon. Normally I attach the hose to it's location about 20cms below water level, open the waste valve (Located well below the pool floor level) and switch on the pump. A huge amount of costly water is lost in the time taken to clean the dirt from the pool bottom. So today I decided to follow the same procedure without the pump running. The pressure differential was still more than adequate to suck the dirt from the bottom with about 50% less water loss. The only problem I see in my A320 is if the gravity feed flow rate is too low for the demand from the engine, could a flameout result at a high thrust setting?
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Only engineers can tell, I guess.
Like I said, the procedure for gravity cross feeding by banking is exclusively laid out for the engine already lost scenario.
Like I said, the procedure for gravity cross feeding by banking is exclusively laid out for the engine already lost scenario.
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Hi Nightstop,
When gravity fuel feeding, there is no such warning of engine misbehaviour in FCOM or QRH & according to http://www.icao.int/Meetings/caaf200...9_IP012_en.pdf
"2.2.4.1 Engine transients:
....
• During transient manoeuvres preformed in normal feed and gravity feed with deaerated fuel, engine 1 showed correct behaviour: no stall or engine misbehaviour was observed."
Hi Microburst2002,
Correct. The procedure ensures that fuel will transfer from the opposite tank to your only running engine at a fast enough rate.
When both engines are being gravity fed & with the cross-feed valve open, fuel from the tank with the bigger contents will tend to be used faster (due to the greater "pressure head" of fuel.) However, there is nothing to stop you from accelerating the balance procedure.
Please show me where the max side slip is published when gravity fuel feeding?
... could a flameout result at a high thrust setting?
"2.2.4.1 Engine transients:
....
• During transient manoeuvres preformed in normal feed and gravity feed with deaerated fuel, engine 1 showed correct behaviour: no stall or engine misbehaviour was observed."
Hi Microburst2002,
the procedure for gravity cross feeding by banking is exclusively laid out for the engine already lost scenario.
When both engines are being gravity fed & with the cross-feed valve open, fuel from the tank with the bigger contents will tend to be used faster (due to the greater "pressure head" of fuel.) However, there is nothing to stop you from accelerating the balance procedure.
Please show me where the max side slip is published when gravity fuel feeding?
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Suction
In normal operation with fuel pumps, engines are supplied fuel under pressure. When pumps fail the only force on the fuel is of gravity. However a running engine generates a suction and fuel is pulled rather than pushed and care needs to be taken to ensure there is no gap in the line. As I mentioned before A320 has climbed to 380 with fuel pumps off before dual flame out and was even relit.
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Armchair Snark, But I Cannot Resist
For a true gravity x-feed between wing tanks and all pumps inop try this:
1. Establish stable flight on desired course and at assigned FL.
(1-A. Suspend cabin beverage service if relevant.)
2. Apply substantial trim sufficient to bank about 30 degrees, heavy wing high. Re-trim as needed to maintain course and altitude.
3. Level wings periodically to recheck fuel balance.
4. Consult OPS/Dispatch as necessary, possibly preparing to land a bit early for repairs, and...
5. Rinse and Repeat as necessary.
1. Establish stable flight on desired course and at assigned FL.
(1-A. Suspend cabin beverage service if relevant.)
2. Apply substantial trim sufficient to bank about 30 degrees, heavy wing high. Re-trim as needed to maintain course and altitude.
3. Level wings periodically to recheck fuel balance.
4. Consult OPS/Dispatch as necessary, possibly preparing to land a bit early for repairs, and...
5. Rinse and Repeat as necessary.
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Hi Goldenrivet
I don't know, there is no limits laid out regarding bank angles nor slip angles.
All I'm saying is that the procedure is not for the all engines operating case, but only for the one engine out case. Which makes sense, because when the engine is already lost, who cares about any maximum slip angle?
I don't know, there is no limits laid out regarding bank angles nor slip angles.
All I'm saying is that the procedure is not for the all engines operating case, but only for the one engine out case. Which makes sense, because when the engine is already lost, who cares about any maximum slip angle?
