A320 FMS inputs
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A320 FMS inputs
Hello,
simple question for any A320 driver here, at least I hope so.
How does the aircraft know how heavy it is and where is the center of gravity?
Let's assume you receive a loadsheet, you do not make your own. Standard things like crew, PAX, etc. Of course all the weights.
What I do not know is what do you put to FMS.
ZFW and fuel? Or TOW? Do you put fuel manually from loadsheet or from instruments or does the aircraft know? What does it do with taxi fuel?
simple question for any A320 driver here, at least I hope so.
How does the aircraft know how heavy it is and where is the center of gravity?
Let's assume you receive a loadsheet, you do not make your own. Standard things like crew, PAX, etc. Of course all the weights.
What I do not know is what do you put to FMS.
ZFW and fuel? Or TOW? Do you put fuel manually from loadsheet or from instruments or does the aircraft know? What does it do with taxi fuel?
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Hello,
simple question for any A320 driver here, at least I hope so.
How does the aircraft know how heavy it is and where is the center of gravity?
Let's assume you receive a loadsheet, you do not make your own. Standard things like crew, PAX, etc. Of course all the weights.
What I do not know is what do you put to FMS.
ZFW and fuel? Or TOW? Do you put fuel manually from loadsheet or from instruments or does the aircraft know? What does it do with taxi fuel?
simple question for any A320 driver here, at least I hope so.
How does the aircraft know how heavy it is and where is the center of gravity?
Let's assume you receive a loadsheet, you do not make your own. Standard things like crew, PAX, etc. Of course all the weights.
What I do not know is what do you put to FMS.
ZFW and fuel? Or TOW? Do you put fuel manually from loadsheet or from instruments or does the aircraft know? What does it do with taxi fuel?
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You enter your ZFW and ZFW CG from the load sheet. This tells the FMS how much the airplane weights and where is the center of gravity WITHOUT THE FUEL.
The FMS will know how much fuel are there in the tanks and with that data will compute and show you the GW (gross weight) and GW CG in the FUEL PRED page of the FMS. The center of gravity of the airplane will be the one of the ZFW corrected by the CG of the fuel (ZFW CG plus or minus a certain amount, the data is in the FMS memory).
After start you should check that the GW CG shown in the FUEL PRED page of the FMS is similar to the one of the load sheet.
After airborne the FMS constantly updates de GW CG after the fuel gets burned, the info is always shown in the FUEL PRED page.
Taxi fuel: the taxi fuel figure is in the INIT B page and it is for planning purposes. After engine start the INIT B page is no longer there, and if you press INIT and then lateral arrow the FMS will take you to FUEL PRED page. The FOB gets updated with the actual amount in the tanks. If in the INIT B page the taxi is 0.2 (200 kgs) but the taxi time is short and the fuel burned during taxi is just 100 kgs, the GW figure shown at the bottom of the System Display and the FUEL PRED page will be 100 kgs higher than then one showed in the INIT B before engine start up.
The FMS will know how much fuel are there in the tanks and with that data will compute and show you the GW (gross weight) and GW CG in the FUEL PRED page of the FMS. The center of gravity of the airplane will be the one of the ZFW corrected by the CG of the fuel (ZFW CG plus or minus a certain amount, the data is in the FMS memory).
After start you should check that the GW CG shown in the FUEL PRED page of the FMS is similar to the one of the load sheet.
After airborne the FMS constantly updates de GW CG after the fuel gets burned, the info is always shown in the FUEL PRED page.
Taxi fuel: the taxi fuel figure is in the INIT B page and it is for planning purposes. After engine start the INIT B page is no longer there, and if you press INIT and then lateral arrow the FMS will take you to FUEL PRED page. The FOB gets updated with the actual amount in the tanks. If in the INIT B page the taxi is 0.2 (200 kgs) but the taxi time is short and the fuel burned during taxi is just 100 kgs, the GW figure shown at the bottom of the System Display and the FUEL PRED page will be 100 kgs higher than then one showed in the INIT B before engine start up.
Last edited by iggy; 28th Jan 2020 at 10:58. Reason: Taxi fuel
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EDIT: "The FMS continously updates the GW anf CG during the flight." it is what is written in the FCOM page description of the FMS. At least in Thales...
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Senior moment it was, only on my side! I quoted a wrong paragraph, this one I suspected.
After start check-list PITCH TRIM item:
____ SET (A320)
____ CHECKED (A330)
Sorry for your trouble, really.
After start you should check that the GW CG shown in the FUEL PRED page of the FMS is similar to the one of the load sheet.
____ SET (A320)
____ CHECKED (A330)
Sorry for your trouble, really.
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It will take some time until I get to my type rating. I work in load sheet department right now and we had a problematic situation today so I was curious. I though exactly the same you wrote me (at least if I understood that right) but there were obviously other opinions.
Let's asume we have A319 on short flight. However there is something wrong with center fuel tank. There is fuel trapped there and it can not be used. According to captain there is 1000 kg in trapped in center tank and total block fuel with this trapped fuel included is 6000 kg. Which means 5000 kg fuel in wings and 1000 kg in center tank. I think this is reported because of something what we call non standard fuel distribution. Normaly, there would be nothing in center tank with 6000 kg of fuel and CG would be a bit different. That is how I imagine it works.
And now there is a plot twist. ZFW is basic weight, crew, pantry (catering) and PAX, bags, cargo. I think we all can agree on that. However in this case someone has the idea to add that 1000 kg of fuel to this ZFW. ZFW is now higher by that part of fuel. To have correct TOW they lower block fuel by 1000 kg. So TOW is correct. But there is a shift in fuel and ZFW. So crew gets the load sheet and now if I understand that correctly they put the increased ZFW (because they do not know it is somehow changed) to FMS and then all the block fuel is added by FMS. That means that ZFW is higer by 1000 kg and TOW is higher by 1000 kg. At least in FMS. When they compare it with load sheet there must be 1000 kg discrepancy. Is this what would happen or is there something I do not understand?
Or is there a possibility to input something else than ZFW? Eg. Manual input of TOW and fuel regardless of what is measuring aircraft fuel system?
Let's asume we have A319 on short flight. However there is something wrong with center fuel tank. There is fuel trapped there and it can not be used. According to captain there is 1000 kg in trapped in center tank and total block fuel with this trapped fuel included is 6000 kg. Which means 5000 kg fuel in wings and 1000 kg in center tank. I think this is reported because of something what we call non standard fuel distribution. Normaly, there would be nothing in center tank with 6000 kg of fuel and CG would be a bit different. That is how I imagine it works.
And now there is a plot twist. ZFW is basic weight, crew, pantry (catering) and PAX, bags, cargo. I think we all can agree on that. However in this case someone has the idea to add that 1000 kg of fuel to this ZFW. ZFW is now higher by that part of fuel. To have correct TOW they lower block fuel by 1000 kg. So TOW is correct. But there is a shift in fuel and ZFW. So crew gets the load sheet and now if I understand that correctly they put the increased ZFW (because they do not know it is somehow changed) to FMS and then all the block fuel is added by FMS. That means that ZFW is higer by 1000 kg and TOW is higher by 1000 kg. At least in FMS. When they compare it with load sheet there must be 1000 kg discrepancy. Is this what would happen or is there something I do not understand?
Or is there a possibility to input something else than ZFW? Eg. Manual input of TOW and fuel regardless of what is measuring aircraft fuel system?
Last edited by Rarife; 28th Jan 2020 at 18:46. Reason: added things
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I do not want to edit anymore.
I just checked manual and there is written that FOB is boxed amber when the quantity shown is not all usable. So aircraft knows it can not use all the fuel but still measures all of it.
Then there is written that MCDU uses FOB so it could be tricked by unusable fuel.
Is this correct?
We had recently problem with B777 and since that they require extra information about this "mess" with ZFW. Maybe Airbus is more inteligent but that is the problem. We do not know. Some people do not doubt but I do.
I just checked manual and there is written that FOB is boxed amber when the quantity shown is not all usable. So aircraft knows it can not use all the fuel but still measures all of it.
Then there is written that MCDU uses FOB so it could be tricked by unusable fuel.
Is this correct?
We had recently problem with B777 and since that they require extra information about this "mess" with ZFW. Maybe Airbus is more inteligent but that is the problem. We do not know. Some people do not doubt but I do.
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On the type, the crew initially would enter the expected fuel mass manually and the FMS shows ZFW+expect.Fuel = AUW during cockpit preparation and loadsheet check (*). Until this point, your colleague's solution would work.
After the engines start, the FMS would erase the manually entered fuel weight and add the crew-ZFW to the actual amount of FOB (**). And the problem unfolds, there's nothing in your post I see amiss.
Too smart of a solution. Probably because your system does not allow to modify the non-standard fuel loading index.
(*) when checking the LDS, before engine start, the crew will verify the manually entered FOB value is the same as the actual fuel load. The difference would be identified as deliberate in your scenario.
(**) That can actually be overwritten but then you are really causing a serious headache.
After the engines start, the FMS would erase the manually entered fuel weight and add the crew-ZFW to the actual amount of FOB (**). And the problem unfolds, there's nothing in your post I see amiss.
Too smart of a solution. Probably because your system does not allow to modify the non-standard fuel loading index.
(*) when checking the LDS, before engine start, the crew will verify the manually entered FOB value is the same as the actual fuel load. The difference would be identified as deliberate in your scenario.
(**) That can actually be overwritten but then you are really causing a serious headache.
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Great. To make it more complicated. Captain called and he said they have 700 kg trapped fuel in center tank and that it is included in total 6300 kg block fuel. It is supposed to be something what we call final fuel and it should be real value that is in the aircraft. I do not where they get this value but I always expected this to be FOB from ECAM. I think that means they really want to have or already have that 6300 kg of fuel on board. This is the value I would put into FMS as expected fuel but maybe they do that earlier. However we use two load sheets for each flight. First is preliminary, sent 30 minutes before STD after recieving final fuel from crew. Second, is final, very short one and this can be sent just before take off. It is just confirmation that there is no or very small difference from the preliminary version.
So it ended up like
Preliminary LS
ZFW was 700 higher than real one
TOF was 700 kg lower (5400 kg take off fuel. Instead of 6100 which would be 6300-200 for taxi)
TOW was ok
Final LS was same.
I understand that crew can not know ZFW. it is our job and they put what they recieve to FMS. But as I pilot I would not like why my take off fuel does not match what I wanted. And after start up my fuel would be ok (I mean ok with what I wanted, not the load sheet) but my TOW would suddenly jump up.Than I recieve the final LS and my TOW on LS is lower by that 700 kg.
We can make non-standard fuel loading. It is ok but there is another box called trapped fuel which moves the amount of fuel from block fuel to ZFW. And it causes all this mess. As I said. For B777 we have to send them that they are supposed to use another ZFW for FMS. Not the one from load sheet but the one from aditional information on LS where we manualy put ZFW lowered by that trapped fuel. Not really lowered but in fact the correct one.
For calculation take off performance, do they use the expected fuel mass they put intially or the real fuel? But I guess it depends on airline when they do that. I think that they use the real values because I guess they can not do performance calculations without load sheet and we send load sheet after we get final fuel from them.
So it ended up like
Preliminary LS
ZFW was 700 higher than real one
TOF was 700 kg lower (5400 kg take off fuel. Instead of 6100 which would be 6300-200 for taxi)
TOW was ok
Final LS was same.
I understand that crew can not know ZFW. it is our job and they put what they recieve to FMS. But as I pilot I would not like why my take off fuel does not match what I wanted. And after start up my fuel would be ok (I mean ok with what I wanted, not the load sheet) but my TOW would suddenly jump up.Than I recieve the final LS and my TOW on LS is lower by that 700 kg.
We can make non-standard fuel loading. It is ok but there is another box called trapped fuel which moves the amount of fuel from block fuel to ZFW. And it causes all this mess. As I said. For B777 we have to send them that they are supposed to use another ZFW for FMS. Not the one from load sheet but the one from aditional information on LS where we manualy put ZFW lowered by that trapped fuel. Not really lowered but in fact the correct one.
For calculation take off performance, do they use the expected fuel mass they put intially or the real fuel? But I guess it depends on airline when they do that. I think that they use the real values because I guess they can not do performance calculations without load sheet and we send load sheet after we get final fuel from them.
Last edited by Rarife; 28th Jan 2020 at 20:31. Reason: more info
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Hi Rarife,
Regarding the fuel and the FMS, there are two things you have to consider:
- Weight: in normal operation the FOB is added to the ZFW, giving you the GW. If it is on ground before engine start the GW will with FOB - TAXI + ZFW. If it is in the air (or in the ground after engine start up) GW will be ZFW plus FOB. This is regardless of the FOB being fully usable or not. If the center tanks valves are stuck in the closed position, then the FOB has a half amber box drawn around it to warn the pilots to re asses the fuel available, but the GW in the FMS will still include the whole amount of FOB on board. I can't find anything in the FCOM or FCTM regarding FMS DATA INSERTION when fuel in a center tank is not usable so I think the best thing is to use the actual FOB for weight and mass calculations, leaving to the pilot the task to consider how much they actually have for the flight.
- Center of gravity: in the FMS, after the pilot receives the load sheet, he only has to input the actual ZFW, the ZFW CG, and the FOB. The FMS will determine the actual CG of the airplane by correcting the ZFW CG with the FOB index that has in his database. No intervention from the pilot is needed regarding the FOB index because the fuel index chart is establish assuming a fuel distribution in accordance with refuel distribution (I am actually paraphrasing FCOM-PER-LOADING-LOADING FUEL-LOADING WEIGHT AND BALANCE-FUEL INDEX TABLES). In other words, the refuel is done automatically by the airplane fuel system and is always done in the same fashion. so for a certain amount the index will always be the same.
In the case you are bringing here the FOB is non standard (the automated refuel system will never leave 700 or 1000 kgs of fuel in one of the center tanks), so the fuel index chart doesn't apply anymore. So, to determine the applicable fuel index in this non standard case, the pilot has to use the tables given the aforementioned chapter of the FCOM, checking the actual amount of fuel in each tank, finding the index for each of them, and adding them. This figure is what has to be used in the load and trim sheet.
So, in your case, I think the pilots should use ZFW + FOB = GW, keeping in mind that 1.000 kgs of that FOB is not usable (hence the amber box), and GW CG = ZFW CG + FOB index taken from the tables in the PER chapter of the FCOM.
I stand to be corrected if there is any other way to do it but I haven't found anything else in the FCOM or FCTM.
Regarding the fuel and the FMS, there are two things you have to consider:
- Weight: in normal operation the FOB is added to the ZFW, giving you the GW. If it is on ground before engine start the GW will with FOB - TAXI + ZFW. If it is in the air (or in the ground after engine start up) GW will be ZFW plus FOB. This is regardless of the FOB being fully usable or not. If the center tanks valves are stuck in the closed position, then the FOB has a half amber box drawn around it to warn the pilots to re asses the fuel available, but the GW in the FMS will still include the whole amount of FOB on board. I can't find anything in the FCOM or FCTM regarding FMS DATA INSERTION when fuel in a center tank is not usable so I think the best thing is to use the actual FOB for weight and mass calculations, leaving to the pilot the task to consider how much they actually have for the flight.
- Center of gravity: in the FMS, after the pilot receives the load sheet, he only has to input the actual ZFW, the ZFW CG, and the FOB. The FMS will determine the actual CG of the airplane by correcting the ZFW CG with the FOB index that has in his database. No intervention from the pilot is needed regarding the FOB index because the fuel index chart is establish assuming a fuel distribution in accordance with refuel distribution (I am actually paraphrasing FCOM-PER-LOADING-LOADING FUEL-LOADING WEIGHT AND BALANCE-FUEL INDEX TABLES). In other words, the refuel is done automatically by the airplane fuel system and is always done in the same fashion. so for a certain amount the index will always be the same.
In the case you are bringing here the FOB is non standard (the automated refuel system will never leave 700 or 1000 kgs of fuel in one of the center tanks), so the fuel index chart doesn't apply anymore. So, to determine the applicable fuel index in this non standard case, the pilot has to use the tables given the aforementioned chapter of the FCOM, checking the actual amount of fuel in each tank, finding the index for each of them, and adding them. This figure is what has to be used in the load and trim sheet.
So, in your case, I think the pilots should use ZFW + FOB = GW, keeping in mind that 1.000 kgs of that FOB is not usable (hence the amber box), and GW CG = ZFW CG + FOB index taken from the tables in the PER chapter of the FCOM.
I stand to be corrected if there is any other way to do it but I haven't found anything else in the FCOM or FCTM.
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For calculation take off performance, do they use the expected fuel mass they put initially or the real fuel?
The confusion seems to be due to the artificial increase of zero fuel weight by 700 kgs.
The trapped unusable fuel in the centre tank simply reduces the maximum zero fuel weight by the same amount. i.e. you can't carry as much baggage / passengers as you might want.
The actual zero fuel weight and actual fuel on board should be entered as usual. The useable fuel for range / endurance calculations = Actual fuel on board - any unusable fuel.
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Great, we all obviously think in the same way. However according to our captain they consider unusable fuel as part of ZFW, then they put into FMS block fuel manualy but it is not block fuel as we all understand that but it is just fuel for mission. So it looks like FOB is not block fuel here. Even though they call it block fuel. And it works only for small Airbus fleet because B777 crews clearly do not like that.
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Yea, the artifical increase of ZFW was the issue for me. I know that unusable fuel reduces maximum ZFW and by the way that is how flight planning department uses that. We however should not do that by reducing MZFW but by increasing ZFW. Then the crew uses block fuel which is not block fuel in fact. And it depends on aircraft type.
Yea, I think it is mess.
Yea, I think it is mess.
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Hi Rarife,
It certainly is. Please see MEL - 28: Fuel CTR TK Pump 1(2) LO PR procedure.
"FLIGHT PREPARATION/LIMITATIONSThe fuel in the center tank should be considered as not usable for the flight and counted as part of the ZFW.
Operational Flight Plan (OFP), Fuel Planning:
The minimum block fuel (TOTAL on the OFP) must be increased by the unusable fuel in the center tank.
This gives the new minimum block fuel to operate with Both Center Tank Pumps inoperative.
Weight and Balance:
Enter the total fuel in the LOADSHEET application (LOADING <F4>
. If there is unusable fuel in the center tank, use the FUEL DISTR <Alt F2> tab and select MANUAL DISTR. Enter the fuel as shown on the ECAM FUEL page.
As the LOADSHEET application cannot include some fuel in the Zero Fuel Weight (ZFW), proceed as follows: Check manually that the Actual Zero Fuel Weight (AZFW) is equal to or lower than the Maximum Structural Zero Fuel Weight minus the unusable fuel (AZFW ≤ MZFW – unusable fuel).
If there is unusable fuel in the center tank, the landing weight CG (LWCG) shown in the RESULTS panel (or MORE<F10> must be within the following limits:
Yea, I think it is mess.
"FLIGHT PREPARATION/LIMITATIONSThe fuel in the center tank should be considered as not usable for the flight and counted as part of the ZFW.
Operational Flight Plan (OFP), Fuel Planning:
The minimum block fuel (TOTAL on the OFP) must be increased by the unusable fuel in the center tank.
This gives the new minimum block fuel to operate with Both Center Tank Pumps inoperative.
Weight and Balance:
Enter the total fuel in the LOADSHEET application (LOADING <F4>
. If there is unusable fuel in the center tank, use the FUEL DISTR <Alt F2> tab and select MANUAL DISTR. Enter the fuel as shown on the ECAM FUEL page.As the LOADSHEET application cannot include some fuel in the Zero Fuel Weight (ZFW), proceed as follows: Check manually that the Actual Zero Fuel Weight (AZFW) is equal to or lower than the Maximum Structural Zero Fuel Weight minus the unusable fuel (AZFW ≤ MZFW – unusable fuel).
If there is unusable fuel in the center tank, the landing weight CG (LWCG) shown in the RESULTS panel (or MORE<F10>
must be within the following limits:- Center tank unusable fuel less than 3 300 kg: LWCG within the MLW envelope reduced by 2 % in the forward and aft limit.
- Center tank unusable fuel between 6 600 kg and 3 301 kg: LWCG within the MLW envelope reduced by 4% in the forward and aft limit."
