737NG Fuel Loading
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737NG Fuel Loading
Hi, The limitations section of the 737 NG stipulates that for Fuel Loading, the main tanks 1 and 2 must be full if the centre tank contains more than 453kgs.
Does this limitation still apply once you are airborne? For instance, you are tanking fuel to destination and you may get ice on the top of the wings due to destination temperature and weather en route as you are scheduled to land full wings. (I know all this comes with pre-flight but leave that aside for a moment). Can you turn off the centre pumps, burn fuel out of the wings, say 1000kgs a side, and then turn on the centre pumps again for descent and landing. On the turn you fill up the wings with nice warm fuel negating the need for de-icing, if that is the airport has any!
Thanks for any answers.
Does this limitation still apply once you are airborne? For instance, you are tanking fuel to destination and you may get ice on the top of the wings due to destination temperature and weather en route as you are scheduled to land full wings. (I know all this comes with pre-flight but leave that aside for a moment). Can you turn off the centre pumps, burn fuel out of the wings, say 1000kgs a side, and then turn on the centre pumps again for descent and landing. On the turn you fill up the wings with nice warm fuel negating the need for de-icing, if that is the airport has any!
Thanks for any answers.
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It's an interesting question, I had always interpreted it as a 'blanket limitation' not just applicable pre dispatch. Nothing in the FCOM wording points towards it being a pre dispatch limitation only, so I would suggest my interpretation is correct. I'm sure someone could think of a scenario where it would be justified, but I wouldn't consider the instance you gave as being one of those. For me it would have to be safety related (maybe a scenario involving a leak of some kind?). Also you would need to burn the best part of 2 tonnes each side to ensure that CSFF would not occur, although I'm sure that may differ depending on the variant (in our 738 operation we plan to land a max of 4.0T in an attempt to eliminate the threat of CSFF. Our wings typically hold 7.8T).
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Don't you have a scavenge pump in the NG (like the CLs do) which runs after the shutoff of the main center pumps and gets as much fuel out the center tank as possible? Believe it transfers it to #1 if I remember correctly.
If that's the case then you should have very little, if any, fuel remaining in the center tank in flight.
1000 kgs of "nice warm fuel" will not deice your wings, if deicing is a concern then just do it and don't resort to cheap tricks in transport aircraft.
A scenario involving a leak of some kind? Good, you get to do whatever you need to do to use as much fuel as possible if it's that much of a concern. Safety of flight (having enough fuel to make it to land) takes precedence manufacturers limitations.
If that's the case then you should have very little, if any, fuel remaining in the center tank in flight.
1000 kgs of "nice warm fuel" will not deice your wings, if deicing is a concern then just do it and don't resort to cheap tricks in transport aircraft.
A scenario involving a leak of some kind? Good, you get to do whatever you need to do to use as much fuel as possible if it's that much of a concern. Safety of flight (having enough fuel to make it to land) takes precedence manufacturers limitations.
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I seem to remember that you "could" do it, as long as you consider the center tank fuel (now considered unusable) as part of your ZFW.
So: Actual ZFW + Center Tank Fuel < Maximum ZFW
Same thing applies when you take up fuel for the next sector and don't fill up the main tanks. Still have to respect the max of 453 kg in the center tank though.
Not an "official " procedure, I guess, but have a look in the MEL/DDG 28-2 concerning the loss of both center tank pumps and " May be inoperative provided: ".....
So: Actual ZFW + Center Tank Fuel < Maximum ZFW
Same thing applies when you take up fuel for the next sector and don't fill up the main tanks. Still have to respect the max of 453 kg in the center tank though.
Not an "official " procedure, I guess, but have a look in the MEL/DDG 28-2 concerning the loss of both center tank pumps and " May be inoperative provided: ".....
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We do have a scavenge but it works sightly differently to the classic. It starts running automatically only once main tank 1 is half full and just continues running until the end of the flight even if the tank is empty.
Back to the topic though, would anyone do this just to avoid CSFF? I heard of people putting on wing anti ice in the descent before but not this.
Back to the topic though, would anyone do this just to avoid CSFF? I heard of people putting on wing anti ice in the descent before but not this.
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No, we don't do this and since boeing approved ice on top of the wings within certain areas we never had a problem there.
However in older planes which do not have the center tank logic mod we have to switch off the center tank pumps for take off with less than 2000 kgs of fuel in the center tank. By the time we reconfigure the pumps (earliest FL100) there is already around a ton of fuel gone form the main tanks.
However in older planes which do not have the center tank logic mod we have to switch off the center tank pumps for take off with less than 2000 kgs of fuel in the center tank. By the time we reconfigure the pumps (earliest FL100) there is already around a ton of fuel gone form the main tanks.
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Unfortunately we are still unable to apply the rule re the marked boxes on top of the wing. As I understand it our stumbling block are the IAA who refuse to authorise this procedure.
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Yes, that will lead to problems, especially in warm and humid climates. If you need fuel in the center tank for the next sector you could try to transfer cold fuel from the main tanks into the center tank before fueling the main tanks with warm fuel. However that is pretty time consuming.
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This happens all the tome on our property. We handle this by ground transferring the fuel out of the wing( to about half, or slightly less) to the center tanks, and then fill the wings with warm fuel. Now if you do not need fuel this obviously does not work. We purposely plan accordingly that we need fuel, as mentioned there are places that do not provide de ice
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Amdram - I believe the 453+kg 'limit' is for c of g protection while loading. Before the Boeing CSFF mod Astraeus used to (very successfully) do as you posted. It was 'almost' an SOP in fact (and I believe it was actually published as a Flight Crew Notice when I joined in 2004) particularly with 20 min turnrounds at 'non-deicing' coastal airfields.The weight of fuel in the centre tank HAS to be part of the ZFW for structural reasons if you do this but is no different to having the same weight in the cargo holds. Regarding c of g considerations, it is important to be aware of the effect on the balance at the end of the flight (worth a quick plot on the trim chart - you will be tail heavy) and to load the fuel CORRECTLY before boarding/loading.
Personally I never burnt the wings below CMR 'just in case'. I was told Boeing had raised a 'no objection' to the procedure which meant it was not actually formally approved, but.....................
With the advent of the CSFF markings/procedure the need ceased.
- want to have a think about your post #9?
. I cannot see using wing de-ice in flight doing ANYTHING since it only warms the LE!
Personally I never burnt the wings below CMR 'just in case'. I was told Boeing had raised a 'no objection' to the procedure which meant it was not actually formally approved, but.....................
With the advent of the CSFF markings/procedure the need ceased.
Originally Posted by ast83
Or even in the winter. I don't think they have any deicing facilities available at all in Malaga
. I cannot see using wing de-ice in flight doing ANYTHING since it only warms the LE!
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Thanks to everyone for taking the time to reply. 
To be a little more precise in my original question. We can take a full load of fuel to an airfield, around 21000kgs but only need to burn about 10000 to get there. This is due to the uber high cost of fuel there. This would leave us with full wings and plenty in the centre. If we left the wings full there would be guaranteed ice outside of the Boeing markings for cold soaked full and yes, the airfield does not provide de-ice and it could be a loooooooong wait in not particulary warm temperatures for it all to clear.
Could you turn off the centre pumps to allow the wing fuel to drop to a level even with fuel in the centre tank in this situation so as to avoid the CSFF.
The Boeing limitation refers to fuel Loading and so I'm not sure if once you're airborne still technically counts as loading as it has been previously loaded.
Sorry if I'm going over ground again but thanks.
PS
As mentioned above, this will have absolutely no effect on the contents of the upper surface of the wing. It will however make the leading edge very hot!!
To be a little more precise in my original question. We can take a full load of fuel to an airfield, around 21000kgs but only need to burn about 10000 to get there. This is due to the uber high cost of fuel there. This would leave us with full wings and plenty in the centre. If we left the wings full there would be guaranteed ice outside of the Boeing markings for cold soaked full and yes, the airfield does not provide de-ice and it could be a loooooooong wait in not particulary warm temperatures for it all to clear.
Could you turn off the centre pumps to allow the wing fuel to drop to a level even with fuel in the centre tank in this situation so as to avoid the CSFF.
The Boeing limitation refers to fuel Loading and so I'm not sure if once you're airborne still technically counts as loading as it has been previously loaded.
Sorry if I'm going over ground again but thanks.
PS
I heard of people putting on wing anti ice in the descent before but not this
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Sorry if I'm going over ground again but thanks.
I think that if you are equipped for and 'allowed' the Boeing alleviation for CSFF you would be on dodgy ground using a 'non-standard' procedure. Your correct avenue then is not to tanker fuel. Of course, using ground transfer actually contravenes the Boeing centre tank 453kg limitation
I think the expression 'you are stuffed'.
Last edited by BOAC; 21st Dec 2011 at 17:48.
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BOAC - have you not heard that one before? It's quite brilliant really. Switching the wing anti ice from approx 20min before landing, until landing creates a continuous flow of warm air over the upper surface of the wing resulting in no CSFF!
You are however quite right. It is an absurd idea and displays a complete lack of understanding of CSFF. I've heard it so many times though that I'm certain that there are aircraft descending into their destination as we speak with wing anti ice on for this very reason!!
On the original point, if you had an approved procedure then fair enough. It doesn't appear to be a Boeing procedure but that is irrelevant. For it to be approved by the authority (which it must be to be in your manuals) then it would have required a 'No Technical Objection' from Boeing.
You are however quite right. It is an absurd idea and displays a complete lack of understanding of CSFF. I've heard it so many times though that I'm certain that there are aircraft descending into their destination as we speak with wing anti ice on for this very reason!!
On the original point, if you had an approved procedure then fair enough. It doesn't appear to be a Boeing procedure but that is irrelevant. For it to be approved by the authority (which it must be to be in your manuals) then it would have required a 'No Technical Objection' from Boeing.
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I think the fuel "loading" restriction is primarily structural. As CaptB737 stated, in this scenario ctr fuel should be included in the ZFW. But if it is an approved procedure it should be included in the AFM, most probably in the limitations section, but it is not!
I can remember the good old MD-80 (with a bad history of wing frost) cured this problem with the "Alternate Fuel Burn System" which modified the fuel pump logic to allow wing fuel usage with ctr tank still containing fuel. But the limitations, ZFW calculation, etc. was documented in detail in the AFM.
Cheers,
b
I can remember the good old MD-80 (with a bad history of wing frost) cured this problem with the "Alternate Fuel Burn System" which modified the fuel pump logic to allow wing fuel usage with ctr tank still containing fuel. But the limitations, ZFW calculation, etc. was documented in detail in the AFM.
Cheers,
b
