Center Tank Pumps Failure and ZFW Limit
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Center Tank Pumps Failure and ZFW Limit
Hello. Need some input on the following scenario.
- B 737-300
- ZFW limit 48.3 tons
- Center Tank Fuel 7 tons
- Main Tanks 9 tons total (4.5 either side)
- Takeoff at 60 tons
- Soon after takeoff the center tank pumps stop working.
According to the checklist you may not be able to continue your flight to destination because of not enough fuel. So going to destination is out.
Now if your maintenance base is at a distance which is within your reach but leaves you with 2.5 tons of fuel in your main tanks. Would it be better to land at the departure aerodrome or continue to the maintenance base.
If one continues to the maintenance base how will he calculate not to bust the ZFW limit.
If (hypothetically) flight is continued and main tanks are emptied the weight would be 60 - 9 = 51 tons i.e. 2.7 tons above ZFW limit. Busted!
That means if no fuel in main tanks leads to a situation that exceeds the ZFW limit by 2.7 tons then the ratio that causes a ZFW structural concern
would be achieved at a point where you still have fuel in your main tanks.
Is there a way to calculate how much fuel remaining in the main tanks would ring the bells? or its better to land back.
The checklist only mentions that going to destination might not be possible and does not say anything else. Thank you.
- B 737-300
- ZFW limit 48.3 tons
- Center Tank Fuel 7 tons
- Main Tanks 9 tons total (4.5 either side)
- Takeoff at 60 tons
- Soon after takeoff the center tank pumps stop working.
According to the checklist you may not be able to continue your flight to destination because of not enough fuel. So going to destination is out.
Now if your maintenance base is at a distance which is within your reach but leaves you with 2.5 tons of fuel in your main tanks. Would it be better to land at the departure aerodrome or continue to the maintenance base.
If one continues to the maintenance base how will he calculate not to bust the ZFW limit.
If (hypothetically) flight is continued and main tanks are emptied the weight would be 60 - 9 = 51 tons i.e. 2.7 tons above ZFW limit. Busted!
That means if no fuel in main tanks leads to a situation that exceeds the ZFW limit by 2.7 tons then the ratio that causes a ZFW structural concern
would be achieved at a point where you still have fuel in your main tanks.
Is there a way to calculate how much fuel remaining in the main tanks would ring the bells? or its better to land back.
The checklist only mentions that going to destination might not be possible and does not say anything else. Thank you.
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Is there a limitation on this aircraft for operating with center tank fuel? If there is a limitation, then it would behoove you to land prior to exceeding that limitaiton if possible. If there is not limitation you're in no jeopardy of busting ZFW limits.
ZFW means Zero fuel weight and you seem to be applying a fuel weight to the ZFW to get a revised ZFW.
EOW would include unusable fuel for predeparture calculations.
BD
ZFW means Zero fuel weight and you seem to be applying a fuel weight to the ZFW to get a revised ZFW.
EOW would include unusable fuel for predeparture calculations.
BD
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Thanks BD. I know ZFW means Zero Fuel Weight but this scenario which I have mentioned is an abnormal situation where you have 7 tons fuel stuck in the main tanks due to pumps failure. So this 7 tons fuel which you routinely burn first is dead weight now. If the fuel weight starts to reduce from the main tanks (as flight continues) we will be heading towards the ZFW limit. Although we have fuel in the center tank but we cant use it and it will behave just like payload.
In non standard refueling i.e. Main tanks not full while there is fuel in the center tanks, the rule for planning is:
Actual ZFW + Fuel in Center Tank should NOT be greater than ZFW Limit
That means even if your center tank fuel gets stuck in flight you will still be safe from busting your ZFW limit, as it is already catered during flight planning.
My scenario is a case of standard refueling where Main tanks are topped up first and then the center tank.
In non standard refueling i.e. Main tanks not full while there is fuel in the center tanks, the rule for planning is:
Actual ZFW + Fuel in Center Tank should NOT be greater than ZFW Limit
That means even if your center tank fuel gets stuck in flight you will still be safe from busting your ZFW limit, as it is already catered during flight planning.
My scenario is a case of standard refueling where Main tanks are topped up first and then the center tank.
Last edited by Haroon; 12th Dec 2009 at 04:19.
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Hi Haroon,
Your thread is very similar to b737ng-centre-tank-ground-transfer.html
If you departed with one center tank pump inop - the MEL would point you in the right direction. From memory, with one center tank pump inop. you'd have to restrict the payload because the center tank fuel will have to be considered as part of the zero fuel weight in the event of the other pump failing.
There is a remote chance that both center tank pumps will fail so your scenario is not considered. Unless there is a QRH procedure for your scenario, I guess you would be permitted to continue the flight up to a point of landing with enough wing tank fuel available to be legal. The fact that you have exceeded the maximum zero fuel weight would result in a landing inspection - so it may be cheaper to divert early.
Your thread is very similar to b737ng-centre-tank-ground-transfer.html
If you departed with one center tank pump inop - the MEL would point you in the right direction. From memory, with one center tank pump inop. you'd have to restrict the payload because the center tank fuel will have to be considered as part of the zero fuel weight in the event of the other pump failing.
There is a remote chance that both center tank pumps will fail so your scenario is not considered. Unless there is a QRH procedure for your scenario, I guess you would be permitted to continue the flight up to a point of landing with enough wing tank fuel available to be legal. The fact that you have exceeded the maximum zero fuel weight would result in a landing inspection - so it may be cheaper to divert early.
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Greetings,
Fuel has to be considered as payload, and to be added to the ZFW, the correct document is the AFM, where fuel restriction regarding using the Wing Fuel with fuel in the center tank, if there is a restriction then you are limited, due to wing to body attach. Sometimes scavenge pumps solve the problem and can transfer the remaining fuel to the wings, but only the AFM will give you the right course of action.
Fuel has to be considered as payload, and to be added to the ZFW, the correct document is the AFM, where fuel restriction regarding using the Wing Fuel with fuel in the center tank, if there is a restriction then you are limited, due to wing to body attach. Sometimes scavenge pumps solve the problem and can transfer the remaining fuel to the wings, but only the AFM will give you the right course of action.
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Thank you Rudder
I agree its remote. But I had to make up this scenario to get to my real question.
there isnt, as far as busting the ZFW limit is concerned
Thats what I really want to know. Is there a way to calculate that?
Whats the chance of damaging the structure after busting the ZFW limit?
Thank you all for your input.
There is a remote chance that both center tank pumps will fail so your scenario is not considered.
Unless there is a QRH procedure for your scenario,
I guess you would be permitted to continue the flight up to a point of landing with enough wing tank fuel available to be legal.
The fact that you have exceeded the maximum zero fuel weight would result in a landing inspection - so it may be cheaper to divert early.
Thank you all for your input.
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Hi Haroon,
Sorry, I meant landing with minimum reserve fuel in the wings.
I don't know - but provided you didn't come too close to the maximum "g" published during the flight, then you should be OK. I'd guess engineering will have a method to calculate the loads at the wing / fuselage box for different wing fuel loads - but I'm only guessing.
I guess you would be permitted to continue the flight up to a point of landing with enough wing tank fuel available to be legal.
What's the chance of damaging the structure after busting the ZFW limit
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Two things are important here
MZFW is based on bending moments, the more fuel in the wing the better so don't loose too much time.
You must stay within the CG envelope for landing. Fuel in center tank may have a serious effect on CG.
In case of doubt just put the plane on the ground then you will have all the time.
MEL ops procedures do not apply when airborne.
It's useful to carry a blank loadsheet in your flightcase.
You must stay within the CG envelope for landing. Fuel in center tank may have a serious effect on CG.
In case of doubt just put the plane on the ground then you will have all the time.
MEL ops procedures do not apply when airborne.
It's useful to carry a blank loadsheet in your flightcase.
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Fuel in center tank may have a serious effect on CG.
this can be a concern for swept wing aircraft (or any aircraft with tanks distributed longitudinally) if you are forced into a non-standard fuel usage pattern.
MEL ops procedures do not apply when airborne.
.. but the wise pilot will use the MEL as a guide to those matters which might be important to think about.
It's useful to carry a blank loadsheet in your flightcase.
but, for the fuel scenario, not much use unless you understand the design of the sheet and how to modify the use to account for the non standard fuel scheduling.
this can be a concern for swept wing aircraft (or any aircraft with tanks distributed longitudinally) if you are forced into a non-standard fuel usage pattern.
MEL ops procedures do not apply when airborne.
.. but the wise pilot will use the MEL as a guide to those matters which might be important to think about.
It's useful to carry a blank loadsheet in your flightcase.
but, for the fuel scenario, not much use unless you understand the design of the sheet and how to modify the use to account for the non standard fuel scheduling.
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-Soon after takeoff the center tank pumps stop working.
Return to base, not worth the hassell, you may have a serious electrical problem which may furthur develop.
My 2cents worth.
Return to base, not worth the hassell, you may have a serious electrical problem which may furthur develop.
My 2cents worth.
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The manual states directly that as soon as the wing tanks are less than full, you may not be carrying more than 1000 lbs (454 kgs) of fuel in the center tank.
So, as soon as you START to use wing tank fuel with more than 1000 lbs (454 kgs) of center tank fuel, you're outside the ZFW limitation.
IMHO get the thing on the ground as soon as.
That's the way I see it!
Cheers...FD...
So, as soon as you START to use wing tank fuel with more than 1000 lbs (454 kgs) of center tank fuel, you're outside the ZFW limitation.
IMHO get the thing on the ground as soon as.
That's the way I see it!
Cheers...FD...
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Thank you all for your inputs
Thanks for highlighting.
That’s correct, MEL is applicable on ground. But there is nothing that stops from referring to the MEL in air. You might want to change your destination in order to avoid a NO-GO situation on ground when MEL is finally applied (at a place where there is no maintenance).
I’ll count that in dollars not cents as it is rare that both pumps would fail simultaneously. There must be something else behind it.
I don’t think that you’ll bust your ZFW limit as soon as you start using your wing tank fuel. But you’ll definitely bust it after sometime and that’s what I am trying to find out i.e. its calculation.
But perhaps it’s not possible to calculate that and due to this fact one should land back on the basis of the limitation which you’ve mentioned. However I am not sure if this limitation refers to what we are discussing as the QRH says nothing about busting any structural limits. All it says is that you might not be able to continue to your destination due to unusable fuel.
You must stay within the CG envelope for landing. Fuel in center tank may have a serious effect on CG.
Thanks for highlighting.
MEL ops procedures do not apply when airborne.
That’s correct, MEL is applicable on ground. But there is nothing that stops from referring to the MEL in air. You might want to change your destination in order to avoid a NO-GO situation on ground when MEL is finally applied (at a place where there is no maintenance).
Return to base, not worth the hassell, you may have a serious electrical problem which may furthur develop
The manual states directly that as soon as the wing tanks are less than full, you may not be carrying more than 1000 lbs (454 kgs) of fuel in the center tank. So, as soon as you START to use wing tank fuel with more than 1000 lbs (454 kgs) of center tank fuel, you're outside the ZFW limitation.
I don’t think that you’ll bust your ZFW limit as soon as you start using your wing tank fuel. But you’ll definitely bust it after sometime and that’s what I am trying to find out i.e. its calculation.
But perhaps it’s not possible to calculate that and due to this fact one should land back on the basis of the limitation which you’ve mentioned. However I am not sure if this limitation refers to what we are discussing as the QRH says nothing about busting any structural limits. All it says is that you might not be able to continue to your destination due to unusable fuel.
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MEL ops procedures do not apply when airborne.
.. but the wise pilot will use the MEL as a guide to those matters which might be important to think about.
.. but the wise pilot will use the MEL as a guide to those matters which might be important to think about.
MEL is basically a recertification (CRS being signed off) and therefore does take into account the effect of an engine failure. With this in mind certain requirements that seem unlogical at first suddenly become more obvious.
It's useful to carry a blank loadsheet in your flightcase.
but, for the fuel scenario, not much use unless you understand the design of the sheet and how to modify the use to account for the non standard fuel scheduling
but, for the fuel scenario, not much use unless you understand the design of the sheet and how to modify the use to account for the non standard fuel scheduling
Last edited by Pitch Up Authority; 16th Dec 2009 at 14:31.
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Part of the type rating course in any company that respects itself.
That may well be the case for some operators.
However, my observation has been that the emphasis in endorsement training usually is USING the sheet correctly as it is designed but not necessarily understanding what goes into it so that it can be used in a non-standard manner to get a result needed for a non-standard situation ...
I won't get into discussing some of the weird and wonderful suggestions which I have observed very experienced folk offer in respect to how this or that bit of the trimsheet is supposed to work ..
That may well be the case for some operators.
However, my observation has been that the emphasis in endorsement training usually is USING the sheet correctly as it is designed but not necessarily understanding what goes into it so that it can be used in a non-standard manner to get a result needed for a non-standard situation ...
I won't get into discussing some of the weird and wonderful suggestions which I have observed very experienced folk offer in respect to how this or that bit of the trimsheet is supposed to work ..
