737 NG-fuel pumps
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Joined: Aug 2001
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From: Europe-the sunshine side
737 NG-fuel pumps
From the fuel diagram,all fuel pump are placed in the centre tank.Is this true?
This is different from the classic,and also I guess it may be wrong ,as the centre tank is emptied first,so,maybe no fuel to cool the wing pumps.
If this is true,how is this requirement solved?
Brgds
Alex
This is different from the classic,and also I guess it may be wrong ,as the centre tank is emptied first,so,maybe no fuel to cool the wing pumps.
If this is true,how is this requirement solved?
Brgds
Alex
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Joined: Aug 2001
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From: Europe-the sunshine side
the restriction was solely for the center pumps,it says also that you should not select center tank pumps if the tank is empty.Nothing about the main tank pumps.
What was the reason for placing them in the centre tank also,why not doing it like the classic?
What was the reason for placing them in the centre tank also,why not doing it like the classic?
Joined: Jan 1999
Aviation Qualifications: ATPL
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From: Brisbane
All fuel pumps in the NG are located in the centre tank.
The wing tank pumps however live in a sealed box filled with fuel, independant of the centre tank quantity - i.e. regardless of the quantity of fuel in the centre tank, the boxes in which the wing tank pumps live is full of fuel.
Because the boxes are always full of fuel there is no risk of a volatile fuel/air mix and therefore I assume no limitations on pump usage as is the case with the centre tank pumps, which are not always covered by fuel.
As for why they are where they are as compared to the classic - can't help - but the other stuff above came from Boeing.
The wing tank pumps however live in a sealed box filled with fuel, independant of the centre tank quantity - i.e. regardless of the quantity of fuel in the centre tank, the boxes in which the wing tank pumps live is full of fuel.
Because the boxes are always full of fuel there is no risk of a volatile fuel/air mix and therefore I assume no limitations on pump usage as is the case with the centre tank pumps, which are not always covered by fuel.
As for why they are where they are as compared to the classic - can't help - but the other stuff above came from Boeing.
Joined: Nov 2003
Posts: 496
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From: UK
Hi Alex,
Just to confirm on the NG the centre tank fuel pumps are physically in the centre tank. They are mounted on the rear spar which is also the forward wall of the wheel well and you can see them from in the wheel well like this:
The classics centre tank pumps are in dry bays in the main tanks.
Both NG and classic main tank pumps are very much inboard to allow all the fuel to be used due to the dihedral.
Wouldn't it be nice if our Vol 1 told us this rather than us having to guess or dredge the AMM for such fundamental information.
S&L
PS Location diagram here
Just to confirm on the NG the centre tank fuel pumps are physically in the centre tank. They are mounted on the rear spar which is also the forward wall of the wheel well and you can see them from in the wheel well like this:
The classics centre tank pumps are in dry bays in the main tanks.
Both NG and classic main tank pumps are very much inboard to allow all the fuel to be used due to the dihedral.
Wouldn't it be nice if our Vol 1 told us this rather than us having to guess or dredge the AMM for such fundamental information.
S&L
PS Location diagram here
Last edited by CaptainSandL; 13th August 2005 at 11:19.
Joined: Dec 2004
Posts: 53
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From: UK
Another fuel pump question
Why, on the older, unmodified 800's, do you switch the right centre fuel pump off when the centre tank quantity reaches 950kg in the cruise, whilst in the descent, you switch off the left pump? I understand the reasoning behind switching one pump off (gives a master caution immediately when one pump runs dry), but why do they specify which pumps to turn off if the pumps are alligned?
Don't know if this question has come up before - I did search for it. THANX!
I
Don't know if this question has come up before - I did search for it. THANX!
I
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Joined: Aug 2001
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From: Europe-the sunshine side
right pump is placed forward,while the left one is aft in the tank.So ,while descending ,the risk to uncover a pump is higher for the aft one,here the indication to put the switch off the left one.
The same for climbing or cruise.
The same for climbing or cruise.
Joined: Dec 2004
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From: UK
Thanx. That's what I thought. Do you by any chance know how far forward it is from the other, because all the schematics show the 2 pumps in line. The FCTM indicates the left pump inlet is forward, and the right is aft.
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Joined: Aug 2001
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From: Europe-the sunshine side
The left and right centre tank boost pump are installed on the rear spar of the center section of the center tank.
The inlets for the center tank boost pumps are installedat different fore-and-aft positionswith respect to the rear spar.
The inlet for the left pump is installed on the left side of the center tank immediately aft of the spanwise beam no.1 ( the spanwise beam immediately forward of the rear spar)
The inlet for the right pump is installed on the right side of the center tank immediately forward of the rear spar.
thus,the left inlet is substantially forward of the right inlet.
All this is from the AMM. Sorry to mislead you in my previous answer.
I have to go fly now,more details if you wish next time.
Brgds Alex
The inlets for the center tank boost pumps are installedat different fore-and-aft positionswith respect to the rear spar.
The inlet for the left pump is installed on the left side of the center tank immediately aft of the spanwise beam no.1 ( the spanwise beam immediately forward of the rear spar)
The inlet for the right pump is installed on the right side of the center tank immediately forward of the rear spar.
thus,the left inlet is substantially forward of the right inlet.
All this is from the AMM. Sorry to mislead you in my previous answer.
I have to go fly now,more details if you wish next time.
Brgds Alex
Joined: Dec 2004
Posts: 53
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From: UK
Alrighty - Thank you. Makes sense. Like I said, the fuel schematic that I've got from the Flight Crew Ops Manual shows the inlets the other way round, but in any case 
, the data that you have must be correct, hence the pump selections.
, the data that you have must be correct, hence the pump selections.
