B744 CWT Transfer pumps fail
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B744 CWT Transfer pumps fail
If both CWT transfer pumps fail is it possible to utilise all of the fuel in the CWT? Will the scavange pumps transfer the fuel? If so what is the transfer rate?
The QRH procedure says if both CWT pumps fail END OF PROCEDURE.
What does "end of procedure" mean, carry on regardless OR you should know the CWT fuel is now unuseable??
The QRH procedure says if both CWT pumps fail END OF PROCEDURE.
What does "end of procedure" mean, carry on regardless OR you should know the CWT fuel is now unuseable??
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CWT Scavenge System
A. The center wing tank scavenge system allows fuel to be removed (scavenged) from the center wing tank into the No. 2 main tank without the use of the override/jettison pumps in the center wing tank
(CWT pumps). 28-15-00
IF IT'S FITTED
(CWT pumps). 28-15-00
IF IT'S FITTED
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30AB-JK
I believe that the Scavange Pump operates automatically when the CWT fuel level reaches a low level (can't remember the exact figure, but around 900-1500kg). It cannot be switched on and therefore cannot be used to remove the fuel.
From memory (I no longer have the manuals), if both the CWT pumps fail then the fuel is unuseable. Perhaps a currect 744 pilot could confirm?
Dave
I believe that the Scavange Pump operates automatically when the CWT fuel level reaches a low level (can't remember the exact figure, but around 900-1500kg). It cannot be switched on and therefore cannot be used to remove the fuel.
From memory (I no longer have the manuals), if both the CWT pumps fail then the fuel is unuseable. Perhaps a currect 744 pilot could confirm?
Dave
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First understand that not all -400's are fitted with a dedicated transfer pump.
1) those that have the pump fitted, scav the remaining fuel and deposit it into the #2 main fuel tank. The transfer rate is very slow and is effectively negligible. i.e the rate of transfer will not keep up with the requirements of engines running. (well maybe just one eng at idle -trans rate is approx 750kgs/hour) In flight it will come on for these reasons (from the manual)
Valves are opened.
2) later aircraft have a 'hydromechanical' transfer system that will transfer fuel from the CWT to both #2 and #3 tanks. It will operate any time there is pressure in the crossfeed manifold but fuel will only transfer to the tanks when a float valve is uncovered to ensure there is capacity in 2 and 3 to receive the fuel. The transfer rate of this system is even slower than the dedicated pump -i.e very slow and not to be relied upon to keep 2 and 3 topped up to allow feed of the engines.
So Yes, if BOTH your CWT trans pumps quit, technically you can get the fuel out, but it will be at a rate that will be of no use to you during flight.
Clear as mud !
.
1) those that have the pump fitted, scav the remaining fuel and deposit it into the #2 main fuel tank. The transfer rate is very slow and is effectively negligible. i.e the rate of transfer will not keep up with the requirements of engines running. (well maybe just one eng at idle -trans rate is approx 750kgs/hour) In flight it will come on for these reasons (from the manual)
Two conditions will cause the pump to run for two hours or until the
pump pressure switch senses a low pressure for five minutes:
• In the air with either CWT Override/Jettison Pump Control
Switch turned on and its respective pump is not developing
pressure,
• A 30 second pump On Command when the Reserve Transfer
pump pressure switch senses a low pressure for five minutes:
• In the air with either CWT Override/Jettison Pump Control
Switch turned on and its respective pump is not developing
pressure,
• A 30 second pump On Command when the Reserve Transfer
Valves are opened.
2) later aircraft have a 'hydromechanical' transfer system that will transfer fuel from the CWT to both #2 and #3 tanks. It will operate any time there is pressure in the crossfeed manifold but fuel will only transfer to the tanks when a float valve is uncovered to ensure there is capacity in 2 and 3 to receive the fuel. The transfer rate of this system is even slower than the dedicated pump -i.e very slow and not to be relied upon to keep 2 and 3 topped up to allow feed of the engines.
So Yes, if BOTH your CWT trans pumps quit, technically you can get the fuel out, but it will be at a rate that will be of no use to you during flight.
Clear as mud !
.
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You might find some clues in your MEL.
For dispatching with one CWT pump inop ours states:
1. With center tank fueled.
A. Center tank fuel must be included as part of Zero Fuel Weight
B. If remaining center tank pump fails at any time, remaining fuel quantity in main wing tanks must be adequate to reach a suitable airport.
With two inop:
May be inoperative deactivated provided:
a) Center tank fuel is included as part of
Zero Fuel Weight, and
b) Center tank fuel is considered unusable
In short, with two inop cwt fuel is unusable.
For dispatching with one CWT pump inop ours states:
1. With center tank fueled.
A. Center tank fuel must be included as part of Zero Fuel Weight
B. If remaining center tank pump fails at any time, remaining fuel quantity in main wing tanks must be adequate to reach a suitable airport.
With two inop:
May be inoperative deactivated provided:
a) Center tank fuel is included as part of
Zero Fuel Weight, and
b) Center tank fuel is considered unusable
In short, with two inop cwt fuel is unusable.
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Thanks very much for the info just left wondering why the Boeing QRH doesnt have a note that centre wing fuel should know be considered unuseable and not just "end of procedure".
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In theory, it's also possible to activate the electric scavenge pump (where fitted) if you select the Scavenge Pump Defuel Switch on on the overhead panel. It's normally reserved for ground ops, but there are no air/ground relays to stop it operating in flight.
(Reference Boeing Wiring Schematic 28-15-01)
Regards
NSEU
(Reference Boeing Wiring Schematic 28-15-01)
Regards
NSEU
