(a)  
Where the fuel is kept.

 (b)  
How the fuel is moved.

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A
747-400 MAINTENANCE MANUAL
 S 663-025
 (3)  Fuel that is open to moisture or the usual atmospheric conditions contains more water than that kept in tightly sealed containers. This water in the fuel, when there is high humidity and temperature conditions that change, can be more than three gallons in each thousand gallons of fuel. As the temperatures decreases, there is a separation of the water and the fuel. The water will collect at the lowest point in the tank and freeze if the temperature is sufficiently low. If the water has collected and frozen in the sumps (shown by no flow from the drain valves), do the step that follows.
 (a)  Apply heat (hot air that is resistant to explosion) to the bottom of the wing in the area of the tank sumps.
 L.  Toilets and Potable Water
 S 613-023
 (1)  The water will not freeze in an airplane that operates because there is sufficient heat in the area. When the airplane does not operate and is let stay in an area that is not heated, more servicing is necessary. Do the steps that follow if the cabin temperature will decrease below the freezing point.
 (a)  
Potable Water

 1)  You must drain all of the water from the potable water system (AMM 12-14-01/301).

 (b)  
Toilets

 1)  To make sure it will not freeze, you must fully drain the toilet flushing system as applicable (AMM 12-17-01/301).
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A
747-400 MAINTENANCE MANUAL
 EXTREME COLD WEATHER MAINTENANCE - SERVICING
____________________________________________
 1.  General
_______
 A.  This procedure has these tasks:
 (1)  
Short term parking at temperatures below -22°F (-30°C).

 (2)  
Overnight or extended parking (airplane unattended) at temperatures below 5°F (-15°C).

 (3)  
Return the airplane to service after overnight or extended parking at temperatures below 5°F (-15°C).

 (4)  
Interior ice removal

 B.  After every 290 flight hours when you operate continuously in cold weather, you must remove all interior ice.
 (1)  In the usual operation of the airplane, air comes through the airplane structure. During flight, the water vapor in the air can condense and freeze in the airplane. When you continuously operate the airplane in cold weather, ground temperatures below the freezing point will not let the ice melt. You must do the Interior Ice Removal tasks to find and remove the ice. Too much ice will lower the performance of the airplane below permitted values.
 C.  In cold weather it is necessary to drain the fuel tank sumps prior to refueling to remove water from the fuel tanks if the airplane has been idle for more than 45 minutes prior to refueling. Drain the fuel tank sumps again after refueling if the airplane has been idle for 2 hours or more after refueling, prior to departure (AMM 12-11-03/301). In cold weather water can freeze, and not let the drain valves open.
 TASK 12-33-02-603-001
 2.  Short Term Parking at Temperatures Below -22°F (-30°C)
______________________________________________________
 A.  General
 (1)  
Short term parking at temperatures below -22°F (-30°C):

 (a)  When the cabin and flight deck temperature is maintained above 32°F (0°C) and the engine oil temperature is maintained above -27.4°F (-33°C) while the airplane is on the ground.

 (2)  
After every 290 flight hours when you operate continuously in cold weather, do the Interior Ice Removal procedure.

 NOTE: Removal of the ice buildup will not impact the airplane's
____
 center of gravity.
　
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