NOTE: You must use the thermal anti-icing system for the
____ engine/nacelle when these conditions occur.
 (a)  
There is moisture you can see such as clouds, fog, rain, snow, sleat or ice crystals.

 (b)  
You will do ground operations with the static air temperature below 50°F.

 S 843-059
 (4)  Before you start the engines, make sure there are no fluids around the exhaust areas that can start ignition.
 K. Fuel Icing
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A 737-300/400/500MAINTENANCE MANUAL
 S 683-060
 CAUTION: IF YOU CAN DRAIN THE FUEL FROM THE DRAIN VALVE AFTER YOU
_______ APPLIED HOT AIR TO THE EXTERIOR FOR 3 TO 5 MINUTES, DO NOT THINK THAT ALL THE ICE IS MELTED. THE ICE ADJACENT TO THE UNIT YOU ARE NOT SURE ABOUT CAN MELT AND LET SOME WATER AND FUEL TO FLOW FROM THE DRAIN. BUT, A PIECE OF ICE CAN STAY BEHIND. IF THE FUEL DOES NOT FLOW FROM THE DRAIN VALVE, CONTINUE TO APPLY HOT AIR FOR A SHORT TIME, AND FREQUENTLY DO A CHECK OF THE FLOW FROM THE DRAIN VALVE. CATCH THE FUEL IN A CONTAINER AND MAKE SURE ALL OF THE WATER IS REMOVED.
 THE HEAT APPLIED TO THE SUMP DRAIN VALVES FOR THE OUTBOARD MAIN AND RESERVE TANKS WILL NOT REMOVE THE ICE WHICH HAS COLLECTED IN THE TANK SUMP OR IN THE DRAIN LINE BETWEEN THE TANK SUMP AND VALVE. TO REMOVE THIS ICE, YOU MUST PUT THE AIRPLANE IN A WARM HANGAR FOR SUFFICIENT TIME TO MELT THE ICE. THEN DRAIN THE SUMPS UNTIL THE WATER IS REMOVED.
 (1)  
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 12-11-00/301). In cold weather water can freeze, and not let the drain valves open.

 S 613-071

 (2)  
The items that follow have the most effect on the quantity of water in aviation fuels.

 (a)  
Where the fuel is kept.

 (b)  
How the fuel is moved.

 S 883-064
 (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 condtions that change, can be more than 3 gallons in each thousand gallons of fuel. As the temperatures decrease, 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.
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A
737-300/400/500MAINTENANCE MANUAL
 L.  Toilets and Potable Water
 S 613-061
 (1)  Toilets
 (a)  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. 1) To make sure it will not freeze, you can add antifreeze
 fluids to the water used to flush the toilet. Be careful in the selection of the materials you use. The antifreeze and the flushing deodorizer detergent can make foam when mixed. Foam can also occur when antifoam agents break down when they mix with a deodorizing detergent. Look at the fluid manufacturers' instructions to see if they can be mixed.
 2)  To make sure it will not freeze, you must fully drain the toilet flushing system, as appicable (AMM 12-17-00/301).
 S 613-065
 (2)  Potable Water
 (a)  You must drain all of the water from the potable water system (AMM 12-14-00/301).
　
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