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MAINTENANCE MANUAL
(g) Wing fuel tank. 1) Frost can occur on the bottom of the wings in the fuel tank areas in temperatures above freezing. This is caused by the condensation of moisture in the air when it touches cold surfaces that are below freezing. The frost will usually melt when you add fuel that is a higher temperature. If the front continues and is more than 1/8-inch thick, remove it before the takeoff. 2) Clear ice can occur on the top of the wing when these conditions occur. a) The temperature of the fuel in the tank is below freezing b) The ambient temperature is above freezing c) There is rain, drizzle or fog.
3) Carefully examine the top of the wing to see if there is clear ice. Use the equipment that is necessary to get sufficient access to the top of the wing to do this check. It is possible that the clear ice can only be found by touch. You must remove clear ice and anti-ice the wing, if it is necessary, before the takeoff.
(h) Miscellaneous 1) Pitot Probe, Static Ports, and Total Air Temperature (TAT) Probes (Fig. 303). a) Look for ice that is attached to the surface four feet or less from the pitot inlets, static port, and TAT probe inlets. Remove all the ice in these areas. b) Do not point a spray of deicing/anti-icing fluid directly at or into the pitot inlets, static ports, or the TAT probes. c) If ice causes a blockage of the static openings, carefully apply warm air until the ice melts. d) If you applied too much fluid to the fuselage near the static ports, examine the nearest in-line drain. Remove the water if is collected there. 2) Drains
a) Examine all of the waste water and condensate drains on the airplane to make sure there are no blockages because of ice or other material. It is not necessary to put a plug on the drains during the ice removal or anti-icing procedure. But, do not point a fluid spray at those drain areas.
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PITOT-STATIC PROBES (4 LOCATIONS)
AIRPLANES WITH CF6-80C SERIES ENGINES (PROBES LOCATED ON ENGINE FAN CASE)
AIRPLANES WITH PW4000 SERIES ENGINES OR RB211-524 SERIES ENGINES (PROBE LOCATED IN ENGINE INLET)
747 Probe Location Figure 303
G34273
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3) Angle of Airflow Sensor (Fig. 303)
4) Make sure that no ice and/or snow is on the sensors. Make sure the sensors are free to move. Apply deicing fluid if it is necessary.
5) Windshield Wiper Blades a) Remove the ice that collected on the windshield wiper blades.
E. Hot Water Ice Removal Procedure
S 663-005
(1)
You can use hot water at 180-200°F maximum tank temperature to remove ice and snow from the airplane surfaces when the ambient temperature is 26°F, stable or on the increase.
S 663-006
(2)
To prevent the water from freezing again you must apply anti-icing fluid to the surface immediately after you remove the ice with hot water.
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