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• visible moisture (clouds, fog with visibility less than one mile, rain,
snow, sleet, ice crystals, and so on) is present, or
• standing water, ice, or snow is present on the ramps, taxiways, or
runways.
CAUTION: Do not operate nacelle or wing anti–ice when total air
temperature (TAT) is above 10°C (50°F).
December 01, 1999
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
SP.16.2 D6-30151-425
Supplementary Procedures -
Adverse Weather
Preflight
Although removal of surface snow, ice or frost is normally a maintenance
function, the flight crew should use additional care and scrutiny during preflight
preparation to inspect areas where surface snow or frost could change or affect
normal system operations.
Exterior Safety Inspection
Surface............................................................................................Check
Takeoff with light coatings of frost, up to 1/8 inch (3mm) in thickness on
lower wing surfaces due to cold fuel, is permissible; however, all leading
edge devices, all control surfaces, and upper wing surfaces must be free of
snow or ice.
Thin hoarfrost is acceptable on the upper surface of the fuselage provided
all vents and ports are clear. Thin hoarfrost is a uniform white deposit of
fine crystalline texture, which usually occurs on exposed surfaces on a cold
and cloudless night, and which is thin enough to distinguish surface
features underneath, such as paint lines, markings, or lettering.
Landing gear doors.........................................................................Check
Landing gear doors should be free of snow or ice.
Air conditioning inlets and exits ......................................................Clear
Verify air inlets and exits, including the outflow valve, are clear of snow or
ice. If the APU is operating, check the outflow valve is full open.
Engine inlets .....................................................................................Clear
Check inlet cowling free of ice or snow and verify the fan is free to rotate.
APU air inlets ................................................................................Check
The APU inlet door and cooling air inlet must be free of snow or ice prior
to APU start.
Fuel tank vents .................................................................................Clear
Check all fuel tank vents. All traces of ice or frost should be removed.
Pitot probes and static ports .............................................................Clear
Check all pitot probes and static ports free of ice and snow.Water rundown
after snow removal may refreeze immediately forward of static ports and
cause an ice buildup which disturbs airflow over the static ports resulting
in erroneous static readings even when static ports themselves are clear.
Flight Deck Preparation
Packs ...........................................................................................NORM
Provides cabin heating.
December 01, 1999
747 Operations Manual
Supplementary Procedures -
Adverse Weather
Copyright © The Boeing Company. See title page for details.
D6-30151-425 SP.16.3
Recirculation Fans ..............................................................................ON
Airplane doors ...............................................................................Closed
Keep airplane doors closed as much as possible to limit heat loss.
Engine Start
Use normal start procedures; oil pressure may be slow to rise.
After Start
Flight controls ................................................................................ Check
Move flight controls through full travel to ensure freedom of movement.
Flaps .............................................................................................. Check
Move flaps through full travel to ensure freedom of movement.
CAUTION: Closely observe the flap position indicator for positive
movement. If the flaps should stop, immediately place
the flap lever in the same position as indicated.
Nacelle Anti–Ice Operation – On the Ground
Nacelle anti–ice must be ON during all ground operations when icing conditions
exist or are anticipated except when SAT is less than -40°C.
WARNING: Do not rely on airframe visual icing cues before
activating nacelle anti–ice. Use the temperature and
visible moisture criteria.
CAUTION: Do not operate nacelle anti-ice when total air
temperature (TAT) above 10° C.
When nacelle anti–ice required (on the ground):
Check area behind airplane is clear.
Nacelle Anti-ice switches ..............................................................ON
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