Icing conditions exist when either:
Engine anti-ice must be ON during all ground and flight operations when icing conditions exist or are anticipated, except during climb and cruise when the temperature is below -40° C SAT.
WARNING: Do not rely on airframe visual icing clues to turn engine anti-ice on. Use the temperature and visual moisture criteria specified in this procedure. Delaying the use of engine anti-ice until ice build-up is visible from the flight deck may result in severe engine damage and/or flameout.
Erratic EPR indications or abnormal EPR relative to N1 may be an indication of engine icing.
On the ground, if icing conditions are present, engine anti-ice must be selected to ON immediately after engine start.
During prolonged ground operations when moderate to severe icing conditions exist, (temperature less than +3°C in fog, drizzle or standing water) increase thrust to a minimum of 60% N1 for approximately 30 seconds at intervals no greater than 30 minutes.
Takeoff in moderate to severe icing or following airplane deicing must be preceded by a static run-up to a minimum of 60% N1 for 30 seconds and stable engine operation checked prior to start of the takeoff roll.
During flight in moderate to severe icing conditions for prolonged periods with N1 settings at or below 70%, or if fan icing is suspected due to high engine vibration, increase thrust on one engine at a time to a minimum of 70% N1 for 10 to 30 seconds every 10 minutes.
CAUTION: Do not operate engine anti-ice when the total air temperature (TAT) is above 10°C.
The wing anti-ice system may be used as a de-icer or anti-icer in flight only. The primary method is to use it as a de-icer by allowing the ice to accumulate before turning wing anti-ice on. This procedure provides the cleanest airfoil surface, the least possible run-back ice formation, and the least fuel penalty. The second method is to select the WING ANTI-ICE switch ON when wing icing is possible and use the system as an anti-icer.
Ice accumulation on the flight deck windshield frames, windshield centre post, windshield wiper post, or side windows can be used as an indication that airframe icing conditions exist.
CAUTION: Do not operate wing anti-ice when the total air temperature (TAT) is above 10° C.
When an accumulation of ice and snow is observed or suspected prior to takeoff, have wing and tail surfaces inspected and ice and snow removed.
Note: 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 all upper wing surfaces must be free of snow or ice.
Note: 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 a cold and cloudless night, and which is thin enough to distinguish surface features underneath, such as paint lines, markings or lettering.
If using de-icing fluid on airplane exterior with APU or engines running:
Approximately 1 minute after completion of de-icing:
Note: De-icing fluid protection time varies considerably, depending on meteorological conditions and methods of application.
Note: Airplane de-icing/anti-icing should be accomplished with the flaps up to prevent ice and slush from accumulating in flap cavities.
If the taxi route is through slush or standing water in low temperatures, taxi with flaps up. Taxiing with flaps extended will subject flaps and flap drives to snow and slush accumulations from the main gear wheels. Leading edge devices are also susceptible to slush accumulations.
WARNING: If the flaps are left up during taxi, complete the before takeoff checklist after flaps are in takeoff configuration.
CAUTION: Use extreme caution when taxiing on ice covered taxiways or runways, as excessive speed or high crosswinds may start a skid. Reduce speed for all turns.
Boeing Aeroplane Operating Manual Volume 1 - Supplementary Procedures - Section 3