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12-40-0 Page 224  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/98 

COLD WEATHER MAINTENANCE
1.  General
A.  Operating airplanes safely in cold weather conditions presents unique problems due to the effects of ice, snow, slush, frost, and low temperatures. Maintenance personnel must recognize the impact of cold weather on operations to minimize costs and lost time. This procedure provides information on protection against or removal of ice, snow, slush and frost from the airplane and various other airplane related aspects of cold weather operation. The operator is responsible for selection and implementation of procedures suitable for existing climatic conditions.
B.  The procedures for operation of equipment to be used during ice, snow and/or frost conditions must be developed by the operator to meet his unique requirements based on his cold weather experiences, equipment and materials availability, and the climatic conditions existing at his bases.
C.  This procedure contains the following topics:
TOPIC PARAGRAPH NO. Equipment and Materials 2. Guidelines 3.
General  3.A.
Specific Requirements 3.B. Control Surfaces 3.B.(1) Wing and Horizontal Tail 3.B.(2) Fuselage and Vertical Tail 3.B.(3) Engines and APU 3.B.(4) Brakes 3.B.(5) Landing Gear and Door 3.B.(6) Wing Fuel Tanks 3.B.(7) Fuel Tank Sumping 3.B.(8) Miscellaneous 3.B.(9)
Hot Water Deicing 4. One-Step Deicing/Anti-icing 5. Two-Step Deicing/Anti-icing 6. Operation Checks 7. Parking 8. Engine Operation 9. Fuel Icing 10. Toilets and Potable Water 11.
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D.  Definitions
(1)  
Deicing is a procedure by which frost, ice or snow is removed from the airplane by applying hot water or a hot mixture of water and deicing/anti-icing fluid.

(2)  
Anti-icing consists of the application of an anti-icing fluid or a mixture of anti-icing fluid and water to the airplane to protect against the accumulation and adherence of ice, snow and/or frost to airplane surfaces.

(3)  
One step deicing/anti-icing consists of the application of deicing/anti-icing fluid or a mixture of fluid and water heated as necessary considering the ambient temperature and weather condition.

(4)  
Two step deicing/anti-icing consists of deciding with hot water or a hot mixture of deicing/anti-icing fluid and water, followed immediately by anti-icing with an overspray of deicing/anti-icing fluid or a mixture of deicing/anti-icing fluid and water. The second step must be performed within 3 minutes of the beginning of the first step, if necessary, area by area.

(5)  
Holdover time is the estimated time anti-icing fluid will prevent frost, ice, or snow from forming or accumulating on the protected surfaces of an airplane.

CAUTION:  THE REPEATED APPLICATION OF TYPE II OR TYPE IV DEICING/ ANTI-ICING FLUIDS WITHOUT THE SUBSEQUENT APPLICATION OF TYPE I FLUIDS OR HOT WATER MAY CAUSE A RESIDUE TO COLLECT IN AERODYNAMICALLY QUIET AREAS. THIS RESIDUE MAY REHYDRATE AND FREEZE UNDER CERTAIN TEMPERATURE, HIGH HUMIDITY AND/OR RAIN CONDITIONS. THIS RESIDUE MAY BLOCK OR IMPEDE CRITICAL FLIGHT CONTROL SYSTEMS. THIS RESIDUE MAY REQUIRE REMOVAL.
NOTE:  The degree of protection, or holdover, is dependent upon the weather conditions and fluid/fluid mixture selected and cannot be precisely determined. The expected protection time should be specified by the operator based on his experience. Under precipitation conditions, the airplane should be deiced as close to departure time as possible.
(6)  
Type I (unthickened) deicing/anti-icing fluids typically contain a minimum of 80% Glycol. Their viscosity is a function only of temperature and is not a function of shear stress. These fluids provide limited anti-icing capability.

(7)  
Type II AND Type IV (thickened) deicing/anti-icing fluids have a minimum Glycol content of 50% with 45% to 50% water plus thickeners and inhibitors. Their viscosity is a function of the applied shear stress as well as temperature. They are usually highly viscous at low shear stress levels, and their viscosity decreases dramatically as shear stress increases. They provide longer holdover time than Type I deicing/anti-icing fluids.

(8)  
In cold weather, it is necessary to drain fuel tank sumps prior to fueling to remove water from fuel tanks if the airplane has been idle for more than 45 minutes prior to fueling. Drain fuel tank sumps again after refueling if the airplane has been idle for 2 hours or more after refueling. In cold weather, water can freeze and not let the drain valves open.
　
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