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R  (8) Holdover time is the estimated time during which anti-icing fluids will prevent the formation of frost or ice and snow accumulations on the protected surfaces of the aircraft. The holdover time starts at the beginning of the anti-icing treatment. 
R  (9) De-/Anti-icing is a combination of the de-icing and the anti-icing procedures and is performed in one or two steps. 
R  (10) One step De-/Anti-icing is carried out with an anti-icing fluid, normally heated. The aircraft is de-iced and the fluid that remains on the aircraft gives limited anti-ice protection. 
R  (11) Two step De-icing/Anti-Icing, as inferred, comprises two completely separate steps : - The first step is to de-ice the aircraft (remove frost, ice, slush and snow accumulations), - The second step is then to immediately follow this with an anti-icing procedure.
 B. Recommendations
 (1) Aircraft performance certification is based upon that aircraft having an uncontaminated or clean structure.
 (2) Ice, snow and frost or combinations of them will disturb the airflow, affecting lift and drag. They also increase the aircraft weight. 
R R  (3) The aircraft, and especially its surfaces that provide lift and stability, must be aerodynamically clean. If they are not, safe operation is not possible.
 (4) If the fuel temperature is below freezing point and the aircraft is subject to precipitation, clear ice may form on the wings (wing tank area), even if the outside temperature is as high as 15 deg.C (59.00 deg.F).
R  (5) An aircraft that is ready for flight must not have ice, snow, slush or frost adhering to its critical flight surfaces (wings, vertical and horizontal stabilizers and rudder).
R R  NOTE : A frost layer less than 3 mm (1/8 in.) on the underside of the____ wing, in the area of fuel tanks, is permitted without effect on takeoff performance if it is caused by cold fuel (low fuel temperature, OAT above freezing and high humidity).

 

R (6) A contamination check of the aircraft must cover all parts of the
R  aircraft. You must do this visual inspection from a position which gives a clear view of all surfaces. Because accumulations of clear ice are sometimes not easily visible, it is recommended that critical surfaces (wings, vertical and horizontal stabilizers and rudder) are inspected with your hands.
 (7)
 Weather conditions determine when the aircraft de-/anti-icing must be carried out.

 (8)
 During checks on the ground, electrical or mechanical ice-detectors must not replace physical checks.

 (9) If the aircraft arrives at the gate with the flaps/slats in a R position other than fully retracted, you must inspect these R flaps/slats, and if necessary de-ice before retraction.
 C. De-icing and/or Anti-icing Equipment and Materials
 (1) Type I Fluids Type I fluids are normally used for aircraft de-icing and have only a limited effect when used for anti-icing purposes. Type I fluids are normally used for aircraft de-icing. These fluids contain at least 80 % by volume of either :
 -Monoethylene-glycol
 -Diethylene-glycol
 -Monopropylene-glycol
 - or a mixture of these glycols.

 -The other 20% comprise inhibitors to restrict corrosion and increase the flash-point together with water and wetting agents. These fluids show a low viscosity which only changes with temperature. The freezing point of a water/glycol mixture will vary with the amount of water contained in the fluid. It must be noted that the lowest freezing point of concentrated TYPE I fluid is approximately -10 deg.C (+14.00 deg.F) whereas the lowest temperature protection will be found with a 60%/40% mixture of TYPE I fluid and water whose freezing point will be below -50 deg.C (-
58.00 deg.F). However, due to the lower viscosity, it flows off the wing more easily. Therefore a 50/50 mixture of TYPE I fluids and water is normally used.
R (2) Type II or Type IV fluids contain at least 50% by volume of either :
 -Monoethylene-glycol
 -Diethylene-glycol
 -Monopropylene-glycol
 - or a mixture of these glycols.
 The other 50% comprises :

 

 -inhibitors to restrict corrosion and increase the flash-point
 -water and wetting agents to allow the fluid to form a uniform film over the aircraft surfaces
 -thickening agents to enable the fluid to adhere to the aircraft surfaces for longer periods. Type II or Type IV fluids have a longer holdover time than type I fluid.
 (3) Fluid dilution Type I, Type II and Type IV fluids can be diluted with water. This may be done if, due to weather conditions, there is no requirement
R for a long conservation time or the higher freezing points are R sufficient for the climatic conditions present.
　
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