22.7 Determining Freezing Point
As the concentration of the fluid is increased from 0% upwards, by volume, the freezing point decreases. The freeze point of the solution is however lower than the pure solvent. Refractometer is used to determine Glycol based Fluid Freezing Point.
22.8 Freeze Point Buffer
A safety buffer to cater for errors in the calculations has now led to a requirement where the freezing point of the anti/de-icing fluids has to be below the ambient temperature by 10°C for Type I fluids, and 7°C for Types II & IV fluids.
22.9 Lowest Operational Use Temperature (LOUT) of De/Anti-icing Fluids
22.9.1 Just as an aircraft has a specific operating envelope within which it is approved to be operated, de/anti-icing fluids are also tested and qualified for operation within a specific temperature envelope.
22.9.2 The qualification of de/anti-icing fluids, also called freezing point depressants (FPD), is a complex and thorough process, which evaluates a multitude of fluid properties and characteristics. The one of particular interest in this case is the Lowest Operational Use Temperature (LOUT). The LOUT is fluid concentration specific. The fluid concentration may change if the fluid is subjected to sustained heating. The LOUT for a given fluid is the higher of:
i. The lowest temperature at which the fluid meets the aerodynamic acceptance test for a given aircraft type, or
ii. The actual freezing point of the fluid plus its freezing point buffer of 10°C, for a Type I fluid, and 7°C for a Type II, Type III, or IV fluid.
NOTE: Manufacturers state that a fluid must not be used when the outside air temperature or skin temperature is below the LOUT of the fluid.
Issue II 02.07.2009 Rev. 0
22.10 Colour
22.10.1 Colours are used as a visual aid in the application of fluids to aircraft surfaces. SAE fluid specifications indicate the appropriate colour for each of the Types of fluids, as follows:
o Type I fluids: Orange
o Type II fluids: Colourless or a pale Straw
o Type III fluids: Light yellow (As of April 2005, SAE has not yet established a colour specification for this fluid)
o Type IV fluids: Emerald Green.
NOTE: If the colour of the fluid being applied to the aircraft is NOT the colour anticipated, the procedure should be stopped and the situation investigated.
Issue II 02.07.2009 Rev. 0
FLUID HANDLING
23.1 General
23.1.1 De-icing/anti-icing fluids are chemical products with an environmental impact. During fluid handling, avoid any unnecessary spillage; comply with local environmental and health laws and the manufacturer’s safety data sheet.
23.1.2 Mixing of products from different suppliers is generally not allowed and needs extra qualification testing.
23.1.3 Slippery conditions due to the presence of fluid may exist on the ground or on equipment following the de-icing/anti-icing procedure. Caution should be exercised due to increased slipperiness, particularly under low humidity or non-precipitating weather conditions.
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