17.3 Type I/II, IV HOT
Due to its properties, Type I fluids form a thin liquid-wetting film, which gives a rather limited holdover time, depending on weather conditions. With this type of fluid, increasing the concentration of fluid in the fluid/water mix would provide no additional holdover time. Type II and Type IV fluids contain a thickener which enables the fluid to form a thicker liquid-wetting film on external surfaces. This film provides a longer holdover time, especially in conditions of freezing precipitation. With this type of fluid, additional holdover time will be provided by increasing the concentration of fluid in the fluid/water mix, with maximum holdover time available from undiluted fluid.
17.4 HOT Tables
Tables 1 and 2 attached as Appendix ‘F’, provide an indication of the protection timeframe that could reasonably be expected under precipitation conditions for the fluids presently approved for use by Transport Canada. Visibility in Snow vs. Snowfall Intensity Chart attached as Appendix ‘G’ enables the crew to more accurately estimate snowfall intensity by day / night in various temperature conditions.
17.5 Variation in HOT
However, due to the many variables that can influence holdover times, these times should not be considered as minimum or maximum, since the actual time of protection may be extended or reduced, depending upon the particular conditions existing at the time.
17.6 Cell Times
The lower limit of the published time span is used to indicate the estimated time of protection during heavy precipitation and the upper limit, the estimated time of protection during light precipitation.
Issue II 02.07.2009 Rev. 0
17.7 Caution:
17.7.1 The protection times represented in these tables are for general information purposes only. These are based on the SAE specifications and taken from the current Transport Canada Holdover Time (HOT) Guidelines. However, local authority requirements may differ. Applicable guidelines and prevailing HOT Guidelines pertinent to the area of operation are to be used.
17.7.2 The protection time will be shortened in severe weather conditions. Heavy precipitation rates or high moisture content, high wind velocity and jet blast may cause a degradation of the protective film. If these conditions occur, the protection time may be shortened considerably. This is also the case when the aircraft skin temperature is significantly lower than the outside air temperature.
17.8 Use of HOT
The indicated times should, therefore, only be used in conjunction with a pre-takeoff contamination inspection of the representative surface.
17.9 Approved Fluids
Fluids approved by the aircraft manufacturer and the relevant regulatory authority are to be used.
17.10 Fluid Specifications
All de/anti-icing fluids following the specifications mentioned below are approved:
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Type I : SAE AMS 1424 standard
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