● Anti-icing codes
It is essential that the flight crew receive clear information from ground personnel concerning the treatment applied to the aircraft. The AEA (Association of European Airlines) recommendations and the SAE and ISO specifications promote the standardized use of a four-element code. This gives flight crew the minimum details to assess holdover times. The use of local time is preferred but, in any case, statement of the reference is essential. This information must be recorded and communicated to the flight crew by referring to the last step of the procedure.
Examples of anti-icing codes:
AEA Type II/75/16.43 local TLS / 19 Dec 99
AEA Type II : Type of fluid used
75 : Percentage of fluid/water mixtures by volume 75% fluid / 25% water
16.43 : Local time of start of last application
19 Dec 99 : Date

ISO Type I/50:50/06.30 UTC/ 19 Dec 99
50:50 : 50% fluid / 50 % water
06.30 : Time (UTC) of start of last application
● Fluid application and holdover time guidelines
Holdover protection is achieved by anti-icing fluids remaining on and protecting aircraft surfaces for a period of time. With a one-step de/anti-icing operation, holdover begins at the start of the operation. With a two-step operation, holdover begins at the start of the second (anti-icing) step. Holdover time will have effectively run out, when frozen deposits start to form/accumulate on aircraft surfaces.
Due to its properties Type I fluid forms 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.
Tables 1, 2 and 3 below provide an indication of the protection timeframe of that could reasonably be expected under precipitation conditions. 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.
62

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.
Caution:
The protection times represented in these tables are for general information purposes only. They are taken from the ISO/SAE specifications, effective October 1st, 1999. However, local authority requirements may differ.
　
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