"Quote: If it then begins to snow as you're on your way to the holding point, am I right in thinking that if you've just been de-iced, you only have minimal protection against further contamination and therefore don't really have any holdover times to rely on???"
It depends on the OAT, rate of precipitation and the concentration of the Type II fluid used. If your company publishes the generic Type II holdovertime table in their Ops. manual and a 75/25 mix was used for the de-/anti-icing operation, guideline times in falling snow would have been between 15 to 30 minutes at 3 deg. C and above (15 minutes in moderate snow to 30 minutes in light snow) and 15 to 25 minutes at below 3 deg. C to 14 deg. C. Should a two-step operation have been carried out and concentrate Type II fluid used for the second step, the guideline times would have been 20 to 45 minutes at 3 deg. C and above and 15 to 35 minutes at below 3 deg. C to 14 deg. C.
Holdovertime tables are available for individual Type II fluids (these are used when compiling the generic table) and there is an option for companies to publish one or more of these fluid specific (brand name) tables in their Ops. Manuals, as well as the generic tables. There are benefits to this in that the table published for the most widely used Type II fluid in the UK shows the guideline times for a 75/25 mix as 30 to 65 minutes at 3 deg. C and above and 25 to 50 minutes below 3 deg. C to 14 deg. C. For concentrate fluids the times are 30 to 60 minutes at 3 deg. C and above and 25 to 45 minutes below 3 deg. C to 14 deg. C.