Deicing question
 

Deicing has, as I understand it, to be undertaken within a specified time before takeoff or the plane has to be deiced again.

Is that time calculated from when the first drop hits the aircraft or the last drop or some other time? In the same vein must the take off roll be started within the alloted time or wheels off or some other measurement point?

Hold over time (time of protection) starts from the first drop.

Do you have a calculator for the time from start of takeoff roll to takeoff? If not, use start of roll.

Holdover times have usually a time range. Something like 25 minutes to 45 minutes. So for the first 25 minutes at the given conditions, protection is assured. Once those 25 minutes are over the flight crew needs to ascertain that the anti-ice protection is still holding, that can be done via a visual inspection. And yes, it is first drop to start of take off roll, during the take off rall the anti-icing fluid will flow mostly off the wings carrying with it the contamination and leaving the wing clean. Once in the air the aircraft installed ani-ice equipment has to take over if needed.

That's rather what I suspected but it's nice to get the proper answer. Thank you all.

Holdover time is calculated using multiple factors such as fluid type/brand, fluid mix, OAT, current weather condition (frost, snow, no precipitation etc etc). There is not a "standard" time

May be of some interest to the OP.

http://www.tc.gc.ca/en/services/avia...N_Original.pdf

Are we talking deicing or anti icing-
2 very different subjects with there own requirements, though both are normally carried out at the same time that is certainly not always the case in all parts of the world or airports.
Deicing is at it says-removing the contamination from the aircraft-thats it.
Anti icing however is a different ball game with many variables, ambient temperature, weather conditions-ie rain, sleet, snow etc, temperature and mix of the fluid being applied and of course the type of fluid-there not all the same-this will directly effect the "hold over time"...can be minutes to hours...once the hold over time has expired you have to "reapply anti/de icing fluid again if the weather conditions/aircraft require it.
And afterwards you need to wash the aircraft as its leaves a sticky mess...

A couple clarifying remarks:

Type 1 de-icing fluid also has different hold-over times dependent upon temperature, precipitation, mix, and airframe composition, to name a few; but Type 1 fluids are not anti-icers, they're de-icers.

You might also have to re-spray an aircraft if the conditions worsen, and in some cases much, much sooner than the hold-over time for the original conditions. The hold-over time, while based on science, is not a guarantee and the fluid can fail well before the calculated hold-over time if conditions worsen. For example, if you spray the aircraft in very light snow conditions, but on the taxi to the runway the rate picks up to moderate or changes to light freezing rain, you might have to go back to the pad well before the original hold-over time. It also depends on if the fluid was mixed and applied properly. I've seen it where the fluid failed well before the hold-over time because it was not applied thick enough in the first place, all because the contractor was trying to stretch their supply to save a buck or two.

Finally, there is no specific need to wash the residual fluid from the aircraft after flight. It will naturally come off in its own time. Perhaps a person will do so on their own private aircraft for aesthetics, but that's it.