De-icing

[citationxls]

Hi guys and girls,

Quick question from new newbie pilot:

Say you arrive at the airport on a clear and cold day (sub zero) and find you have ice on you aircraft. Can you chose to de-ice with type I well in advance before the pax arrive or is there a risk of the Type I freezing on the wings?
I guess there is no published HOT for a clear day?

Sorry for my ignorance!

Thanks in advance!

[Checkboard]

It depends on how sub zero you are talking about. The Lowest Operation Use Temperature (LOUT) for the fluid used depends on the mix ratio. The de-icing operator would determine that for you.

If it is a clear day (no precipitation or active frost), then only the clean wing concept applies - there is no hold over limit.

[RAT 5]

De-icing before ready to taxi has risks. On a clear cold day it would depend of the temp of the a/c skin and the remaining fuel in the wings, and the % of fuel for full wings. If you de-iced with Type 1 = no anti-ice, then the skin temp and fuel content would have an unknown effect and could only determined by inspection just before taxi. You could find you have to do it again.

[safewing]

Each fluid manufacturer generally produces documentation on their fluids.

A fluids concentration, derives its LOUT or lowest operational use temperature. For Type I this is the fluids freezing point to which 10°C is added.

The freezing points are concentration specific up to a point but above approx 75%-80% concentration the glycol in the fluid concentrate is such that it does not freeze.

While this seems like an ideal scenario the fluids viscosity behaviour changes and can become a sticky substance that will not eliminate as designed during the take off if these temperatures are encountered.

The problem that then arises is when concentrated type I is mixed with water to acceptable ratios when will it freeze?

As the other contributors have stated this can be difficult to assess. Because Type I fluids are by their design low viscosity (runny) the fluid layer is usually very thin.

This thin layer couple with the fact a certain amount of evaporation and transpiration is taken place means Type I fluids have a tendency to fast freeze and require close observation.

[Rcaf914]

Some good info here... http://web.adga.ca/tables/HOT%20Guidelines%202012-13.pdf

Specifically pages 12-13 will answer your questions. Type I fluid does have some "holdover" properties.