De-icing
 

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!

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.

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.

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.

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

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