Chapter 5 - Ground Crew Supplement

FPD Fluid Strength When Applied

28.  The ratio of FPD ingredients to water, or fluid strength, is a significant factor in the de-icing fluid properties. HOT tables present guidelines for holdover times achieved by SAE Type I, SAE Type II, Type III and Type IV fluids as a function of fluid strength, weather conditions and outside air temperature (OAT).

Caution:

Do not use pure (100%) ethylene glycol or pure propylene glycol fluids in non-precipitation conditions. The reasons for this caution are explained below:

  • Pure ethylene glycol has a much higher freezing point than ethylene glycol diluted with water. Slight temperature decreases can be induced by factors such as cold-soaked fuel in wing tanks, reduction of solar radiation by clouds obscuring the sun, wind effects, and lowered temperature during development of wing lift;
     
  • Undiluted propylene glycol, having a strength of about 88% glycol at temperatures less than -10°C (+14°F), is quite viscous. In this form, propylene glycol based fluids have been found to cause lift reductions of about 20%.

29.  Propylene glycol FPD fluids are not intended to be used in the undiluted state unless specifically recommended by the aircraft manufacturer.

30.  Check the concentrations of the fluids you have available and know how they react under various conditions. If you do a quality assurance test as part of your procedure, don't skimp. If the test results are borderline, get help from your supervisor. Check with your supervisor, operations or maintenance to get the most up-to-date information available.