Chapter 4 - Preventative Measures and Deicing Procedures

Variables That Can Influence Holdover Time

57.  The following list are some of the major variables that can influence the effectiveness of FPD fluids, especially when the fluids are being diluted by precipitation:

  • Aircraft component inclination angle, contour, and surface roughness;
  • Ambient temperature;
  • Aircraft surface (skin) temperature;
  • FPD fluid application procedure;
  • FPD fluid aqueous solution (strength);
  • FPD fluid film thickness;
  • FPD fluid temperature;
  • FPD fluid type;
  • Operation in close proximity to aircraft, equipment or structures;
  • Operation on snow, slush or wet ramps, taxiways or runways;
  • Precipitation type and rate;
  • Presence of FPD fluids;
  • Radiation cooling;
  • Residual moisture on the aircraft surface;
  • Relative humidity;
  • Solar radiation; and
  • Wind speed and direction.

58.  Holdover time guidelines are given in standard tables for different types of fluids, as a function of precipitation type and rate, and temperature to assist pilots.