What factors influence holdover time?

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Holdover time is the window during which a de-ice/anti-ice fluid remains effective on aircraft surfaces before new ice can form. The key factors that determine this window are ambient temperature, the type of precipitation, and the state of the surface contamination. Temperature affects the fluid’s behavior—its viscosity, evaporation rate, and interaction with contaminants—so the protective film lasts longer or shorter depending on how warm or cold it is. The precipitation type matters because different forms (rain, snow, sleet) interact with the fluid in different ways, washing it off or diluting it at different rates, which can shorten or extend holdover time. The condition of the aircraft surface is crucial: whether it’s clean, frosted, or already contaminated with ice or snow changes how well the fluid can spread and maintain a continuous protective layer. Together, these factors determine how long the holdover protection remains valid, usually guided by fluid-specific holdover time charts. Other listed factors, like wind speed, cloud cover, runway slope, color of the aircraft, or operational details such as NOTAMs or crew shifts, don’t directly alter the chemical performance of the fluid in the holdover calculation.