Deicing

Deicing is the process of removing ice, frost, snow, or slush from aircraft surfaces prior to flight. Even a thin layer of frozen contamination on wings and control surfaces can dramatically alter aerodynamic performance, reducing lift and increasing drag to potentially catastrophic levels.

The deicing process typically involves spraying the aircraft with heated fluid:

• Type I fluid: Heated (60-80°C), low-viscosity orange fluid used to remove existing contamination. It flows off surfaces quickly and provides minimal holdover time
• Type II/III/IV fluid: Thicker, unheated green or yellow fluid applied after deicing to prevent re-contamination (anti-icing). These fluids have longer holdover times and shear off during takeoff roll

The holdover time (HOT) is the estimated period during which the anti-icing fluid will prevent new ice or snow accumulation. If holdover time expires before takeoff, the aircraft must return for re-treatment. Pilots are responsible for confirming that the aircraft is clean before takeoff — a visual check called the clean aircraft concept.