Which parameter can extend holdover times significantly?

Applying a thicker layer of de-icing fluid on aircraft surfaces can significantly extend holdover times due to the increased amount of fluid that acts as a barrier between ice and the aircraft's surfaces. Thicker layers are more effective at resisting the accumulation of ice and snow, as they can absorb and retain more heat, delaying the onset of freezing and adhering snow.

Moreover, the surface physics come into play; a thicker application can also help in enhancing the fluid's viscosity and provide better adhesion to the aircraft, which aids in maintaining a protective layer for a longer period.

While other factors, such as temperature and brand of de-icing fluid, can influence holdover times, the thickness of the fluid is a direct and quantifiable parameter that can be controlled at the time of application to provide better protection against ice buildup.