When does holdover time begin during operations?

Holdover time refers to the period during which de-icing or anti-icing fluids effectively prevent the accumulation of ice, snow, or frost on an aircraft's critical surfaces. This time frame is crucial for ensuring the aircraft remains safe and operationally ready.

The correct answer indicates that holdover time begins at the moment when the final application of fluid is completed. This is significant because the effectiveness of the de-icing or anti-icing fluid must be intact when the aircraft is readying for takeoff. The timing of the application is critical; if the fluid is applied too early or before conditions are particularly conducive to icing, it may lose its effectiveness before the aircraft departs.

Other scenarios that might be considered, such as beginning when taxiing starts or when the aircraft powers up, would not accurately reflect the operational validity of the holdover time, as these activities occur after the application of the fluid and do not influence its intended protective effects on the aircraft.