When should de-icing be performed before departure?

De-icing should be performed as close to departure as possible to ensure the aircraft is clear of ice and snow immediately before takeoff. This approach minimizes the time the aircraft is exposed to environmental conditions that could lead to re-icing, which is critical for safe operations. Ice and snow accumulation can impact the aircraft's performance, including lift and control, so timely de-icing ensures that the surfaces remain clean and aerodynamic attributes are preserved right up until the moment of departure.

De-icing performed too far in advance increases the risk that contaminants will accumulate again due to temperature changes or precipitation, potentially leading to unsafe flight conditions. Other options suggest performing de-icing only during specific pre-flight checks or after refueling, which doesn't address the critical timing needed for optimal aircraft performance immediately prior to takeoff. Such considerations make conducting de-icing as close as possible to departure the safest and most effective practice.