Under what condition should vehicles avoid going off the paved surface?

The correct condition under which vehicles should avoid going off the paved surface is when yielding to taxiing aircraft. This is crucial for maintaining safety and ensuring that aircraft can move freely without obstruction. The paved surface is specifically designed to support vehicle movement and provide safe and efficient access for both vehicles and aircraft.

Yielding to taxiing aircraft involves giving priority to aircraft as they maneuver on the airfield, which is vital for maintaining the flow of operations and preventing accidents. Vehicles encroaching into areas not designated for their traffic could disrupt aircraft movements, leading to potential safety hazards or operational delays.

In other situations, such as inclement weather, vehicles being inoperative, or during routine traffic flow, while caution may still be exercised, they do not carry the same stringent requirement to remain on paved surfaces as when facilitating the safe passage of aircraft. Therefore, the imperative of yielding to taxiing aircraft stands out as a critical priority in airfield driving practices.