When is it acceptable for fixed-wing aircraft to move ailerons or rudder while on the ground?

The correct answer indicates that fixed-wing aircraft are allowed to move ailerons or rudder while on the ground from sunrise to sunset. This practice is often related to ensuring proper control surface movement checks and is fundamental for pilots to verify that their control surfaces are functioning correctly before an aircraft takes off.

During daylight hours, pilots can conduct these checks safely, visually confirming that the ailerons and rudder are responding appropriately without the additional complications of night operations or low visibility conditions. This ensures that they are prepared for flight and have a clear understanding of how the aircraft will respond to inputs once airborne.

In contrast, the other options present conditions that would typically be less favorable for control surface checks. Nighttime operations may restrict visibility, making it harder to visually confirm the movement of control surfaces. Low visibility conditions may create similar challenges, as pilots might not be able to see the effects or functions of the ailerons and rudder effectively. Taxiing introduces a scenario where aircraft must follow ground traffic rules and avoid unnecessary movements that could complicate the movement on taxiways. Thus, performing these actions on the ground is best suited for the hours of daylight when conditions are optimal for safety and functionality checks.