Which of the following is NOT a standard hand signal for directing aircraft on the ground?

Answer: C — Ascend

In aircraft ground operations, hand signals are essential tools for communication, especially when pilots and ground personnel need to coordinate movements without relying on radio communication. Each standardized hand signal has a specific and recognized meaning to ensure safety and clarity. The standard hand signals for directing an aircraft typically include commands such as "stop," which indicates the aircraft should halt immediately, "turn left," which directs the aircraft to make a left turn, and "go forward," which instructs the aircraft to move ahead. Each of these signals corresponds to common operational movements needed on the ground. However, "ascend" is not a standard hand signal used for aircraft on the ground. This command pertains to movements specifically in flight, such as gaining altitude, and is not applicable during taxiing or ground navigation. Ground operations require clear and concise signals that relate to the aircraft's movement along the surface rather than actions associated with airborne maneuvers. Thus, the lack of a hand signal for "ascend" reinforces the focus on ground-specific movements and the necessity for clarity in communication on the runway or taxiway.