Which two methods can be used to issue specific instructions for aircraft movement?

Radio and directional light signals are essential methods for issuing specific instructions for aircraft movement. Radio communication allows for real-time, clear, and direct interaction between air traffic controllers and pilots, facilitating the relay of critical information regarding takeoffs, landings, and taxiing. This method is widely used because it provides a reliable and efficient means of communication, especially in busy airspace where immediate instructions are necessary for safety.

Directional light signals, on the other hand, serve as an auxiliary means of communication, especially in situations where radio communication may not be viable, such as during communications failure or noise-related issues at the airport. These light signals can convey various instructions visually, serving as a critical fallback when audio communication is compromised.

Other methods, like visual signals or hand gestures, are typically less formal and might not be used for all critical instructions. Phone calls or written notes could introduce delays and might not be suitable for immediate aircraft movement instructions. Similarly, audible alarms or wands are not standard methods for issuing specific flight instructions; wands are often used for directing ground traffic but don't serve as a primary communication method for instructions. Thus, radio and directional light signals are integral for maintaining a safe and efficient operational environment in air traffic control.