Which of the following is NOT one of the four commonly used methods of coordination?

The correct choice identifies a method that is not typically used for air traffic coordination. The commonly used methods of coordination for air traffic control include automated systems, interphone communication, and verbal/physical methods.

Automated coordination often involves the use of systems and software that facilitate data sharing between controllers, reducing the chance of human error. Interphone communication is a standard method allowing air traffic controllers to communicate directly with each other using a telephone-like system, facilitating real-time coordination. Verbal/physical coordination can involve face-to-face communication or gestures to ensure clarity and mutual understanding among controllers on the ground or in the tower.

Visual signals, while they can be used in specific circumstances such as controlling ground traffic at airports, are not broadly categorized as one of the primary methods of coordination between air traffic controllers in the general sense. This makes the identification of visual signals as the method that is not commonly used in standard air traffic coordination contexts accurate.