Description

Most communication between pilots and controllers is done by voice. CPDLC has become an alternative in recent years though it is only intended to be used in situations that are not time-critical.

Visual signals have been used for communication by pilots and air traffic controllers since the early days of aviation when radio was not widespread and the equipment was unreliable. These included flags and light signals. Unlike CPDLC which can be used in a wide variety of situations, the visual signals are limited to a few safety-critical messages.

Nowadays visual signals are still used at aerodrome control towers as a backup in case of radio failure. The controller uses a light gun or a flare gun to send the messages.