This blog provides an overview of the tower light signals used in the event of a radio communication failure.

Visual signals have been used for communication by pilots and air traffic controllers since the early days of aviation when radio was not developed not that much and the equipment was trustworthy .

These included flags and light signals. Unlike Controller Pilot Data Link Communications (CPDLC) which can be used in a wide variety of situations, the visual signals are limited to a few safety-critical messages.

These days visual signs are as yet utilized at aerodrome control towers as a backup if there should be an occurrence of radio failure . The ATC utilizes a light or a flare gun to send the messages.

Light Gun

Very large light gun is a yet at the same time handheld like projector which is focused on the airplane. The ATC utilizes a trigger to communicate with either a progression of heartbeats or a persistent stream of light and may pick the shade of the bar (red, green or white).

Signal	To Aircraft in Flight	To Aircraft on the Ground
Steady green	Cleared to land	Cleared to takeoff
Steady red	Give way to other aircraft and continue circling	Stop
Series of green flashes	Return for landing*	Cleared to taxi
Series of red flashes	Aerodrome unsafe, do not land	Taxi clear of landing area in use
Series of white flashes	Land at this aerodrome and proceed to apron*	Return to starting point on the aerodrome

NOTE

In the USA, another signal is used – alternating red and green pulses meaning “Exercise extreme caution”. Note that this is not an ICAO standard and is therefore not universally adopted.The meanings of the signals are printed on the side of the light gun for reference.

Affirmation from the AIRCRAFT:

During sunlight hours, ATC signals are recognized by PILOTS :

1. shaking the airplane’s wings if the airplane is in flight.
2. moving the airplane’s ailerons or rudder if the airplane is on the ground.

During the long stretches of haziness, affirmation is made by glimmering on and off double the airplane’s arrival lights or, by turning on and off the route lights twice.

Flare Gun

The flare gun, is a small gun that discharges projectiles which produce light as they burn and generally, various colours for flares are available. In the tower, however, the only colour used is red and the message is “Notwithstanding any previous instructions, do not land for the time being”. Unlike light gun signals, the flare is not addressed to a particular aircraft.