ATC Light Gun Signals: What You Need To See and Know

Air traffic controllers use light gun signals to communicate instructions to non-radio aircraft, ground vehicles, and people on the ground within the airfield perimeter. The signals are an essential means of reaching aircraft that do not have radios installed or that are experiencing a radio failure. They may also come into play if ATC radio equipment fails. 

Light gun signals emit a bright light visible from great distances, allowing a controller to issue instructions or warnings to a pilot. The signal may be transmitted using a handheld directional lamp operated by an air traffic controller in the tower or on the apron, or it may be from a beacon fixed to the tower.

Signal Colors and Indications

There are three different colors of lights: red, green, and white. These signals can either be steady or flashing and have different meanings for aircraft on the ground and in the air.

Steady red light gun signal

When an airborne pilot sees this signal, they should give way to other aircraft and continue circling. Typically, ATC uses this signal when continuing to land would not be safe for some reason. The pilot should obey the command and continue a good lookout, not just for other aircraft in the vicinity of the airfield but also for the next signal from the air traffic controllers.

When ground vehicles and aircraft on the ground see this signal, they should stop immediately. Instructions to come to a complete stop suggest a risk to traffic on the ground. All vehicles and aircraft should take a good look around and wait for the next instruction.

Flashing red light gun signal 

For aircraft in the air, a flashing red signal from the control tower means it is unsafe to land. There could be all sorts of reasons why this may be the case. For example, debris or animals may be on the runway.

When aircraft on the ground see this signal, they should taxi clear of the active runway. Ground vehicles and personnel should also move away from the runway or taxiway.

Steady green light gun signal 

A steady green light directed at aircraft in the air confirms it is safe to land. This signal means the runway is clear, and you can land on it. However, the pilot in command should maintain the same lookout for other traffic.

This signal also clears aircraft on the ground for takeoff and ground vehicles and personnel to proceed.

Flashing green light gun signal

This one often catches people out, as green is typically associated with safety. However, the actual instruction behind a flashing green light directed at aircraft in the air is to return for landing at the airfield. Usually, ATC directs this signal at aircraft in the circuit. If seen, the pilot should keep a good lookout for a steady green that indicates it is safe to land.

On the ground, a flashing green light clears the aircraft for taxi. It does not signal anything to ground vehicles or personnel.

Flashing white light gun signal 

Under Federal Aviation Administration regulations, there is no meaning behind a flashing white light for aircraft in the air.

Under International Civil Aviation Organization rules, a flashing white light means the aircraft should land at the airfield and proceed to the apron. However, it is not clearance to land or taxi. The pilot should look out for the steady green and flashing green that should follow this instruction.

For aircraft, vehicles, and personnel on the ground, a flashing white light signals they should return to the starting point on the airfield. 

There is no meaning behind a steady white light, which could come from many sources and cause confusion if ATC used it as a signal.

Alternating red and green signals

A pilot who sees alternating red and green lights in the vicinity of an airfield should exercise extreme caution. ATC uses this combination as a general warning signal, which usually indicates a serious problem on the airfield or within its airspace. There could be a hazard caused by converging aircraft, a mechanical problem with the aircraft the pilot has not noticed, or airfield or runway obstructions.

The FAA notes that this signal is to warn, not prohibit. Accordingly, ATC may follow this signal with another one.

	Color and Indication	Aircraft in the Air	Aircraft on the Ground	Vehicles and Personnel
	Steady red	Give way to other aircraft and continue circling	STOP	STOP
	Flashing red	Do not land (not safe to land)	Taxi clear of active runway	Move away from the active runway or taxiway
	Steady green	Safe to land	Cleared for takeoff	Cleared to proceed
	Flashing green	Return to the airfield for landing	Cleared for taxi	Not applicable
	Flashing white	FAA: N/A ICAO: Land at this airfield (when given the green light)	Return to the starting point on the airfield	Return to the starting point on the airfield
	Alternating red and green	Exercise extreme caution	Exercise extreme caution	Exercise extreme caution

Acknowledging Light Gun Signals

During the day, the pilot in command can acknowledge a light gun signal by moving the ailerons or the rudder. At night the PIC can switch the navigation lights or the landing light off and on again.

ATC issues all these light gun signal warnings and instructions with the proviso that the pilot remains in command. Ultimately, the safety of the aircraft and its passengers remains their responsibility.