Definition
A light gun signal from the control tower, shown as a beam alternating between red and green flashes, meaning 'exercise extreme caution.' It is used to warn an aircraft on the ground or in flight of a hazardous condition without giving a specific clearance or instruction.
Plain English
The tower is flashing red and then green at you, over and over. It means: be very careful — something out there is a problem. It is a warning, not a permission to do anything specific.
Context Anchor
Seen in light gun signal tables and used during lost communication procedures near a towered airport.
Why Pilots Care
Alerts the pilot to an unspecified hazard or abnormal condition that requires immediate extra vigilance to avoid an incident.
Grounding Statement
Picture the tower using a bright signal lamp to warn you when they cannot reach you by radio.
Intuition Check
Do not read the colors separately as a red command followed by a green clearance. Together, alternating red and green means one message: exercise extreme caution.
Example Sentence 1
After losing radio contact on final, the pilot saw an alternating red and green light from the tower and immediately scanned the runway for traffic before continuing the approach.
Example Sentence 2
During the no-radio arrival the alternating red and green signal prompted the pilot to proceed with extreme caution and expect further light signals.