Definition
A light gun signal used by air traffic control tower controllers to communicate with aircraft when normal radio communication is not available. A flashing red light directed at an aircraft in flight means 'airport unsafe — do not land.' When directed at an aircraft on the ground, it means 'taxi clear of the runway in use.'
Plain English
A red light from the tower that blinks on and off. If you are flying, it tells you the airport is not safe to land on right now. If you are on the ground, it tells you to get off the active runway.
Context Anchor
Seen in tower light gun signals, especially when a pilot cannot use the radio to receive normal instructions.
Why Pilots Care
Landing on an unsafe airport can lead to runway incursions, collisions, or other hazards; the signal forces a diversion to protect the flight.
Grounding Statement
Flashing red is a warning signal: on the ground, get clear of the runway; in the air, stay away from landing.
Intuition Check
Do not read flashing red as only meaning “stop.” In this FAA signal, its exact meaning depends on whether the aircraft is on the ground or in flight.
Example Sentence 1
After their radio failed on approach, the pilot saw a flashing red light from the tower and broke off the landing, knowing the airport was unsafe.
Example Sentence 2
While approaching the non-towered field with radio failure, a flashing red signal from the ramp confirmed the runway was closed.