Definition
A rotating light installed at an airport that flashes alternating colors to identify the airport's location and type from the air at night or in reduced visibility. A civilian land airport shows alternating white and green flashes; a military airport shows alternating white-white-green (a double white flash followed by a green); a lighted water airport shows alternating white and yellow. When operated during daylight hours at a controlled field, it generally indicates that the weather at the airport is below basic VFR minimums (ceiling less than 1,000 feet and/or visibility less than 3 statute miles).
Plain English
A spinning light at an airport that flashes specific colors so pilots can spot the airport from the air and tell what kind of airport it is. If it's running in the daytime at a tower-controlled airport, it usually means the weather is poor enough that you need an instrument clearance to fly in.
Context Anchor
Pilots encounter an airport rotating beacon when visually looking for an airport from the air or on the ground, especially during night operations.
Derivation
‘Beacon’ comes from Old English ‘beacen,’ meaning a sign or signal — historically a fire or light used to guide or warn. The aviation use keeps that original sense: a light that signals the location of something important.
Why Pilots Care
Provides positive identification of the airport from miles away at night, allowing pilots to orient and navigate safely before runway or taxiway lights become visible.
Analogy
It works like a lighthouse for an airport: the light sweeps around and catches your eye from a distance.
Intuition Check
Do not assume the airport rotating beacon lights the runway or gives permission to land. It helps identify the airport; landing clearance and runway visibility are separate matters.
Example Sentence 1
On the night cross-country, the student spotted the alternating white and green flashes of the airport rotating beacon ten miles out and used it to confirm the field's location.
Example Sentence 2
During the night flight, the student used the rotating beacon to confirm the correct airport before starting the descent.