What do the beacon colours and flashes mean?
White alternating with green marks a land aerodrome, white with yellow marks a water aerodrome, and the rate is 20 to 30 flashes a minute.
The colours on an aerodrome beacon tell a pilot what kind of aerodrome it is. A land aerodrome beacon flashes white alternating with green, and a water aerodrome beacon flashes white alternating with yellow. Some aerodromes use white flashes only. The coloured flash has to sit inside the colour limits that ICAO defines, so the filter and light source are chosen to match.
The total flash rate is 20 to 30 flashes per minute, with white and coloured flashes counted together, and the white flash is at least 2,000 cd. On a rotating beacon the rate is beams × turns per minute, so a two-beam beacon needs 10 to 15 turns a minute. The FAA asks for 24 to 30 flashes a minute, so a two-beam beacon turning 12 to 15 times a minute meets both. An identification beacon is a separate light that flashes a Morse code group, in green on land and yellow on water, so a pilot can tell which aerodrome it is. The Morse is sent slowly, about 6 to 8 words a minute, so each dot lasts roughly 0.15 to 0.2 seconds.
Frequently Asked Questions
Q1What colours does an aerodrome beacon use?
A land aerodrome beacon flashes white alternating with green, and a water aerodrome beacon flashes white alternating with yellow. Some aerodromes use white flashes only. The coloured flash must fall inside the colour limits that ICAO sets.
Q2How many flashes per minute should a beacon give?
ICAO sets the total flash rate at 20 to 30 flashes per minute, with white and coloured flashes counted together. The FAA uses 24 to 30 for its airport beacons, so a two-beam beacon turning 12 to 15 times a minute meets both.
Q3How do I set the flash rate on a rotating beacon?
Flashes per minute equal the number of beams times the turns per minute. With two beams, 10 turns a minute gives 20 flashes, 12 gives 24 and 15 gives 30. Set the motor speed to land inside the range.
Q4Why do land and water aerodromes use different colours?
So a pilot can tell the kind of aerodrome from the beacon. Green marks a land aerodrome and yellow marks a water aerodrome, and the white flash is common to both.
Q5What does an identification beacon flash?
A Morse code group that identifies the aerodrome, in green for a land aerodrome and yellow for a water aerodrome. It is separate from the aerodrome beacon and is used only where the aerodrome needs to be told apart from others.
See It. Understand It. Then Learn How to Engineer It.
Recognising an AGL system visually is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how each light, sign and circuit works as part of a complete airport lighting system, not just as an isolated diagram.