AIM 2-1-9

Airport and heliport beacons have a vertical light distribution to make them most effective from one to ten degrees above the horizon; however, they can be seen well above and below this peak spread. The beacon may be an omnidirectional capacitor-discharge device, or it may rotate at a constant speed which produces the visual effect of flashes at regular intervals. Flashes may be one or two colors alternately. The total number of flashes are: 24 to 30 per minute for beacons marking airports, landmarks, and points on Federal airways.

30 to 45 per minute for beacons marking heliports.

The colors and color combinations of beacons are: White and Green- Lighted land airport.

*Green alone- Lighted land airport.

White and Yellow- Lighted water airport.

*Yellow alone- Lighted water airport.

Green, Yellow, and White- Lighted heliport. NOTE-

*Green alone or yellow alone is used only in connection with a white-and-green or white-and-yellow beacon display, respectively.

Military airport beacons flash alternately white and green, but are differentiated from civil beacons by dualpeaked (two quick) white flashes between the green flashes.

In Class B, Class C, Class D and Class E surface areas, operation of the airport beacon during the hours of daylight often indicates that the ground visibility is less than 3 miles and/or the ceiling is less than 1,000 feet. ATC clearance in accordance with 14 CFR part 91 is required for landing, takeoff and flight in the traffic pattern. Pilots should not rely solely on the operation of the airport beacon to indicate if weather conditions are IFR or VFR. At some locations with operating control towers, ATC personnel turn the beacon on or off when controls are in the tower. At many airports the airport beacon is turned on by a photoelectric cell or time clocks and ATC personnel cannot control them. There is no regulatory requirement for daylight operation and it is the pilot's responsibility to comply with proper preflight planning as required by 14 CFR section 91.103.