What does a rotating airport beacon showing alternating white and green indicate?

2-1-8. Pilot Control of Airport Lighting
Radio control of lighting is available at selected airports to provide airborne control of lights by keying the
aircraft's microphone. Control of lighting systems is often available at locations without specified hours for
lighting and where there is no control tower or FSS or when the tower or FSS is closed (locations with a part-time
tower or FSS) or specified hours. All lighting systems which are radio controlled at an airport, whether on a single
runway or multiple runways, operate on the same radio frequency. (See TBL 2-1-1 and TBL 2-1-2.)
Airport Lighting Aids 2-1-9

 AIM 2/20/25
FIG 2-1-10
Runway Entrance Lights
FIG 2-1-11
Takeoff Hold Lights
2-1-10 Airport Lighting Aids

2/20/25 AIM
FIG 2-1-12
Taxiway Lead-On Light Configuration
TBL 2-1-1
Runways With Approach Lights
Lighting System No. of Int.
Steps
Status During
Nonuse Period
Intensity Step Selected Per No. of Mike Clicks
3 Clicks 5 Clicks 7 Clicks
Approach Lights (Med. Int.) 2 Off Low Low High
Approach Lights (Med. Int.) 3 Off Low Med High
MIRL 3 Off or Low   
HIRL 5 Off or Low   
V ASI 2 Off   
NOTES:  Predetermined intensity step.
 Low intensity for night use. High intensity for day use as determined by photocell control.
TBL 2-1-2
Runways Without Approach Lights
Lighting System No. of Int.
Steps
Status During
Nonuse Period
Intensity Step Selected Per No. of Mike Clicks
3 Clicks 5 Clicks 7 Clicks
MIRL 3 Off or Low Low Med. High
HIRL 5 Off or Low Step 1 or 2 Step 3 Step 5
LIRL 1 Off On On On
V ASI 2 Off   
REIL 1 Off Off On/Off On
REIL 3 Off Low Med. High
NOTES:   Low intensity for night use. High intensity for day use as determined by photocell control.
  The control of V ASI and/or REIL may be independent of other lighting systems.
Airport Lighting Aids 2-1-11

AIM 2/20/25
a. With FAA approved systems, various combinations of medium intensity approach lights, runway lights,
taxiway lights, V ASI and/or REIL may be activated by radio control. On runways with both approach lighting
and runway lighting (runway edge lights, taxiway lights, etc.) systems, the approach lighting system takes
precedence for air-to-ground radio control over the runway lighting system which is set at a predetermined
intensity step, based on expected visibility conditions. Runways without approach lighting may provide radio
controlled intensity adjustments of runway edge lights. Other lighting systems, including V ASI, REIL, and
taxiway lights may be either controlled with the runway edge lights or controlled independently of the runway
edge lights.
b. The control system consists of a 3-step control responsive to 7, 5, and/or 3 microphone clicks. This 3-step
control will turn on lighting facilities capable of either 3-step, 2-step or 1-step operation. The 3-step and 2-step
lighting facilities can be altered in intensity, while the 1-step cannot. All lighting is illuminated for a period of
15 minutes from the most recent time of activation and may not be extinguished prior to end of the 15 minute
period (except for 1-step and 2-step REILs which may be turned off when desired by keying the mike 5 or 3
times respectively).
c. Suggested use is to always initially key the mike 7 times; this assures that all controlled lights are turned
on to the maximum available intensity. If desired, adjustment can then be made, where the capability is provided,
to a lower intensity (or the REIL turned off) by keying 5 and/or 3 times. Due to the close proximity of airports
using the same frequency, radio controlled lighting receivers may be set at a low sensitivity requiring the aircraft
to be relatively close to activate the system. Consequently, even when lights are on, always key mike as directed
when overflying an airport of intended landing or just prior to entering the final segment of an approach. This
will assure the aircraft is close enough to activate the system and a full 15 minutes lighting duration is available.
Approved lighting systems may be activated by keying the mike (within 5 seconds) as indicated in TBL 2-1-3.
TBL 2-1-3
Radio Control System
Key Mike Function
7 times within 5 seconds Highest intensity available
5 times within 5 seconds Medium or lower intensity
(Lower REIL or REIL-off)
3 times within 5 seconds Lowest intensity available
(Lower REIL or REIL-off)
d. For all public use airports with FAA standard systems the Chart Supplement contains the types of lighting,
runway and the frequency that is used to activate the system. Airports with IAPs include data on the approach
chart identifying the light system, the runway on which they are installed, and the frequency that is used to
activate the system.
NOTE-
Although the CTAF is used to activate the lights at many airports, other frequencies may also be used. The appropriate
frequency for activating the lights on the airport is provided in the Chart Supplement and the standard instrument approach
procedures publications. It is not identified on the sectional charts.
e. Where the airport is not served by an IAP, it may have either the standard FAA approved control system
or an independent type system of different specification installed by the airport sponsor. The Chart Supplement
contains descriptions of pilot controlled lighting systems for each airport having other than FAA approved
systems, and explains the type lights, method of control, and operating frequency in clear text.