In the case of a radio failure or aircraft not equipped with a radio, or in the case of a deaf pilot, air traffic control may use a signal lamp (called a "signal light gun" or "light gun" by the FAA[1][2]) to direct the aircraft. ICAO regulations require air traffic control towers to possess such signal lamps.[3][4] The signal lamp has a focused bright beam and is capable of emitting three different colors: red, white and green.[5][6] These colors may be flashed or steady, and have different meanings to aircraft in flight or on the ground.[5][2][7] Planes can acknowledge the instruction by rocking their wings, moving the ailerons if on the ground, or by flashing their landing or navigation lights during hours of darkness.[6][7] Air traffic control signal light guns are typically specified with a (white) center beam brightness of > 180,000 - 200,000 candela,[1][8][9] and are visible for roughly 4 miles in clear daylight conditions.[9][10][11] The table below describes the meaning of the signals.[5][2][7] The use of handheld combination red/green/white signal lamps for air traffic control dates back to at least the 1930s.[12]
| Signal | Aircraft in flight | Aircraft on the ground | Ground vehicles or personnel |
|---|---|---|---|
| Flashing white | ICAO – Land at this airport and proceed to apron (this is not a clearance to either land or taxi. Clearances to land and taxi will follow.) FAA – Not applicable |
Return to starting point on airport | Return to starting point on airport |
| Steady green | Cleared to land | Cleared for takeoff | Cleared to cross, proceed or go |
| Flashing green | Return for landing | Cleared to taxi | Not applicable |
| Steady red | Give way to other aircraft and continue circling | STOP | STOP |
| Flashing red | Airport unsafe, do not land | Taxi clear of the runway in use | Clear the taxiway/runway |
| Alternating red and green | Exercise extreme caution | Exercise extreme caution | Exercise extreme caution |
See also
References
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