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In the case of a radio failure or
aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engine ...
not equipped with a radio, or in the case of a deaf pilot,
air traffic control Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airs ...
may use a
signal lamp Signal lamp training during World War II A signal lamp (sometimes called an Aldis lamp or a Morse lamp) is a semaphore system using a visual signaling device for optical communication, typically using Morse code. The idea of flashing dots and da ...
(called a "signal light gun" or "light gun" by the
FAA The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
) to direct the aircraft. ICAO regulations require air traffic control towers to possess such signal lamps. The signal lamp has a focused bright beam and is capable of emitting three different colours: red, white and green. These colors may be flashed or steady, and have different meanings to aircraft in flight or on the ground. 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. Air traffic control signal light guns are typically specified with a (white) center beam brightness of > 180,000 - 200,000 candela, and are visible for roughly 4 miles in clear daylight conditions. The table below describes the meaning of the signals. The use of handheld combination red/green/white signal lamps for air traffic control dates back to at least the 1930s.


References

{{Reflist Airport infrastructure Aviation communications Air traffic control Optical communications