Aviation light signals

{{Short description|Use of visible electromagnetic radiation to conduct air traffic control}}

File:Air Traffic Control Journeyman, SENIOR AIRMAN Bryan Greenwood of the 86th Operation Support Squadron does a maintenance check on a light gun which allows planes to land safely if th - DPLA - 8ade36e34b217823f71235bfe18c36c2.jpeg airman with a signal light gun that can be used to control aircraft with radio failure.]]File:Signal Light Gun Hulbert Field.jpg

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{{cite web |title=TBL 4-3-1, Airport Traffic Control Tower Light Gun Signals |url=https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap4_section_3.html#TBL_4_3_1 |website=Section 3. Airport Operations |publisher=Federal Aviation Administration |accessdate=12 May 2019}}) to direct the aircraft. ICAO regulations require air traffic control towers to possess such signal lamps.{{cite book |title=Aerodromes: Volume I Aerodrome Design and Operations |date=July 2013 |publisher=International Civil Aviation Organization |page=8-2 |edition=6th}}{{cite book |title=Civil Aviation Regulations (CAR 001 – Aerodrome Standards & Certification Regulations) 2018 |date=April 19, 2018 |publisher=Kingdom of Bahrain Ministry of Transportation and Telecommunications |page=68 |url=http://www.transportation.gov.bh/sites/default/files/car001_2018_0.pdf |access-date=May 12, 2019 |archive-date=September 25, 2020 |archive-url=https://web.archive.org/web/20200925233159/http://transportation.gov.bh/sites/default/files/car001_2018_0.pdf |url-status=dead }} The signal lamp has a focused bright beam and is capable of emitting three different colors: red, white and green.{{cite web |title=4-3-13. Traffic Control Light Signals |url=https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap4_section_3.html |website=Section 3. Airport Operations |publisher=Federal Aviation Administration |accessdate=12 May 2019}} These colors may be flashed or steady, and have different meanings to aircraft in flight or on the ground.{{cite web |title=3. SIGNALS FOR AERODROME TRAFFIC |url=https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=celex:32012R0923 |website=EUR-Lex |publisher=European Union |accessdate=12 May 2019}} 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,{{cite book |last1=Federal Aviation Administration |title=Gun, Signal Light, Portable, FAA-E-2214a Amendment-2 |date=July 5, 1973 |publisher=Department of Transportation |page=5 |url=https://faaco.faa.gov/index.cfm/attachment/download/22930 |accessdate=30 Apr 2017 |archive-url=https://web.archive.org/web/20170430215936/https://faaco.faa.gov/index.cfm/attachment/download/22930 |archive-date=30 April 2017 |url-status=live}}{{cite book |title=Light, Airport Traffic Control, SDU-4/U, MIL-DTL-25971D |date=February 18, 2015 |publisher=Department of Defense |page=7 |url=http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=18207 |accessdate=12 May 2019 |archive-date=12 May 2019 |archive-url=https://web.archive.org/web/20190512011611/https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=18207 |url-status=dead }}{{cite web |last1=MICC Fort Rucker |title=58--Tower Signal Light Guns |url=https://www.usaopps.com/government_bids/detail/ADP14422440980000347.htm |website=USAOPPS |accessdate=12 May 2019}} and are visible for roughly 4 miles in clear daylight conditions.{{cite web |title=Signal Light Gun |url=http://atiavionics.com/ |publisher=ATI Avionics, Inc. |accessdate=12 May 2019}}{{cite web |title=LED Signal Light Gun |url=http://www.signallightgun.com/ |publisher=PPS Technical |accessdate=12 May 2019}} The table below describes the meaning of the signals.{{cite book |title=Rules of the Air: Annex 2 to the Convention on International Civil Aviation|date=July 2005 |publisher=International Civil Aviation Organization |page=APP 1–3 |edition=10th |url=http://www.icao.int/Meetings/anconf12/Document%20Archive/an02_cons%5B1%5D.pdf |accessdate=12 May 2019}} The use of handheld combination red/green/white signal lamps for air traffic control dates back to at least the 1930s.{{cite book |last1=Harding |first1=W |title=US Patent 2,085,020 Combination Sight and Indicator for Traffic Control Projectors |date=June 29, 1937 |publisher=USPTO |url=https://patents.google.com/patent/US2085020A/en |accessdate=13 May 2019}}

class="wikitable"
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

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