A signal square is an

aerodrome An aerodrome (Commonwealth English) or airdrome (American English) is a location from which aircraft flight operations take place, regardless of whether they involve air cargo, passengers, or neither, and regardless of whether it is for publ ...

equipment internationally defined at the annex 14 of the

Convention on International Civil Aviation The Convention on International Civil Aviation, also known as the Chicago Convention, established the International Civil Aviation Organization (ICAO), a specialized agency of the United Nations charged with coordinating international air trave ...

by the

International Civil Aviation Organization The International Civil Aviation Organization (ICAO, ) is a specialized agency of the United Nations that coordinates the principles and techniques of international air navigation, and fosters the planning and development of international sc ...

. It contains ground symbols to indicate visually the conditions on the aerodrome to over-flying aircraft. There are four basic signals. Prohibition-of-landing.gif, A horizontal red square panel with yellow diagonals when displayed in a signal area indicates that landings are prohibited and that the prohibition is liable to be prolonged. Need-for-special-precautions-while-approaching-or-landing.gif, A horizontal red square panel with one yellow diagonal when displayed in a signal area indicates that owing to the bad state of the manoeuvring area, or for any other reason, special precautions must be observed in approaching to land or in landing. Use-of-runways-and-taxiways-01.gif, A horizontal white dumb-bell when displayed in a signal area indicates that aircraft are required to land, take off and taxi on runways and taxiways only. Use-of-runways-and-taxiways-02.gif, The horizontal white dumb-bell but with a black bar placed perpendicular to the shaft across each circular portion of the dumb-bell when displayed in a signal area indicates that aircraft are required to land and take off on runways only, but other manoeuvres need not be confined to runways and taxiways. Directions-for-landing-or-take-off-01.gif, The landing T, showing the wind direction on an all-over landing field with the tail of the T pointing downwind. On airfields with runways it indicates the landing and take-off direction. Right-hand-traffic.gif, The right hand circuit

indicator Indicator may refer to: Biology * Environmental indicator of environmental health (pressures, conditions and responses) * Ecological indicator of ecosystem health (ecological processes) * Health indicator, which is used to describe the health ...

. Air-traffic-services-reporting-office.gif, Air traffic services reporting office. Closed-runways-or-taxiways.gif, Closed runways or taxiways. Directions-for-landing-or-take-off-02.gif, Directions for landing or take off, runway in use. Glider-flights-in-operation.gif, Glider flights in operation.

References

Air traffic control {{aviation-stub