Signal square

A signal square is an aerodrome equipment internationally defined at the annex 14 of the Convention on International Civil Aviation by the International Civil Aviation Organization.^[1] It contains ground symbols to indicate visually the conditions on the aerodrome to over-flying aircraft. There are four basic signals.^[2]

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  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.
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  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.
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  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.
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  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.
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  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.
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  The right hand circuit indicator.
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  Air traffic services reporting office.
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  Closed runways or taxiways.
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  Directions for landing or take off, runway in use.
• 
  Glider flights in operation.

References