Segmented Circle

Airports · 2 min read · Apr 02, 2022
Segmented circle

A segmented circle is a basic visual indicator system for pilots designed to provide information regarding traffic patterns. This method of indication is used by pilots from the ground and in the air at airports with no air traffic control services. Most airports in the world are unequipped with air traffic control services, there are 20000 uncontrolled airports in the US alone.

Components of the segmented circle

Components of a segmented circle include a wind direction indicator, landing runway indicators, a landing strip indicator, and traffic pattern indicators installed on it. Wind direction and speed are determined by a windsock placed inside a segmented circle. Instead of windsocks, tetrahedrons are also used for a similar purpose at a few smaller airports. However, tetrahedrons are uncommon, and tower instructions take precedence over them.

An illustration of the components of a segmented circle.
Image source:

Traffic pattern indicators

Landing runways and traffic patterns are identified on the circle by symbolizing landing paths i.e. left or right-hand paths. At aerodromes without a functioning control tower, a system of visual indicators is used to provide traffic pattern information. Segmented circles are usually made up of steel boxes that are coated in white powder. Tubes are expanded to create the shape of a circle while the area of the circle depends upon the requirements of a particular airport. It is located in a position affording maximum visibility to pilots in the air and on the ground.

Traffic pattern information

Segmented circles are important for remote and smaller airports that do not support a sophisticated air traffic control system. It enables a uniform approach and, take-off paths to avoid collision and traffic conflict.

An airport segmented circle is usually placed at the center of the airport so that it is visible to pilots from an adequate distance. The panels form a circle that has extensions on its side, these extensions represent runways and the direction of the flight pattern is nonstandard. The L shape extension on the left means aircraft will follow the left turn while landing and take-off. A wind direction and speed indicator are placed in the center of the circle, this wind indicator is placed such that pilots can observe and indicate wind direction according to the runway. Airports with lightning systems contain a segmented circle with floodlights on top for night flying operations.


What is a segmented circle?

It is a visual identification system for pilots that provide information regarding traffic pattern, wind direction, and speed. Such systems are used at uncontrolled airports to maintain uniform flight operations without the aid of ATC.

How do you read an airport segmented circle?

An airport segmented circle consists of a windsock surrounded by a circle, the wing cone defines the landing direction for pilots as the aircraft will always land in the direction of the wind. Around the circle there are traffic pattern indicators in the shape of the symbol L, these provide information regarding landing and takeoff paths on the runway.

What can you see inside a segmented circle?

It provides useful information to pilots in an uncontrolled airport regarding flight pattern, wind direction, and, wind speed. A pilot observing a segmented circle from the sky will identify the runway and correct traffic patterns by looking into a segmented circle. A segmented circle includes a runway complex, a wind direction indicator, and, a traffic pattern indicator in the form of an L shape. Runway numbers are not identified on the circle and usually, it is mounted for the adjacent runway.

What is a Landing Strip Indicator?

The L-shape symbols on the segmented circle identify the traffic pattern of the runway. on this symbol, there is one short leg and one long leg of the letter L. The longer leg of the L symbolizes the end of a runway’s approach. The traffic pattern indicators are the short sides at the bottom of the L-shaped symbols that represent the base leg.

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Aeroclass Team
A team of professionals with a deep passion for the aviation industry bringing you the newest and the most striking industry-related news and content.

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