What does a segmented circle at an airport provide?

The segmented circle gathers into one ground installation the two things a pilot must know to join a pattern at an airport without a control tower. At its centre is a wind indicator — a wind sock or tetrahedron — giving direction and rough speed, which determines which runway is favoured since aircraft operate into the wind. Around it are traffic pattern indicators, L-shaped extensions positioned to show the turn direction for each runway, so a pilot can see at a glance whether a runway uses standard left traffic or non-standard right traffic. Together they let a pilot overflying the field determine both the active runway and the side of the field the pattern occupies without a single radio call. For a remote pilot planning near such a field, the same information predicts where descending aircraft will be, which is the practical reason to read it.

The segmented circle combines a central wind indicator giving direction and rough speed with traffic pattern indicators showing the turn direction for each runway.

The segmented circle houses a wind indicator at its centre and traffic pattern indicators around it, allowing pilots at non-towered airports to determine the favoured runway and the direction of pattern turns visually.

Which Runway and Which Way Round. The sock answers the first, the indicators answer the second.

Right traffic is the non-standard case worth watching for, since it places descending aircraft on the opposite side from the default assumption.

• •Reading only the wind indicator and assuming left traffic
• •Confusing the segmented circle with airspace depiction
• •Overlooking it entirely when planning near a non-towered field