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SEGMENTED CIRCLES & TRAFFIC PATTERNS



Pilots need to learn the traffic rules, traffic procedures, traffic pattern layouts including the basic rectangular pattern in use at airports, and to be able to make proper approaches and departures from most airports, regardless of whether or if they have a control tower or not. Should know how to interpret the airport visual markings and signs that may be encountered.


Compliance with basic rectangular traffic patterns and traffic rules reduces the possibility on the ground or in the air conflicts, as well as reducing the probability of a midair collision.


The airport visual markings and types of traffic patterns used at airports are:

  • Segmented Circle

  • Traffic patterns


Segmented Circle

Non-towered airports which do not have any ATC communication, have a segmented circle visual indicator system, if any are installed. This are used to provide traffic pattern information to approaching aircraft. Segmented circles are placed in a highly visible location that can be seen from the air and on the ground.


Segmented circles are made up of:

  • Wind direction indicator (windsock, wind tee or Tetrahedron)

  • Landing runway/strip indicators

  • Traffic pattern indicators

Traffic pattern indicators are installed in pairs and are used to show the direction of the turns when there is a variation from the standard left traffic pattern.



How do we determine which runway to use?

When approaching the airport look to see what direction the wind is blowing via the windsock. Then determine which runway and traffic pattern should be used by looking at the runway and traffic pattern indicators. Always land and takeoff into the wind.


In the example below, the wind is blowing from the west per the windsock. With that said, the landing traffic pattern is right traffic to land on runway 27 into the wind.


If there is not a segmented circle at the airport, traffic pattern indicators may be installed on or near the end of the runway.




Traffic Patterns

A traffic pattern is a rectangular course around the airport. There are 5 parts to the traffic pattern you need to know.

  • Departure or Upwind

  • Crosswind

  • Downwind

  • Base

  • Final

Remember, a standard traffic pattern is left traffic.


Downwind

The downwind leg, is the most important leg, it is a course flown parallel to the landing runway, but in a direction opposite to the intended landing direction. This leg is flown approximately 1/2 to 1 mile out from the landing runway and at the specified traffic pattern altitude.

  • Complete all before-landing checks and extend the landing gear if applicable.

  • Maintain pattern altitude until at least abeam the approach end of the landing runway. At the abeam point begin reducing the power and begin a descent while continuing down the downwind leg. At approximately 45⁰ from the approach end, begin the turn on the base leg.



At most airports including military bases the traffic pattern altitude for piston aircraft is 1,000 feet above the airport elevation. Traffic pattern altitude for any airport can be found in the Chart Supplement U.S. book. When entering a traffic pattern there are a few ways to do it:

  • Towered Airports

  • Non-towered Airports

Towered Airports:

When operating at a towered or controlled airport in the traffic pattern the traffic pattern altitude (TPA) should be maintained unless otherwise directed by ATC. The tower controller can instruct pilots to enter the traffic pattern at any point or to make a straight-in approach without flying the usual rectangular pattern.


Pilots may deviate from an ATC instruction in an emergency but must advise ATC for the deviation as soon as possible.



Non-towered Airports:

At non-towered airports pilots should enter the traffic pattern at pattern altitude. When flying at non-towered pilots need to always use situational awareness, scan for other aircraft. As a safe pilot always make it a habit to announce your position and intentions.


There are a few different ways to enter the traffic pattern depending on the direction of arrival.

The preferred way to enter the pattern is to fly on a 45-degree angle to the downwind leg and join the pattern at midfield. When crossing midfield to enter the traffic pattern, cross over midfield 500 feet above traffic pattern altitude. For an example if the traffic pattern altitude is 1,000 feet above ground level (AGL), then cross over at 1,500 feet.


However, if large or turbine aircraft operate at the airport, remain 2,000 feet AGL so there is no conflict with their traffic pattern.


The other method is to enter the pattern is to cross midfield at pattern altitude, again always scanning for other traffic and announcing your position and intentions. Then turn to the downwind leg. Always, give way to aircraft on the 45-degree leg, and aircraft already established on the downwind leg.


When two or more aircraft are approaching an airport for the purpose of landing, the aircraft at the lower altitude has the right-of-way. This doesn't mean that you can just cut off someone that is on final approach.


Keep in mind that both of these traffic pattern entries are not just for non-towered airports, they may be used at towered airports if ATC instructs you to do it.




Remember:

Standard traffic pattern is left traffic.


Parts of a traffic pattern:

  • Departure or Upwind

  • Crosswind

  • Downwind

  • Base

  • Final

Traffic pattern altitude (TPA) for piston aircraft is recommended 1,000 feet AGL above airport elevation, unless otherwise established.


Turbojet aircraft the TPA is 1,500 feet AGL above airport elevation and extend up to 2,500 feet AGL, unless otherwise established.

​Scan for other traffic, announce your position and intentions.


Right-of-way - Are aircraft that are established on the 45-degree leg or on downwind leg. The aircraft that is at the lower altitude, or any aircraft that is in an emergency situation.



References:

Part 91.155


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