out straighter in strong winds and tends to move back and  forth when the wind is gusting. Wind tees and tetrahedrons  can swing freely and align themselves with the wind direction.  Since a wind tee or tetrahedron can also be manually set to  align with the runway in use, a pilot should also look at the  wind sock for wind information, if one is available.  At airports without an operating control tower, a segmented  circle visual indicator system ,  if installed, is designed to  provide traffic pattern information.  [Figure 14-38]  Usually  located in a position affording maximum visibility to pilots in  the air and on the ground and providing a centralized location  for other elements of the system, the segmented circle consists  of the following components: wind direction indicators,  landing direction indicators, landing strip indicators, and  traffic pattern indicators.  A tetrahedron is installed to indicate the direction of landings  and takeoffs when conditions at the airport warrant its use.  It may be located at the center of a segmented circle and  may be lighted for night operations. The small end of the  tetrahedron points in the direction of landing. Pilots are  cautioned against using a tetrahedron for any purpose other  than as an indicator of landing direction. At airports with  control towers, the tetrahedron should only be referenced  when the control tower is not in operation. Tower instructions  supersede tetrahedron indications.  Landing strip indicators are installed in pairs and are used to  show the alignment of landing strips.  [Figure 14-38]  Traffic  pattern indicators are arranged in pairs in conjunction with  landing strip indicators and used to indicate the direction of  turns when there is a variation from the normal left traffic  pattern. (If there is no segmented circle installed at the airport,  traffic pattern indicators may be installed on or near the end  of the runway.)  It is important for a pilot to know the direction of the wind. At  facilities with an operating control tower, this information is  provided by ATC. Information may also be provided by FSS  personnel either located at a particular airport or remotely  available through a remote communication outlet (RCO), or  by requesting information on a CTAF at airports that have the  capacity to receive and broadcast on this frequency.  When none of these services is available, it is possible  to determine wind direction and runway in use by visual  wind indicators. A pilot should check these wind indicators  even when information is provided on the CTAF at a given  airport because there is no assurance that the information  provided is accurate.  The wind direction indicator can be a wind cone, wind sock,  tetrahedron, or wind tee. These are usually located in a central  location near the runway and may be placed in the center  of a segmented circle, which identifies the traffic pattern  direction if it is other than the standard left-hand pattern.  [Figures 14-37  and  14-38]  At most airports and military air bases, traffic pattern altitudes  for propeller-driven aircraft generally extend from 600 feet  to as high as 1,500 feet above ground level (AGL). Pilots  can obtain the traffic pattern altitude for an airport from the  Chart Supplement U.S. (formerly Airport/Facility Directory).  Also, traffic pattern altitudes for military turbojet aircraft  sometimes extend up to 2,500 feet AGL. Therefore, pilots of  en route aircraft should be constantly on alert for other aircraft  in traffic patterns and avoid these areas whenever possible.  When operating at an airport, traffic pattern altitudes should  be maintained unless otherwise required by the applicable  distance from cloud criteria according to Title 14 of the Code  of Federal Regulations (14 CFR) part 91, section 91.155.  Additional information on airport traffic pattern operations  The wind sock is a good source of information since it not  only indicates wind direction but allows the pilot to estimate  the wind velocity and/or gust factor. The wind sock extends  14-20  Wind Direction Indicators  Figure 14-36.  Takeoff Hold Lights (THL).  Figure 14-35.  Runway Entrance Lights (REL).  Traffic Patterns 