AIM 

4/20/23 

(c) 

Radar energy that strikes dense objects will be reflected and displayed on the operator’s scope thereby 

blocking out aircraft at the same range and greatly weakening or completely eliminating the display of targets 

at a greater range. Again, radar beacon and MTI are very effectively used to combat ground clutter and weather 

phenomena, and a method of circularly polarizing the radar beam will eliminate some weather returns. A 

negative characteristic of MTI is that an aircraft flying a speed that coincides with the canceling signal of the MTI 

(tangential or “blind” speed) may not be displayed to the radar controller. 

(d) 

Relatively low altitude aircraft will not be seen if they are screened by mountains or are below the 

radar beam due to earth curvature. The historical solution to screening has been the installation of strategically 

placed multiple radars, which has been done in some areas, but ADS

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B now provides ATC surveillance in some 

areas with challenging terrain where multiple radar installations would be impractical. 

(e) 

There are several other factors which affect radar control. The amount of reflective surface of an 

aircraft will determine the size of the radar return. Therefore, a small light airplane or a sleek jet fighter will be 

more difficult to see on primary radar than a large commercial jet or military bomber. Here again, the use of 

transponder or ADS

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B equipment is invaluable. In addition, all FAA ATC facilities display automatically 

reported altitude information to the controller from appropriately equipped aircraft. 

(f) 

At some locations within the ATC en route environment, secondary

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radar

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only (no primary radar) 

gap filler radar systems are used to give lower altitude radar coverage between two larger radar systems, each 

of which provides both primary and secondary radar coverage. ADS

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B serves this same role, supplementing both 

primary and secondary radar. In those geographical areas served by secondary radar only or ADS

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B, aircraft 

without either transponders or ADS

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B equipment cannot be provided with radar service. Additionally, 

transponder or ADS

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B equipped aircraft cannot be provided with radar advisories concerning primary targets 

and ATC radar

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derived weather. 

REFERENCE

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Pilot/Controller Glossary Term

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 Radar. 

(g) 

With regard to air traffic radar reception, wind turbines generally do not affect the quality of air traffic 

surveillance radar returns for transponder and ADS

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B Out equipped aircraft. Air traffic  interference issues apply 

to the search radar and Non

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Transponder/Non

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ADS

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B Out equipped aircraft. 

NOTE

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Generally, one or two wind turbines don’t present a significant radar reception loss. A rule of thumb is three (3) or more 

turbines constitute a wind turbine farm and thus negatively affect the search radar product. 

(1) 

Detection loss in the area of a wind turbine farm is substantial. In extreme circumstances, this can 

extend for more than 1.0 nautical mile (NM) horizontally around the nearest turbine and at all altitudes above 

the wind turbine farm. (See FIG 4

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5

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2.) 

FIG 4

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5

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2 

Wind Turbine Farm Area of Potential Interference 

4

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5

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2 

Surveillance Systems