36. Use of Visual Clearing Procedures
36.1 Before Takeoff. Prior to taxiing onto a runway or landing area in preparation for takeoff, pilots should scan the approach areas for possible landing traffic, executing appropriate clearing maneuvers to provide them a clear view of the approach areas.
36.2 Climbs and Descents. During climbs and descents in flight conditions which permit visual detection of other traffic, pilots should execute gentle banks, left and right at a frequency which permits continuous visual scanning of the airspace about them.
36.3 Straight and Level. Sustained periods of straight and level flight in conditions which permit visual detection of other traffic should be broken at intervals with appropriate clearing procedures to provide effective visual scanning.
36.4 Traffic Patterns. Entries into traffic patterns while descending create specific collision hazards and should be avoided.
36.5 Traffic at VOR Sites. All operators should emphasize the need for sustained vigilance in the vicinity of VORs and airway intersections due to the convergence of traffic.
36.6 Training Operations. Operators of pilot training programs are urged to adopt the following practices:
36.6.1 Pilots undergoing flight instruction at all levels should be requested to verbalize clearing procedures (call out, “Clear” left, right, above, or below) to instill and sustain the habit of vigilance during maneuvering.
36.6.2 High.wing Airplane. Momentarily raise the wing in the direction of the intended turn and look.
36.6.3 Low.wing Airplane. Momentarily lower the wing in the direction of the intended turn and look.
36.6.4 Appropriate clearing procedures should precede the execution of all turns including chandelles, lazy eights, stalls, slow flight, climbs, straight and level, spins, and other combination maneuvers.
37. Surveillance Systems
37.1 Radar
37.1.1 Capabilities
37.1.1.1 Radar is a method whereby radio waves are transmitted into the air and are then received when they have been reflected by an object in the path of the beam. Range is determined by measuring the time it takes (at the speed of light) for the radio wave to go out to the object and then return to the receiving antenna. The direction of a detected object from a radar site is determined by the position of the rotating antenna when the reflected portion of the radio wave is received.
37.1.1.2 More reliable maintenance and improved equipment have reduced radar system failures to a negligible factor. Most facilities actually have some components duplicated . one operating and another which immediately takes over when a malfunction occurs to the primary component.
37.1.2 Limitations
37.1.2.1 It is very important for the aviation community to recognize the fact that there are limitations to radar service and that ATC controllers may not always be able to issue traffic advisories concerning aircraft which are not under ATC control and cannot be seen on radar. (See FIG ENR 1.1.23).
FIG ENR 1.1.23
Limitations to Radar Service
Precipitation Attenuation
The nearby target absorbs and scatters so much of the out-going and returning energy that the radar does not detect the distant target.
Federal Aviation Administration Twentieth Edition
a) The characteristics of radio waves are such that they normally travel in a continuous straight line unless they are:
1) “Bent” by abnormal atmospheric phenomena such as temperature inversions.
2) Reflected or attenuated by dense objects such as heavy clouds, precipitation, ground obstacles, mountains, etc.
3) Screened by high terrain features.
b) The bending of radar pulses, often called anomalous propagation or ducting, may cause many extraneous blips to appear on the radar operator’s display if the beam has been bent toward the ground, or may decrease the detection range if the wave is bent upward. It is difficult to solve the effects of anomalous propagation, but using beacon radar and electronically eliminating stationary and slow moving targets by a method called moving target indicator (MTI) usually negate the problem.
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 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.
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