Figure 5-17 -- Examples of off-centered PPI scope.
Remember that bearing and range information are relative to the main bang on the off-
centered scope just as in a normal-centered presentation. It is very simple to obtain
bearing information when you use the centered scope. In the center of the surrounding
compass rose is the main bang. It may be used as a reference point until you become
more familiar with bearing information. Because off-centering displaces the main bang
from the center of the compass rose, imagine a 360-degree compass rose surrounding
the main bang wherever you have placed it on the scope.
Precision Approach RADAR Indicator (OJ-333)
The precision approach RADAR indicator OJ-333 displays azimuth, elevation, and
range information and enables the controller to closely observe aircraft position during
the approach. The indicator used for this presentation is called the AZ-EL indicator for
azimuth and elevation. The elevation presentation appears on the upper portion of the
display and the azimuth on the lower portion. On the elevation portion, a bright line
indicates the glide path. On the azimuth portion, a bright line indicates the runway
course line. The bright lines are commonly called cursors. In addition to these cursors,
range marks are also electronically traced on the AZ-EL indicator. These range marks,
occurring at one-mile intervals, are spaced in logarithmic relationship. The first mile from
touchdown on the display occupies a greater distance than the second mile, and so
forth. This has the effect of expanding the display as the aircraft approaches the runway
and provides the controller with increasingly precise indications of the aircraft's flight
path (see Figure 5-18).