Page 146 - Planning and Design of Airports

Air Traf fic Management 115

FIGURE 3-9 Automatic direction fi nder.

Very High Frequency Omnirange Radio
The advances in radio and electronics during and after World War II
led to the installation of the very high frequency omnirange (VOR)
radio stations. These stations are located on the ground and send out
radio signals in all directions. Each signal can be considered as a
course or a route, referred to as a radial that can be followed by an
aircraft. In terms of 1° intervals, there are 360 courses or routes that
are radiated from a VOR station, from 0° pointing toward magnetic
north increasing to 359° in a clockwise direction. The VOR transmit-
ter station is a small square building topped with what appears to be
a white derby hat. It broadcasts on a frequency just above that of FM
radio stations. The very high frequencies it uses are virtually free of
static. The system of VOR stations establish the network of airways
and jet routes and are also essential to area navigation. The range of a
VOR station varies but is usually less than 200 nm. A typical VOR
beacon is illustrated in Fig. 3-10.
Aircraft equipped with a VOR receiver in the cockpit have a dial
for tuning in the desired VOR frequency. A pilot can select the VOR
radial or route he wishes to follow to the VOR station. In the cockpit
there is also an omnibearing selector (OBS) which indicates the head-
ing of the aircraft relative to the direction of the desired radial and
whether the aircraft is to the right or left of the radial. An illustration
of an OBS is provided in Fig. 3-11.

Distance Measuring Equipment
Distance measuring equipment (DME) has traditionally been installed
at VOR stations in the United States. The DME shows the pilot the