Very High Frequency Omnidirectional Range. That's what a VOR is. It is a navigation station that operates in the frequency range between 108.00 and 117.95 megaHertz. It is used for aeronautical navigation only and some can reach great distances.

The VOR transmits a signal in a resolution of 360 degrees, or one signal for every degree of azimuth. These are called "radials", much like spokes on a wheel. VORs are used for determining the Victor airways (low altitude airways) and the Jet Routes (high altitude airways) and for point-to-point navigation. 

They are also used for determining fixes, waypoints, and intersections on charted routes, for station-to-station navigation, and for non-precision approaches. This is the backbone of the air navigation system in the US.

Coupled with TACAN, a VOR can provide distance measurements to pilots. A TACAN is a Tactical Air Navigation system operated by the military which is of greater accuracy than the VOR. Only the distance measuring capabilities of TACAN are available for civilian use. A VOR/TACAN combination is known as a VORTAC.

The VOR can be accessed by dialing the proper frequency in a navigation radio. The VOR readout, called a "VOR head", is shown in figure 1 below. Notice the azimuth card and the cross hairs inside the bezel. The azimuth card is that circle with the heading numbers and N,S,E and W on it. It rotates when you turn the OBS (Omni Bearing Selector) knob.

A single VOR is shown in figure 2. This is the normal depiction of the secondary navigation radio.

When the VOR is coupled with an Instrument Landing System (ILS) as in figure1, the heavy horizontal line shown at a slant, provides glide slope or vertical guidance. The heavy vertical line or localizer needle provides horizontal guidance when tuned to a VOR/Localizer station. There is also a window with a "TO/FROM" flag that indicates the direction of flight.

Fig 3

Figure 3 above shows an instrument panel. Figure 4 below shows the instrument cluster. The instrument outlined by the yellow box is the VOR. The Instrument outlined by the red box is a Horizontal Situation Indicator or HSI. The HSI combines a Directional Gyro (DG) and VOR1 for an all-in-one instrument.

Fig 4

The images shown here depict a triangular type (arrow) TO/FROM flag. In the HSI it can be seen slightly to the right and above the horizontal line. In the VOR it is shown at the bottom center, right next to the word "Nav" in figure 4.

The VOR signal follows a line-of-sight path, that is, it won't go through mountains or buildings. So, there is a necessity to switch VOR stations when flying through mountainous terrain or when there is terrain obscuration. These requirements are usually noted in the aviation charts.

Notice in figure 3 that the vertical needle (localizerneedle) is deflected to the right. This indicates that the VOR radial is to the right of the airplane. The needle always points to the radial. The pilot would have to make a right turn to intercept the radial and line up with it.

If a new radial was desired to be flown from the present location directly to the station, the pilot would turn the Omni Bearing Selector (OBS - the azimuth knob) in the direction of the needle to center it. Once the needle centers with the OBS having a "TO" flag the pilot reads the heading indicated on the OBS, then he turns the aircraft to that heading.

This is a very simple explanation of the VOR receiver. In the next articles we will discuss how to intercept a given radial and how to navigate with the VOR.

Happy flying.

Jim Ramos