A VOR (VHF Omnidirectional Range) operates within the 108.0 to 117.95 MHz VHF band. There are three classes of VOR’s: 

1. Terminal (T) VOR’s which provide service from 1000-12,000 feet AGL at radial distances out to 25 NM. T–VORs are typically located on or adjacent to airports and are used primarily for instrument approaches.

2. Low (L) VOR's provide service from 1000-18,000 feet AGL at radial distances out to 40 NM.

3. High (H) VOR’s provide service from 1000-14,500 feet AGL at radial distances out to 40 NM. From 14,500 feet to 60,000 feet AGL they provide service out to 100 NM. Between 18,000 feet and 45,000 feet AGL their range extends out to 130 NM.

Below 18,000 feet MSL, VOR navigational aids should not be more than 80 NM apart in order to receive an adequate signal. Between 14,500 feet MSL and 17,999 feet MSL in the coterminous U.S., (H) VOR facilities should not be more than 200 NM apart.

DME

A single coded identifier with a repeat interval every 30 seconds indicates Distance Measuring Equipment (DME) is operative. If no identification is received, the facility has been taken off the air for tune-up or repair, even though intermittent or constant signals may be received. Not all VOR stations have the capability for providing distance information to aircraft equipped with DME. Aircraft receiving equipment ensures the reception of azimuth and distance information from a common source only when designated as VOR/DME, VORTAC, ILS/DME, and LOC/DME stations.

To Track inbound TO a VOR:

1. Select the VOR frequency

2. Identify the station using the Morse Code as shown on chart or the Voice Ident)

3. Check to make sure the red OFF warning flag is not displayed

4. Use the Omni-Bearing Selector (OBS) to select the desired course

5. Use the Heading Indicator (HI) to point the aircraft toward the desired course. The circle at the center of the VOR receiver will represent the aircraft and the Course Deviation Indicator (CDI) will represent the desired course; to intercept turn toward the CDI)

6. Keep the CDI centered with a TO indication to remain on course

To track outbound FROM a VOR: 

Follow the same procedure outlined above, but remain on course by keeping the CDI centered with a FROM indication.

These procedures will only work when the aircraft heading is roughly the same direction as the course selected on the OBS; otherwise the indicator will show reverse sensing. Reverse sensing occurs when the VOR needle indicates the reverse of normal operation. For example, if the aircraft is headed toward the station with a FROM indication or when the aircraft is headed away from the station with a TO indication, the CDI needle will move away from the desired course selected with the OBS; flying toward the needle will take the aircraft further away from the desired course. Also, unless the aircraft has reverse sensing capability and it is in use, when flying inbound on the back course or outbound on the front course of an ILS, reverse sensing will occur.

Procedure for determining the proper intercept angle when intercepting a VOR radial:

1. Turn to a heading that parallels the desired course—the same direction as the course to be flown 

2. Determine the difference in degrees between the radial to be intercepted and the radial on which you are located 

3. Double the difference to determine the interception angle, which will not be less than 20° nor greater than 90°

4. Rotate the OBS to the desired radial 

5. Turn to the interception heading

6. Hold this heading constant until the CDI centers, which indicates the aircraft is on course (With practice in judging the varying rates of closure with the course centerline, you learn to lead the turn to prevent overshooting the course)

7. Turn to the MH corresponding to the selected course, and follow tracking procedures inbound or outbound. (Note: steps 1 through 3 may be omitted if you turn directly to the intercept the course without initially turning to parallel the desired course.

VOR Accuracy Checks

VOR navigation is accurate to +/-1°. A full scale deflection of the CDI needle = 10 degrees off course; a half-scale deflection = 5 degrees off course. VOR accuracy may be checked by means of a VOR Test Facility (VOT), ground or airborne checkpoints, or by checking dual VORs against each other. The locations of VOTs, ground and airborne ground checkpoints are published in the Chart Supplements. To be legal for IFR flight, the accuracy of the VOR receiver must have been checked within the preceding 30 days. The person making the check must also record the date, place, and bearing error, and sign the aircraft log or other reliable record (Remember SPED: Signature, Place, Error, Date). A repair station can also make the check using a radiated test signal, but only the technician performing the test can make an entry in the logbook.

To check VOR receiver accuracy with a VOT, first tune in the VOT frequency. With the CDI centered, the OBS should read 0 degrees with a FROM indication or 180 degrees with a TO indication (Remember: "Cessna 182" for 180 TO). Allowable error is +/-4°. To use a ground checkpoint, taxi to the designated location on the airport and tune in to the VOR frequency. The CDI should center within +/-4° of the specified radial. To use an airborne checkpoint, set the OBS to the specified radial. When the aircraft is over the designated checkpoint, the CDI should center with a FROM indication. Allowable error is +/-6°. If the aircraft is equipped with dual VORs, they can be checked against each other by tuning in to the same VOR frequency and selecting the same radial. The CDI needles must not vary by more than 4°.