Do you remember the service limits of a VOR? How about how to avoid reverse-sensing? Here's what you need to know about how VORs work for your next flight.

What Exactly Is A VOR Station?

A VHF Omni Directional Range Radio (VOR) is the most common ground-based navigational aid (NAVAID) you'll use. VOR navigation allows your to fly point to point along established airways between VORs. Here's what a VOR station looks like:

While some VORs are being slowly phased out by the FAA, there are still hundreds of VOR stations around the country. They're valuable sources of position information for cross country flights, instrument approach procedures, and if you get lost, they can help you quickly pinpoint your position.

How VORs Work

The frequency range for a VOR is between 108.0 MHz and 117.95 MHz. Every VOR is oriented to magnetic north (more on this in a bit), and emits 360 radials from the station. The VOR sends out one stationary master signal, and one rotating variable signal. These are also called "reference" and "variable" phases.

An aircraft's VOR antenna, which is usually located on the tail, picks up this signal and transfers it to the receiver in the cockpit. The aircraft's VOR receiver compares the difference between the VOR's variable and reference phase, and determines the aircraft's bearing from the station. This bearing is the radial that the aircraft is currently on.

Most VORs have distance measuring equipment (DME) or tactical air navigation equipment (TACAN) installed within the VOR station. When a VOR is collocated with DME, it's labeled as "VOR-DME." On the other hand, when a VOR is collocated with a TACAN, it's called a VORTAC. You can find them charted on VFR Sectional Charts, IFR Low Charts, IFR High Charts, SIDs, STARs, and Instrument Approaches. Here's what VOR symbols look like:

The vast majority of VORs have DME, and when they do, you can tell how far you are from the station by using a readout display in your cockpit.

Know Your Service Volumes

VORs are limited to line-of-sight. Obstacles, terrain, and even the slope of the earth interfere with VOR signals. There's no restriction on how many airplanes can use a single VOR simultaneously. There are three classes of VORs: Terminal (T), Low (L), and High (H). You can look your VOR up in the FAA Chart Supplement to determine what category it is.

The farther away you are from a VOR, the higher you need to fly to get signal reception. This is why VOR service volumes have a slope at the lowest altitude, to account for terrain and curvature of the earth.

Even though VORs have been around since the 1940s, they're not going away anytime soon.