The VOR Radio System
About The VOR Systems
The abbreviation, VOR, stands for Variable Omnidirectional Radio system, sometimes called VHF Omnidirectional Range...I prefer to use the first definition. Once we understand a little bit about how the VOR system works, these instruments are invaluable in helping us to find airports we cannot see with the eye. Components required for a functional VOR system are shown below:
Some aircraft are equipped with two VOR systems, and they work exactly the same, with the exception that VOR-1 may have Glideslope capabilities. The purpose for dual systems is so that you can view two stations simultaneously...perhaps Nav-1 is tuned to an ILS runway, and Nav-2 is tuned to a local VOR station. Or perhaps you want to monitor two different VOR stations to get a "positional fix" of your exact location (we'll do this later on). The beauty of VOR is that neither one cares what you tune in: You can tune VOR-2 to an ILS runway, and it will track the Localizer just fine; although VOR-2 does not have Glideslope capability for and ILS approach.
How Does The VOR System Work?
From the picture above, we see that a VOR system is comprised of a radio station positioned at an airport, and instruments in the aircraft which intercept and interpret those radio signals and present the results to us in a format that's meaningful for navigation. You've probably gathered from other discussions here that we pilots deal primarily with two types of radio navigation systems: Directional, and non-directional. Recall that the ADF system is non-directional and that signals are sent out from the station tower in all directions at once...much the same concept as a light bulb sends out light-beams in all directions at once. ADF is indeed a very powerful navigation tool, but without directional capabilities, ADF cannot point you at the airport from (or to) a specific direction. While just getting to the airport is fine in some cases, in other instances we want to be aligned with the runway, or perhaps we wish to approach the airport from a specific direction for other reasons. Thus, we have VOR, which allows us to do just that!
In order to establish controlled and consistent directional capabilities, the VOR station located at an airport emits a unique signal for each of the 360-degree points of a full circle, and we'll call each of these unique signals a VOR Radial. Note in the picture below that the 270-degree radial is actually on the opposite (90-degree) side of the station, which brings us to the issue of TO/FROM; something we have to deal with in using VORs. Let's clear that up quickly and easily: It's possible (and sometimes necessary) to fly outbound FROM the station on an INBOUND radial...for example, I could fly to the East on that 270-degree radial. But generally we fly TO the VOR station on an inbound radial, and they are setup with that in mind. In the picture below, if I wanted to approach the airport TO THE WEST, I'd fly inbound on the 270-degree radial.
Range Of A VOR Station
The range of reception for a VOR station is subject several variables: Weather, terrain, aircraft altitude, and transmission power of the station itself. VORs can be picked up as far away as 175 miles or more, and some work only within a 50-mile range, or so. Remember that VOR stations are essentially line-of-sight communications, so it may be necessary to increase altitude to reach that desired station.
Does Every VOR Station Include DME?
No...most do, but many do not include DME (Distance Measuring Equipment) capability. This will be defined in the Airport Information for that airport, and will show VOR or VOR/DME.