VHF omnidirectional Radio Range (VOR) is an analog navigational system used by pilots as a backup navigational aid.
VOR systems use a ground-based transmitter and a receiver on the plane to receive information.
Pilots primarily use VOR as a backup for conventional landing aids and navigational approaches like ILS.
Pilots still use VOR systems today, but they will likely be replaced with GPS systems in the future, as GPS has a better range and provides better service than VOR.
VOR systems have been used since the 1960s before GPS was even invented.
How VOR Works
VOR has a frequency range between 108.0 MHz and 117.95MHz.
The VOR emits a stationary master signal and a variable rotational signal, referred to as the ‘reference’ and ‘variable’ signals, respectively.
Aircraft have a VOR antenna, normally in their tails, that detects these signals and sends them to the cockpit.
The VOR receiver compares the difference between the VOR’s reference and variable signals to determine the plane’s position from the station.
2 Components of a VOR System
A VOR system consists of a receiver and a ground component. The ground component provides guidance to pilots.
1. Antenna and VHF
The antenna and VHF radio are the receiver components of the VOR system.
The exact receiver system differs for different aircraft but normally includes the following:
- A horizontal situation Indicator (HSI)
- An Omni-Bearing Indicator (OBI)
- A Radio Magnetic Indicator (RMI)
2. Distance Measuring Equipment (DME)
The DME informs a pilot of their plane’s distance from the VOR station.
The 3 Types of VOR
1. Terminal VOR
Terminal VORs have the smallest service volume and are typically co-located with airports.
Terminal VORs provide navigational information to the local area as far as 25 N.M. and between 1,000 to 12,000 feet above the receiver.
2. Low VOR
Low VORs provide navigational information to the local area as far as 40 N.M. and between 1,000 to 18,000 feet above the transmitter.
3. High VOR
High VORs provide a higher range but have more complex constraints.
A high VOR’s reception starts at a range of 40 N.M.s between 1,000 to 14,500 feet above the station.
A high VOR’s range extends to 100 NMs between 14,500 to 18,000 feet.
The next layer extends from 18,000 to 45,000 feet above the station and has a range of 130 NM.
Lastly, the final layer extends between 45,000 and 60,000 feet above the stations with a range of 100 NMs.
Why Pilots Use VOR
Pilots mostly use VOR over ILS when ILS isn’t available, as not all airports provide ILS approaches. Additionally, some airports that provide ILS may not provide it during bad weather, in which case pilots would use VOR.
A VOR approach may also be more convenient for a pilot than a full ILS in some cases.
Pilots also recognize that it’s beneficial to practice more than one approach.
So, sometimes pilots may use VOR just for practice.
Pilots Still Use VOR
Many pilots actively use VOR systems for landing. At the least, most pilots will use VOR as a backup navigational system for landing.
But, VORs will likely be retired soon because airplanes are increasingly being equipped with GPS receivers instead.
Environmental factors can easily disrupt VOR signals because they’re analog. Things like water tanks, buildings, and antennas could all scramble VOR signals. Also, VOR signals are less effective at higher altitudes.
Number of VOR Stations in the U.S.
The Federal Aviation Authority (FAA) operates 957 VOR systems in the continental United States.
The FAA also has another 100 non-federal VORs scattered around the country.
These 100 non-federal VORs are not needed to create a minimum operational network.
- VOR systems are analog navigational systems that pilots can use if their main navigation approaches, GPS or ILS, are unavailable.
- VOR systems involve a ground station and a receiving unit on the airplane, usually on its tail.
- Pilots primarily use VOR when their main navigation system isn’t available or when VOR is simpler.
- Both range and environmental impact limit VOR systems.
- VOR systems can’t easily transmit data at high altitudes, and their signals are vulnerable to being scrambled by environmental obstacles.
- Pilots continue to use VOR systems today, but GPS will likely replace them in the future.
- GPS systems are preferable to VOR because GPS is more accurate and doesn’t have the same limitations as VOR.