Radio is the primary way that pilots communicate with air traffic control and with other aircraft.
Radio in various forms and using different frequencies is widely used in aviation for aircraft to communicate with each other and with air traffic control or other ground stations. Most voice communication is either VHF, HF, or UHF:
- VHF (Very High Frequency) communication uses a dedicated band of frequencies from 118 through 137 megahertz (MHz), in a region of the spectrum known as the airband (which also includes an adjacent range of frequencies from 108 through 117.95 MHz used by vor stations for radio-navigation purposes, as well as for the localizer portion of an ils system). Most radio traffic to and from civilian aircraft is VHF, except over the oceans or in extremely remote or mountainous areas (VHF transmissions are line-of-sight, meaning that they cannot, under normal circumstances, be used to communicate with stations or aircraft beyond the horizon). A dedicated emergency, or "guard", channel exists at 121.5 MHz.
- HF (High Frequency) communication uses a number of frequency bands scattered throughout the portion of the spectrum from 2 to 30 MHz. Unlike VHF transmissions, transmissions in the HF bands reflect off the Earth's upper atmosphere, making them useful for communicating with aircraft or ATC facilities beyond the horizon. Like the VHF band, the HF bands include a guard channel, located at 2.182 MHz.
- UHF (Ultra High Frequency) communication uses a dedicated band from 225 MHz through 400 MHz, and is used almost exclusively by military aircraft (as the higher frequency of the signal allows the use of smaller and lighter transmitters, making it easier to set up an ATC station in the field), who use it for the same purposes for which civilian aircraft use VHF; it is legal, in most countries, to install a UHF radio in a civilian aircraft, but there is little point in doing so unless you're planning to talk to military aircraft. The main civilian use of this UHF band is for ILS glideslope transmitters, which are not generally used, or useful, for voice communications. The UHF guard channel is located at 243 MHz.
Other frequencies may also be used for voice and/or data transmissions.
Light aircraft are typically equipped only for voice communication; airliners and other larger aircraft frequently have telemetry systems that provide data links to the ground. Some countries may require pilots to have a specific license and/or training before being allowed to use aircraft radio transmitters.
Use this tag for all questions about radio communication systems on board aircraft, including topics like frequencies, radio procedures, equipment, phraseology and so on. It may also be appropriate for questions about ground-based radio navigation aids like VORs; those questions should usually be tagged navigation (or, if one exists, the tag for the specific type of navaid - for instance, vor), but in some cases both tags may be useful (e.g. voice communication over a VOR).
For more information, see the Wikipedia articles on: