Air band or avionic radios are used in aviation as for both navigation and two way communication. If you are into aviation, you probably already know how important it is to have a radio while in the air.
Air Band Basics
Air Band radios use VHF frequencies in the 108 MHz - 137 MHz range. VHF air band channels are different than those used for land based radios and are specifically allotted by the FCC for use in avionics. In addition to the VHF channels, trans-oceanic aircraft may use HF frequencies as well. But that's another topic for another time. For now, we will focus exclusively on VHF.
VHF provides optimal coverage in open spaces with a clear line of sight. Since air band radio transmissions primarily occur in the air or air to ground from high altitudes, range will generally be much greater than land-based radios. This means typical 5 watt handheld airband radios in flight will reach considerably farther than typical 5 watt UHF or VHF radios communicating ground to ground. Panel mounted NAV/COM airband radios around 8 watts can go even farther.
Air band is divided into COM and NAV channels. COM channels use the higher end of the band and are programmed to frequencies used specifically for voice communication. In the US, the frequencies assigned for amplitude modulated voice communication are between 118.000 MHz to 136.975 MHz. NAV channels use the lower end of the band and are assigned the frequencies from 108.000 MHz to 117.95 MHz for navigational assistance. These frequencies are split into 200 narrow-band channels of 50 kHZ.
One navigation system is the VHF Omnidirectional Range (VOR). It is a system of short-range radio beacons developed by the US in 1937 to help pilots determine their position and stay on course. It is now a global standard for navigation in aviation with around 3000 VOR stations worldwide.
In addition to the COM and NAV channels, VHF air band radios typically support NOAA marine weather channels and NOAA weather alerts. Air band also includes an emergency communication frequency at 121.5 MHz with a 100 kHz bandwidth. This frequency is known as International Air Distress (IAD).
Until the mid 1990's, a license was required to operate air band radios in most countries, including the US. On October 25, 1996, the FCC released a Report and Order in WT Docket No. 96-82, 11 FCC Rcd 14849, FCC 96-421 (pdf) eliminating the individual licensing requirement for aircraft radio stations operating domestically which are not required by law to carry a radio.
Currently In Part 87 Subpart B of Title 47, the FCC rules are as follows:
(a) Except as noted in paragraph (b) of this section, stations in the aviation service must be licensed by the FCC either individually or by fleet.
(b) An aircraft station is licensed by rule and does not need an individual license issued by the FCC if the aircraft station is not required by statute, treaty, or agreement to which the United States is signatory to carry a radio, and the aircraft station does not make international flights or communications. Even though an individual license is not required, an aircraft station licensed by rule must be operated in accordance with all applicable operating requirements, procedures, and technical specifications found in this part.
Types of Air Band Radios
There are three basic types of air band radios. A handheld air band radio is about the same design as a typical handheld portable land mobile two way radio. Panel mount air band radios generally mount in the cockpit of an airplane or other aircraft, much like the typical mobile radio in a vehicle. A ground station refers to an air band radio that operates on the ground, whether mounted in a vehicle or sitting on a desk.