Airbands

300px|thumb|Example of an ACARS message In aviation, ACARS (; an acronym for Aircraft Communications Addressing and Reporting System) is a digital data communication system for transmission of short messages between aircraft and ground stations via airband radio or satellite. The protocol was designed by ARINC and deployed in 1978, using the Telex format. More ACARS radio stations were added subsequently by SITA.

thumb|A typical aircraft VHF radio. The display shows an active frequency of 123.5 MHz and a standby frequency of Aircraft emergency frequency|121.5 MHz. The two are exchanged using the button marked with a double-headed arrow. The tuning control on the right only affects the standby frequency. Airband or aircraft band is the name for a group of frequencies in the VHF radio spectrum allocated to radio communication in civil aviation, sometimes also referred to as VHF, or phonetically as "Victor". Different sections of the band are used for radionavigational aids and air traffic contr

radio frequency reserved for aeronautical emergencies