ACARS: Aircraft Communications, Addressing and Reporting System
ACARS is a digital data link system for the transmission of messages between aircraft and ground stations, which has been in use since 1978. At first it relied exclusively on VHF channels but more recently, alternative means of data transmission have been added which have greatly enhanced its geographical coverage. There has also been a rapid trend towards the integration of aircraft systems with the ACARS link. Both have led to rapid growth in its use as an operational communications tool. Modern ACARS equipment now includes the facility for automatic as well as manual initiation of messaging. ARINC guidelines have been defined for all the various avionic components of ACARS.