Aircraft Communications Addressing and Reporting System

In aviation, ACARS (/ˈeɪkɑːrz/; an acronym for Aircraft Communications Addressing and Reporting System) is a digital datalink 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.

Prior to the introduction of datalink in aviation, all communication between the aircraft and ground personnel was performed by the flight crew using voice communication, using either VHF or HF voice radios. In many cases, the voice-relayed information involved dedicated radio operators and digital messages sent to an airline teletype system or successor systems.

Further, the hourly rates for flight and cabin crew salaries depended on whether the aircraft was airborne or not, and if on the ground whether it was at the gate or not. The flight crews reported these times by voice to geographically dispersed radio operators. Airlines wanted to eliminate self-reported times to preclude inaccuracies, whether accidental or deliberate. Doing so would also reduce the need for human radio operators to receive the reports.

In an effort to reduce crew workload and improve data integrity, the engineering department at ARINC introduced the ACARS system in July 1978, as essentially an automated time clock system. Teledyne Controls produced the avionics and the launch customer was Piedmont Airlines. The original expansion of the abbreviation was "Arinc Communications Addressing and Reporting System". Later, it was changed to "Aircraft Communications, Addressing and Reporting System". The original avionics standard was ARINC 597, which defined an ACARS Management Unit consisting of discrete inputs for the doors, parking brake and weight on wheels sensors to automatically determine the flight phase and generate and send as telex messages. It also contained a MSK modem used to transmit the reports over existing VHF voice radios. Global standards for ACARS were prepared by the Airlines Electronic Engineering Committee (AEEC). The first day of ARINC operations saw about 4,000 transactions, but ACARS did not experience widespread use by the major airlines until the 1980s.

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