ACARS — Aircraft Communications Addressing and Reporting System

ACARS — Aircraft Communications Addressing and Reporting System

ACARs is the foundation of air-ground digital communication in commercial aviation. Introduced in the late 1970s, it replaced voice radio for routine operational messages, improving accuracy, reducing workload and creating an automatic data record of flight events.

OOOI Times

ACARs automatically captures and transmits four key event times: Out (aircraft leaves the gate — off-block), Off (wheels leave the runway — takeoff), On (wheels touch the runway — landing), In (aircraft arrives at gate — on-block). These OOOI times feed directly into the airline's OCC, the AODB, maintenance tracking and crew duty calculation systems.

ACARS Message Types

ACARs carries: automatic position reports (ADS-C position messages), weather data and ATIS (Automatic Terminal Information Service) downloads, digital clearances (DCL — datalink clearance delivery), ACARS-based ATIS and pre-departure clearances, maintenance messages (engine trend monitoring, system fault reports), operational messages (load sheet transmission, fuel order confirmations).

Transmission Media

ACARs operates over VHF radio (ground-based, short range), HF radio (oceanic, longer range) and satellite (global coverage — SATCOM ACARS). Modern implementations increasingly use IP-based datalink over aviation broadband.

ACARS and Aircraft Tracking

ACARs position reports are one of the primary data sources for flight tracking services. The absence of ACARS data was a factor in several accident investigations, including the search for MH370.