ACARS (Aircraft Data Communication System)

ACARS (Aircraft Communications Addressing and Reporting System) is a digital data link system that enables automatic or manual transmission of text-based messages between aircraft and ground stations via radio or satellite frequencies. In civil aviation, it is used to enhance flight safety and reduce crew workload for maintenance, operational and commercial purposes.

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Because the system can transmit in real time a wide range of data obtained from the aircraft’s Flight Data Recorder, it functions operationally as an online black box. Through this system, the aircraft’s position data, in-flight performance metrics, engine parameters, fuel levels and onboard malfunctions can be directly reported to relevant maintenance units and manufacturers.

Before the development of the ACARS system, all communication between aircraft and ground personnel in aviation was conducted orally via HF or VHF radios by the cockpit crew. The necessity for continuous oral communication with ground units during phases such as departure from the gate, takeoff, landing and parking increased the workload on flight and cabin crews and failed to ensure the accuracy of real-time information.

To address these issues, the system was developed in April 1978 by Aeronautical Radio, Inc. (ARINC). Its original name was ARINC Communications Addressing and Reporting System, but the term ARINC was later changed to Aircraft. The first airline to adopt the system was Piedmont Airlines. Over subsequent years, ACARS was updated both hardware and software-wise, integrating with digital data bus interfaces, Flight Management Systems and cockpit printers to enhance the support capabilities provided to aircraft.

ACARS transmissions are carried out via UHF, VHF or HF radio waves or SATCOM (Satellite Communication) infrastructure, depending on the aircraft’s location and communication conditions. VHF is the primary communication channel for short distances and over land areas. However, when aircraft operate far from ground stations, particularly on transoceanic routes, SATCOM becomes mandatory. The system operates in the AM band, with each transmitted message limited to 220 characters and a transmission duration under one second. Depending on geographic region, ACARS data in Europe can be monitored on the 131.725 MHz frequency.

Data transmitted from the aircraft is collected by ground stations and forwarded to central computers. Globally, two main central computers process these data: ARINC located in Chicago and SITA located in Singapore. Through these centers, the data is converted into standardized message formats and transmitted via terrestrial networks to the airline’s main operational base.

Messages transmitted via ACARS are structurally divided into three main categories: Air Traffic Control messages, Operational Control messages related to flight airworthiness, and Airline Management Control messages. The primary data and message types include:

In aviation, OOOI refers to the phases of aircraft departure from the gate (Out of the gate), liftoff (Off the ground), touchdown (On the ground) and arrival at the gate (Into the gate). These flight phases are automatically detected by ACARS through sensors integrated into the aircraft’s doors, parking brakes and landing gear and are reported to ground operations units.

ACARS interfaces with the aircraft’s Flight Management System to transfer weather reports and flight plans received from the ground. This integration enables the flight crew to evaluate changing weather conditions during flight and update alternative flight plans accordingly.

The system sends real-time status updates of the aircraft’s structural and operational systems to ground stations. When abnormal conditions directly affecting flight airworthiness, such as engine failures or hard landings, are detected, ACARS automatically generates detailed fault messages. This allows ground technicians to prepare repair and maintenance plans before the aircraft even lands. Additionally, data used in civil aviation to evaluate energy and fuel efficiency are extracted from the Digital Flight Data Recorder and transmitted via the ACARS infrastructure to technical departments.

In addition to automatic transmissions, ACARS allows pilots to send manual text messages to ground units via the Multi-Function Control and Display Unit. Test messages containing no data may also be transmitted between the ground station and the aircraft to verify the system’s active status.