ACARS (Aircraft Communications Addressing and Reporting System)

ACARS

This is a neat way used to bypass the intentional or unintentional human error on reporting flight information during or after flight. Before 1978 AD, this information was given via, voice logs, where captain verbally records the phase of flight and time. This brought human error in the data reporting and was extra work to the pilots. 

What ACARS does is acts as a reporting machine which reports flight information in different phases of flight to the Ground team. Initially ARINC developed this method for just 4 messages per flight, but now it has turned into a robust means of data link between not just aircraft and ground station but also between aircraft. 

ACARS (Aircraft Communications Addressing and Reporting System) is a data communications system used for air-ground communication between an aircraft and their own operations centers, air traffic control, and national aviation authorities. ACARS can be used anywhere in the world by connecting to a global network of VHF / VDLM2 ground stations and orbiting Iridium / Inmarsat satellite constellations.

The types of messages in ACARS are:

1. ATC message (Air Traffic Control)

ATC messages include aircraft requests for clearances and ATC issue of clearances and instructions to aircraft. They are often used to deliver Pre-Departure, Datalink ATIS and en-route Oceanic Clearances. However, whilst the ACARS system is currently fulfilling a significant 'niche' role in ATC communications, it is not seen as a suitable system for the more widespread ATC use of datalink referred to as Controller Pilot Data Link Communications (CPDLC).

2. AOC message (Airline Operational Control)

AOC (Airline Operational Control) messages can be organized into two distinct categories. 

The first category of AOC messages serve to enhance an airlines operations and provide beneficial functionality to increase efficiency, reduce fuel usage, and ensure timely communication and information exchange, logistics, data collection, etc. 

The second category of AOC messages enable flight crews and Air Traffic Control (ATC) operators to communicate navigation information, aircraft position reporting, departure and oceanic clearances, as well as weather and runway conditions.

3. AAC message

The messages can also be categorized as uplink and downlink messages.

 

AOC and AAC messages are used for communications between an aircraft and its base. These messages may be of standard form or as defined by users, but all must then meet at least the guidelines of ARINC Standard 618. Any message content is possible including such examples as:

·        upload to the aircraft of final load and trim sheets;

·        upload of weather or NOTAM information;

·        download from the aircraft of status, position, eta, and any diversion;

·        download of spot weather observations from aircraft sensors:

·        download of technical performance data including automatically triggered exceedance or abnormal aircraft system status information, and

·        'housekeeping' information such as catering uplift requirements, special passenger advice and ETA.

Free Text messaging is also possible.

A. Uplink messages include

    a) Pre-Flight: 

           1. Flight Plans

           2. Fuel Load Sheets

           3. Load Sheets

           4. Weather data

    5. NOTAM

    b) During flight:

            1. sudden change in weather information

B: Downlink 

    a) OOOI messages. (Out of the gate, Off the ground, On the ground, In to the gate)

    this includes times like:

            1. Flight information

            2. Fuel on board

            3. Gross weight

            4. Position message

            5. ETA

            6. Diversions

               and other technical information from different sensors like

                i) Strain gauge

                ii) accelerometers

                iii) Pitot tube

                iv) anemometer and so on

Architecture of ACARS:

A) On Board A/C Equipment

B) Datalink Service Provider (DSP)

                i) VHF limited by line of sight

                ii) SATCOM limited by non-polar regions

                iii) HF/HFDC specially added for polar regions.

C) Ground Processing System 

 

"ACARS is an important system to graps the communication system that happens between the aircraft and ground station. Here i try to give a pictorial explanation of what an ACARS system is, its architecture and important aspecs. I am not an expert of this field, would love to hear if someone has to add more to this. :) (ep9)" 

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