What is ACARS?

ACARS stands for:
Aircraft Communications Addressing and Reporting System.

This system is a digital data system which uses the VHF air band radios. The usage of ACARS is for the flight operators to communicate with numbers of aircraft in their fleet. This saves the already crowed VHF voice AM channels from being overcome with many messages from ground to air.



How is
ACARS used?



ACARS message’s use a single AM 6k channel and can send quite a lot of information in a single data burst. These messages vary in content from take off times to location reports. The aircraft operators also receive reports from the aircraft for broken equipment and ill passengers. Here is an example of a general ACARS message.



ACARS mode: G Aircraft reg: .PH-BXR

Message label: Q0 Block id: 5 Msg. no: S61A

Flight id: KL0904



Even this small piece of data can contain a lot of useful information. The aircraft reg is simply the registration of the aircraft. All the other data is data which when received by a ground station can be logged, and matched to data already on the system. The ACARS system can be used for the aircraft to send it position to the ground.stations. This is an example of a map plot message



ACARS mode: 2 Aircraft reg: .N475QS

Message label: 15 Block id: 2 Msg. no: M41A

Flight id: GS0001

Message content:-

(2N35433W120102--- 41389-49(Z

-------------------------------------[08/02/2003 22:30]



In this message is a map reference way point. With the right software, you can get these plots onto a map and usually follow the aircraft in the sky.



How does ACARS work?



ACARS uses the VHF radio of a plane, In the aircraft there is a staff control unit, where the pilots can send information to the ground stations, there is also a receiver which receives the messages and displays them in the cockpit for the pilots to view, or reply to. Most of the messages sent from the aircraft are automatic, like eta’s and times. On the ground, the system is controlled by ARINC (Aeronautical Radio, Inc) and consists of many ground receiving and transmitting stations. The message’s when received from the aircraft, are decoded on a computer on the ground station, and then sent to the right airline by computer. Also when sending messages, the airline send the message to the ground station via computer, where it is then encrypted and sent. This is an advantage for airline operators, who may have aircraft on the other side of the globe, because they can send and receive message from other places then their base.



How do I decode ACARS?



Using a simple piece of software you can decode these messages with no other hardware. Simply tune into the correct frequency, and watch as the messages are decoded and shown on your screen. You may also use your own air band receiver by simply connecting the output of your receiver into your soundcard.





What frequencies do I use to receive these messages?


In Australia 131.550MHz






Set the frequency with the squelch set to 0