Aircraft Communications Addressing and Reporting System
ACARS ( aircraft communications addressing and reporting English system) is one of Aeronautical Radio Incorporated in the 1970s developed, digital radio data transmission system for transmitting messages between commercial aircraft and ground stations. It allows airlines to communicate with their aircraft by means of exchange of simple messages and so saves radio messages on the congested especially in urban areas radio frequencies.
History
Before the use of ACARS flight operations reports were made via radio, resulting in a high load on the radio channels emerged. Routine messages such as departure reports, arrival reports, load and fuel reports, reports of engine conditions, etc. can be transmitted digitally in a short time since the introduction of ACARS.
ACARS was initially intended only for the transmission of AOC News (german airline operational control ). But then the use of the intelligence service for more and more applications was discovered as a solution to improve efficiency and the number of sent through the ACARS system messages increased steadily. The air traffic control also sends since the early 1990s, Air Releases ( clearances ) via ACARS.
Current Situation
Today, the ACARS frequencies are overloaded at least as well as the communication frequencies especially near major airports. In addition, the ACARS protocol on some inherent limitations that the development of additional Data Links necessitated in the 1990s. Nevertheless, ACARS is still indispensable for many airlines which sometimes operate their complete fleet management through the exchange of AOC messages via ACARS.
With the crash of the Air France flight AF 447 in June 2009, the ACARS signals important information first have delivered and so the extension of the system into a kind of black box online is discussed. The previous principle now seems antiquated. Currently, a flight data recorder must record several times per second to more than a hundred parameters - today's ACARS system would be overtaxed. In addition, the satellite links are too expensive for these data streams. As a middle way is discussed to provide more frequent position reports to Air Traffic Control, instead that the management of the airline only every 10-20 minutes will receive such.
Since 2009, ACARS will be replaced in Europe by VDL2 ( In America VDL3 ). VDL2 is often equated with the new system CPDLC (Controller -pilot data link communication), which was introduced in 2013 by the Swiss flight control Skyguide and all newly registered aircraft since January 1, 2014 is mandatory equipment.
Application
The ACARS application includes a news service for automatically and manually generated messages and looks for before special board hardware.
The management unit reacts to events in the on-board systems and automatically sends messages (originally only the so-called OOOI News: Out, Off, On, In). In detail, this represents
- Out: aircraft leaves its parking place for the pushback
- Off: Weight -off wheels, the plane has taken off
- On: Weight -on -wheels, the plane has landed on the runway
- In: The plane comes to a parking position and turns off the engines.
These messages are received by the ground stations and relayed by telex or satellite to the respective Operation Center of airlines, bringing the flight can be constantly monitored.
In addition to the fully automatic technical data reports any other messages between the cockpit and Operation Center can also be transmitted via the Control Unit (consisting of printer, monitor and keyboard ), such as information about delays, weather reports, personal communications to passengers,
Main provider of network infrastructure for routing on the ground and the delivery of ACARS messages is in Europe SITA, ARINC in North America.
Example of a typical Delta Airlines ACARS message:
The text is transmitted via FSK at 2400 bps.
Data Link
ACARS operates in the VHF range. The ACARS protocol is character-oriented, limited to a length of 220 characters per transmission, has a data rate of 2.4 kbps and to access the channels a stop- n -wait- method will be used. From the ICAO a Data Link under the name VDL Mode 1 was defined on the ACARS data link based, but never gained practical importance.
Free receptivity
Radio enthusiasts now have the ability to decode the ACARS signals and thus to obtain an insight into aviation. Although it is not itself connected to the global ground station network, you can receive with any aeronautical radio receiver / scanner and the corresponding decoder messages from their own region. A good outdoor antenna increases while the radius of the observable region.
Since the beginning of 2004, it is also possible without its own airport radio scanner to receive the ACARS signals. End of 2003 / beginning of 2004, the ACARS network was established, which connected to the Internet allows users worldwide to experience in real-time ACARS. The only requirement is a software that gives it free for Linux & Windows. In the meantime, you can follow live ACARS also with a web browser current generation.
There are also network- controlled receiver, where ACARS signals can be received.
Some major European airlines (for example, German Lufthansa, Condor service, Austrian Airlines ) encrypt the ACARS messages so that they are no longer legible without the matching key in plain text. Encrypts only the content of an ACARS message, not the headers.