Aircraft Communication Addressing and Reporting System

Aircraft Communications Addressing and Reporting System (ACARS) is a digital datalink system for transmission of short, relatively simple messages between aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

and ground stations via radio

Radio

Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

or satellite

Satellite

In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

. The protocol, which was designed by ARINC

ARINC

Aeronautical Radio, Incorporated , established in 1929, is a major provider of transport communications and systems engineering solutions for eight industries: aviation, airports, defense, government, healthcare, networks, security, and transportation...

to replace their VHF voice service and deployed in 1978, uses telex formats. SITA

SITA

SITA is a multinational information technology company specialising in providing IT and telecommunication services to the air transport industry...

later augmented their worldwide ground data network by adding radio stations to provide ACARS service. Over the next 20 years, ACARS will be superseded by the Aeronautical Telecommunications Network

Aeronautical Telecommunications Network

The Aeronautical Telecommunication Network is an internetwork architecture that allows ground/ground, air/ground, and avionic data subnetworks to interoperate by adopting common interface services and protocols based on the ISO OSI Reference Model....

(ATN) protocol for Air Traffic Control communications and by the Internet Protocol for airline communications.

History of ACARS

Prior to the introduction of datalink, all communication between the aircraft (i.e., the flight crew) and personnel on the ground was performed using voice communication. This communication used either VHF or HF

High frequency

High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...

voice radios, which was further augmented with SATCOM

SATCOM

SATCOM or Satcom may refer to:* Short for Satellite Communications and used frequently in the context of VSAT * Communications satellites or comsats...

in the early 1990s. In many cases, the voice-relayed information involves dedicated radio operators and digital messages sent to an airline teletype system or its successor systems.

Introduction of ACARS systems

The Engineering Department at Aeronautical Radio, Inc

ARINC

(ARINC), in an effort to reduce crew workload and improve data integrity, introduced the ACARS system in July 1978. The first day operations saw about 4000 transactions. A few experimental ACARS systems were introduced earlier but ACARS did not start to get any widespread use by the major airline

Airline

An airline provides air transport services for traveling passengers and freight. Airlines lease or own their aircraft with which to supply these services and may form partnerships or alliances with other airlines for mutual benefit...

s until the 1980s.

The original ARINC development team was headed by Crawford Lane and included Betty Peck, a programmer, and Ralf Emory, an engineer. The terrestrial central site, a pair of Honeywell Level 6 minicomputers, (AFEPS) software was developed by subcontractor, Eno Compton of ECOM, Inc.

Although the term ACARS is often taken into context as the datalink

Data link

In telecommunication a data link is the means of connecting one location to another for the purpose of transmitting and receiving information. It can also refer to a set of electronics assemblies, consisting of a transmitter and a receiver and the interconnecting data telecommunication circuit...

avionics

Avionics

Avionics are electronic systems used on aircraft, artificial satellites and spacecraft.Avionic systems include communications, navigation, the display and management of multiple systems and the hundreds of systems that are fitted to aircraft to meet individual roles...

line-replaceable unit

Line-replaceable unit

A line-replaceable unit is a modular component of an airplane, ship or spacecraft that is designed to be replaced quickly at an operating location. An LRU is usually a sealed unit such as a radio or other auxiliary equipment...

installed on the aircraft, the term actually refers to a complete air and ground system. The original meaning was Arinc Communications Addressing and Reporting System http://www.arinc.com/downloads/product_collateral/acars_first_datasheet.pdf . Later, the meaning was changed to Airline Communications, Addressing and Reporting System.

On the aircraft, the ACARS system was made up of an avionics computer called an ACARS Management Unit (MU) and a Control Display Unit (CDU). The MU was designed to send and receive digital messages from the ground using existing VHF radios.

On the ground, the ACARS system was made up of a network

Telecommunications network

A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the terminals. Networks may use circuit switching or message switching. Each terminal in the network must have a unique address so messages or connections...

of radio transceiver

Transceiver

A transceiver is a device comprising both a transmitter and a receiver which are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s...

s, managed by a central site computer called AFEPS (Arinc Front End Processor System), which would receive (or transmit) the datalink messages, as well as route

Routing

Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network , electronic data networks , and transportation networks...

them to various airlines on the network.

The initial ACARS systems were designed to the ARINC standard 597. This system was later upgraded in the late 1980s to the ARINC 724 characteristic. ARINC 724 addressed aircraft installed with avionics supporting digital data bus interfaces. This was subsequently revised to ARINC 724B, which was the primary characteristic used during the 1990s for all digital aircraft. With the introduction of the 724B specification, the ACARS MUs were also coupled with industry standard protocols for operation with flight management system

Flight management system

A flight management system is a fundamental part of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that modern aircraft no longer carry flight engineers or navigators. A...

MCDUs using the ARINC 739 protocol, and printers using the ARINC 740 protocol. The industry has defined a new ARINC characteristic, called ARINC 758, which is for CMU systems, the next generation of ACARS MUs.

OOOI events

One of the initial applications for ACARS was to automatically detect and report changes to the major flight phases (Out of the gate, Off the ground, On the ground, and Into the gate); referred to in the industry, as OOOI. These OOOI events were determined by algorithm

Algorithm

In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...

s in the ACARS MUs that used aircraft sensors (such as doors, parking brake and strut switch sensors) as inputs. At the start of each flight phase, the ACARS MU would transmit a digital message to the ground containing the flight phase, the time at which it occurred, and other related information such as fuel on board or origin and destination. These messages were primarily used to automate the payroll

Payroll

In a company, payroll is the sum of all financial records of salaries for an employee, wages, bonuses and deductions. In accounting, payroll refers to the amount paid to employees for services they provided during a certain period of time. Payroll plays a major role in a company for several reasons...

functions within an airline

Airline

, where flight crews were paid different rates depending on the flight phase.

Flight management system Interface

In addition to detecting events on the aircraft and sending messages automatically to the ground, initial systems were expanded to support new interfaces with other on-board avionics

Avionics

. During the late 1980s and early 1990s, a datalink interface between the ACARS MUs and Flight management system

Flight management system

s (FMS) was introduced. This interface enabled flight plans and weather information to be sent from the ground to the ACARS MU, which would then be forwarded to the FMS. This feature gave the airline the capability to update FMSs while in flight, and allowed the flight crew to evaluate new weather conditions, or alternate flight plan

Flight plan

Flight plans are documents filed by pilots or a Flight Dispatcher with the local Civil Aviation Authority prior to departure...

Maintenance Data Download

It was the introduction in the early 1990s of the interface between the FDAMS / ACMS systems and the ACARS MU that resulted in datalink gaining a wider acceptance by airlines. The FDAMS / ACMS systems which analyze engine, aircraft, and operational performance conditions, were now able to provide performance data to the airlines on the ground in real time using the ACARS network. This reduced the need for airline personnel to go to the aircraft to off-load the data from these systems. These systems were capable of identifying abnormal
flight conditions and automatically sending real-time messages to an airline. Detailed engine reports could also be transmitted to the ground via ACARS. The
airlines used these reports to automate engine trending activities. This capability enabled airlines to better monitor their engine performance and identify and plan repair and maintenance activities.

In addition to the FMS and FDAMS interfaces, the industry started to upgrade the on-board Maintenance Computers in the 1990s to support the transmission of maintenance related information real-time through ACARS. This enabled airline maintenance personnel to receive real-time data associated with maintenance faults on the aircraft. When coupled with the FDAMS data, airline maintenance personnel could now start planning repair and maintenance activities while the aircraft

Aircraft

was still in flight.

Interactive Crew Interface

All of the processing described above is performed automatically by the ACARS MU and the associated other avionics

Avionics

systems, with no action performed by the flight crew. As part of the growth of the ACARS functionality, the ACARS MUs also interfaced directly with a control display unit (CDU), located in the cockpit

Cockpit

A cockpit or flight deck is the area, usually near the front of an aircraft, from which a pilot controls the aircraft. Most modern cockpits are enclosed, except on some small aircraft, and cockpits on large airliners are also physically separated from the cabin...

. This CDU, often referred to as an MCDU or MIDU, provides the flight crew with the ability to send and receive messages similar to today’s email

Electronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the...

. To facilitate this communication, the airline

Airline

s in partnership with their ACARS vendor, would define MCDU screens that could be presented to the flight crew and enable them to perform specific functions. This feature provided the flight crew flexibility in the types of information requested from the ground, and the types of reports sent to the ground.

As an example, the flight crew could pull up an MCDU screen that allowed them to send to the ground a request for various weather information. Upon entering in the desired locations for the weather information and the type of weather information desired, the ACARS would then transmit the message to the ground. In response to this request message, ground computers would send the requested weather information back to the ACARS MU, which would be displayed and/or printed.

Airlines began adding new messages to support new applications (Weather, Winds, Clearances, Connecting Flights, etc.) and ACARS systems became customized to support airline unique applications, and unique ground computer requirements. This results in each airline having their own unique ACARS application operating on their aircraft. Some airlines have more than 75 MCDU screens for their flight crews, where other airlines may have only a dozen different screens. In addition, since each airline’s ground computers were different, the contents and formats of the messages sent by an ACARS MU were different for each airline.

In the wake of the crash of Air France Flight 447

Air France Flight 447

Air France Flight 447 was a scheduled airline flight from Rio de Janeiro-Galeão to Paris-Roissy involving an Airbus A330-200 aircraft that crashed into the Atlantic Ocean on 1 June 2009, killing all 216 passengers and 12 aircrew. The investigation is still ongoing, and the cause of the...

, there has been discussion about making the ACARS into an "online-black-box

Flight recorder

A flight recorder is an electronic recording device placed in an aircraft for the purpose of facilitating the investigation of an aircraft accident or incident. For this reason, flight recorders are required to be capable of surviving the conditions likely to be encountered in a severe aircraft...

." If such a system were in place, it would avoid the loss of data due to: (1) black-box destruction, and (2) inability to locate the black-box following loss of the aircraft. However the cost of this, due to the high bandwidth requirements, would be excessive and there have been very few incidents where the black boxes were not recoverable.

How it works

A person or a system on board may create a message and send it via ACARS to a system or user on the ground, and vice versa. Messages may be sent either automatically or manually.

VHF subnetwork

A network

Telecommunications network

of VHF ground radio stations ensure that aircraft can communicate with ground end systems in real-time from practically anywhere in the world. VHF communication is line-of-sight

Line-of-sight propagation

Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...

, and provides communication with ground-based transceiver

Transceiver

s (often referred to as Remote Ground Stations or RGSs). The typical range is dependent on altitude, with a 200-mile transmission range common at high altitudes. Thus VHF communication is only applicable over landmasses which have a VHF ground network

Telecommunications network

installed.

A typical ACARS VHF transmission.
Mode	A
Aircraft	B-18722
Ack	NAK
Block id	2
Flight	CI5118
Label	B9
Msg No.	L05A
Message	/KLAX.TI2/024KLAXA91A1

SATCOM and HF subnetworks

SATCOM provides worldwide coverage, with the exception of operation at the high latitudes (such as needed for flights over the poles). HF datalink is a relatively new network whose installation began in 1995 and was completed in 2001. HF datalink is responsible for new polar routes. Aircraft with HF datalink can fly polar routes and maintain communication with ground based systems (ATC centers and airline operation centers). ARINC is the only service provider for HF datalink.

Datalink message types

ACARS messages may be of three types:

Air Traffic Control
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...

(ATC)
Aeronautical Operational Control
Aeronautical Operational Control
Aeronautical Operational Control A group or the entirety of applications used for communication of an aircraft with its airline or service partner pendants on the ground. An AOC application was traditionally hosted on an ACARS MU or CMU....

(AOC)
Airline Administrative Control (AAC)

ATC messages are used to communicate between the aircraft and Air traffic control

Air traffic control

Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...

. These messages are defined in ARINC Standard 623. ATC messages are used by aircraft crew to request clearances, and by ground controllers to provide those clearances.

AOC and AAC messages are used to communicate between the aircraft and its base. These messages are either standardized according ARINC Standard 633 or defined by the users, but must then meet at least the guidelines of ARINC Standard 618. Various types of messages are possible, and these include fuel consumption, engine performance data, aircraft position, as well as free text data.

Departure delay downlink

A pilot may want to inform his flight operations department that departure has been delayed by Air Traffic Control (ATC). The pilot would first bring up a CMU MCDU screen that allows him to enter the expected time of the delay and the reason for the delay. After entering the information on the MCDU, the pilot would then press a “SEND” key on the MCDU. The CMU would detect the SEND key being pushed, and would then generate a digital message containing the delay information. This message may include such information as aircraft registration number, the origination and destination airport codes, the current ETA before the delay and the current expected delay time. The CMU would then send the message to one of the existing radios (HF, SATCOM or VHF, with the selection of the radio based on special logic contained within the CMU). For a message to be sent over the VHF network, the radio would transmit the VHF signals containing the delay message. This message is then received by a VHF Remote Ground Station (RGS).

The majority of ACARS messages are typically only 100 to 200 characters in length. Such messages are made up of a one-block transmission from (or to) the aircraft. One ACARS block is constrained to be no more than 220 characters within the body of the message. For downlink messages which are longer than 220 characters, the ACARS unit will split the message into multiple blocks, transmitting each block to the RGS (there is a constraint that no message may be made up of more than 16 blocks). For these multi-block messages, the RGS collects each block until the complete message is received before processing and routing the message. The ACARS also contains protocols to support retry of failed messages or retransmission of messages when changing service providers.

Once the RGS receives the complete message, the RGS forwards the message to the datalink service provider's (DSP) main computer system. The DSP ground network uses landlines to link the RGS to the DSP. The DSP uses information contained in their routing table to forward the message to the airlines or other destinations. This table is maintained by the DSP and identifies each aircraft (by tail number), and the types of messages that it can process. (Each airline must tell its service provider(s) what messages and message labels their ACARS systems will send, and for each message, where they want the service provider to route the message. The service provider then updates their routing tables from this information.) Each type of message sent by the CMU has a specific message label, which is contained in the header information of the message. Using the label contained in the message, the DSP looks up the message and forwards to the airline’s computer system. The message is then processed by the airline’s computer system.

This processing performed by an airline may include reformatting the message, populating databases for later analysis, as well as forwarding the message to other departments, such as flight operations, maintenance, engineering, finance or other organizations within an airline. In the example of a delay message, the message may be routed via the airline’s network to both their operations department as well as to a facility at the aircraft’s destination notifying them of a potential late arrival.

The transmission time from when the flight crew presses the send key to send the message, to the time that it is processed within an airline’s computer system varies, but is generally on the order of 6 to 15 seconds. The messages that are sent to the ground from the CMU are referred to as a downlink message.

Weather report uplink

For a message to be transmitted to the aircraft (referred to as an uplink message), the process is nearly a mirror image of how a downlink is sent from the aircraft. For example, in response to an ACARS downlink message requesting weather

Weather

Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...

information, a weather report is constructed by the airline’s computer system. The message contains the aircraft registration number in the header of the message, with the body of the message containing the actual weather information. This message is sent to the DSP's main computer system.

The DSP transmits the message over their ground network to a VHF remote ground station in the vicinity of the aircraft. The remote ground station broadcasts the message over the VHF. The on-board VHF radio receives the VHF signal and passes the message to the CMU (with the internal modem transforming the signal into a digital message). The CMU validates the aircraft registration number, and processes the message.

The processing performed on the uplink message by the CMU depends on the specific airline requirements. In general, an uplink is either forwarded to another avionics computer, such as an FMS or FDAMS, or is processed by the CMU. For messages (such as a weather report uplink) destined for the CMU, the flight crew can go to a specific MCDU screen which contains a list of all of the received uplink messages. The flight crew can then select the weather message, and have the message viewed on the MCDU. The ACARS unit may also print the message on the cockpit printer (either automatically upon receiving the message or upon flight crew pressing a PRINT prompt on the MCDU screen).

FDAMS message downlink

Messages are sent to the ground from other on-board systems in a similar manner as the delay message example discussed previously. As an example, an FDAMS system may have a series of algorithms active to monitor engine exceedance conditions during flight (such as checking engine vibration or oil temperature exceeding normal operating conditions). The FDAMS system, upon detecting such an event, automatically creates an engine exceedance condition message, with applicable data contained within the body of the message. The message is forwarded to the CMU, using what is referred to as ARINC 619 data protocols. The CMU would then transmit the message to the ground. In this case, the service provider routing table for an engine exceedance message is typically defined to have the message routed directly to an airline’s maintenance department. This enables airline maintenance personnel to be notified of a potential problem, in real time.

There are three major components to the ACARS datalink system:

Aircraft equipment
Service provider
Ground processing system

Aircraft equipment

The heart of the datalink system on board the aircraft is the ACARS Management Unit (MU). The older version of MU is defined in ARINC Characteristic 724B. Newer versions are referred to as the Communications Management Unit (CMU) and are defined in ARINC Characteristic 758.

Aircraft equipment consists of airborne end systems and a router. End systems are the source of ACARS downlinks and the destination for uplinks. The MU/CMU is the router. Its function is to route a downlink by means of the most efficient air-ground subnetwork. In many cases, the MU/CMU also acts as an end system for AOC messages.

Typical airborne end systems are the Flight Management System

Flight management system

(FMS), datalink printer, maintenance computer, and cabin terminal. Typical datalink functions are:

FMS - sends flight plan change requests, position reports, etc. Receives clearances and controller instructions.
Printer - as an end system, can be addressed from the ground to automatically print an uplink message.
Maintenance Computer - downlinks diagnostic messages. In advanced systems, in-flight troubleshooting can be conducted by technicians on the ground by using datalink messages to command diagnostic routines in the maintenance computer and analyzing downlinked results.
Cabin Terminal - Often used by flight attendant
Flight attendant
Flight attendants or cabin crew are members of an aircrew employed by airlines primarily to ensure the safety and comfort of passengers aboard commercial flights, on select business jet aircraft, and on some military aircraft.-History:The role of a flight attendant derives from that of similar...

s to communicate special needs of passengers, gate changes due to delays, catering, etc.

ACARS messages are transmitted over one of three air-ground subnetworks.

VHF is the most commonly used and least expensive. Transmission is line-of-sight so VHF is not available over the oceans.
SATCOM
Communications satellite
A communications satellite is an artificial satellite stationed in space for the purpose of telecommunications...

provides worldwide coverage (except in polar regions) by means of the INMARSAT
Inmarsat
Inmarsat plc is a British satellite telecommunications company, offering global, mobile services. It provides telephony and data services to users worldwide, via portable or mobile terminals which communicate to ground stations through eleven geostationary telecommunications satellites...

satellite network. It is a fairly expensive service.
HF
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...

is the most recently established subnetwork. Its purpose is to provide coverage in the polar regions where SATCOM coverage is unreliable.

The router function built into the MU/CMU determines which subnetwork to use when routing a message from the aircraft to the ground. The airline operator provides a routing table that the CMU uses to select the best subnetwork.

Datalink Service Provider

The role of the datalink service provider (DSP) is to deliver a message from the aircraft

Aircraft

to the ground end system, and vice versa.

Because the ACARS network

Telecommunications network

is modeled after the point-to-point telex network, all messages come to a central processing location. The DSP routes the message to the appropriate end system using its network of land lines and ground stations. Before the days of computers, messages would come in to the central processing location and be punched to paper tape. The tape would be physically carried to the machine connected to the intended destination. Today the routing function is done by computer, but the model remains the same.

There are currently two primary service providers of ground networks in the world (ARINC

ARINC

and SITA

SITA

SITA is a multinational information technology company specialising in providing IT and telecommunication services to the air transport industry...

), although specific countries have implemented their own network, with the help of either ARINC or SITA. ARINC operates a worldwide network and has also assisted the CAAC

Civil Aviation Administration of China

The Civil Aviation Administration of China , formerly the General Administration of Civil Aviation of China , is the aviation authority under the Ministry of Transport of the People's Republic of China. It oversees civil aviation and investigates aviation accidents and incidents...

in China, as well as Thailand and South America with the installation of VHF networks. SITA

SITA

SITA is a multinational information technology company specialising in providing IT and telecommunication services to the air transport industry...

has operated the network in Europe, Middle East, South America and Asia for many years. They have also recently started a network in the US to compete with ARINC.

Until recently, each area of the world was supported by a single service provider. This is changing, and both ARINC and SITA are competing and installing network

Telecommunications network

s that cover the same regions.

Ground End System

The ground end system is the destination for downlinks, and the source of uplinks. Generally, ground end systems are either government agencies such as CAA/FAA, an airline operations headquarters, or in the case of small airlines or general aviation consumers, a subscription based solution. CAA end systems provide air traffic services such as clearances. Airline and general aviation operations provide information necessary for operating the airline or flight department efficiently, such as gate assignments, maintenance, passenger needs, etc. In the early history of ACARS most airlines created their own host systems for managing their ACARS messages. Commercial off-the-shelf products are now widely available to manage the ground hosting.

ARINC Specifications

Much of the processing performed by the CMU as well as basic requirements of the hardware are defined by ARINC specifications. The following is a list of the major ARINC specifications that define standards that govern many aspects of ACARS systems:

ARINC documents and their specifications
ARINC 744	Specification for interfacing to cockpit Printers.
ARINC 607	Design Guidance for Avionics Equipment. Includes definition of Aircraft Personality Module (APM), required for ARINC 758 CMU installation.
ARINC 429	Specification for receiving and broadcasting ARINC 429 broadcast data (data transfer between avionics LRUs). ARINC 429 is the one way communication data bus (one pair of data bus use for transmit data and another pair of data bus use for receive data)
ARINC 618	Defines the air / ground protocols for communicating between the ACARS / CMU and VHF ground systems. Also defines the format of the ACARS messages sent by the ACARS / CMU as well as received by the ACARS CMU. The format of this message is called a Type A message. This characteristic has been updated to define the future VDL Mode 2 AOA operation.
ARINC 619	Defines the protocols for the ACARS / CMU to use to transfer file data between other avionics in the aircraft. ARINC 619 covers file protocols that are used to interface with FMS, FDAMS, Cabin Terminal, Maintenance Computers, SATCOM systems and HF Voice Data Radios.
ARINC 620	Defines ground-to-ground communication protocols. This includes the message format of messages routed between a service provider and an airline or other ground system. This is referred to as a Type B message (the air/ground Type A message is reformatted to a Type B message for ground transmissions).
ARINC 622	Describes the processing associated with sending ATC application messages over today’s ACARS links (including ARINC 623 ATC messages).
ARINC 623	This characteristic identifies ATC related messages that can be generated or received by an ACARS MU / CMU system (does not include FANS-1 or FANS-A messages that are processed by the FMS)
ARINC 629	Specification for receiving and broadcasting ARINC 629 broadcast data (data transfer between avionics LRUs). ARINC 629 was introduce to use on B777 commercial airplane. ARINC 629 is the two ways communication data bus (one pair of data bus is use for transmit and receive data).
ARINC 631	Specification for VHF DIGITAL LINK (VDL) MODE 2. This specification provides general and specific design guidance for the development and installation of the protocols needed to exchange bit-oriented data across an air-ground VHF Digital Link (VDL) in an Open System Interconnection (OSI) environment.
ARINC 724B	Specification for an ACARS MU for ARINC 724B wiring.
ARINC 739	Specification for interfacing with Multi-purpose Cockpit Display Units
ARINC 740	Specification for interfacing to cockpit Printers.
ARINC 758	Specification for a CMU relative to ARINC 758 wiring. This specification actually identifies various levels of functionality, these defining future growth phases for the CMU. Initial CMU systems which perform today’s ACARS functions are classified as Level OA.
ARINC 823	Two-part specification that defines a security framework for protecting ACARS datalink messages exchanged between aircraft and ground systems. Security services include confidentiality, data integrity, and message authentication. Part 1, ACARS Message Security (AMS), specifies the security protocol, and Part 2, Key Management, specifies life-cycle management of the cryptographic keys necessary for secure and proper operation of AMS.

Acronyms and Glossary

It has been rumored that the introduction of datalink into the airline industry originated as part of a contest to see how many acronyms could be developed around a specific technology. Whether this is true or not, the industry is at the point where acronyms are now nested within acronyms. For example, AOA is an acronym for ACARS Over AVLC, where AVLC itself is an acronym for Aviation VHF Link Control and VHF is also an acronym for Very High Frequency.

ACARS : Aircraft Communications Addressing and Reporting System
ACMS : Aircraft Condition Monitoring System
AMS : ACARS Message Security, as specified in ARINC 823
AOA : ACARS Over AVLC. With the introduction of VDL Mode 2, the ACARS protocols were modified to take advantage of the higher data rate made possible by Mode 2. AOA is an interim step in replacing the ACARS protocols with ATN protocols.
ATN

Aeronautical Telecommunications Network

: Aeronautical Telecommunications Network. As air traffic increases, ACARS will no longer have the capacity or flexibility to handle the large amount of datalink communications. ATN is planned to replace ACARS in the future and will provide services such as authentication

Authentication

Authentication is the act of confirming the truth of an attribute of a datum or entity...

, security, and a true internetworking

Internetworking

Internetworking is the practice of connecting a computer network with other networks through the use of gateways that provide a common method of routing information packets between the networks...

architecture. Europe is leading the US in the implementation of ATN.
AVLC : Aviation VHF Link Control. A particular protocol used for aeronautical datalink communications.
CDU : Control Display Unit
CMF : Communications Management Function. The software that runs in a CMU, and sometimes as a software partition in an integrated avionics computer.
CMU : Communications Management Unit. Successor to the MU, the CMU performs similar datalink routing functions, but has additional capacity to support more functions. CMU standards are defined in ARINC Characteristic 758.
FDAMS : Flight Data Acquisition and Management System
FMS : Flight Management System

Flight management system

. FMS standards are defined in ARINC Characteristic 702 and 702A.
HFDL : High Frequency Data Link

High Frequency Data Link

-High Frequency Data Link :High Frequency Data Link is an ACARS communications media used to exchange data such as Aeronautical Operational Control messages, Controller Pilot Data Link Communication messages and Automatic Dependent Surveillance messages between aircraft end-systems and...

is an ACARS communications media used to exchange data such as Airline Operational Control (AOC) messages, Controller Pilot Data Link Communication (CPDLC) messages and Automatic Dependent Surveillance (ADS) messages between aircraft end-systems and corresponding ground-based HFDL ground stations.
HF

High frequency

: High Frequency. A portion of the RF spectrum.
LRU : Line Replaceable Unit

Line-replaceable unit

. An avionics "black box" that can be replaced on the flight line, without downing the aircraft for maintenance.
MCDU : Multifunction Control Display Unit. A text-only device that displays messages to the aircrew and accepts crew input on an integrated keyboard. MCDU standards are defined in ARINC Characteristic 739. MCDUs have seven input ports and can be used with seven different systems, such as CMU or FMS. Each system connected to an MCDU generates its own display pages and accepts keyboard input, when it is selected as the system controlling the MCDU.
MIDU : Multi-Input Interactive Display Unit (often used as a third cockpit CDU).
MU : Management Unit. Often referred to as the ACARS MU, this is an avionics LRU that routes datalink messages to and from the ground.
OOOI : Shorthand for the basic flight phases—Out of the gate, Off the ground, On the ground, In the gate.
POA : Plain Old ACARS. Refers to the set of ACARS communications protocols in effect before the introduction of VDL Mode 2. The term is derived from POTS (Plain old telephone service

Plain old telephone service

Plain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world....

) that refers to the wired analog telephone network.
SATCOM

Communications satellite

A communications satellite is an artificial satellite stationed in space for the purpose of telecommunications...

: Satellite Communications. Airborne SATCOM equipment includes a satellite data unit, high power amplifier, and an antenna with a steerable beam. A typical SATCOM installation can support a datalink channel as well as several voice channels.
VDL : VHF Data Link

VHF Data Link

The VHF Data Link or VHF Digital Link is a means of sending information between aircraft and ground stations . Aeronautical VHF data links use the band 117.975 - 137 MHz assigned by the International Telecommunication Union to Aeronautical Mobile Route Services...

VHF : Very High Frequency. A portion of the RF spectrum, defined as 30 MHz to 300 MHz.

GIS and Data Discovery

In 2002, ACARS was added to the NOAA Observing System Architecture
NOAA Observing System Architecture
*The NOAA Observing System Architecture is a collection of over 100 of NOAA's environmental datasets.*NOSA was established to develop an observational architecture that helps NOAA:...

. NOSA provides near real time WMS maps and an ID search from the NOSA homepage.

External links

ARINC, inventors of ACARS
acarsd, free ACARS decoder software for Linux/Windows
ACARS on NOSA
ARINC Standards Document List, list and describe the ARINC standards

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

History of ACARS

Introduction of ACARS systems

OOOI events

Flight management system Interface

Maintenance Data Download

Interactive Crew Interface

How it works

VHF subnetwork

SATCOM and HF subnetworks

Datalink message types

Departure delay downlink

Weather report uplink

FDAMS message downlink

Aircraft equipment

Datalink Service Provider

Ground End System

ARINC Specifications

Acronyms and Glossary

GIS and Data Discovery

See also

External links