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Aircraft Communications Addressing and ReportingSystemFrom Wikipedia, the free encyclopedia

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Aircraft Communications Addressing and Reporting System (ACARS) is a digital datalink system fortransmission of short, relatively simple messages between aircraft and ground stations via radio or satellite.The protocol, which was designed by Aeronautical Radio, Incorporated (ARINC) to replace their very highfrequency (VHF) voice service and deployed in 1978,[1] uses telex formats. SITA later augmented theirworldwide 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 Over the next 20 years,ACARS will be superseded by the Aeronautical Telecommunications Network (ATN) protocol for Air TrafficControl communications and by the Internet Protocol for airline communications.

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Contents [hide]

1 History of ACARS1.1 Introduction of ACARS systems1.2 OOOI events1.3 Flight management system interface1.4 Maintenance data download1.5 Interactive crew interface

2 How it works2.1 VHF subnetwork2.2 SATCOM and HF subnetworks2.3 Datalink message types

3 Example transmissions3.1 Departure delay downlink3.2 Weather report uplink3.3 FDAMS message downlink

4 Aircraft equipment5 Datalink service provider6 Ground end system7 ARINC specifications8 Acronyms and glossary9 GIS and data discovery10 See also11 References12 External links

History of ACARS

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

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or HF voice radios, which was further augmented with SATCOM in the early 1990s. In many cases, thevoice-relayed information involved dedicated radio operators and digital messages sent to an airline teletypesystem or its successor systems.

Introduction of ACARS systemsThe engineering department at Aeronautical Radio, Inc (ARINC), in an effort to reduce crew workload andimprove data integrity, introduced the ACARS system in July 1978. The first day of operations saw about4,000 transactions. A few experimental ACARS systems were introduced earlier, but ACARS did not startto get any widespread use by the major airlines until the 1980s.

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

Although the term ACARS is often understood as the data link avionics line-replaceable unit installed onaircraft, the term actually refers to a complete air and ground system. The original expansion of theabbreviation was Arinc Communications Addressing and Reporting System.[2] Later, it was changed toAirline Communications, Addressing and Reporting System.

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

On the ground, the ACARS system was made up of a network of radio transceivers managed by a centralsite computer called AFEPS (Arinc Front End Processor System), which received (or transmitted) thedatalink messages as well as routed them to various airlines on the network.

The initial ACARS systems were designed to ARINC Characteristic 597. This was later upgraded in the late1980s by the publication of ARINC Characteristic 724. ARINC 724 is intended for aircraft installed withavionics supporting digital data bus interfaces. ARINC 724 was updated to the current standard ARINCCharacteristic 724B, which is the predominate standard for all digital aircraft.[clarification needed] With theintroduction of ARINC 724B, the ACARS MUs were also coupled with industry standard protocols foroperation with flight management system MCDUs (ARINC 739), and printers (ARINC 740 and ARINC 744).

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The ACARS MU has been since expanded to serve broader needs using a Communications ManagementUnit (CM) defined by ARINC Characteristic 758. Today, new aircraft designs integrate CM functions inIntegrated Modular Avionics (IMA). ARINC Standards are prepared by the Airlines Electronic EngineeringCommittee (AEEC).

OOOI eventsOne of the initial applications for ACARS was to automatically detect and report changes to the major flightphases (Out of the gate, Off the ground, On the ground, and Into the gate), referred to in the industry asOOOI.[3] These OOOI events are determined by algorithms that use aircraft sensors (such as doors,parking brake and strut switch sensors) as inputs. At the start of each flight phase, a digital message istransmitted to the ground containing the flight phase, the time at which it occurred, and other relatedinformation such as amount of fuel on board or flight origin and destination. These messages are used totrack the status of aircraft and crews.

Flight management system interfaceIn addition to detecting events on the aircraft and sending messages automatically to the ground, initialsystems were expanded to support new interfaces with other on-board avionics. During the late 1980s andearly 1990s, a datalink interface between the ACARS MUs and Flight Management Systems (FMS) wasintroduced. This interface enabled flight plans and weather information to be sent from the ground to theACARS MU, which would then be forwarded to the FMS. This feature gave the airline the capability toupdate FMSs while in flight, and allowed the flight crew to evaluate new weather conditions, or alternativeflight plans.

Maintenance data downloadThe introduction in the early 1990s of the interface between the FDAMS / ACMS systems and the ACARSMU resulted in datalink's gaining wider acceptance by airlines. The FDAMS / ACMS systems whichanalyze engine, aircraft, and operational performance conditions were now able to provide performance datato the airlines on the ground in real time using the ACARS network. This reduced the need for airlinepersonnel to go to the aircraft to off-load the data from these systems. These systems were capable of

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identifying abnormal flight conditions and automatically sending real-time messages to an airline. Detailedengine reports could also be transmitted to the ground via ACARS. The airlines used these reports toautomate engine trending activities. This capability enabled airlines to better monitor their engineperformance and identify and plan repair and maintenance activities.

In addition to the FMS and FDAMS interfaces, the industry started to upgrade the on-board maintenancecomputers in the 1990s to support the transmission of maintenance-related information in real-time throughACARS. This enabled airline maintenance personnel to receive real-time data associated with maintenancefaults on the aircraft. When coupled with the FDAMS data, airline maintenance personnel could now startplanning repair and maintenance activities while the aircraft was still in flight.

Interactive crew interfaceAll of the processing described above is performed automatically by the ACARS MU and other associatedavionics systems, without flight crew intervention. As part of the growth of ACARS functionality, the ACARSMUs also interfaced directly with a control display unit (CDU), located in the cockpit. This CDU, oftenreferred to as an MCDU or MIDU, provides the flight crew with the ability to send and receive messagessimilar to today’s email. To facilitate this communication, the airlines in partnership with their ACARSvendor defined MCDU screens that could be presented to the flight crew and enable them to performspecific functions. This feature provides the flight crew flexibility as to the types of information requestedfrom 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 arequest for various types of weather information. After the desired locations and type of weather informationwere entered, ACARS transmitted this information to the ground. In response to this request message,ground computers sent the requested weather information back to the ACARS MU, which was thendisplayed and/or printed.

Airlines began adding new messages to support new applications (weather, winds, clearances, connectingflights, etc.) and ACARS systems were customized to support airline-unique applications, and uniqueground computer requirements. This resulted in each airline having its own unique ACARS applicationoperating on its aircraft. Some airlines have more than 75 MCDU screens for their flight crews, where othermay have only a dozen different screens. In addition, since each airline’s ground computers were different,

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Sample ACARS VHF transmission

The sound of an ACARS VHF transmissionmade on 130.025 MHz, recorded at Petaluma,California on 15 August 2006

Problems listening to this file? See media help.

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, there has been discussion about making ACARS an"online-black-box."[4] If such a system were in place, it would avoid the loss of data due to: (1) black-boxdestruction, and (2) inability to locate the black-box following loss of the aircraft. However the cost, due tothe high bandwidth requirements, would be excessive and there have been very few incidents where theblack 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 theground, and vice versa. Messages may be sent either automatically or manually.

VHF subnetworkA network of VHF ground radio stations ensure that aircraft can communicate with ground end systems inreal-time from practically anywhere in the world. VHF communication is line-of-sight, and providescommunication with ground-based transceivers (often referred to as Remote Ground Stations or RGSs). Thetypical range is dependent on altitude, with a 200-mile transmission range common at high altitudes. ThusVHF communication is only applicable over landmasses which have a VHF ground network installed.

A typical ACARS VHFtransmission.

Mode A

Aircraft B-18722

Ack NAK

Block id 2

Flight CI5118

Label B9

Msg No. L05A

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Message /KLAX.TI2/024KLAXA91A1

SATCOM and HF subnetworksSATCOM can provide worldwide coverage. Depending on the satellite system in use, coverage may belimited or absent at high latitudes (such as needed for flights over the poles). HF datalink is a relatively newnetwork whose installation began in 1995 and was completed in 2001. Aircraft with HF or global SATCOMdatalink can fly polar routes and maintain communication with ground based systems (ATC centers andairline operation centers). ARINC is the only service provider for HF datalink.

Datalink message typesACARS messages may be of three types:

Air Traffic Control (ATC)Aeronautical Operational Control (AOC)Airline Administrative Control (AAC)

ATC messages are used to communicate between the aircraft and Air Traffic Control. These messages aredefined in ARINC Standard 623 . ATC messages are used by aircraft crew to request clearances, and byground controllers to provide those clearances.

AOC and AAC messages are used to communicate between the aircraft and its base. These messages areeither standardized according to ARINC Standard 633 or defined by the users, but in the latter case theymust meet at least the guidelines of ARINC Standard 618 . Various types of messages are possible, forexample, relating to fuel consumption, engine performance data, aircraft position, in addition to free text .

Example transmissions

Departure delay downlinkA pilot wants to inform his flight operations department that departure has been delayed by Air TrafficControl. The pilot loads a CMU MCDU screen that allows him to enter the expected length of and reason forthe delay. After entering the information on the MCDU, he depresses a “SEND” key on the MCDU. The

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CMU detects that the SEND key was pushed, and then generates a digital message containing the delayinformation. This message may include such information as aircraft registration number, the origination anddestination airport codes, the current Estimated Time of Arrival (ETA) before the delay and the currentexpected duration of the delay. The CMU then sends the message to an existing radio (HF, SATCOM orVHF, with the selection of the radio based on special logic contained within the CMU). For a message to besent over the VHF network, the radio transmits the VHF signals containing the delay message, which isthen received by a VHF Remote Ground Station (RGS).

Most ACARS messages are 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 220characters within the body of the message. For downlink messages which are longer than 220 characters,the ACARS unit splits the message into multiple blocks, transmitting each block to the RGS (there is aconstraint that no message may be made up of more than 16 blocks). The RGS collects each block ofsuch multi-block messages until the complete message is received before processing and routing themessage. ACARS also contains protocols to support a retry of failed messages or retransmission ofmessages whenever the service provider changes.

Once the RGS receives the complete message, the RGS forwards the message to the datalink serviceprovider's (DSP) main computer system. The DSP ground network uses landlines to link the RGS to theDSP. The DSP uses information contained in their routing table to forward the message to the airlines orother destinations. This table is maintained by the DSP and identifies each aircraft (by tail number) and thetypes of messages that it can process. (Each airline must tell its service provider(s) what messages andmessage labels their ACARS systems will send, and, for each message, where they want the serviceprovider 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 headerinformation of the message. Using the label contained in the message, the DSP looks up the message inthe table and forwards it to the airline’s computer system. which then processes message.

This processing performed by an airline may include reformatting the message, populating databases forlater analysis, or 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, it may berouted via the airline’s network to both their operations department as well as to a facility at the aircraft’s

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destination, notifying them of a potential late arrival.

The elapsed transmission time from the moment the flight crew presses the send key to the moment it isprocessed by an airline’s computer system varies, but is generally on the order of 6 to 15 seconds. Themessages that are sent to the ground from the CMU are referred to as downlink messages.

Weather report uplinkFor a message to be transmitted to the aircraft (referred to as an uplink message), the process is nearly amirror image of how a downlink is sent from the aircraft. For example, in response to an ACARS downlinkmessage requesting weather 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 themessage containing the actual weather information. This message is sent to the DSP's main computersystem.

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

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 isprocessed by the CMU. For messages destined for the CMU (such as a weather report uplink), the flightcrew refers to a specific MCDU screen which contains a list of all received uplink messages. The flight crewthen selects the weather message for viewing on the MCDU. The ACARS unit may also print the messageon the cockpit printer (either automatically upon receiving the message or in response to the flight crew'spressing a PRINT prompt on the MCDU screen).

FDAMS message downlinkMessages are sent to the ground from other on-board systems in a manner similar to the delay messageexample discussed above. As an example, an FDAMS system may have a series of active algorithms

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monitoring engine exceedance conditions during flight (such as checking whether engine vibration or oiltemperature exceeds normal operating conditions). Upon detecting such an event, the FDAMS systemautomatically creates an engine exceedance condition message, with applicable data contained within thebody of the message. The message is forwarded to the CMU, using what is referred to as ARINC 619 dataprotocols. The CMU then transmits the message to the ground. In this case, the service provider's routingtable for an engine exceedance message is typically defined to have the message routed directly to anairline’s maintenance department. This enables airline maintenance personnel to be notified of a potentialproblem in real time.

There are three major components to the ACARS datalink system:

Aircraft equipmentService providerGround processing system

Aircraft equipment

The heart of the datalink system on board the aircraft is the ACARS Management Unit (MU). The olderversion of MU is defined in ARINC Characteristic 724B . Newer versions are referred to as theCommunications 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 ACARSdownlinks and the destination for uplinks. The MU/CMU is the router. Its function is to route a downlink bymeans of the most efficient air-ground subnetwork. In many cases, the MU/CMU also acts as an endsystem for AOC messages.

Typical airborne end systems are the Flight Management System (FMS), datalink printer, maintenancecomputer, and cabin terminal. Typical datalink functions are:

FMS - sends flight plan change requests, position reports, etc. Receives clearances and controllerinstructions.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 troubleshootingcan be conducted by technicians on the ground by using datalink messages to command diagnostic

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routines in the maintenance computer and analyzing downlinked results.Cabin terminal - Often used by flight attendants to communicate special passenger needs, gatechanges 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 notavailable over the oceans or other vast expansions of uninhabited surface, such as the Amazon Basin.SATCOM is a fairly expensive service that provides (near) worldwide coverage. The Inmarsat satellitenetwork does not cover the polar regions. The Iridium satellite network became usable for ACARStransport in 2007 and provides excellent coverage in the polar regions.

HF is a more recently established subnetwork. Its purpose is to provide coverage in the polar regionswhere Inmarsat coverage is unreliable.

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

Datalink service provider

The role of the datalink service provider (DSP) is to deliver a message from the aircraft to the ground endsystem, and vice versa.

Because the ACARS network is modeled after the point-to-point telex network, all messages come to acentral processing location. The DSP routes the message to the appropriate end system using its networkof land lines and ground stations. Before the days of computers, messages came to the central processinglocation and were punched on paper tape. The tape was then physically carried to the machine connectedto the intended destination. Today, the routing function is done by computer, but the model remains thesame.

There are currently two primary service providers of ground networks in the world (ARINC and SITA),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 Civil Aviation Administration of China

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(CAAC), as well as Thailand and South America with the installation of VHF networks. SITA has operatedthe network in Europe, Middle East, South America and Asia for many years. They have also recentlystarted a network in the USA to compete with ARINC.

Until recently, each area of the world was supported by a single service provider. This is changing, and bothARINC and SITA are competing and installing networks that cover the same regions.

Ground end system

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

ARINC specifications

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

ARINC documents and their specifications

ARINC607

Design Guidance for Avionics Equipment. Includes definition of the Aircraft Personality Module(APM) required for ARINC 758 CMU installation.

ARINC429

Specification for receiving and broadcasting ARINC 429 broadcast data (data transfer betweenavionics LRUs). ARINC 429 is the one-way communication data bus (one pair of data bus use fortransmit data and another pair of data bus use for receive data).

Defines the air/ground protocols for communicating between the ACARS/CMU and VHF ground

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ARINC618

systems. Also defines the format of the ACARS messages sent by the ACARS/CMU as well asreceived by the ACARS CMU. The format of this message is called a Type A message. Thischaracteristic has been updated to define the future VDL Mode 2 AOA operation.

ARINC619

Defines the protocols for the ACARS/CMU to use to transfer file data between other avionics in theaircraft. ARINC 619 covers file protocols that are used to interface with FMS, FDAMS, the cabinterminal, maintenance computers, SATCOM systems and HF voice data radios.

ARINC620

Defines ground-to-ground communication protocols. This includes the format of messages routedbetween a service provider and an airline or other ground system. This is referred to as a Type Bmessage (the air/ground Type A message is reformatted to a Type B message for groundtransmissions).

ARINC622

Describes the processing associated with sending ATC application messages over today’sACARS links (including ARINC 623 ATC messages).

ARINC623

This characteristic identifies ATC related messages that can be generated or received by anACARS MU/CMU system (does not include FANS-1 or FANS-A messages that are processed bythe FMS).

ARINC629

Specification for a bi-directional data bus for sending and receiving data between multiple avionicsLRUs. The specification was initially developed for use on Boeing 777 commercial airplanes, butwas published as an ARINC industry standard in 1999.

ARINC631

Specification for VHF Data Link (VDL) Mode 2. This specification provides general and specificdesign 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.

ARINC724B

Specification for an ACARS MU for ARINC 724B wiring.

ARINC739

Specification for interfacing with Multi-purpose cockpit display units.

ARINC

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740Specification for interfacing to cockpit printers.

ARINC744

ARINC758

Specification for a CMU relative to ARINC 758 wiring. This specification identifies various levels offunctionality, these in turn defining future growth phases for the CMU. Initial CMU systems whichperform today’s ACARS functions are classified as Level OA.

ARINC823

Two-part specification that defines a security framework for protecting ACARS datalink messagesexchanged between aircraft and ground systems. Security services include confidentiality, dataintegrity, and message authentication. Part 1, ACARS Message Security (AMS), specifies thesecurity protocol, and Part 2, Key Management, specifies life-cycle management of thecryptographic 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 contestto 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 anacronym for ACARS Over AVLC, where AVLC itself is an acronym for Aviation VHF Link Control and VHFis 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 takeadvantage of the higher data rate made possible by Mode 2. AOA is an interim step in replacing the

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ACARS protocols with ATN protocols.ATN

Aeronautical Telecommunications Network. As air traffic increases, ACARS will no longer have thecapacity or flexibility to handle the large number of datalink communications. ATN is planned to replaceACARS in the future and will provide services such as authentication, security, and a trueinternetworking 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 asoftware partition in an integrated avionics computer.

CMU Communications Management Unit. Successor to the MU, the CMU performs similar datalink routingfunctions, but has additional capacity to support more functions. CMU standards are defined in ARINCCharacteristic 758.

FDAMS Flight Data Acquisition and Management System

FMS Flight Management System. FMS standards are defined in ARINC Characteristic 702 and 702A.

HFDL High Frequency Data Link is an ACARS communications media used to exchange data such as AirlineOperational Control (AOC) messages, Controller Pilot Data Link Communication (CPDLC) messagesand Automatic Dependent Surveillance (ADS) messages between aircraft end-systems andcorresponding ground-based HFDL ground stations.

HF High Frequency. A portion of the RF spectrum.

LRU

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Line Replaceable Unit. An avionics "black box" that can be replaced on the flight line, without downingthe aircraft for maintenance.

MCDU Multifunction Control Display Unit. A text-only device that displays messages to the aircrew andaccepts crew input on an integrated keyboard. MCDU standards are defined in ARINC Characteristic739. MCDUs have seven input ports and can be used with seven different systems, such as CMU orFMS. Each system connected to an MCDU generates its own display pages and accepts keyboardinput, 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 datalinkmessages 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 theintroduction of VDL Mode 2. The term is derived from POTS (Plain old telephone service) that refers tothe wired analog telephone network.

SATCOM Satellite Communications. Airborne SATCOM equipment includes a satellite data unit, medium to highpower amplifier, and an antenna, possibly with a steerable beam. A typical SATCOM installation cansupport a datalink channel as well as one or more voice channels.

VDL VHF Data Link

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

GIS and data discovery

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[show ]V · T · E ·

[show ]V · T · E ·

[show ]V · T · E ·

In 2002, ACARS was added to the NOAA Observing System Architecture. NOSA provides near realtime WMS maps and an ID search from the NOSA homepage.

See also

Acronyms and abbreviations in avionicsSELCAL

References1. ^ Carlsson, Barbara (October 2002), "GLOBALink/VHF: The Future Is Now" , The Global Link: 4, retrieved

2007-01-242. ^ http://www.arinc.com/downloads/product_collateral/acars_first_datasheet.pdf3. ^ http://aspmhelp.faa.gov/index.php/OOOI_Data4. ^ Online-Black-Box soll Crashs schneller aufklären . (German) Spiegel-Online. June 6, 2009. Accessed

on: June 6, 2009.

External links

ARINC , inventors of ACARSacarsd , free ACARS decoder software for Linux/WindowsACARS on NOSAARINC Standards Document List , list and describe the ARINC standards

Earth-based meteorological equipment and instrumentation

Earth-based meteorological observation systems and weather stations

Telecommunications

Categories: 1978 introductions Aircraft instruments Aviation communications AvionicsMeteorological data and networks

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