ACARS
AIRCRAFT(ARINC)
COMMUNICATION,
ADDRESSING AND
REPORTING
SYSTEM
ACARS
• WAS DEVELOPED IN 1970S AS AIRCRAFT
BEGAN TO BE EQUIPPED WITH DIGITAL
AVIONICS
• WAS DEVELOPED TO PROVIDE
AUTOMATICALLY, THE ARRIVAL AND
DEPARTURE TIMES AND AIR GROUND
EXCHANGE OF OPERATIONAL DATA
BETWEEN AIRCRAFT AND AIRLINES
OPERATIONS CENTERS
AIRLINE DATALINK EVOLUTION
• DATA LINK WAS FIRST INTRODUCED TO
PROVIDE AIRCRAFT MOVEMENT REPORT
IN PLACE OF AIR GROUND VOICE REPORT
• ONE COMMON USE NOW IS TO PROVIDE
AIRCRAFT SYSTEM STATUS REPORT TO
THE AIRLINE ON REAL TIME BASIS
• PROVISION OF FLIGHT CREW INITIATED
INFORMATION REQUEST AND GROUND
INITIATED REQUESTS
ACARS USE
• ALLOWS AIRCREW TO SEND
ARRIVAL/DEPARTURE TIMES, FUEL STATUS,
FLIGHT DELAY etc.
• GROUND MONITORING CAPABILITY OF
AIRCRAFT ENGINE AND OTHER PARAMETERS,
EFFICIENT EXCHANGE OF INFORMATION
CONCERNING CONNECTING FLIGHTS AND
RELIABLE SELECTIVE CALLING SYSTEM
ACARS AVIONICS
• TO COMMUNICATE VIA AN ACARS NETWORK,
AN AIRCRAFT MUST BE EQUIPPED WITH
AVIONICS THAT PROCESSES THE ACARS
PROTOCOL. THE ORIGINAL IMPLEMENTATION
OF THE ACARS PROTOCOL IN AVIONICS WAS IN
ACARS MANAGEMENT UNIT (MU). THE MAJOR
SUPPLIERS OF ACARS MU ARE TELEDYNE,
ROCKWELL COLLINS AND HONEYWELL
ACARS IMPLEMENTATION
• ON BOEING • ON AIRBUS
AIRCRAFT ACARS AIRCRAFT,
MU IS PERFORMED AEROSPATIALE HAS
BY THE AIRCRAFT DEVELOPED AN AIR
INFORMATION TRAFFIC SERVICE
UNIT (ATSU) WHICH
MANAGEMENT
HANDLES ACARS MU
SYSTEMS (AIMS)
FUNCTIONS AND
DEVELOPED BY ALSO HOSTS ATS
HONEYWELL APPLICATIONS
HOW ACARS WORKS
• DATA CONCERNING DEP/ARR TIMES, FUEL
STATUS, FLIGHT RELATED PARAMETERS etc.
AUTOMATICALLY COLLECTED OR ENTERED
INTO SYSTEM, CONVERTED INTO IT5 (7 UNIT
WITH 8TH FOR PARITY) AND FORMED INTO
BLOCKS OF 220 CHARACTERS MAX.
• MESSAGE TRANSMITTED TO GROUND WHICH
IS SENT TO ARINC/SITA CENTRAL SWITCH.
HOW ACARS WORKS
• WORKS IN TWO MODES:
– 1. DEMAND MODE: EITHER THE GROUND OR AIRBORNE
SYSTEM TO INITIATE COMMUNICATION. AIRBORNE
SYSTEM WILL INITIATE WHENEVER A PREDEFINED EVENT
HAPPENS OR WHEN PILOT COMMAND IS ENTERED.
GROUND STATION DETERMINES IF MESSAGE IS ERROR
FREE, ROUTES IT TO DESTINATION AND ISSUES ACK. IF
ERROR IS FOUND, ACK MESSAGE IS NOT ISSUED AND
AIRCRAFT MAKES UPTO 6 ATTEMPTS AND THEN ALERT
THE CREW. IN UPLINK MESSAGE HOWEVER NEG. ACK
(NAK) MESSAGE IS ISSUED
HOW ACARS WORKS
• - 2. POLLED MODE: ALLOWS ONLY
GROUND PROCESSOR TO INITIATE.
GROUND SYSTEM CONTINUOUSLY
POLL MESSAGES AND ANALYSES
AIRCRAFT REPLIES.
Message Content
• ACARS messages may be of three types
based upon their content:
• Air Traffic Control (ATC)
• Aeronautical Operational Control (AOC)
• Airline Administrative Control (AAC)
• 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).
• 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.
• The Service Provider
• A Datalink Service Provider (DSP) is responsible for the
movement of messages via radio link, usually to/from its
own ground routing system. ACARS messages are
transmitted using one of three possible data link methods:
• VHF or VDL (VHF Data Link) which is line-of-sight
limited
• SATCOM which is not available in polar regions
• HF or HFDL (HF Data Link) which has been added
especially for polar region communications
• The main primary DSPs are ARINC and SITA. Until quite
recently, each part of the world was covered by a single
DSP but competitive offerings are now increasingly
available.
