1. AIRCRAFT(ARINC) COMMUNICATION, ADDRESSING AND REPORTING SYSTEM
ACARS
AIRCRAFT(ARINC) COMMUNICATION, ADDRESSING AND REPORTING SYSTEM

2. 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

3. 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

4. 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

5. 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

6. ACARS IMPLEMENTATION
ON BOEING AIRCRAFT ACARS MU IS PERFORMED BY THE AIRCRAFT INFORMATION MANAGEMENT SYSTEMS (AIMS) DEVELOPED BY HONEYWELL
ON AIRBUS AIRCRAFT, AEROSPATIALE HAS DEVELOPED AN AIR TRAFFIC SERVICE UNIT (ATSU) WHICH HANDLES ACARS MU FUNCTIONS AND ALSO HOSTS ATS APPLICATIONS

7. DATA LINK ACCESS FOR AIRCRAFT SYSTEM
ACARS AVIONICS DEVELOPED SINCE 1990 PROVIDE OTHER AIRCRAFT COMPUTER DATA SUCH AS PERFORMANCE MONITORING AND FLIGHT MANAGEMENT SYSTEMS ACCESS TO AIR GROUND DATA LINK
AIR GROUND PROTOCOL AND MODULATION SCHEME IS SPECIFIED IN AEEC SPECIFICATIONS 618 “AUR/GROUND CHARACTER ORIENTED PROTOCOL SPECIFICATION”
CHANNELS USED IN THE AERONAUTICAL MOBILE EN-ROUTE SERVICE OR AM(R)S MHz
EACH CHANNEL HAS 25 KHz BANDWIDTH

8. DATA LINK ACCESS FOR AIRCRAFT SYSTEM
MU CONTAINS A MODEM THAT USES MINIMUM SHIFT KEYING (MSK) AMPLITUDE MODULATION PROVIDING A DATA RATE OF 2400 BITS/SECOND
VHF ACARS STATIONS ON GROUND PROVIDE OVERLAPPING RANGE USING THE SAME FREQUENCY
AS ON 31ST DEC, 1999 THERE WERE 517 REMOTE GROUND STATIONS WERE OPERATING
ASSIGNED FREQUENCIES ARE:
MHz FOR EUROPE, SOUTH AMERICA, CARIBBEAN, MIDDLE EAST, AFRICA AND ST. PIERRE ET MIQUELON(FRENCH CANADA)
MHz FOR ASIA, NEW ZEALAND AND THE PACIFIC
MHz FOR United States of America AND CANADA
TO PARTLY MEET THE REQUIREMENT OF DENSE TRAFFIC IN EUROPE, MHz PROVIDED FOR ENROUTE AND MHz PROVIDED FOR USE ON GROUND

9. DATA LINK ACCESS FOR AIRCRAFT SYSTEM
TO SWITCH AIRCRAFT FROM ONE FREQUENCY TO THE OTHER WHILE ENROUTE, VHF MULTI FREQUENCY MANAGEMENT SYSTEM (VMMS) IS USED WHICH AUTOTUNES THE AIRBORNE SYSTEM
VMMS RECEIVES COPIES OF AIRCRAFT FLIGHT MOVEMENT MESSAGES TO IDENTIFY WHEN THE AIRCRAFT IS AIRBORNE AND SHOULD USE THE ENROUTE FREQUENCY AND WHEN IT IS ON GROUND SHOULD USE AIRPORT FREQUENCY
AEEC 620 PROTOCOL SUPPORTS EXCHANGE OF MESSAGES CONTAINING APPLICATION DATA ENCODED AS CHARACTER. USES A 2 CHARACTER ACARS LABEL ON AIR GROUND CONNECTION AND 3 CHARACTER STANDARD MESSAGE IDENTIFIER (SMI) ON THE INTERFACE TO GROUND SYSTEM

10. DATA LINK ACCESS FOR AIRCRAFT SYSTEM
AIRCRAFT, SUITABLY EQUIPPED CAN ACCESS THE DATA LINK VIA INMARSAT AERONAUTICAL MOBILE SATELLITE SERVICE (AMSS)
FOUR GEOSTATIONARY SATELLITES PARKED OVER ATLANTIC OCEAN (WEST), ATLANTIC OCEAN (EAST), INDIAN OCEAN AND PACIFIC OCEAN PROVIDE COVERAGE BETWEEN 80 DEG NORTH AND 80 DEG SOUTH
AIRBORNE/GROUND SYSTEM MAY INDICATE A PREFERENCE FOR THE USE OF VHF OR AMSS MEDIA

11. 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.

12. 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

13. HOW ACARS WORKS
- 2. POLL MODE: ALLOWS ONLY GROUND PROCESSOR TO INITIATE. GROUND SYSTEM CONTINUOUSLY POLL MESSAGES AND ANALYSES AIRCRAFT REPLIES

14. MESSAGE FORMAT BLOCK IDENTIFIER(1) (UPLINK ONLY) LABEL(2) SUFFIX (1)
END OF TEXT OR
END OF BLOCK
ACKNOWLEDGEMENT(1)
END OF PREAMBLE(1)
(START OF TEXT)
ADDRESS(7)
BCS
SUFFIX
MODE(1)
START OF HEADING(1)
TEXT (220)
BLOCK CHECK
SEQUENCE (2)
16 BITS
CHARACTER SYNC(2)
BIT AMBIGUITY(2)
PERKEY(16)
PREAMBLE

15. MESSAGE FORMAT
Preamble:Identifies the message, synchronization of message
Prekey: 16 char for MU to establish bit and character sync
Bit Ambiguity: two char (+,*) to establish bit recognition correct
Char Synchronization: Two consecutive char are sent to establish char synchronization
Start of Heading: Char sent to indicate start of message heading also block check sequence
Mode: To be used in future (RTCA)
Address: Identifies destination. MU matches the address. Down link identifies aircraft originating
Acknowledgement: MU clears from memory last down link message only after receiving ACK message. Upon receiving NAK ground will retransmit
Label: Identifies message type like ‘QT’ for departure report, ‘5D’ ATIS request etc.
Up link Block Identifier: Changes char every time a new message or general message is sent
End of Preamble: Identified by characters ‘ETX’ for message containing no TEXT and ‘STX’ for message containing TEXT.
Text: Free talk included + others
Suffix: End of Text(ETX)/End of Block(ETB)
Block Check Seq: Gen. ACK or NAK

16. ATN/VDL HISTORY 1988 FANS Committee proposes concept of ATN Internet
1990 ICAO decides to specify ATN subnet provision over a VHF Link
1991 Aeronautical Mobile Communications Panel initiates VDL Standards
1997/98 ICAO adopts VDL and ATN Standards

17. ATN INTERNET
ATN Internet provides transparent data connectivity across diverse terrestrial and air-ground network
Difference compared to generic Internet is the ATN addresses which contain airline or country codes and creates a routing domain for each airline/civil aviation authority

18. ATN INTERCONNECTION
ATN user system communicates via ATN routers which handle the ATN Internet Protocols
ATN Systems are interconnected by subnetworks which provide the foundation for ATN internet
ATN subnetwork can be provided using the X.25 protocol

19. ATN SUBNETWORK
ATN ground systems connect over existing X.25 networks such as SITA etc.
ATN avionics can connect to ATN ground systems using the X.25 based services of AMSS, VDL, Mode ‘S’ and HFDL
There is no limit to message length over VDL X.25 connections
Aircraft can establish an explicit VDL a/g link using a unique address for each ground station

20. VDL SERVICE PERFORMANCE
One VDL channel provides a 20 fold capacity increase over one ACARS channel
VDL link protocol reduces transmission overhead
Applications:
ACARS based
AOC bit oriented
ATS bit oriented