ACARS is an aircraft communication system that enables planes to communicate with ground systems. It was created in 1978 to reduce workload and costs. ACARS uses digital data links to transmit messages between onboard equipment, ground-based transceivers, and service providers. Onboard equipment includes a management unit that routes communications and chooses transmission bands, as well as printers and maintenance computers. Messages are transmitted via VHF, HF, or satellite, depending on location. ACARS has improved aviation operations and safety through automated reporting of events and transmission of weather, maintenance, and air traffic control data.

1. ACARS - Aircraft Communication
Adressing and Reporting System
PRESENTATION
Digital Systems
André Baptista
ACARS
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2. A bit of history
Created in 1978.
Developed due the necessity of reducing workload and costs of
operation.
Only funcion: automated time clock system.
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3. ACARS – What is it?
Stands for: Aircraft Communication Adressing and Reporting
System.
9 million ACARS communications every week.
It is a Data-link system that enables an airplane to communicate
with land based systems, through a network of transcievers.
Consists of equipment on board, equipment on the ground, and
a service provider.
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4. Components
Board equipment
Land equipment
DSP – Service Provider
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5. Components
Board equipment
 Managment Unit – Heart of equipment
 Interface with Flight Managment System.
 Routes Comms. to earth
 Automatic choice of band used.
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6. Components
Board equipment
 DataLink Printer
 Prints Uplink Comms from earth.
 Maintenance computer
 Downlink diagnostic and fault messages to base.
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7. Components
Earth Equipment
 Network of transcivers that enables the system do work in the entire world.
 Comms to destination, mostly in VHF.
 End systems
 Central units and user Computers in land based systems.
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8. Components
DSP – Service Provider
Manage the comms that deliver the messages.
The are the owner´s of the netwroks.
SITA and ARINC – Prime DSP´s.
They send the messages from the VHF stations to end-systems.
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9. Components
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10. Messages
ATC - Air Traffic Control Messages
ATC messages are used to communicate between the aircraft and
Air Traffic Control – Clearences.
AOC - Aeronautical Operational Control Messags
AAC – Airline Administrative Control Messages
AOC and AAC messages are used to communicate between cabin or
flight crew and the base operational office.
Standard Messages or user defined.
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11. Sample Messages
Departure Information Downlink
Weather information Downlink
FDAMS Message Downlink
OOOI Events
Out of Gate, Off the Ground, On the Ground, Into the gate.
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12. Sample Messages
Free text uplink message Printed Free text uplink message
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13. Sample Messages
Pre-flight ACARS downlink message Weather request ACARS message
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14. Communications
Three types of Communication:
VHF.
HF.
SatCom
Automatically chosen by the MU - Management Unit.
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15. Communications
VHF: preferred method.
Frequencies between 121.00 MHZ and 132.00 MHZ.
A network of VHF stations assures that the airplane is able to
communicate with ATC, AOC, AAC.
Communication done in line-of-sight.
Maximum distance Airplane - Antenna: 300km .
Not available in Polar locations of the world.
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16. Communications
HF.
Frequencies between 3 MHZ and 30.00 MHZ.
Available since 2001 – relatively new.
Less bandwith than VHF os SATCOM.
Only used in remote locations: Polar locations.
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17. Communications
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Wave propagation diferences between VHF and HF 17
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18. Communications
SATCOM.
New way of communicating.
INMARSAT AND IRIDIUM.
Frequencies between 3 and 30 Gigahertz.
More bandwith than VHF or HF.
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19. Communications
SATCOM.
ACARS
SATCOM communication diagram
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20. Communications
ACARS
Antennas location in an aircraft
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21. DATA CODING
CODING
Data Exchange between VHF-3 and transciever it is coded by
1200HZ and 2400HZ tones.
1200hz tone: bit change (Change of signal – 0 to 1 or 1 to 0).
2400hz tone: no bit change (signal remains the same).
Transmission rate of 2400 bits per second.
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22. DATA CODING
CODING
When all bits are set to 1: enables adjustment of VHF transmition
and reception levels.
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23. DATA CODING
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Thruth table

24. DATA CODING ACARS
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25. QUESTIONS???
CHEERS.
Sistemas Digitais – 3º ano
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