ACARS over SATCOM (Satellite Communications) is a communication method used in aviation that enables reliable data exchange between aircraft and ground systems, regardless of the aircraft’s location. It integrates the standard ACARS (Aircraft Communications Addressing and Reporting System) with satellite technology to maintain consistent communication even when flying beyond the range of traditional ground-based radio systems.
Satellite ACARS specifically refers to the transmission of short, text-based messages via satellite links instead of conventional VHF (Very High Frequency) or HF (High Frequency) radios. This method extends ACARS coverage globally, including over oceans, polar regions, and remote airspaces.
As a component of the broader ACARS system, satellite ACARS supports the automatic and manual exchange of critical operational information between pilots, air traffic control, and airline operations centers. Typical message types include:
- Flight plans
- Weather updates
- Position reports
- Maintenance data
- Communications between pilots and airline dispatchers
When an aircraft travels through regions where VHF or HF connectivity is unavailable or unreliable, SATCOM ensures uninterrupted communication, enhancing safety, efficiency, and situational awareness throughout the flight.
HOW DOES IT WORK
The Aircraft’s ACARS system uses satellites to relay messages between aircraft and ground stations, ensuring continuous communication regardless of the aircraft’s location. When a message is generated on board, either automatically by the aircraft systems (such as a position report or maintenance alert) or manually by the pilot (such as a request for weather). it is transmitted from the aircraft’s satellite communication terminal to a satellite orbiting above. Depending on the system in use (such as Inmarsat or Iridium), the satellite then relays this message to a ground station connected to service provider who then forward them to the airline’s operations center or air traffic control. Conversely, messages from the ground follow the reverse path, they are sent up to the satellite and then down to the aircraft.
ADVANTAGES
The advantages of ACARS over SATCOM are as follows
-
Global Coverage
-
Real-time Data Exchange
-
Enhanced Bandwidth
-
Proactive Maintenance
-
Improved Operational Efficiency
-
Two-way Communication
-
Global Emergency Situations
EMERGING TECHNOLOGY: ACARS OVER INTERNET PROTOCOL
ACARS over IP (AoIP) is a modern enhancement of the traditional Aircraft Communications Addressing and Reporting System (ACARS), which facilitates digital communication between aircraft and ground stations. Traditionally, ACARS messages were transmitted via radio frequencies like VHF, HF, or satellite links. AoIP transitions this communication to internet-based networks, utilizing broadband connections such as cellular networks on the ground or onboard WiFi network working on satellite internet while airborne .
Benefits of ACARS over IP
-
Increased Data Capacity: Modern aircraft generate significantly more data than older models. AoIP can handle this increased volume efficiently, alleviating congestion on traditional communication channels .
-
Cost Efficiency: Transmitting data over IP networks can be more cost-effective compared to traditional methods, especially for non-critical information.
-
Enhanced Coverage: In areas where traditional radio communication is limited, such as remote or mountainous regions, AoIP allows data transmission via available cellular networks.
-
Real-Time Data Sharing: AoIP enables faster transmission of operational data, supporting timely decision-making and improved maintenance planning.
SATELLITE SPECIFICATION
Inmarsat and Iridium are two prominent satellite communication providers used for transmitting ACARS data. While both Inmarsat and Iridium offer global coverage, they differ in their satellite network characteristics and approach to communication.
SATELLITE: INMARSAT
1. ABOUT SATELLITE
Inmarsat operates a constellation of geostationary satellites positioned around the globe. These satellites remain fixed relative to the Earth’s surface, ensuring stable communication links with aircraft. Inmarsat’s network provides high-speed data transmission, making it ideal for ACARS data exchange. ACARS messages from the aircraft are routed through the Inmarsat satellite network to reach designated ground stations. This system enables real-time data exchange, including flight plans, weather updates, operational messages, and maintenance reports. The integration of ACARS with Inmarsat ensures seamless and reliable communication regardless of the aircraft’s location, making it particularly valuable for long-haul flights and remote regions.
2.TECHNICAL SPECIFICATION
| Parameter | Value |
|---|---|
| Frequency Range | L-band (1.525–1.660 GHz uplink; 1.6265–1.6605 GHz downlink) for aviation terminals; C-band (6/4 GHz) for feeder links . |
| Operation Modes | Forward (Ground-to-Air) 1. P channel (Packet-switched): 600 bps, 1200 bps (A-BPSK), 10.5 kbps (A-QPSK). 2. C channel (Circuit-switched SCPC):** 8.4/10.5 kbps (A-QPSK). Return (Air-to-Ground): 1. R-channel (Slotted Aloha): 600 bps–10.5 kbps (A-BPSK/QPSK). 2. T-channel (TDMA): 600 bps–10.5 kbps (A-BPSK/QPSK) . |
| Symbol Rate & Modulation | Modulation: Aviation-BPSK (A-BPSK, differential SDPSK), Aviation-QPSK (A-QPSK, offset OQPSK). Symbol Rates: 600–10.5 kbps, adaptive based on channel conditions. FEC: Convolutional coding (R = 1/2, 2/3; constraint length k = 7) . |
| Signal Requirements | C/N₀: >15 dB (20 dB recommended for robust link margin). Doppler Compensation: Minimal (GEO satellite motion <0.1° station-keeping) . |
| Channel Types | P-channel (Packet-switched): ACARS message delivery C-channel (Circuit-switched): Reserved for high-priority voice/data. R-channel (Random Access): Slotted Aloha for uplink requests. T-channel (TDMA): Scheduled uplink transmissions. |
| Network Architecture | Satellites: 4 GEO satellites (I-4 F1-F4) at 98°W, 25°E, 64°E, 143.5°E. Coverage: Regional beams (6 global beams for Aero-H/H+). Latency: ~600 ms (round-trip) . |
| Antenna Type | Directional L-band antennas (e.g., high-gain phased array/HGA for SwiftBroadband; omnidirectional LGA for Classic Aero). |
SATELLITE: IRIDIUM
1. About Satellite
Iridium operates a constellation of low Earth orbit (LEO) satellites. Unlike geostationary satellites, LEO satellites orbit the Earth at lower altitudes, resulting in shorter signal propagation delays and improved coverage at higher latitudes. Iridium’s network consists of interconnected satellites that provide global coverage. ACARS data from the aircraft is sent to Iridium satellites, which relay the information to ground stations. Iridium offers reliable and low-latency communication for ACARS messages, making it suitable for real-time data exchange. Its continuous coverage is particularly advantageous in polar regions and areas with limited ground infrastructure.
2.Technical Specification
| Parameter | Value |
|---|---|
| Frequency Range | L-band (1.616–1.6265 GHz) for user links; Ka-band (23.18–23.38 GHz) for inter-satellite cross-links 12. |
| Operation Modes | Forward (Ground-to-Air): 1. Packet-switched messaging (ACARS blocks) with adaptive rates. 2. Circuit-switched voice/data (optional). Return (Air-to-Ground): 1. Slotted Aloha for random access. 2.ACARS message fragmentation due to LEO satellite handoffs 5. |
| Symbol Rate & Modulation | Modulation: A-BPSK (Aviation Binary Phase Shift Keying) and A-QPSK (Aviation Quadrature Phase Shift Keying) variants 11. Data Rates: Up to 10.5 kbps for forward/return channels, optimized for low-latency LEO transmission 512. FEC: Convolutional coding (rate 1/2, constraint length 7) 11. |
| Signal Requirements | C/N₀: >15 dB (20 dB recommended for stable decoding) 5. Doppler Compensation: Required due to LEO satellite motion (~±30 kHz shift) 12. |
| Channel Types | P (Packet-switched): ACARS message blocks with ARINC 618/619 protocols 9. C (Circuit-switched): Voice or high-priority data 15. R (Random Access): Slotted Aloha for uplink requests 11. |
| Network Architecture | Constellation: 66 LEO satellites at 781 km altitude, 86.4° inclination 12. Coverage: Global, including polar regions 1013. Latency: <1.5 seconds end-to-end (vs. GEO systems) 1112. |
| Antenna Type | RHCP (Right-Hand Circular Polarization) L-band antennas (e.g., passive LGA or active HC610) |
Decoding satellite ACARS messages, including those transmitted via Inmarsat satellites, may be subject to local, national, and international laws and regulations regarding privacy, telecommunications interception, and unauthorized access. This article is intended for educational and informational purposes only. Readers are responsible for ensuring that their actions comply with all applicable laws in their jurisdiction before attempting to receive or decode any satellite or radio signals. Unauthorized decoding or use of protected communications may result in legal penalties. Respect the privacy and security of all users and operators.
HARDWARE REQUIREMENT
Receiver - RTL-SDR Kit
| Antenna | Gain | Best For | |
|---|---|---|---|
| RTL-SDR Active L-Band Patch Antenna (Recommended) | Moderate | Beginners and general L-band reception | |
| Nooelec Satellite Mesh Antenna (Inmarsat Setup) | High | Suitable for professional setups where signal strength is a priority. | |
| GPS-Style Active L-Band Patch Antenna | Low | Best option for budget setups |
Ultra-Low Noise Amplifier- Nooelec SAWbird iO (Inmarsat AERO/STD-C (only for Nooelec Satellite Mesh Antenna Setup )
Software / Driver Installation - WINDOWS
To begin decoding Inmarsat signals, you will need to install the following software/driver components:
1. SDRSDRSharp: A software-defined radio application used for receiving and analyzing radio signals.
Installing SDR Software
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Step 1: Download Software Defined Radio Package from site: Link
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Step 2: Extract the file and launch the application SDRSharp.dotnet9.
New user need to install the .NET Desktop Runtime for the application to run. The application will start upon launch if it’s already installed in your PC.
2. JAERO: A decoder specifically designed for processing and decoding ACARS messages transmitted via Inmarsat satellites. - - Download
3. Zadig: A Windows application that installs generic USB drivers.
Installing Zading
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Step 1: Download Zadig RTL-SDR Drivers: Link
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Step 2: Once Dowload is completed. Connect RTL-SDR to PC and launch Zadig Software.
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Step 3: Click on options, then List All Devices
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Step 4: Select Bulk-In, interface (Interface 0)
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Step 5: Now click on install WCID Driver. For me it showing Replace Driver as i’m replacing the existing driver of my RTL-SDR.
The PC will recognize RTL-SDR as a USB device when the above step is completed.
4. VB-Audio Virtual Cable: A virtual audio driver that routes the audio output from SDR# to JAERO for decoding. - - Download
5. RTL-biastee Driver: A driver in the RTL-SDR software stack that enables 4.5–5V DC power output from rtl-sdr through the antenna port to power active antennas or low-noise amplifiers (LNAs), removing the need for an external power source. - - Bias tee driver
Configuration
SDRSharp
When you launch the application, you will be greeted with the following interface.
Radio Settings
- Mode: Select USB (Upper Side Band)
- Bandwidth: Set between 3,000 - 4,000 kHz
- Source: RTL-SDR USB
- Device: Generic RTL2832U OEM
Click on the gear icon to access RTL-SDR Controller
- Device: Generic RTL2832U OEM
- Sample Rate: Configure to 2.048 MHz (adequate for L-band coverage)
- Sampling Mode: Quadrate Sampling
- Offset Tuning / RTL AGC / TUNER AGC: Check the Box
- Critical: Ensure “Filter Audio” is UNCHECKED
- Output Device: Select “[Windows DirectSound] Cable Input (VB-Audio)”
- Latency: Set to 100ms
- Volume: Adjust to approximately 75% level
Jaero
- CPU Optimization: Click the black CPU square to turn it green
- Logging: DISABLE unless specifically needed to improve performance
- Audio Beeps: UNCHECK to avoid constant notification sounds
- Click the gear icon to access Settings
- Select your VB-CABLE as the audio input device
Decoder Settings:
- Data Rate: Select appropriate rate based on signal type:
- 600 baud: Lower speed channels
- 1200 baud: Medium speed channels
- 10500 baud: High-speed data channels
- 8400 baud: Voice channels (C-channels)
Signal Processing:
- AFC (Automatic Frequency Control): ENABLE this feature
Satellite Coverage
Inmarsat operates geostationary satellites positioned over the equator.
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Inmarsat-4 F3: 98° West longitude – Americas. → Live Tracking
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Inmarsat-3 F5: 54° West longitude – Atlantic Ocean Region-East, covering Europe, the Middle East, and Africa. → Live Tracking
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Inmarsat-4A F4 (Alphasat): 25° East longitude – Europe, Africa, and parts of Asia. → Live Tracking
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Inmarsat-4 F1: 143.5° East longitude – Asia-Pacific region. → Live Tracking
Antenna Setup // Alignment // Run the Sofware
To effectively receive signals from these satellites, follow these general steps:
Step 1: Determine Your Location: Note your latitude and longitude coordinates.
Step 2: Select the Appropriate Satellite: Choose the satellite that provides optimal coverage for your region (as outlined above).
Step 3: Azimuth / Elevation Alignment:
- Create an account in N2yo and enter the Coordinates of your location by clicking on More stuff.
- Once done, choose the satellite which is giving coverage to your area by clicking the Live Tracking Link above will give you information on where to point, which will give you an approximate angle to point the antenna.
Step 4: Elevation Alignment: Tilt your antenna vertically to match the calculated elevation angle.
- Polarization: Inmarsat satellites use Right-Hand Circular Polarization (RHCP). Ensure your antenna supports RHCP or adjust accordingly.
Step 4: Run the Software:
- Before running the software, close SDR-Sharp to enable biastee.
- Open the RTL-Biastee file, click on bias_tee_on file, make sure rtl-sdr is plugged in before running the file & it is connected to the antenna. you’ll see a command prompt opening and closing. Don’t worry, it’s how the file enables the biastee in rtl-sdr.
- Now open SDR-SHARP, tune to 1.545.000.000. Once done, hit play on the top left icon. Voilà you’ll now start to receive signals from inmarsat.
Step 5: Fine-Tune the Position:
- Monitor signal strength using your SDR software.
- Make slight adjustments to azimuth and elevation to maximize signal quality.
Step 6: Secure the Antenna: Once optimal alignment is achieved, firmly secure the antenna to prevent movement.
Step 7: Visual Indicators :
Run Jaero Now, you’ll see 3 dots on the bottom left indicating volume, signal, data.
- Volume Icon (Left): Must be GREEN
- Red: Signal too strong - reduce gain
- Gray: Signal too weak - increase gain
- Yellow: Borderline - fine-tune gain settings
- Signal Icon (Center): Should be GREEN
- Indicates proper signal detection and lock
- Data Icon (Right): Turns GREEN when successfully decoding packets
- When Jaero starts to decode the messages, you can see the messages in ACARS Section.
- For More Organized log, click on log icon above to get Plane Log.
Decoded ACARS Messages
Here are some of the ACARS Messages i’ve logged.
Message from IOCC
08:09:48 26-06-23 UTC AES:781D13 GES:50 2 .B-328A ! RA Z Airbus A319 153NSL China Southern Airlines
QUCANXMCZ~1RA260808
B-328A
DEAR CAPT,
PLEASE PAY ATTENTION TO THE FUEL AND WX, TELL US IF YOU NEED HELP.
16:15:08 02-08-22 UTC AES:5002A3 GES:82 2..T7HUA ! RA F
QUARINCXA~1GRD 2 AIR MSG
DEAR CAPT
JUST GOT MSG FM GH
SAID THE TANOA INT'L, HOTEL IS ALL FULL BOOKING AND DO U HV ANY OTHER OPTION Q
GH CAN HELP TO MAKE RSVN FOR U SIR
AY KU
Cargo manifest // Weight & Balance
11:33:39 23-05-23 UTC AES:020066 GES:C5 2 .CN-ROE ! C1 U Boeing 737NG 8B6/W Royal Air Maroc
.MUCKMAT 231129
AGM
AN CN-ROE/GL CMN/MA 003A
- SPECIAL LOAD NOTIFICATION TO CAPTAIN FINAL EDNO 1
FROM FLIGHT DATE A/C REG
CMN AT940/23 23MAY23 CN-ROE
***************************************************************
*** DANGEROUS GOODS ***
TO AWB CL/DV UN/ID SUB PCS QTY/TI RRR PCK IMP CAO POS
NR COMP NR RSK CAT GRP DRIL ULD/CODE
---------------------------------------------------------------
NO DANGEROUS GOODS UPLIFTED EX CMN
***************************************************************
*** OTHER SPECIAL LOAD ***
TO AWB CONTENTS PCS QTY IMP POS
NR CODE ULD/CODE
---------------------------------------------------------------
001. FISH/SEAFOOD FOR HUMA 18 190KG PES 31
FCO FRESH FISH BULK
44145986
...............................................................
002. FISH/SEAFOOD FOR HUMA 25 188KG PES 31
FCO FRESH FISH BULK
44133946
***************************************************************
SI FCO FRE 544
***************************************************************
THERE IS NO EVIDENCE THAT ANY DAMAGED OR LEAKING PACKAGES
CONTAINING DANGEROUS GOODS HAVE BEEN LOADED ON THE AIRCRAFT.
***************************************************************
LOADING SUPERVISOR CAPTAIN
(NAME AND SIGNATURE) (NAME AND SIGNATURE)
EMERGENCY TELEPHONE NUMBER 212 522 49XXXX
11:35:25 23-05-23 UTC AES:020066 GES:C5 2 .CN-ROE ! C1 E Boeing 737NG 8B6/W Royal Air Maroc
MACDLW 19.9
MACZFW 25.9
MACZFW TWO-FIVE-DECIMAL-NINE
MACTOW 26.3
MACTOW TWO-SIX-DECIMAL-THREE
MACLAW 26.0
MACLAW TWO-SIX-DECIMAL-ZERO
FWD-LMT ACTL AFT-LMT
TOMAC 12.84 26.25 31.53
LWMAC 10.05 25.99 30.01
STAB:
FUEL DENSITY 0.803
CENTRE 3643
WINGS 7857
A7 B77 C68
SEATROW TRIM
SI BW 41256
BI 42.6
DOW 43122
DOI 44.1
LOAD IN CPTS 0/0 1/0 2/1540 3/1332 4/
340
CHECKED BAGGAGE PIECES FCO 2/Y/90
FCO 3/Y/46 4/F/12/T/4
FCO BAG 2668 FRE 544
POS 0 TRA 0
FUEL IN TANKS 11500
CREW CODE STANDARD
CREW EFFECT 470 / 3.2 -
PANTRY CODE C
PANTRY EFFECT 1159 / 1.5
SERVICE WEIGHT ADJUSTMENT WEIGHT/INDEX
ADD
FCO FULL WATER
237 3.3
DEDUCTIONS
NIL
NOTOC: YES
CHECKED BY MOUNIA BOUZIANE
APPROVED BY
LAST MINUTE CHANGES
DEST SPEC CL/CPT - WEIGHT
11:37:35 23-05-23 UTC AES:020066 GES:C5 2 .CN-ROE ! C1 L Boeing 737NG 8B6/W Royal Air Maroc
.MUCKMAT 231130
AGM
AN CN-ROE/GL CMN/MA 002A
- LOADSHEET FINAL 1229 EDNO1
AT940/23 23MAY23
CMN FCO CN-ROE 2/4
ZFW 58560 MAX 62731
ZFW FIVE-EIGHT-FIVE-SIX-ZERO
TOF 11300
TOW 69860 MAX 75069
TOW SIX-NINE-EIGHT-SIX-ZERO
TIF 6800
LAW 63060 MAX 66360 L
LAW SIX-THREE-ZERO-SIX-ZERO
UNDLD 3300
PAX/7/145 TTL 152
PAX 152 PLUS 0
BI 42.6
DOI 44.1
DLI 44.8
LIZFW 60.3
LITOW 64.4
LILAW 61.7
MACDLW 19.9
MACZFW 25.9
MACZFW TWO-FIVE-DECIMAL-NINE
MACTOW 26.3
MACTOW TWO-SIX-DECIMAL-THREE
MACLAW 26.0
MACLAW TWO-SIX-DECIMAL-ZERO
FWD-LMT ACTL AFT-LMT
TOMAC 12.84 26.25 31.53
LWMAC 10.05 25.99 30.01
STAB:
FUEL DENSITY 0.803
CENTRE 3643
WINGS 7857
A7 B77 C68
SEATROW TRIM
SI BW 41256
BI 42.6
DOW 43122
DOI 44.1
LOAD IN CPTS 0/0 1/0 2/1540 3/1332 4/
340
CHECKED BAGGAGE PIECES FCO 2/Y/90
FCO 3/Y/46 4/F/12/T/4
FCO BAG 2668 FRE 544
POS 0 TRA 0
FUEL IN TANKS 11500
CREW CODE STANDARD
CREW EFFECT 470 / 3.2 -
PANTRY CODE C
PANTRY EFFECT 1159 / 1.5
SERVICE WEIGHT ADJUSTMENT WEIGHT/INDEX
ADD
FCO FULL WATER
237 3.3
DEDUCTIONS
NIL
NOTOC: YES
CHECKED BY MOUNIA BOUZIANE
APPROVED BY
LAST MINUTE CHANGES
DEST SPEC CL/CPT - WEIGHT
ATC
12:19:17 23-05-23 UTC AES:AE0472 GES:C1 2 .71459S ! 14 M Boeing KC-135R United States Air Force
FTX/ID71459S,RCH603,QEN590682138/MR0,/FXWHEN DO YOU EXPECT TO DEPT I WILL NEED TO DELAY YOU4645
CPDLC
13:24:54 07-10-25 UTC AES:71BF82 GES:82 2 .HL7782 ! AA I Boeing 777 3B5ER Korean Air
/OAKODYA.AT1.HL7782E29CD620521311FC7F56
FANS-1/A CPDLC Message:
CPDLC Uplink Message:
Header:
Msg ID: 5
Msg Ref: 14
Timestamp: 13:24:32
Message data:
CLEARED TO DEVIATE UP TO [distanceoffset] [direction] OF ROUTE
Offset: 20 nm
Direction: right
REPORT BACK ON ROUTE
ATIS
13:13:10 07-10-25 UTC AES:780191 GES:82 2 ..B-HLQ ! A9 Z Airbus A330 343X Cathay Pacific Airways
/HKGATYA.TI2/VHHH DEP ATIS Q
1234Z
DEPARTURES, RWY 07R.
WIND 150/06KT VIS 10KM CLD FEW 2500FT T3
0 DP22 QNH 1013HPA=
ACKNOWLEDGE INFO Q ON FIRST CTC WITH DELIVERY..A270
Clearance
09:57:44 06-10-25 UTC AES:780191 GES:82 2 ..B-HLQ ! A3 V Airbus A330 343X Cathay Pacific Airways
/HKGCPYA.DC1/CLD 0957 251006 VHHH PDC 634
CPA328 CLRD TO ZSSS OFF 07R VIA LEKEN1X
SQUAWK 3343 NEXT FREQ 122.150 ATIS X
CLIMB VIA SID TO 5000FT. ACK PDC. CTC DELIVERY ON 122.15 WHEN READY TO START0684
Hawaiian Airlines, Emirates, Qatar Airways, South African Airways, Lufthansa, TAP Portugal, All Nippon Airways (ANA), Cathay Pacific, Singapore Airlines, Thai Airways, Turkish Airlines, Air France, KLM, United Airlines, Delta Airlines, Air India, Ethiopian Airlines, Philippine Airlines, Air Algerie are some of the major airlines along with Over 200+ airlines including business jets, military aircraft using imarsat serivce.
SOURCE: Wikipedia, ICAO, Wavecom, RTL-SDR, SkyBrary, thebaldgeek, github, Inmarsat.com
Future Topics
- Receiving & Decoding Live ACARS from Iridium - Part II
- Listening to Local ATC | Real-Time
- Building an ADS-B Receiver | Live Flight Tracking
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