ACARS

What Is It & How To Decode It Using Your Scanner & Software or Hardware.

 

ACARS: Aircraft Communications Addressing and Reporting System is a digital system transmitted over the VHF aircraft band around 131 MHz AM and the HF airband. Traffic is handled by a computer network, in Australia., the Civil Aviation Authority (CASA) and the Department of Transport & Air Safety are responsible but in other countries different organizations are responsible. Not all aircraft are equipped with ACARS but the mode is becoming more widely used.

 

Data does not simply comprise of text messages (although requests for tickets and shower facility at airport terminals have been noted). A series of sensors on the aircraft automatically collate information from the management unit and control units, these relate to height, speed, outside temperature, wind, fuel, engine performance etc, this information being transmitted by ACARS along with general positional data and more.

 

The ACARS data is processed into packets of serial data for efficient handling. The transceiver on-board the aircraft checks the frequency before transmission to ensure that it is clear then produces the short burst of data lasting less than one second.

 

Transmission takes place from air to ground (down-link) and from ground to air (uplink). A flurry of data may be passed at take-off and landing (termed DEMAND MODE as it is triggered by events) but positional transmissions may only occur occasionally, up to an hour apart so it is best to catch transmissions close to a major airport or flight paths to and from. General transmissions during flight (such as weather reports) may not be specifically acknowledged at the time of transmission (to minimise congestion) but reception will be acknowledged when the next transmission occurs.

 

Primary ACARS frequencies are: 131.550 MHz in the USA, Canada & Pacific (secondary being 132.025, 129.125 MHz), 131.450 MHz in Japan and 131.725 MHz in Europe. New London ACARS frequency from December 1999, 136.900 MHz. Additional frequencies in Europe have been reported to include: 131.525 MHz and 136.925 MHz.

 

Sample of typical abbreviations used by ACARS:

 

AL (or FL) Flight level

CZ Cruising speed

DP Dew point

HD Heading

WX Weather

ADF Automatic direction finding

ALT Altitude

CPT Captain

ENG Engine data

FOB Fuel on board

GND Ground

OAT Outside air temperature

TRB Turbulence

POSWX Position weather

WXRQ Weather request

 

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AirNav ACARS Decoder is by far the best ACARS decoder currently available for the aviation enthusiast.

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You just need a VHF receiver. Then using a simple audio cable connect it to the line-in of your Sound Card.

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Q: What do I need to use the program?

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Q: What information will I be able to receive?

A: Each ACARS message comes with Aircraft Registration, Flight Number and other interesting fields, even with free text. AirNav ACARS Decoder will retrieve the aircraft type, company and origin/destination of the flight.

 

Q: How does AirNav ACARS Decoder (ANAD) work?

A: The program receives in realtime information from your Sound Card. It then works the received data and show you not only the received data but also available data for the received message (aircraft type, company, origin and destination of the flight).

 

Q: What is the decoding success rate?

A: AirNav ACARS Decoder decoding success rate is maybe the best available in within any ACARS decoder available. Take in account that AirNav ACARS Decoder does not need any kind of special external hardware. Using only your sound card you will find it much more accurate than current expensive ACARS decoders.

 

BRIEF ACARS EXPLANATION:

(courtesy of ACARS Online Homepage)

ACARS ([A]ircraft [C]ommunication [A]ddressing and [R]eporting [S]ystem) is a digital data link system transmitted via VHF radio which allows airline flight operations departments to communicate with the various aircraft in their fleet.

 

This VHF digital transmission system, used by many civilian aircraft and business jets, can be likened to "email for airplanes," as the registration of each aircraft is it's unique address in the system developed by aeronautical radio giant ARINC (Aeronautical Radio, Inc.). Traffic is routed via ARINC computers to the proper company, relieving some of the necessity for routine voice communication with the company. With ACARS, such routine items as departure reports, arrival reports, passenger loads, fuel data, engine performance data, and much more, can be requested by the company and retrieved from the aircraft at automatic intervals. Before the advent of ACARS, flight crews had to use VHF to relay this data to their operations on the ground.

 

OK...so you've heard a lot about this communications medium. Here's a detailed look at what ACARS is all about:

 

What exactly is ACARS anyway? ACARS ([A]ircraft [C]ommunication [A]ddressing and [R]eporting [S]ystem) is a digital data link system transmitted via VHF radio which allows airline flight operations departments to communicate with the various aircraft in their fleet.

 

This VHF digital transmission system, used by many civilian aircraft and business jets, can be likened to "email for airplanes," as the registration of each aircraft is it's unique address in the system developed by aeronautical radio giant ARINC (Aeronautical Radio, Inc.). Traffic is routed via ARINC computers to the proper company, relieving some of the necessity for routine voice communication with the company. With ACARS, such routine items as departure reports, arrival reports, passenger loads, fuel data, engine performance data, and much more,can be requested by the company and retrieved from the aircraft at automatic intervals. Before the advent of ACARS, flight crews had to use VHF to relay this data to their operations on the ground.

 

The ACARS system is comprised of the following elements:

 

1. The Airborne Subsystem, onboard the aircraft, which consists of the:

 

a.) Management Unit Receives ground-to-air messages via the VHF radio transceiver, and also controls the replies.

b.) Control Unit is the air crew interface with the ACARS system, consisting of a

display screen and printer.

 

2. The ARINC Ground System, which consists of all the ARINC ACARS remote transmitting/receiving stations, and the ARINC computer and switching systems.

 

3. The Air Carrier C2 (Command and Control) and Management Subsystem, which is basically all the ground based airline operations such as operations control, maintenance, crew scheduling and the like, linked up with the ACARS system.

 

Messages can be categorized in two ways: "Downlinks" which are those ACARS transmissions which originate in the aircraft, and "uplinks" are those messages sent from the ground station to the aircraft.

 

A typical series of ACARS transmissions will look something like this example of United 767-300ERs departing from Washington Dulles International (IAD):

 

ACARS mode: 2 Aircraft reg: .N651UA

Message label: QF Block id: 1 Msg. no: M82A

Flight id: UA0978

Message content:-

IAD2241FRA

-----------------------------------------------------------[05/08/1997 22:41]

 

The message label QF refers to an ACARS OFF report/message. The nose gear struts are now retracting, and the ACARS system duly notes this event as the off time. Departure airport and destination station are noted to the left and right of the OFF time respectively.

 

ACARS mode: 2 Aircraft reg: .N651UA

Message label: SA Block id: 2 Msg. no: S82A

Flight id: UA0978

Message content:-

0LS224151V

-----------------------------------------------------------[05/08/1997 22:41]

 

In this example, we see a downlink response to an uplinked weather report,sent by crew request or automatically by the flight operations.

 

ACARS mode: 2 Aircraft reg: .N651UA

Message label: H1 Block id: 3 Msg. no: D89A

Flight id: UA0978

Message content:-

#DFBE13C24651'''''''''''' 8 5972240TO

132202 294 25103269 220

1440 947 520 97418600250107179 5341565144173014923812143 262528 11

0201

-----------------------------------------------------------[05/08/1997 22:42]

 

 

ACARS mode: 2 Aircraft reg: .N651UA

Message label: H1 Block id: 4 Msg. no: D89B

Flight id: UA0978

Message content:-

#DFB89 0 0 0 661 147 47

A6F003980000080000D2A0000000000000000000002A3

B4F4039C8000080000D2A0000000000000000000002A3

1440 950 536

-----------------------------------------------------------[05/08/1997 22:42]

 

In this series of two messages, we see a takeoff (TO) engine performance report.

 

ACARS mode: 2 Aircraft reg: .N651UA

Message label: H1 Block id: 5 Msg. no: D89C

Flight id: UA0978

Message content:-

#DFB97418853250111173 5541565144173614933782162 261527 15

0201 89 -2 0 0 671 146 27

A6F4039C8000080000D32000000000000000000000423

 

-----------------------------------------------------------[05/08/1997 22:42]

ACARS mode: 2 Aircraft reg: .N651UA

Message label: H1 Block id: 6 Msg. no: D89D

Flight id: UA0978

Message content:-

#DFB

B4F083980000080000D32000000000000000000000423

 

-----------------------------------------------------------[05/08/1997 22:42]

 

The engine performance data continues to be downlinked in the above three transmissions.

 

ACARS mode: 2 Aircraft reg: .N651UA

Message label: 5Z Block id: 7 Msg. no: M83A

Flight id: UA0978

Message content:-

/R3 IADFRA 0978-05 IAD

-----------------------------------------------------------[05/08/1997 22:44]

 

This is a downlink response to an uplinked HOWGOZIT report (shown below), which is a United Airlines flight data report format:

 

ACARS mode: 2 Aircraft reg: .N658UA

Message label: RA Block id: J Msg. no: QUHD

Flight id: QWDUA~

Message content:-

10978-23 HOWGOZIT

UA978 IADFRA

IAD 2214/2249 887A

SWANN 2259 37 849

BROSS 2301 37 839

OOD 2307 37 815

RBV 2312 37 801

ACK 2337 37 757

WHALE 2354 37 728

BANCS 0108 37

-----------------------------------------------------------[23/07/1997 22:51]

 

Waypoints are shown in the lefhand column, just below the OUT and OFF times from IAD. OUT refers to doors closing on the aircraft at the gate, and OFF refers to time of departure as outlined above. ETAs at the waypoints along the route are shown in the middle column, requested/expected flight level next

and fuel remaining figures are shown in the right hand column.

 

ACARS mode: 2 Aircraft reg: .N651UA

Message label: _ Block id: 0 Msg. no: S87A

Flight id: UA0978

-----------------------------------------------------------[05/08/1997 22:44]

 

This is a frequent vistor to the ACARS screen, a signal that the aircraft is in the process of receiving uplinked messages.

 

ACARS mode: 2 Aircraft reg: .N651UA

Message label: H1 Block id: 4 Msg. no: D90A

Flight id: UA0978

Message content:-

#DFB/PIREPUA.E22C246510978KIADEDDF 8 5972250CL

122 DATA NOT AVAILABLE

38.9850 -77.46532241 1757 18.0324 14

39.0942 -77.51132243 6802

-----------------------------------------------------------[05/08/1997 22:50]

 

ACARS mode: 2 Aircraft reg: .N651UA

Message label: H1 Block id: 5 Msg. no: D90B

Flight id: UA0978

Message content:-

#DFB 7.5332 13

39.1518 -77.22502247 11805 -4.3307 17

 

-----------------------------------------------------------[05/08/1997 22:50]

 

These two messages are position and weather data downlinked from the aircraft automatically to the ground station.

 

ACARS mode: 2 Aircraft reg: .N642UA

Message label: H1 Block id: 9 Msg. no: F39A

Flight id: UA0970

Message content:-

#M1BPOSN39092W076136,SWANN,215516,230,GOLDA,215624,BROSS,M21,28214,958/TS2155

16,100897B166

-----------------------------------------------------------[10/08/1997 21:55]

 

This is a good example of a position report along the aircraft's flight route. In this case, United flight 970 is a North latitude 39.09.2 and West longitude 76.13.6, which happens to be the waypoint named SWANN, and they were over SWANN at 2155.16 UTC, at FL230 (Flight Level 230 or 23,000 feet),

and they are estimating next waypoint GOLDA at 2156.24, next position BROSS. Outside air temperature is a minus 21, wind 282/14.

 

The following frequencies are used to transmit VHFACARS data to and from the aircraft (see below for HF frequencies):

Updated 25th October, 2003

Frequencies in Mhz

 131.550

 Primary Channel worldwide-AUSTRALIA

 129.125

Additional channel for USA & Canada

 130.025

Secondary channel for USA and Canada

 130.425

Additional channel for USA

 130.450

Additional channel for USA & Canada

 131.125

Additional channel for USA

 131.450

Primary channel for Japan

 131.475

Air Canada company channel

 131.525

European secondary

 131.725

Primary channel in Europe

 136.700

Additional channel for USA

 136.750

Additional channel for USA

 136.800

Additional channel for USA

 136.900

European secondary

 136.925

ARINC European Channel

 136.85

SITA North American Frequency

136.750

New European frequency

131.850

New European frequency

Notes:                  

1/ 130.45 appears to have taken over as the major frequency for US domestic flights between major US airports. 130.025 now has mostly traffic originating/terminating in secondary airports PLUS an increasing number of international flights for ARINC customers.

2/ Although 131.55 is the primary channel in the U.S., several airports such as Chicago and Boston have noted more traffic on the secondary frequencies of 130.025 and 130.45.

3/ The Air Canada channel is only used in Canada. Recently activity has ceased on this channel and it may now be decommissioned. 

4/ 136.925 is a new frequency in Europe. It has been monitored mostly in the London UK area. It is an ARINC channel (verified by all messages being ACARS mode 2) and is used by those airlines who have signed up with ARINC as the exclusive provider. Aircraft already registered with SITA continue to appear on the SITA frequencies for now. Some of this traffic does appear on the SITA freqs but only very occasionally.

5/ 131.125 and 136.800 are new US frequencies that have been noted in the Chicago and New York areas. 131.125 appears to be a major ground frequency in the New York area. 

6/ 136.85 is a new SITA frequency that has been implemented throughout North America.

 

HF ACARS

The following frequencies are used for HF ACARS. All are USB and Mhz.

AUCKLAND

5.583, 10.084, 13.352

BAHRAIN

8.885, 10.045, 11.312, 17.967, 21.982

BARROW

6.646, 8.936

BOLIVIA

11.318, 13.315, 21.997

CALIFORNIA

4.672, 8.559, 10.081, 11.327, 13.276, 21.934

GUAM

8.927, 11.306

HAT YAI

13.270, 17.928

HAWAII

8.912, 10.075, 11.312, 11.348, 17.936

JOHANNESBURG

4.681, 8.834, 21.949

KRASNOYARSK

10.087, 13.321

NEW YORK

5.523, 8.912, 11.315, 13.275, 17.919, 21.934

REYKJAVIK

5.720, 6.712, 8.977, 11.184, 15.025

SHANNON

5.547, 6.532, 8.843, 8.942, 11.384

 

©2003 The Australian Scanning Encyclopedia. All Rights Reserved.

 

There are many ACARS decoding software packages. Some commercial, some shareware and some freeware, I”v einlcuded trial versions of the commercial software and full-working versions of free/shareware ACARS decoders so you too can learn to decode ACARS>

 

The AOR Company make a hardware version of the acars/navtex decoder called “ARD-2” it is no longer made new, but available second-hand. Click here for the ARD 2 Sales brochure

 

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