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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You just need a VHF receiver. Then using a simple audio
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Q: What information will I be able to receive?
A: Each ACARS message comes with Aircraft Registration,
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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
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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
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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
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