Receiving / Decoding ACARS Transmissions from Aircraft With Your Macintosh

Introduction

One of the more interesting digital modes that can be monitored are ACARS transmissions from commercial aircraft. Many of the routine messages that were formerly sent by voice are now sent by an ACARS digital link between the radio and ground. This messages can be received on any scanner type radio that tunes the VHF Aircraft band (118-136 MHz) using our MultiMode software, without the need for extra hardware.

You'll need a radio that tunes the above-mentioned band, in AM mode. Most scanners will do this fine. You'll then need to connect the audio output of that radio into the sound input (microphone) jack of your Mac. If your Mac doesn't have sound input, you can always use an iMic or other USB based sound input device.

Next, fire up a copy of MultiMode and selec ACARS mode.

Now, tune your radio to one of the ACARS frequencies. There are several to choose from:

131.550			Primary Channel worldwide
130.025			Secondary channel for USA and Canada
129.125			Additional channel for USA & Canada
130.450			Additional channel for USA & Canada
131.125			Additional channel for USA
136.700			Additional channel for USA
136.800			Additional channel for USA
131.725			Primary channel in Europe
131.525			European secondary
131.475			Air Canada company channel
131.450			Primary channel for Japan
136.900			European secondary
136.925			ARINC European Channel
136.850			SITA Canadian Frequency

Next you'll want to know what you should be hearing. Click here to listen to a typical ACARS packet You'll find that weekdays are the busiest times to listen, often you can hear a packet sent every few seconds. Due to the height of aircraft (30,000 feet or more), their ACARS transmissions can be heard for great distances, up to a few hundred miles.

Many of the messages are routine, such as:

.N643DL  Q0 0   [26 Jan 2004   16:28:05][DAL Boeing 757 23997]
S77A DL2581

N643DL is the tail number of the plane. Q0 0 is the message type. The date and time are automatically stamped by MultiMode. The aircraft database file that comes with MultiMode has identified the tail number, and displayed information about the airplane, which type it is. Finally the message itself is displayed on the next line.

Some of the messages are less routine, and more interesting. I won't divulge any here, but they include unruly passengers, and equipment failures onboard the aircraft, usually involving the lavatory.

ACARS is a fun mode to monitor, and quite easy. Just connect your radio to your Mac, run a copy of MultiMode, and sit back and watch the messages. You can even set up MultiMode to automatically write all the information received to a log file, so you can monitor unattended, such as during the daytime, and then come back and view what has been received.

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Chris Smolinski