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Black Cat Absolute ACARS

A full featured program that decodes and displays VHF ACARS transmissions directly from SDR I/Q recording files, and is available for macOS and Windows.

Most traditional ACARS decoding programs only decode audio from one frequency at a time, some can handle a few frequencies. This means you're missing out and not receiving ACARS messages on the frequencies you're not monitoring.

And even with decoders that can handle multiple audio sources, you need to set up receivers in your SDR software for each frequency (up to whatever limit it has) along with multiple virtual audio cables to pass audio from the SDR software to the ACARS decoding program. What a mess.

This program does away with those limitations. It directly demodulates and decodes ACARS transmissions from SDR I/Q recording files, covering several MHz of bandwidth. It monitors the directory your SDR program saves I/Q files in, detects when a new file has been created, waits for that file to be finished written to, then opens it, decodes on all the selected ACARS frequencies, and then deletes the file, so your hard drive doesn't fill up. As new I/Q files are written every minute or two, there's minimal delay in seeing the ACARS messages.

You can even run this decoding program on a second computer, and access files on the computer with the SDR software creating writing the I/Q files over your local network.

In addition to displaying decoded messages, both on a per channel basis as well as all frequencies combined into one display, messages can be written to text logging files, either with a manually selected filename, or into rolling timestamped files.

Messages are also sorted by message type, aircraft tail number, flight number, and frequency. Display/logging of messages of specified types can also be disabled, reducing the amount of "clutter" of unwanted messages.

The Open Sky Network database file can also be used with this program, to display information about aircraft along with their messages.

Currently within the USA, VHF ACARS transmissions are found in the 128.975 – 131.850 MHz frequency range. Centering your SDR at approximately 130.4 MHz with at least a 3 MHz effective bandwidth (which usually means about a 4 MHz sample rate) will cover this entire range, allowing you to decode every ACARS channel at the same time.

You can change the color scheme and font type/size to your preferences.

Received messages can be sorted by flight:

Received messages are also sorted by plane:

And by frequency:

There's also a sorted list by message types:

Click on a line in either list to view all the messages from that plane, or of that type:

Black Cat Absolute ACARS is available for download and trial prior to purchase, so you can make sure it works correctly with your setup. It's available for Windows 8, 10, and 11 (Windows 7 is not supported) as well as macOS.

Beta Versions:

Remember these are betas, and updates can break things. When downloading a new copy, please keep your existing copy, in case you need to go back to it. As updates can always break things, or change program features/operation, please be sure to keep a copy of your existing version when download a new version.

Download a copy of Black Cat Absolute ACARS version 0.2.1b1 for Windows 8, 10, and 11: (February 24, 2024)

Download a copy of Black Cat Absolute ACARS version 0.2.1b1 for macOS 10.10 and later, 64 Bit Application: (February 24, 2024)

If macOS complains it cannot open the app, right click the app icon, and select Open.

Email your comments and questions to

Last modified February 24, 2024