ACARS

ACARS (Aircraft Communications Addressing and Reporting System) is a digital data link protocol used to exchange short messages between aircraft and ground stations over VHF radio. This app decodes ACARS frames and displays the extracted fields in a scrolling console.

Settings

• Frequency: Default 131.825 MHz (primary ACARS VHF frequency in Europe and globally). Adjustable via encoder knob or tap for keypad. Other common frequencies include 129.125 MHz and 130.025 MHz depending on region and airline.
• RF Amp (0 or 1): Enables/disables the internal RF amplifier.
• LNA gain (0–40): Low-noise amplifier gain. See Receive Quality Issues.
• VGA gain (0–62): Variable-gain amplifier gain.
• LOG: Checkbox to enable logging to file. When checked, decoded messages are written to LOGS/ACARS.TXT. The log file is opened automatically on startup; the checkbox controls whether entries are written.

Decoded Message Fields

Each received and CRC-verified ACARS frame is decoded into the following fields, displayed in the console:

• CRC: OK if the CRC-16/CCITT checksum over the frame matches the two trailing CRC bytes; FAIL otherwise. Frames with CRC failures are still displayed but should be treated as potentially corrupt.
• Registration: 7-character aircraft registration (tail number), e.g. D-ABCD or N12345.
• Label: 2-character message type code identifying the category of message (e.g. flight plan update, ATIS, position report).
• BlockID: 1-character sequence counter for multi-block messages.
• MsgNum: 3-character message number within the current session.
• FlightID: 6-character flight identifier, typically the IATA flight number.
• Message: Free-text payload of variable length. Content depends on the label type and airline ground system.

A minimum valid frame must be at least 23 bytes (21-byte fixed header + 2 CRC bytes). Frames shorter than this are shown with an error message in the text field instead of decoded content.

Logging

When LOG is enabled, each decoded message is written as a single timestamped entry to LOGS/ACARS.TXT. The file is always opened on launch; entries are only written when the checkbox is active. Settings are saved to rx_acars.ini.