Guide ACARS message log

Guide: the ACARS message log

What it is. ACARS is the short text-message system between aircraft and ground. The ACARS mode in OnAir shows the messages it decodes in a log you can filter, read in full and save, next to an aircraft map. This guide covers the log (the Messages screen). For setting up the receiver, see Tutorial: ACARS and the ACARS mode page.

What you will see

Choose ACARS in the mode list and start the receiver. The mode panel has these parts: messages, the aircraft map, channels and the decoding state (State: Searching, Carrier, Decoding; blocks OK as a percentage).

The message list

Columns: Time UTC, MHz, Reg (registration), Flight, Label, Meaning and Text (a preview). Click a row to read the whole message in the detail pane below. The preview shows the decoded reading in brackets before the text when OnAir could interpret it.

The detail pane shows:

• time, frequency and level;
• aircraft: registration and flight;
• direction (downlink or uplink), the mode, block id and whether it is the last block or more blocks follow;
• the label and its meaning from the label table ("not in the table" if unknown), the message number, prefix and ack (ACK or NAK);
• how many bits were repaired by the parity check, if any;
• reading (a plain interpretation) and the position when the message holds one;
• Decoded ADS-C blocks, when present, and the raw Text.

Filters

• Label: show only blocks whose label starts with this, for example H1 or 5Z.
• Registration / flight: matches either field.
• downlink only: leaves out the uplinks (ground to aircraft).

When nothing matches, the list says "no message matches the filter"; with no traffic yet it says "no message yet".

Saving

The save button above the list writes the messages that pass the filter as a table with these columns: time, frequency_hz, mode, direction, registration, flight, label, meaning, text (see Settings and files for the formats). Clear (and Clear all in the top bar) empties the lists.

Channels and sensitivity

On the channel side you can choose which carriers to decode: leave the field empty ("all on the 25 kHz grid") or type your own list in MHz. The Carrier threshold is the carrier over noise needed to start decoding a channel: lower finds weaker aircraft but also decodes noise. An extra attenuation setting for the last channel of the set helps when a weak channel sits next to strong ones. A preset for Europe and North America is offered for the channel list.

Aircraft map

Positions come from the aircraft's own reports (ADS-C, text position messages): every few minutes per aircraft, not live like ADS-B. Blue means an ADS-C report, amber a text report, grey older than 30 minutes. On VHF the aircraft transmit directly, so you only hear aircraft within line of sight. The Predict positions and uncertainty switches fill the gaps; see Position prediction.

Sharing messages on the map

By default only positions go to the public map. Server > Also share interesting ACARS messages is a separate opt-in: free text, crew, operations, company and maintenance messages show on the aircraft's card for 48 hours, with phone numbers and e-mail addresses removed first. Position reports and link tests are not part of it. See Map sharing.

Troubleshooting

• No messages: wrong frequency list for your region, or no traffic in line of sight. Check Frequency database for ACARS entries.
• Many messages with garbage text: the carrier threshold is too low, or the signal is weak. Raise the threshold or move the antenna.
• Flight column empty on some rows: the Flight column is filled for downlinks only (uplinks show the registration).

Legal note

ACARS traffic is operational and sometimes personal. Whether you may keep or publish it depends on your country; see Legal.

Related

ACARS mode | VDL2 | HFDL | Position prediction | Map sharing