Pastimes for the really bored!                                                                24 Nov 2006        GM1SXX

Plane spotter types will probably like this.  I was a bit bored, being laid up with a lung problem so to make some use of my time, I decided to experiment with ACARS.

Here's what Wikipedia says about ACARS...    In essence, ACARS is a packet radio system for aircraft.  My experiments to date suggest that ACARS is carried mainly by 'heavies', large transport or passenger aircraft to ease to workload on the pilots.  Some smaller aircraft also use ACARS including business jets. I've seen quite a bit of data from Royal Bank of Scotland Bizzjets. (maybe thats why their interest rates are so poor!).   I'd like a Dassault Falcon myself, but it's a bit beyond my financial reach <grin>.

Still, back to ACARS.  In essence its rather like ordinary AX25 1200 bauds packet but with 1200/2400tones (like UoSAT2) rather than 1200/2200 ones like packet.  It sounds just like the all familiar 'seagull squawk' of terrestrial 1200 bauds packet.   The aircraft communicate with ground stations at airports around the world. Some of the smaller airfields also support ACARS operations.

The data itself is coded so much of it looks like gibberish. This is where the decoding software comes it. It keeps a database of message codes and aircraft registrations and routes so it can make sense of the coded packets.

In Europe, the primary ACARS frequency is 131.725Mhz AM 6Khz and I've been using my ICOM PCR-1000 set to the 6Khz filter setting. From there, I take the audio via a 3.5mm jack lead to the Line input of one of my PC's.  The software I've been using is called WACARS and you can download matching map overlays for your specific area.


European Frequencies


131.725 AM 6k Primary European

131.525 AM 6k Secondary European

136.925 AM 6k ARINC European

136.750 AM 6k Secondary European

131.850 AM 6k Secondary European

136.900 AM 6k Secondary European


US and
Canada Frequencies


131.550 AM 6k Worldwide Primary/US Primary channel

130.025 AM 6k USA and Canada Secondary

129.125 AM 6k USA and Canada Overflow

130.450 AM 6k USA and Canada Overflow

130.425 AM 6k USA Overflow

131.125 AM 6k USA Overflow

136.700 AM 6k USA Overflow

136.750 AM 6k USA Overflow

136.800 AM 6k USA Overflow

136.850 AM 6k North American SITA allocation

131.475 AM 6k Air Canada


Japan Frequencies

131.450 AM 6k Japan Primary


WACARS can be downloaded from ... and

Here's a screenshot of WACARS in action.  Much of the traffic is engineering information with some data carrying WX reports or information on aircraft weight, fuel load  etc.  Just the thing to keep a geek happy.  One think I did notice is the number of aircraft flying with faults in their flight  computers.  Some errors are in the form of a numeric data dump... about as useful as that encountered when MS Windows BSD's and presents you with that screen of gobbledeygook that can only be decoded by a dedicated techie!



Other useful links include.




Airnav Systems



PDW v2.14 - Windows ACARS Decoder


ACARS Online

PC-HFDL ARINC 635-3 Decoder


Happy Hunting.