[Scan-DC] Something different -- ACARS (131.55 MHz)

[merlin at merlinjacobs.com]

I have not done ACARS is about 15 years. I also remember accessing the 
company frequencies that showed messages between the pilot and the airline. 
I’ll have to go back through my notes and see how I did it.  It was fun.
Merlin

-----Original Message----- 
From: Andrew Clegg
Sent: Monday, March 26, 2012 8:30 PM
To: Scan-DC at mailman.qth.net
Subject: [Scan-DC] Something different -- ACARS (131.55 MHz)

For a change of pace, this weekend I experimented with decoding "Aircraft
Communications Addressing and Reporting System" (ACARS) messages from
airplanes. I know a lot of people on this list know all about ACARS
decoding, but this was one of my first forays, and it was quite interesting.
It's also very simple -- all you need is an analog scanner that can tune the
regular air band, an audio cable, and a computer. The software I used,
called acarsd, is free (http://www.acarsd.org/).

acarsd decodes the digital bursts, and displays the decoded data on your
screen. The data can include simple check-ins, maintenance messages,
operations requests, weather, and a bunch of other things. The data include
the tail number of the aircraft, and the airline and flight number if it's a
commercial flight. acarsd displays this info, and keeps a persistent
database of all the aircraft you've heard (by tail number). It will even
display a photo of the specific plane you've caught, if it has a picture on
file. (I put a screen grab at http://www.w4je.com/acarsd.png)

The fun I had was tracking how far away some of the planes were. Once acarsd
decodes the airline and flight number, I could look up the flight on
flightaware and see exactly where it was. I was surprised that I was hearing
flights as far away as southwestern NC, southern NY, and over the Eastern
Shore. The planes were at cruising altitude, so their radio line-of-sight
distance is hundreds of km, but still, it's cool to be able to decode
signals from that far away. I was out at my house in Shenandoah County in a
fairly benign RF environment, using an outdoor discone with a pre-amp at the
feed point. With that setup, I was catching an ACARS burst every 15 seconds
or so during heavy flight times like Sunday evening. I was tuned to the
national primary ACARS frequency, which is 131.55 MHz.

For those of you who haven't tried ACARS, it's worth a listen, especially
since it might give a renewed purpose to a dusty old analog scanner in your
closet. Having an outdoor antenna will help, but here in the DC area,
there's probably enough close-by flights to be able to get at least some
ACARS hits with an indoor antenna near a window. You can quickly judge how
successful your setup might be just by tuning to 131.55 and seeing how many
bursts you hear.

I'm still experimenting, and have it running now at my apartment in
Arlington, getting bursts about every ten seconds or so with my rooftop
discone (no pre-amp, since there's too much RF in the area). I need to learn
more about deciphering some of the ACARS information.

Highly simplified tips and tricks from ACARS experts would be appreciated --
for example, are there "local" ACARS frequencies for DCA and/or IAD?

Cheers,
Andy

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