What's the legality of this? I was thinking of doing something similar but with POCSAG but from what I can tell it would be illegal because of ECPA(Electronic Communications Privacy Act)
18 U.S.C. § 2511(2)(g)(ii)(I/IV):
"It shall not be unlawful under this chapter or chapter 121 of this title for any person to intercept any radio communication which is transmitted by any station for the use of the general public, or that relates to ships, aircraft, vehicles, or persons in distress;... or by any marine or aeronautical communications system."
But so were analog mobile phones and pagers, and in some countries, even receiving unencrypted voice ATC radio isn't legal.
What/how is making listening in on that illegal ok?
That said, it's supposedly still being very much enforced against e.g. planespotters at airshows in some places – no idea what the point of that is.
That said, this is no different than listening to any other unencrypted, non-cellular radio traffic. Totally legal everywhere (except a few rare exceptions, like the UK).
And as I mentioned in my other comment, in the US the ECPA specifically says you can listen to aeronautical radio traffic.
And (after a cursory search) Spain, Portugal, Germany, Austria, maybe France... In other words, legal in some places, illegal in others.
> Text-based ATC communications is done over a different system called CPDLC (FANS-1/A)
ACARS is both an application and a (legacy) lower layer suite of protocols supporting it, but modern ACARS versions and CPDLC can use the same underlying digital channel, as far as I understand (i.e. VDL Mode 2).
As a result, many of these tracking sites can capture both, as well as presumably "legacy/analog" ACARS.