ACARS

Aircraft Communications Addressing and Reporting System (ACARS)

ACARS data is used to send messages to and from commercial airlines' aircraft.

129.125  United States
130.025  United States
131.55   United States
136.8    United States
136.85   United States

In general, all that is necessary to hook up a receiver and PC to receive ACARS is a good shielded connection from the speaker to the soundcard. A discriminator tap is not required, since it is not involved in AM reception
There's a brief sync tone sent before each transmission; if the software doesn't receive it, no decoding will occur. Most scanners' squelch cannot open up fast enough, so keep the squelch off