This posting on RTL-SDR.com provides a good explanation of how to receive and decode the aeronautical digital communications known as Aircraft Communications Addressing and Reporting System (ACARS) generally found on 131.55 MHz. Their technique uses the RTL-SDR dongle tuned by SDR# which feeds into the decoding program. The tutorial also contains links to several videos demonstrating the use of RTL-SDR with the PlanePlotter and acarsd decoding programs.