The VHF Data Link (VDL) Mode 2 radios support Controller Pilot Data Link Communications – sending information between aircraft and ground stations.
The RTA-44D / 50D VDR systems are airborne VHF communications transceivers that provide voice and data communication between on-board aircraft systems, other aircraft systems, and ground-based systems. Each operates in analog DSB-AM analog voice mode, VHF ACARS data modes (Mode A and Mode 0), and VDL Mode 2 data mode. It also provides future support for VDL Mode 3 digital voice and data modes.
The latest upgrade to the VHF data link communications has been the addition of Mode 2 data, or VDL Mode 2 capability. VDL Mode 2, in its broadest sense, is the term that is used to describe a suite of air-ground protocols that increase the data rate of the air-ground link to 31,500 bits per second. VDL Mode 2 allows transitioning from an infrastructure that relies on character-oriented ACARS protocols for end-to-end delivery of messages to one that uses bit-oriented Aeronautical Telecommunications Network (ATN) protocols using the same VHF ground and aircraft radios.