The Mark II+ Communications Management Unit (CMU) enables data and messaging transfers between airborne and ground based systems by hosting communications protocols that allow for messages to be routed over various channels.
The Mark II+ CMU supports Protected Mode - Controller Pilot Data Link Communication (PM-CPDLC), the datalink recording mandate, and it is certified for FANS 1/A+ data routing and operation.
As the primary airborne component, the Mark II+ communicate primarily through an external Very High Frequency (VHF) transceiver, although optional airborne equipment may include a Satellite Data Communication System (SDCS) to provide datalink capability via satellite. The aircraft FMS provides the interface between the pilots and the Mark II+. By default, the CMU communicates via the land-based Aircraft Communication Addressing and Reporting System (ACARS) VHF network.