IFD500 Series Pilot Guide
System Overview 1-33
Third Party Radio Control Display Units
Other remote tuning and frequency swapping capability is present
when dedicated third-party radio control display units are wired
into the aircraft. Usually in these cases, when the radio control
display unit is active, the Active and Standby frequencies are only
displayed on that external control display unit and not on the IFD,
even though the actual radio is still housed inside the IFD.