Garmin GTN XI Series Manual page 37

Tower Transmission
(Active Frequency)
ATIS Broadcast
(Standby Frequency)
Enabling monitor mode allows you to listen to the standby
frequency while the unit continues monitoring the active
COM channel.
When the COM active frequency receives a signal, the unit
automatically switches back to the active frequency. Once
activity on the COM active channel ceases, the unit returns
to listening to the standby frequency.
You can load active or standby
frequency values to any radio
from a search tab or waypoint
information page (i.e., Airport,
VOR). Selecting a frequency
from one of these locations
opens a pop-up.
Select the Active or Standby
key for the appropriate radio.
Monitor mode is useful when
you want to listen to a recorded
broadcast (e.g., ATIS) on the
standby channel, but still receive
control tower transmissions on
the active channel.