Avidyne IFD540 Pilot's Manual page 76

As described in Section 1 of the manual, pressing the NRST
function key will bring up the Nearest tab in the split Map-Nearest
view.
Each subsequent push of the "NRST" function key will step to the
next nearest data type.
If the Nearest page is left for 60 seconds or more and then is
returned to, the Nearest Airports selection will be the active
nearest data type no matter what the last nearest data type may
have been. For example, if the Nearest VORs selection was the
most recent display of nearest data, and then the pilot selects a
map page for more than 60 seconds, when the Nearest tab is
next selected, Nearest Airports data is now displayed and not
Nearest VORs.
TIPS AND TECHNIQUES
Emergency Return to Departure Airfield
If on departure leg and an emergency return to the
departure airfield is deemed necessary, the
recommended technique is to press the –D-> button
on the bezel, twist the bottom right IFD knob
counter-clockwise to pre-fill the departure airfield
and press ENTR, ENTR to make that the active
waypoint. Then press the PROC key to produce a
dropdown list of approaches and select the desired
one. To quickly get the tower frequency of that
airfield, press the NRST button on the bezel,
confirm the departure airfield is the highlighted row
and press the bottom right IFD knob to nominate
that frequency into the #1 standby slot for swapping.
NOTE
Nearest Lists Capped at 100nm
Most Nearest lists will only display entries that are
within 100nm of the current aircraft position.
2-38 FMS Pages