Avidyne IFD550 Pilot's Manual page 370

IFD500 Series Pilot Guide
Enabled Missed Approach on Map
When executing the missed approach, apply go-around power,
establish a climb attitude, reconfigure the aircraft as necessary,
ensure the aircraft is trimmed properly, and consider using the
autopilot to smoothly execute the assigned or published missed
approach.
The Nav Source will automatically toggle back to "GPS" shortly
after crossing the MAP, if it weren't already set to "GPS" unless
you had manually switched the Nav Source to "VLOC" prior to
being established on final with the localizer tuned and identified –
in that case, it will stay in "VLOC" until you manually change it.†
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