Occasionally, I hear the G1000 and G3000 give me an audible warning along with displaying an A or M on my PFD. I’ve man-looked (ie skimmed) through some Garmin documentation but didn’t find what those warnings mean.
Can anyone shed some light on this poor confused sim-pilot?
Where is the A or M displayed on the PFD?
At the top left of the altimeter tape.
Are you by an airport? I think the M is for middle marker beacon.
Hmm, have to see about the A…
EDIT: On some older marker beacon receivers, instead of the “O”, “M” and “I” indicators (outer, middle, inner), the indicators are labeled “A” (or FM/Z), “O” and “M” (airway or Fan and Z marker, outer, middle).
Yes. That’s it. Typically that happens near airports. Thank you!
I guess now I need to figure out what marker beacons are and what their purpose is.
Marker beacons are for ILS approaches to let you know how far from the threshold you are. Typically, you report them to the tower, too. Plus they’ll be on your approach plate.
You might find this handy: https://manualmachine.com/garmin/g1000cessnanaviiipilotsguide/1156175-user-manual/
I’ve noticed those warnings before, but they didn’t really register with me. I was on a visual approach to KLAX earier during a VFR flight, and those warnings were going off like crazy as I was doing my left pattern for RWY 7L. This time I decided I’d go looking for them as they could be something important.
Than you again. I appreciate you taking the time to explain. Looks like I still have a lot to learn.
You’re welcome! 
Basically they are more kind of relicts from the past. As far as I know many airports replace them with DME which provides the same information but continuously. So you won’t find them everywhere even if there’s an ILS present.
In some situations,
you can use that sound of MM as warning to go around or do missed approach in case of bad weather and you don’t have runway inside. Of course you need use minima section of approach chart but it can be used as point of start to do not landing procedure. Typical example is ILS approach. Not good is that in MSFS is OM not heard (sound missing or code bug) but MM is ok.
That seems to tell me that I can continue to “not worry about it” when I hear those audible markers. Thanks @anon67824105. I much appreciate the insight here. Not if they can just add the function in the Garmins to turn off the audible warning like you can in the real ones (yes, I’ve been reading up on it).