I’ve learnt a lot in the 172 G1000 over the last week its been fun. Sometimes however I’ll get a yellow square with an M in it next to the altimeter tickertape and a beep to go along with it, anyone know what this is?
That is the Middle Marker beacon - M. Before GPS ILS(instrument) landings are done using radio transmit/receiver, so you had to know where you are in the approach to the runway. You are on glide slope and at the MM position.
https://mediawiki.ivao.aero/index.php?title=Marker_Beacon_(Instrument)
6 Likes
Thank you sir! You are a gentleman and a scholar. 
By the way, you may also see an “O” in that area for “outer marker” and occasionally an “I” for “inner marker”.
1 Like
Nice i’ll keep an eye out for that! Been playing with VORs lately so that might be it.