Mission Planner will display rings around airports. This is a good thing for flying safely and avoiding low level air traffic.
But some of us have noticed that some airports do not seem to be displayed, where other nearby airports are displayed. Often these airports that are not displayed are busy local or regional airports. There seemed to be no logic to this as some of these airports that were not displayed are very busy with air traffic, where some of the other nearby airports that are displayed had little to no traffic.
I finally learned the logic behind deciding which airport is, or is not displayed.
In the past, any 'small airport' will not be displayed, no matter how busy it may be. However any airport designated as a 'heliport' or a 'seaplane base' was displayed.
I've been told that the logic will be changed to not display any airport designated as a 'small airport', 'heliport' or 'seaplane base'.
Here is a link to the discussion about it:
Personally, I'd like to see a tunable in Mission Planner to allow the user the option to display these smaller airports, perhaps defaulting to 'display all' to be safe. Then let the user decide to hide smaller airports if they so choose.
At least we now know why some airports are displayed and others are not. Please keep this in mind when flying (don't only rely on the airport rings in MP).
I suggest that this should be mentioned in the MP documentation.