I had a huge datum vs coordinate system post typed, then I lost it all... logged back on and see it isn't needed.

UTM is great, and we operate with it more often then not, however the aviation folks (and wildland folks) don't use UTM/UPS. My solution to this when using a GPS is to change my trip computer display to show both UTM and Lat/log (most garmin units allow this) this allows me to give my position immediately when talking to an aircraft.

There is no easy way if they are giving you a coord in lat and long, I just write it down and the swicth my GPS over to Lat/long and enter it... a PITA but I haven't found an easier way.

If no GPS or my GPS is giving me the finger at the moment, I carry a UTM and a Lat/long plotter card for my map. That way I have the ability to figure locations out either way. I draw both my UTM (solid) and Lat/long (wide gap dashed) on my maps.

As for datum, most Aircraft GPS systems can change datum as needed. Not all though, I have encounted a few pilots at wildland fires that were unable to change their Datum on the A/C GPS... almost all had personal GPS with them that they could change.

Aircraft or other ground unit, I always ask "What Datum are you using" when getting coords from someone. You would be supprised how many people never check to make sure their map and gps datum match!