Martin, UTM is not datum. You message is confusing to me as to what you're asking.

When I plot ground coords I usually use NAD27 because that's what the USGS maps use. The error can be 0.1 mi if coordinates in one datum are entered in another (seen it).
Coordinate systems between UTM and Lat/Lon would best be worked out with the agencies you talk to. My bet is that aviation agencies, and their flight GPS units use Lat/Lon

unimogbert