"The proper significance of lower case hex codes is to identify ADS-R messages whereby a ground station relays data, in some cases with a fictional hex code, from non-Mode-S aircraft. To the best of my knowledge, this is only operational in USA so in Europe you should not see lower case codes except, temporarily, for the RPi tests that are currently in the testing phase"
"The proper significance of lower case hex codes is to identify ADS-R messages whereby a ground station relays data, in some cases with a fictional hex code, from non-Mode-S aircraft. To the best of my knowledge, this is only operational in USA so in Europe you should not see lower case codes except, temporarily, for the RPi tests that are currently in the testing phase"