https://www.faa.gov/air_traffic/publications/media/atpb_feb_2023.pdf
all aircraft must guard 121.5 and 243.0 if able
all atc must monitor 121.5 and 243.0 at all times - and do weekly checks
all uhf radios receive 243.0 when there is a nearby transmission -
??????? - maybe this means that all military aircraft and all ATC
towers have dedicated receivers on 243.0 - like federal wildfire
aircraft have dedicated receivers on 168.625
also info on missed approaches
ELTs are now on 406.00 with also a low power 121.50 transmitter - or
something like that