What is the difference between ACARS and ADS-B?
One can easily get lost in the alphabet soup that is datalink.

Both ACARS and ADS-B provide datalink applications – which can be broken down in terms of CNS: Communication, Navigation, and Surveillance.


ACARS is used for:


Communication: includes uplinking (ground → aircraft) weather data upon a downlink request to the company/service provider – not a public service
Navigation: if you consider flex-routing
Surveillance: position reports in the North Atlantic for example (CPDLC over ACARS).

ADS-B is used solely for Surveillance; broadcasting (OUT) own location – and can include ownship surveillance by receiving (IN) traffic information.


If this IN setup is via the UAT frequency, then the aircraft can also receive weather information using FIS-B (free service). Its only relation to ADS-B in this particular instance is the UAT frequency, and it is more of a general aviation (and low-flying commercial) service.




Source: https://www.faa.gov/nextgen/programs/adsb/pilot/#fisb