What's the relationship between FANS and CPDLC? I'm confused about Future Air Navigation System (FANS) and Controller–pilot data link communications (CPDLC). Someone said FANS includes CPDLC, another said it does not.
Someone said FANS includes CPDLC, another said it does not.


It depends on the region and/or airplane generation.

There is the ICAO-compliant CPDLC used in Europe (via ATN-B1), and there is the Oceanic/US CPDLC (via ACARS).


A plane fitted with FANS 1/A+ has the Oceanic/US CPDLC, but not the European one.
New long-range planes like the 787 and A350 use FANS 2/B, which has both CPDLCs.$^a$




$^a$ This integration may be offered as a retrofit if it is possible. For example for Airbus – using Airbus' lingo – the A+B package was first introduced on the A350, then became available as a retrofit on the A380 (see slide below by Airbus).


(Airbus via ICAO)



For a brief historical context, see the history section I put together here.