FANS is basically nothing more than a CPDLC system that uses the ICAO Aeronautical Telecommunications Network (ATN) over Satcom or VHF and Automatic Dependent Surveillance – Contract (ADS-C) as specified by the ICAO. You can read more about those here:
I was a staff officer at the Pentagon when I first heard about FANS and thought it was madness. It was envisioned as a system that completely revolutionized communications, navigation, and surveillance when flying anywhere in the world and, in 1992, it sounded like science fiction. Three years later the Boeing Aircraft Company came up with a way to do the communications part and that became FANS-1. A few years later Airbus did their version and that was known as FANS-A. Now we have a few variants but they are basically called FANS-1/A and you must have FANS-1/A to fly in some parts of the world. So what is FANS-1/A? Nothing more than ADS-C and CPDLC.
Oh yes, that other stuff. Yes we have realized much of the science fiction with other aspects of Performance Based Navigation but they are not a part of FANS-1/A.
Everything here is from the references shown below, with a few comments in an alternate color.
[ICAO Doc 10037, table 1-1]
FANS mandates were a big deal about ten years ago, with everyone fretting on how they were going to comply. Most of the mandatory dates have come to pass and you will be denied some airspace throughout the world if you are not FANS compliant. But you hardly ever see that terminology any more. The mandatory requirements are given for CPDLC and ADS-C. Some parts of Europe require ATN B1 for datalink and having any version of FANS that doesn't include ATN B1 will exclude you from datalink.
ICAO Document 10037 AN/509 - Global Operational Data Link (GOLD) Manual, Advance edition (unedited), First Edition, 2017
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