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: Automatic Dependent Surveillance-Contract (ADS-C) and Controller Pilot Data Link Communications (CPDLC).
— James Albright
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.
- FANS 1/A — Initial future air navigation system (FANS 1/A) ATS applications, AFN, CPDLC and ADS-C, supported by FANS 1/A over ACARS. Note.— FANS 1/A typically involve communication (CPDLC), navigation (RNAV/RNP) and surveillance (ADS-C). This document refers to the FANS 1/A for the data link system, which includes the CPDLC and ADS-C applications. Refer to Doc 9613 for guidance material on navigation (RNAV/RNP) qualification and use.
- FANS 1/A+ — Same as FANS 1/A, except with additional features, such as the message latency monitor function, described in DO-258A/ED-100A, 126.96.36.199.
- FANS 1/A ADS-C — ATS applications, AFN and ADS-C, supported by FANS 1/A over ACARS. FANS 1/A ADS-C - complies with AFN and ADS-C applications, No CPDLC.
- ATN B1 — ATS applications, CM and CPDLC, supported by aeronautical telecommunication network – baseline 1 (ATN B1): a) Context management (CM) application for data link initiation capability (DLIC); b) CPDLC for ATC communications management (ACM), ATC clearance (ACL), and ATC microphone check (AMC), except that: 1) CONFIRM ASSIGNED LEVEL and SYSU-5 USE OF LOGICAL ACKNOWLEDGEMENT PROHIBITED will not be used by the ATSU; and 2) ASSIGNED LEVEL (level) is not required by the aircraft. Note.— Interoperability for departure clearance (DCL), downstream clearance (DSC), data link – automatic terminal information service (D-ATIS), and flight plan consistency (FLIPCY) data link services, which are defined in DO-280B/ED-110B, are not supported.
- FANS 1/A –ATN B1 — Enables the use of CPDLC along a route of flight where data link services are provided by FANS 1/A technology in some airspaces and ATN B1 in other airspaces.
Source: 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