Future Air Navigation Systems (FANS): AFN, CPDLC, and ADS-C Contracts

022-10-02Pablo Asensio Martínez2026-03-272 min

Concept and Objectives

FANS is a system architecture developed by ICAO to improve communication, navigation, and surveillance (CNS) for air traffic management.

  • Main Objective: To handle increased air traffic safely and efficiently, particularly in oceanic and remote areas where radar coverage and direct radio contact are limited.
  • Key Shift: Moving from voice communication to digital Data Link.

Core Applications (FANS 1/A)

FANS 1/A is the avionics package typically installed on commercial aircraft (Boeing/Airbus) to support these functions.

1. ATS Facility Notification (AFN)

Also known as the "Log On". Before using FANS services, the aircraft must identify itself to the Air Traffic Services Unit (ATSU).

  • Process: The pilot allows the aircraft system to send a "Log On" message (usually via the MCDU).
  • Data Transmitted:
    • Aircraft Callsign.
    • Data Link Capabilities (what the plane can do).
    • Flight Plan information.
  • Result: Establishes the electronic handshake required for CPDLC and ADS-C.

2. CPDLC (Controller-Pilot Data Link Communications)

A two-way data-link system allowing the exchange of text messages between the pilot and the air traffic controller.

  • Usage: Non-urgent clearance requests, frequency changes, and reporting.
  • Advantages:
    • Reduced Frequency Congestion: Frees up voice channels for critical comms.
    • Clarity: Eliminates accents, static, and readback/hearback errors.
    • Efficiency: Allows complex clearances (e.g., "Climb to reach FL350 by 1230Z") to be reviewed and printed.

3. ADS-C (Automatic Dependent Surveillance - Contract)

A surveillance technique where the aircraft automatically transmits position data derived from its onboard navigation systems (GPS/FMS) to the ATC center.

  • "Contract": The reporting rate is controlled by the ground station (ATC), not the pilot.
    • Periodic Contract: Send position every X minutes/seconds.
    • Event Contract: Send position if altitude/heading changes or a waypoint is passed.
    • Demand Contract: Send position immediately upon request.
  • Emergency Mode: If a MAYDAY is triggered, the system switches to a high-rate reporting contract.

Note: Do not confuse ADS-C (Point-to-Point contract with ATC via Satcom/VHF) with ADS-B (Broadcast to everyone via 1090MHz ES). FANS primarily uses ADS-C.