2.4. AIRCRAFT IDENTIFICATION AND POSITION REPORTING WITH FANS
FANS A/A+ systems (namely ATSU for A320/A330/A340 aircraft and ATC applications for A380 aircraft) host the Automatic Dependent Surveillance – Contract application, whereas Mode S transponders hosts ADS-B OUT.
The ADS-C application is quite different from the ADS-B application. The ADS-C application is only used for ATC purposes, contrary to ADS-B that serves the traffic awareness for both ATC and aircraft capable of ADS-B IN.
The ADS-C application provides surveillance data to map the traffic on ATC controller’s screen in areas that are not covered by SSR (i.e. oceanic and remote areas). The ADS-C application takes the place of SSR in those areas but they are not comparable. Indeed, the ADS-C application reports the aircraft position and its intents according to conditions (i.e. contract) fixed by the ATC controller. The ATC controller can set up a periodic, on-event (e.g. when the aircraft sequences a waypoint) or on-demand (i.e. at ATC controller’s discretion) contract. When the ATC controller sets up a periodic contract, the ADS-C application reports the aircraft position on a periodic basis between 15 and 30 minutes. Therefore, the ATC controller cannot use ADS-C to provide the same separation as with SSR.
Nevertheless, ADS-C removes the requirement for tiring HF voice position reporting. ADS-C makes also the aircraft eligible for long-range operations with reduced separations (i.e. lateral and longitudinal separations reduced to 50 NM or 30 NM).
The ADS-C coverage is larger than the SSR one thanks to the FANS technology
(i.e. a data link through satellites or HF, and ACARS network connects aircraft to ATC centers).
For more details, please refer to the Getting to grips with FANS brochure (see AIRBUS References).
2.5. OPERATIONAL RECOMMENDATIONS FOR TRANSPONDER
2.5.1. CONVENTIONAL TRANSPONDER OPERATIONS
2.5.1.1. FOR THE AIRLINE
Refer to 3.2 – Operational Recommendations for TCAS.
2.5.1.2. FOR THE FLIGHT CREW
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In normal operations, set the transponder to AUTO and the altitude reporting function to ON. Transponder settings affect TCAS operations.
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