ADS-C — Automatic Dependent Surveillance – Contract

FANS has two pillars: CPDLC for communication (articles 3–4) and ADS for surveillance. This article covers the half of surveillance that belongs to this chapter — ADS-C (Automatic Dependent Surveillance – Contract): the aircraft automatically reports position and intent to connected ATC centres per a controller-defined "contract", letting oceanic and remote controllers "see" you.

ADS-C's character is the opposite of CPDLC's: CPDLC is crew-driven dialogue; ADS-C is fully automatic and transparent to the crew.

1. What ADS-C is — automatic, transparent

The FCOM defines it. Per FCOM DSC-46-10-30-30:

The Automatic Dependent Surveillance – Contract (ADS-C) application provides information and surveillance data reports to one or more connected ATC centers. This activity is automatic and transparent to the flight crew. Note: Therefore, the ADS-C reporting does not require a flight crew action, datalink notification, and/or an initiation of CPDLC application. The air traffic controller defines the content and the frequency of the reports.

[!note]- What "contract" means An ADS-C "contract" is an agreement between controller and aircraft: the ground defines what to report (content) and how often (frequency), and the aircraft fulfils it automatically. There are three contract types (GTG-FANS / AMM 46-22): periodic (report every interval), event (report on an event), and demand (a one-off ground request); a centre may hold one periodic plus one event contract at once, and issue successive demand contracts. The crew do nothing — it runs in the background. That is "automatic dependent surveillance" — the aircraft "automatically", "dependent" on its own navigation data, for the ground to "survey".

2. Three states — Armed / Connected / Off

The ground initiates the connection, provided the aircraft state is armed or connected. Per FCOM DSC-46-10-30-30:

The ATC center initiates the ADS-C connection provided that, the ADS-C status of the aircraft is armed or connected. [...] Armed — The ADS-C function is armed by default. If the ADS-C is armed, up to 5 ATC centers can connect. Connection is at the ATC's discretion. When one ATC center is connected, the ADS-C status changes from armed to connected.

Connected and off. Per FCOM DSC-46-10-30-30:

Connected — [...] the CONNECTION STATUS page indicates the connected status; the ADS-C DETAIL page/ADS DETAIL page provides a list of all ADS-C connected centers; the DCDU indicates the number of ADS-C connected centers. Off — All active ADS-C connections stop, and the ADS-C connection cannot be established from the ground. [...] Note: The ADS-C should not be turned off, unless the flight crew is instructed to do so (for example, via an ATC request).

[!warning]- ADS-C is armed by default — do not turn it off ADS-C is armed by default — you do nothing and the ground can connect and watch you. Do not turn it off — off means the ground cannot see you, and only if ATC explicitly requests (rare) should you. This is the opposite of a "switch off when done" instinct: ADS-C is the oceanic safety net that keeps a controller watching you, and it should normally stay on.

3. ADS-C versus CPDLC

[!note]- One line: CPDLC talks one-to-one, ADS-C reports one-to-many CPDLC is "you and the centre currently working you" (one active); ADS-C is "up to five centres watching your automatic position reports in the background". The two coexist — over an oceanic sector you may simultaneously be in CPDLC dialogue with one centre, watched by several centres over ADS-C, and reporting position via CPDLC (article 4). Three parallel channels, no conflict.

4. Position source and emergency

ADS-C's reported position comes from the same source as CPDLC position reporting: ADIRS + GPS → FMGEC → ATSU (article 1 architecture; hybrid position at ATA-34-04). Emergency linkage (article 3): send MAYDAY → ADS-C enters emergency mode automatically, so the ground watches you intensively.

Boundary restated (article 1): ADS-B (broadcast) is not in this chapter — it broadcasts via the Mode S transponder to all equipped users and belongs to ATA-34. ADS-C (contract, point-to-point, via the ATSU) is in 46; ADS-B (broadcast, via the transponder) is in 34.

Self-test

[!note]- Q1. What does ADS-C report, to whom, and who sets the frequency? Does the crew do anything? What are the three contract types? Position/intent surveillance to one or more connected centres; the controller sets content and frequency; it is automatic and transparent (no crew action). Types: periodic, event, demand.

[!note]- Q2. What are the three ADS-C states, how many centres can connect when armed, and when does it become connected? Armed / Connected / Off. Up to 5 centres when armed; it becomes connected when one connects.

[!note]- Q3. How do ADS-C and CPDLC differ on centres connected, crew action, and handshake? CPDLC: one active, crew-driven, needs a handshake. ADS-C: up to five, automatic/transparent, no handshake.

[!note]- Q4. When may ADS-C be turned off, and why keep it on normally? Only if ATC instructs; keep it on as the oceanic safety net so the ground can see you.

[!note]- Q5. Where does ADS-C's position come from, what happens on a MAYDAY, and why is ADS-B not in this chapter? From ADIRS+GPS via the FMGEC/ATSU. A MAYDAY switches ADS-C to emergency. ADS-B broadcasts via the transponder (ATA-34).

Key takeaways

References

• FCOM DSC-46-10-30-30 — ADS-C automatic/transparent, controller-defined content/frequency, armed by default up to 5 centres, armed/connected/off states, do not turn off.
• AMM 46-22-00; GTG-FANS — periodic/event/demand contract types.
• FCOM DSC-46-10-30-20 — ADS-C emergency on MAYDAY.

Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.