ADS, CPDLC, ATC COM, ACARS, AOC, Whaaah? Here's how we keep this straight:
ADS-C procedures are closely aligned with those for CPDLC:
What follows comes from the references shown below. Where I think it helpful, I've added my own comments in blue.
[ICAO GOLD, pg. 104] Automatic dependent surveillance — contract (ADS-C). A means by which the terms of an ADS-C agreement will be exchanged between the ground system and the aircraft, via a data link, specifying under what conditions ADS-C reports would be initiated, and what data would be contained in the reports.
[AC 91-70A, ¶5-4]
An ADS Contract is an agreement from you, the pilot, to the Air Traffic Service (ATS), to provide information. You can provide information through various types of contracts and you can do this with up to four different ATS providers. The data is extracted automatically from various electronics in your aircraft. In exchange they grant you access to the airspace you are in, or coordinate with nearby airspace. ADS-C will take the place of voice position reports in many regions of the world. You need special equipment and authorization to use ADS-C.
Figure: Examples of applying RCP and RSP specifications, from ICAO GOLD, Tables 2-3 and 2-4.
[ICAO GOLD, ¶126.96.36.199] The Safety and Performance Standard for Air Traffic Data Link Services in Oceanic and Remote Airspace (Oceanic SPR Standard, RTCA DO-306/EUROCAE ED-122), provides operational, safety and performance criteria for data link services that are applicable in airspace, where procedural separation is being applied, for normal ATC communication and surveillance to support separation assurance, route conformance monitoring, re-routes, and weather deviation management. These criteria include specifications for required communication performance (RCP) and required surveillance performance (RSP), taking into consideration the following data link applications:
ADS-C gives you a better Required Surveillance Performance (RSP) and CPDLC gives you better Required Communication Performance (RCP). Combined, they allow you to fly in airspace with tighter separation minima which means you have a greater selection of airspace available to you.
[AC 91-70A, ¶5-4.d.] A periodic contract, event contract, and demand contract all define three types of reporting. The aircraft may also initiate emergency reporting, which is a special case of periodic reporting. In response to a periodic contract, the aircraft assembles and transmits a message containing the fields at the interval specified in the contract request. Event contracts define certain events (such as an altitude change), which causes the aircraft to send a report, independent of any periodic contract in effect. Send one demand contract each time the ATS provider system commands it. The contract request may specify several different data groups. These include the basic position report, which contains 3-D position and time, and additional on-request groups. These groups include aircraft and wind velocity, vertical speed, and limited waypoint information.
[ICAO GOLD, ¶188.8.131.52]
The ATSU determines what information it wants and how often it wants it. From the flight crew standpoint, you will see differing numbers of items on the periodic contract. The example photo shows the contract from YQXE2YA wants FLIGHT ID and METEORO information every 1088 seconds.
[ICAO GOLD, ¶184.108.40.206.6] An event contract allows an ATSU to request an ADS-C report whenever a specific event occurs. An ATSU can establish only one event contract with an aircraft at any one time. However, the event contract can contain multiple event types. These types of optional events include:
In the example photo, the ATS will be notified automatically if the aircraft's vertical velocity exceeds 5,056 fpm, lateral deviation exceeds 5 nm, the altitude goes below 40,700 or above 41,300 feet, and at every waypoint change. The waypoint change is determined by the FMS so anything you do to the FMS that affects the next waypoint and the waypoint one after that will be reported. For example, you you were to insert your ETP before the next waypoint, that gets reported.
[ICAO GOLD, ¶220.127.116.11.4] A demand contract allows an ATSU to request a single ADS-C periodic report. A demand contract does not cancel or modify any other ADS contracts that may be in effect with the aircraft.
Photo: G450 MCDU, ADS Armed, from Eddie's aircraft.
[ICAO GOLD, ¶18.104.22.168] The logon is the first step in the data link process. A logon, initiated either by the flight crew or by another ATSU, is performed prior to the ATSU establishing a CPDLC and/or ADS-C connection. The purpose of the logon is to:
The log on procedure will vary with aircraft. In the case of a Gulfstream 450/550, for example, the ADS-C log on takes places as a consequence of the CPDLC log on. The CPDLC FIR region code is entered into the ATC LOGON STATUS page of the MCDU after ensuring all other items are correct. The information is sent and once accepted the MCDU scratch pad will show "ADS ESTABLISHED" and the ADS ARMED entry will change to ADS ACTIVE. For more about how to do this, see: Communications / CPDLC: Logon.
[ICAO Gold, ¶5.6.3]
Note.— In an ADS-C environment, the flight crew should not provide position reports or revised waypoint estimates by CPDLC or voice, unless otherwise instructed or under conditions in certain airspace as stipulated in Regional Supplementary Procedures or AIP (or other appropriate publication).
Appendix E of the ICAO GOLD manual lists which regions require and which do not require the additional position report.
Note.— If the flight crew activates a non-ATC cleared route into the aircraft system, the ADS-C reports will include information that will indicate the aircraft is flying a route that is deviating from the cleared route.
If you are in the habit of inserting your equal time points into the FMS you are wrong on several counts and you can add this to the list. More about this: Equal Time Points.
[ICAO Gold, ¶5.6.2]
You don't have to worry about flying a Strategic Lateral Offset because your FMS will sequence the waypoints even if your are two miles away from the intended course. But if you are further than the tolerance allowed by your FMS, it may not sequence. If that happens, the position report will not be made.
Figure: Waypoint sequencing anomaly, from ICAO Gold, figure 5-2.
[ICAO Gold, ¶5.6.1]
As shown in [the figure], when an aircraft passes abeam a waypoint in excess of the defined sequencing parameter (refer to , paragraph F.7) for specific aircraft types), the FMS will not sequence the active waypoint. If the flight crew does not sequence the waypoint, incorrect information will be contained in ADS-C reports, CPDLC position reports and FMC waypoint position reports – the next waypoint in these reports will actually be the waypoint that the aircraft has already passed.
The point here is do not use ARINC 424 format. The ATSU doesn't understand "N3030" but wants to see the full latitude and longitude.
[ICAO GOLD, ¶5.2.3]
Note.— The flight crew should not need to reinitiate a logon.
[ICAO GOLD, ¶5.2.5]
Note.— ADS contracts are managed (e.g. established and terminated) by ATSUs per paragraph 4.5.3.
Note.— Some ATSUs may maintain ADS contracts with an aircraft for a period of time (e.g. 15 minutes) after the aircraft has left the airspace.
[ICAO GOLD, ¶22.214.171.124] The aircraft system sends specific aircraft data in different groups of an ADS-C report. Each group contains different types of data. An ADS-C event report contains only some of the groups, which are fixed. The ADS-C periodic report can contain any of the ADS-C groups, which the ATSU specifies in the contract request.
Figure: ADS-C Basic Group, from ICAO Gold, figure 2-38.
Figure: ADS-C Flight Identification Group, from ICAO Gold, figure 2-39.
Figure: ADS-C Earth Reference Group, from ICAO Gold, figure 2-40.
Figure: ADS-C Air Reference Group, from ICAO Gold, figure 2-41.
Figure: ADS-C Airframe Identification Group, from ICAO Gold, figure 2-42.
Figure: ADS-C Meteorological Group, from ICAO Gold, figure 2-43.
Figure: ADS-C Predicted Route Group, from ICAO Gold, figure 2-44.
Figure: ADS-C Fixed Projected Intent Group, from ICAO Gold, figure 2-45.
Figure: ADS-C Intermediate Projected Intent Group, from ICAO Gold, figure 2-46.
Portions of this page can be found in the book International Flight Operations, Part V, Chapter 3.
Advisory Circular 91-70A, Oceanic and International Operations, 8/12/10, U.S. Department of Transportation
Asia/Pacific Information Package, FAA Flight Technologies and Procedures Division (AFS-400), June 15, 2012
FANS-1/A Operations Manual, FAA Aeronautical Communications Aviation Safety (AVS), Version 6.0, 25 September 2008
Guidance Material for ATS Data Link Services in NAT Airspace, The North Atlantic FANS Implementation Group (NAT FIG), The North Atlantic Systems Planning Group (NAT SPG), Version 19.1, 14 September 2009
Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.
Gulfstream G450 Airplane Flight Manual, Revision 35, April 18, 2013
Gulfstream Operating Manual Supplement for G350, G450, G500, and G550 Airplanes, Supplement Number GAC-OMS-4, Future Air Navigation System (FANS 1/A), Automatic Dependent Surveillance (ADS-C), Controller Pilot Data Link Communications (CPDLC), Revision 1, July 1, 2012
ICAO Doc 4444 - Air Traffic Management, Fourteenth Edition, Procedures for Air Navigation Services, International Civil Aviation Organization, 2001 *
ICAO Doc 4444 - Air Traffic Management, Fifteenth Edition, Procedures for Air Navigation Services, International Civil Aviation Organization, 2007 *
* Not all of Doc 4444 seems to have been reproduced in the 15th edition, so you might need to look at the 15th edition and then then 14th edition for some sections.
ICAO Global Operational Data Link Document (GOLD), International Civil Aviation Organization, Second Edition, 26 April 2013