1. Currently the NAT Region only uses ADS-B where ground stations are present; those northern routes within range of ground stations in Canada, Greenland and Iceland. For the remainder of the NAT, ADS-C is used with data being downlinked to ATS units via satellite.
2. Not sure what is seen by the pilot but as per the previous post I suspect it relates to ADS-C. The controller will see the following sequence of messages for a
Waypoint Event Contract (ADS-C):
- AFN contact received from flight
- AFN contact with flight has been established
- Auto ADS Waypoint Event Contract issued for fight
- Flight accepts the Event ADS contract. Contract number:1
AFN = ATS (Air Traffic Service) Facilities Notification.
In the case of a
Periodic Contract, for example a Met Contract, (reporting every 30 minutes), the controller will see:
- Default ADS Periodic Contract issued for flight
- Flight accepts the Periodic ADS Contract: Contract number: 2
The "Contract number" is not associated with the type of contract. Other Periodic Contracts can be issued for Reduced Longitudinal Separation Minima, (reporting every 18 minutes), and in Emergency, (reporting every 10, 5, or 1 minute, depending upon aircraft type and any pre-exisiting Periodic Contract being in place prior to the selection of Emergency).
There is also a
Demand Contract, which when issued by the controller instantly downlinks a Waypoint Position Report; 'big brother' can then see if somebody is not where they should be.
With our equipment most of the above goes on behind the scenes and is only visible to the controller if they choose to look in the stored historical data for individual flights. A visual clue as to the ADS and CPDLC status of the flight appears on the data screens, with examination of the data process in the flight's history being conducted only if there is a logging on issue.