12th Dec 2011, 18:49
Some questions about ADS.
First one. If Iīm right ATC getīs the position either via a tranponder or via ADS. For ADS-B thereīs a ground station required which receives the ADS-B signal and sends it to the ATC station. How does that work in remote areas like the NAT region where no ground stations are available.
When looging on to a ATC unit via the CPDLC menu there often comes beside the active ATC message the message ADS connected. Is that called ADS-C (contract) ?
13th Dec 2011, 09:41
1. ADS-B is entirely reliant on the ground station, so if you're out of range we get no signal & you have to provide position reports via voice or ADS-C. Just as for radar.
2. I'm a controller not a pilot so can't say for certain but CPDLC & ADS-C are closely related so I'd expect it's referring to ADS-C. It wouldn't be ADS-B.
13th Dec 2011, 10:59
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. :E
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.
14th Dec 2011, 15:51
Thanks four your explanations.
Is ADS-B send out by the transponders !?
14th Dec 2011, 16:17
Well, via the 1090MHz extended squitter which is used by Mode S as well. Therefore usually ADS-B is closely related to Mode S. For example europe requires Mode S enhanced surveillance which in itself is very close to ADS-B out, it just misses the aircraft position. Most Mode S enhanced surveillance installations send that data additionally and therefore fulfill ADS-B out although it is not currently required in europe.
You could try the Eurocontrol CASCADE (https://www.eurocontrol.int/cascade/public/subsite_homepage/homepage.html) website which should have quite a bit of information about ADS-B.
Of course you could take the IANS course about ADS (https://trainingzone.eurocontrol.int/ATMTraining/PreCourse/SUR/ADS/Course%20Description/TEMPL32517.5.1279/Default.html), or take a look at the pre course.