Radar Tracking

[Nate Johns]

This thread is a digression from the topic "ASDE-X on VATSIM" specifically devoted to the discussion of how real radar tracking works relative to the current operation of VATSIM radar clients. It is intended to be educational in nature.

 

 

 

Warning: The following is some (lengthy) step-by-step explanation for what is a pretty simple process in practice. This is more of a discussion about tracking up beacon targets, not primaries, for primaries though... you can just about ignore the whole section about entering a departure message. This is also applicable to the US FAA ARTCC environment only. I know TRACONs can start random tracks too, but the method might differ.

 

Also, as a disclaimer, I am far from an expert on this. I have just been able to play with the computer a lot in the course of my en-route ATC training. Anyone with better knowledge and corrections is more than welcome to fix my bumbling.

 

 

 

Our area's common technique is when clearing a guy off the ground off a smaller airport, we start a track at the location of the airport (or nearby VORTAC of the same identifier) with the aircraft's callsign to remind us that there's a guy departing off there shortly. The action is like this:

 

1.) Clear N12345 off XYZ airport, initial altitude 100 (filed FL250).

 

2.) Start track on N12345 at XYZ airport as follows:

 

Type: QT //XYZ N12345 (Where QT is the "Track" button, //XYZ is the input for location, and then the callsign, //XYZ may be substituted with a trackball pick which is essentially a mouse click that records the coordinates of the mouse click in the command line for a location)

 

Hitting enter generates a datablock that appears like the following:

 

N12345 ----- #

N

987

 

Where the datablock includes the callsign and the computer ID. The # sign is the position symbol of the aircraft, in this instance, a coast track. In reality, it starts as a small diamond (a FLAT track symbol that we're used to when we own an aircraft at the center level normally), then moves to a small triangle (Free Track, not emulated in VATSIM) before going to coast. This is due to the computer [Mod - Happy Thoughts]uming you are starting a track on someone in the system first, searching, not finding, then eventually going to the default state of coast since it isn't [Mod - Happy Thoughts]ociated with anyone.

 

The 'N' is just stating that there is no Mode C or reported altitude entered in to the system. 987 is the Computer ID (CID).

 

Since we departed him climbing to 100 initially, we enter that in as an interim altitude (QQ, or F8 for VATSIM) as a self-reminder of where he's climbing to. This would make the datablock:

 

N12345 ----- #

100N

987

 

Now here is where we come to a significant difference in how flight plans work in real life as opposed to VATSIM. In real life, IFR flight plans are only proposals until they are activated. On VATSIM, flight plans are always "active," per-se. When someone calls up ATC after departing a smaller, non-approach control airport, the center enters a "Departure Message" (AKA - DM's the guy) to activate their flight plan.

 

3.) Enter the Departure Message for the aircraft:

 

Type: DM (AID / CID)

 

When the DM is entered, the ATC computer now knows that there is or soon will be an aircraft operating on a squawk code that ties (or correlates) the aircraft on radar to the flight plan in the computer. The computer now starts looking for that aircraft, and as long as the aircraft is squawking the proper beacon code and the callsign of the "random" track matches the flight plan callsign, the track will jump to (or acquire) on the radar return with the given beacon code. From there, it's pretty much business as usual.

 

 

 

Now, that was a terribly long explanation for something that really takes about 5 seconds to do. The background is important to understand though to know what the computer is thinking with the entries of these commands. From the controller's standpoint, these actions are truly quick and easy to do, as well they should be when there's a mess of traffic out there.

 

I'll stop here for now, but am more than willing to entertain specific questions in this thread.

 

~Nate

[Nate Johns]

Nate,

 

I for one find this very interesting! I have always been curious about how the real systems actually work when compared to what we have on VATSIM. Maybe, our radar clients will continue to become more and more realistic

 

Just one question though. When you create the initial datablock after clearing him off the airport, the altitude shows just an "N". Does the computer not yet [Mod - Happy Thoughts]ociate the datablock with a flight plan? I [Mod - Happy Thoughts]ume so, but I just want to make absolutely sure. One would think that the cruise altitude would be displayed without having to set it, then would be replaced with the temp altitude. If you did not set a temp altitude, I would [Mod - Happy Thoughts]ume that the cruise altitude would automatically appear in the datablock as soon as you entered the Departure Message?

 

Thanks, and please keep these coming! It's nice to read a bit about how real ATC works and compare it with what we do on VATSIM.

 

Short answer:

 

No, the computer doesn't [Mod - Happy Thoughts]ociate a random track with a flight plan. Since there is no flight plan [Mod - Happy Thoughts]ociation, it doesn't know anything about flight plan altitudes (requested altitudes anyway). If you don't set a temp altitude, yes, when you DM the guy, a hard altitude matching the flight plan requested altitude appears in the data block.

 

 

Must longer answer:

 

As far as I'm aware, when you start a track on a scope, it remains independant of any flight plan information stored in the computer until you activate the flight plan itself. After the flight plan is activated via departure message (see list below), the computer begins to look for an aircraft squawking a code matching the one [Mod - Happy Thoughts]igned and stored in the flight plan. If the computer sees a beacon code matching an active flight plan, the track will jump over to the aircraft on the beacon code, changing the aircraft from a limited to a full data block.

 

Now, this doesn't mean that one must start a track when clearing someone off. You can DM someone, and the computer will search for the code, and the computer is more than capable of generating a track on its own via an auto-acquire. The ARTCC computer is a little slow sometimes though (I mean, we are talking some seriously ancient technology here), and an auto-acquire takes some time; ergo, starting a track prior usually tags an aircraft up faster than the auto. The only drawback is that where an auto-acquire is considered making a positive radar ID of an aircraft, a pre-created track is not, and the radar controller must independantly identify the aircraft, most typically from the most exhaulted IDENT feature.

 

Now, the center computer is at least partially aware of who has track control of various aircraft. In-house (within your specific facility) it can tell you which sector owns it. Out-of-house, I'm not quite sure how precise its information is. I need to observe live operations (I'm still stuck in the DYSIM lab for 2 more weeks) a little more to get some clarity with that, but shouldn't take too long. Anyway... realizing that I'm a little hazy on this part, I believe the computer is aware that for in-TRACON departures, the TRACON has track control of the aircraft, and hence doesn't auto-acquire. That I can and will ask about before I try and delve in any further.

 

To this end, there are a variety of methods of which I'm aware that a flight plan is activated:

 

• From the ARTCC: A DM is directly entered in to the computer, or the controller enters a flight plan from scratch that is not a proposal (e.g. - in-flight IFR pick-up).
  From a TRACON: ARTS or STARS transmits a DM to the ARTCC upon "seeing" the appropriate in radar coverage.
  From a Tower with FDIO Interface: Tower controller inputs a DM which is sent to the center.
  From a Tower without FDIO Interface: Tower controller calls center on a land line and center controller enters DM message.

 

A TRACON may certainly initiate an in-flight IFR pickup as well like the center.

 

Anyway... I can expand more later on. Time to hit the store.

 

~Nate