ADSB and ATC

[WannFly]

ATC guys out there - do you track us on ADSB now? Just heard over the radio today MSP center telling someone that his ADSB is not working, she isn’t getting a “ADSB hit”. I couldn’t hear the other side of the conversation but got me wondering.... along with squawk code , does the ADSB actually show up on your scope?

 

[Jmcmanna]

I am terminal, not at a center, so I can’t speak for them. But, we have an option on our scopes to turn on ADS-B. We don’t really need it for anything, so most controllers don’t have it on, but I do just because I can.

If you are on a discrete code, your target doesn’t show anything different as long as you ADS-B out is working properly. If you don’t have ADS-B out, a little dot shows up in your datatag. If your ADS-B is on but something isn’t working right, the little dot is a clear circle. It doesn’t tell us what isn’t working though.

If you aren’t tagged up on a discrete code, I can click on your 1200 code target and get your callsign and your hex code. An aircraft type would be useful for calling traffic, but we don’t get that information. I have gone to the N-number registry too look up an aircraft type before, but only because the aircraft appeared to be doing survey work or something and was criss-crossing an arrival into O’Hare for a long time.

Tl;dr.....all we can see from your ADS-B is your callsign and hex code if we make the required keystrokes.

 

[N1120A]

I was doing an Angel Flight last week and hadn't actually done one since ADS-B became mandatory, and thus the change of the Flight ID was necessitated. On my way to pick up the passengers, I asked the controller to test the function for me and he happily obliged, so they definitely can look it up pretty easily.

My understanding is that the biggest benefit currently is that ADS-B out causes a much quicker radar return - like every second instead of every 6.

 

[Velocity173]

I was doing an Angel Flight last week and hadn't actually done one since ADS-B became mandatory, and thus the change of the Flight ID was necessitated. On my way to pick up the passengers, I asked the controller to test the function for me and he happily obliged, so they definitely can look it up pretty easily.

My understanding is that the biggest benefit currently is that ADS-B out causes a much quicker radar return - like every second instead of every 6.

Typical 1 sec vs 4.5 secs for TRACONs. A lot of TRACONs are using overlapping radars (FUSION) these days which can give 1 sec refresh rates as well without ADS-B.

My brother just retired from the FAA last month and said the same thing as Jmc said above. Most have the function off and the only benefit he saw was getting ID on a 1200. Despite the increase in refresh rate and increased coverage at lower altitudes, it hasn’t reduced their separation requirements or lowered MVAs.

 

[Let'sgoflying!]

So 99% of the whole program was for in-cockpit benefits, not ATC?

And.. is a flightaware text “N1234 was spotted in flight” giving the same info (your adsb is functioning normally) as the atc report as described above?

 

[Groundpounder]

I noticed that since Jan 1st, if I call up Boston Approach after departing my home airport asking for advisories, they say "radar contact, squawk XXXX". Used to be that I would not get the "radar contact" call till after I squawk a discreet code. I would assume this is an ADS-B thing.

 

[WannFly]

I thought a big point of having this ADSB thing is to have better optics in separation of traffic in busy terminal environment along with helping us looking at the iThing

 

[N1120A]

So 99% of the whole program was for in-cockpit benefits, not ATC?

And.. is a flightaware text “N1234 was spotted in flight” giving the same info (your adsb is functioning normally) as the atc report as described above?

No, cause the FlightAware spot could be a result of an IFR or VFR data block hitting on radar. When my Tiger had a temporary non ADS-B out Mode C, before the mandate, it would hit when you hit radar with a code.

I noticed that since Jan 1st, if I call up Boston Approach after departing my home airport asking for advisories, they say "radar contact, squawk XXXX". Used to be that I would not get the "radar contact" call till after I squawk a discreet code. I would assume this is an ADS-B thing.

Might be that the controller is using ADS-B. Might also be that they see no one else at your location.

I thought a big point of having this ADSB thing is to have better optics in separation of traffic in busy terminal environment along with helping us looking at the iThing

There's lots of stuff folks will point to as the "big point" of ADS-B. Some more conspiratorial than others. The original justification was to fill in the final gaps in radar.

 

[Timbeck2]

I am terminal, not at a center, so I can’t speak for them. But, we have an option on our scopes to turn on ADS-B. We don’t really need it for anything, so most controllers don’t have it on, but I do just because I can.

Same for me. When I learned how to turn it on and off it was sort of anti-climactic.

 

[bobmrg]

Radar shows the controller where you were (when the radar beam rotated past your position)...ADS-B shows the controller where you are.

Bob

 

[John Collins]

So 99% of the whole program was for in-cockpit benefits, not ATC?

And.. is a flightaware text “N1234 was spotted in flight” giving the same info (your adsb is functioning normally) as the atc report as described above?

No, 0.0001 % was for in-cockpit benefits, the rest was for ATC. ATC could care less if you benefited from ADS-B.

 

[mcmanigle]

Just as one additional data point: Was flying into RDU (my home base) maybe 6 months ago, probably 20-25 miles out, waiting for an opening on the approach frequency to say hello. They had the usual constant stream of arrivals and departures for time of day. Then, before I keyed up, approach called me, asked if I was on frequency and incoming, and gave me a squawk, vector, and runway. I assume they must have seen the 1200 return heading towards them and checked ADS-B. I thought it was pretty cool anyway.

 

[Salty]

Radar shows the controller where you were (when the radar beam rotated past your position)...ADS-B shows the controller where you are.

Bob

ADS-B has lag, and it only shows where you ARE the last time a station picked up a message from you. Depending on where you are, that may be quite a while ago.

 

[GeorgeC]

ATC folks, between radar sweeps, are targets propagated based on last known heading/velocity, or do they just jump when a new measurement is received?

 

[Jmcmanna]

ATC folks, between radar sweeps, are targets propagated based on last known heading/velocity, or do they just jump when a new measurement is received?

My facility is on Fusion, which takes the data from multiple radar sites and ADS-B and figures out your position with 1 second updates. I believe most ATC facilities are like this now. I have never seen an ADS-B target that wasn’t correlated with a radar target. I could see this being different in a mountainous area, though. I would suspect if your target hasn’t updated in a certain amount of time (a few seconds), it would just disappear from the scope.

 

[Seanaldinho]

ATC folks, between radar sweeps, are targets propagated based on last known heading/velocity, or do they just jump when a new measurement is received?

I've seen update rates as long as 6 seconds, but in general the computer does not "guess" where a target is inbetween sweeps. Most places are using much more modern radars like Jmcmanna said and don't have such big gaps.

As far ADS-B for ATC - the intention is ultimately to lower separation standards in busy terminal environments but ADS-B is just one part. There is a lot of interesting work being done on time based separation and systems that account for wind automatically to reduce or increase wake turbulence separation on final. As with everything these systems take time to develop and test. The FAA is also far from the leading edge of these technologies. The people providing ATC in Europe that are private or semi-private companies are leading the way on this since sometimes they have to compete to provide ATC services. In the UK, Gatwick and Edinburgh are controlled by a subsidiary of the German ANSP, DFS. Marketing reduced separation and therefore more efficient traffic is one way of winning more airports.

 

[Velocity173]

Talking to a Center friend yesterday, he did say they’re working on reducing sep from 5 miles to 3 miles below FL230. He works above 230 so he hasn’t seen any reduction. Said when Hurricane Michael took out some panhandle Radar sites, ADS-B filled in the gaps.

So yeah, some benefit but I don’t see anything significant. I don’t see terminal sep getting closer than the current separation. You’re gonna have wake turbulence accidents left and right. Even with an increased refresh rate, you won’t have enough of a buffer for the controller to intervene. On a PAR you’ve got about a half second refresh and it still requires a min of 2.5 / 3 miles sep on final.

 

[luvflyin]

I noticed that since Jan 1st, if I call up Boston Approach after departing my home airport asking for advisories, they say "radar contact, squawk XXXX". Used to be that I would not get the "radar contact" call till after I squawk a discreet code. I would assume this is an ADS-B thing.

That's not all that rare. They can 'identify' you based on position. You say "I'm here" and tell them what direction you are Tracking, they see a Target 'there' that's moving in that direction, you can be Identified. It's really not all that common though.

b. Observing a target whose position with respect
to a fix (displayed on the video map, scribed on the
map overlay, or displayed as a permanent echo) or a
visual reporting point (whose range and azimuth from
the radar antenna has been accurately determined and
made available to the controller) corresponds with a
direct position report received from an aircraft, and
the observed track is consistent with the reported
heading or route of flight.

 

[luvflyin]

ATC folks, between radar sweeps, are targets propagated based on last known heading/velocity, or do they just jump when a new measurement is received?

Computerized Radars Track. In between sweeps they 'predict' and the Secondary Radar(transponder) Target moves along between sweeps. What the Radar doesn't do though is take into account if the airplane is in a turn. On the next actual radar 'hit,' the Target kinda does a little 'sideways jump. It can be significant at Centers where it's 12 seconds between sweeps.

EDIT: It's been awhile since I retired. From reading above from Current Controllers it looks like things have 'smoothed' out at a lot of the places with more Modern Radars.

 

[luvflyin]

My facility is on Fusion, which takes the data from multiple radar sites and ADS-B and figures out your position with 1 second updates. I believe most ATC facilities are like this now. I have never seen an ADS-B target that wasn’t correlated with a radar target. I could see this being different in a mountainous area, though. I would suspect if your target hasn’t updated in a certain amount of time (a few seconds), it would just disappear from the scope.

What is Fusion using to calculate Ground Speed? Average of last 2 'hits,' 3, 4......?

 

[Jmcmanna]

Fusion is taking all of the radar sites and ADS-B and averaging them out into 1-second updates. The radar is calculating the ground speed based on that. It isn’t instantaneous though...your groundspeed readout lags several seconds behind groundspeed changes as the STARS computer figures it out.

 

[Jmcmanna]

So yeah, some benefit but I don’t see anything significant. I don’t see terminal sep getting closer than the current separation. You’re gonna have wake turbulence accidents left and right. Even with an increased refresh rate, you won’t have enough of a buffer for the controller to intervene. On a PAR you’ve got about a half second refresh and it still requires a min of 2.5 / 3 miles sep on final.

Totally agree, and want to take your point one step further. The notion that ADS-B might mean we can run tighter spacing and increase airport capacity isn’t going to happen...we can already run 2.5 miles to a lot of runways, and less than that means there won’t be the required runway separation, which ADS-B can’t change. ADS-B can’t reduce the amount of wake turbulence separation, as you mentioned either. I think there could be some advantages in the enroute environment and in areas where there is no radar coverage, but it isn’t going to increase airport capacity most places.

 

[luvflyin]

Fusion is taking all of the radar sites and ADS-B and averaging them out into 1-second updates. The radar is calculating the ground speed based on that. It isn’t instantaneous though...your groundspeed readout lags several seconds behind groundspeed changes as the STARS computer figures it out.

How long have you been there? Did you work with just ARTS. If so did the ‘feel’ of speed reductions change when the new stuff came online?

 

[Jmcmanna]

I’ve been around long enough to work ARTS IIE (at GRB), CARTS, and STARS. We started using fusion before we got STARS, and the biggest issue that I had was that my perception of how fast a target was moving got thrown way off because before fusion, a fast airplane’s target would make a big jump, and a slower one’s made a little jump. With 1 second updates, they all move about the same with each update...the fast airplane’s target doesn’t move that much more than the slow airplane’s because of how often it updates. I got used to looking at each airplane’s history trail to figure out how fast it was going.

When we got STARS, limited data blocks now had ground speeds displayed, which ARTS didn’t have. So now I can see a target with a ground speed of 400 knots without having to watch it move...I know it’s going 400 knots because it’s in the data block. That has been a big improvement.

When I slow an aircraft for in-trail spacing, like on final, I have always used distance and groundspeed together to know when I needed to make the next speed reduction. That hasn’t changed, but with ATPA and fusion, it is easier to get really precise with the spacing between two airplanes on final and make small (10 knot) adjustments that keep pressure on a runway.