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ADS and CPDLC

Old 28th Jan 2012, 01:57
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ADS and CPDLC

I understand that ADS is a psuedo radar point on the ATCO's screen and CPDLC is a text type messaging system. My question is, besides the aircrafts callsign and altitude, does ADS show other information like the ETA of the next waypoint etc? Is CPDLC real time visible for the ATCO ie the controller sees what the pilot sees on the aircraft equipment at anytime or is it only readerble as a position report sent by the pilot. Also can the ATCO call the CPDLC info down anytime he wants? Thanks
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Old 28th Jan 2012, 08:06
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ADS gives a position update at a set rate, position or an on demand snap shot. CPDLC downlinks mesages as responses to other messages or when intentionally set. Neither are a constant data flow.
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Old 28th Jan 2012, 22:06
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My question is, besides the aircrafts callsign and altitude, does ADS show other information like the ETA of the next waypoint etc?
The ADS-B spec does indeed have provision for a TCP/TCP+1 message (Current/Next Trajectory Change Point) as Format Type Code 29.

This contains either a 3D (lat/lon/altitude) or 4D (plus Time-to-Go) description of the next TCP.

Having said that, AFAIK it's not currently in use.
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Old 29th Jan 2012, 03:13
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Thanks for the reply. I asked as I was crossing the Atlantic, was wondering how ATC picked up our predicted Crew Rest change over position (coordnates) that we put into the FMS Flt plan. Was the predicted point displayed on their ADS or CPDLC on the ATCO's screen?? I thought ADS was just real time transmitted positions and does not have predicted waypoints. Are there any links on the internet for me to see what ADS displays look like?? Just curious.
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Old 29th Jan 2012, 06:51
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You're mixing up ADS-B and ADS-C.

CPDLC is only a procedure, you can use different technical means to have it , e.g. over the North atlantic is normally via FANS/1A ( ACARS) if your aircraft is equipped. ( you can also have it via ADS-C or VDL mode 2 , etc..)

Downloading of FMS parameters to ATC is via Mode S ( Radar) , definitively not over the Atlantic.
Do a bit of goolgle to find out how the different systems work.
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Old 29th Jan 2012, 08:34
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ADS B gives Mode S ES squitter out DAPS. compatible ground systems can read both.
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Old 29th Jan 2012, 11:50
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Your Oceanic cleared route is thus:

ATSIX 62N020W 63N030W 63N040W 62N050W 59N060W LAKES

You've already got this route loaded into the FMC, as you were fortunate enough to get your flight planned route, and within that route stored in the FMC is a crew swap reminder at 6107N01500W.

You've set up the ADS-C Waypoint Event Contract which will downlink, via satellite, all waypoint position reports during the crossing and, additionally, you've logged on to EGGX for CPDLC.

As you progress ATSIX, ADS will downlink to ATC:

ATSIX/1305 33O 6107N01500W/1318 NEXT 62N020W

(Waypoint/ATA, Level, Ensuing waypoint/ETA, Next ensuing waypoint - identical to the HF voice format)

Because the above ADS waypoint position report does not exactly correspond to those significant waypoints in your cleared route, ATC must ask you to confirm the ETA for 20W and the co-ords of the "NEXT" waypoint (30W) reflected in the clearance. An HF message may be sent by ATC asking you to do this, or a CPDLC format message may be uplinked by ATC, e.g:

[CONFIRM ENSUING WAYPOINT]

[CONFIRM NEXT WAYPOINT ETA]

[CONFIRM NEXT ENSUING WAYPOINT]

The format of the ADS report which ATC would expect to see, corresponding exactly to the cleared route, would have been:

ATSIX/1305 330 62N020W/1338 NEXT 63N030W

Should anything other than the above be downlinked, ATC will query those elements which do not correspond to the cleared route/level/credible ATA/ETA.

This situation applies to all waypoints on the route stored in the FMC to highlight FIR boundaries, crew rest/swaps, turnback/diversion points, etc. which are in addition to those significant waypoints specified in the oceanic clearance.

For info, we see everything you do in terms of adjusting the route once within oceanic airspace, be it to set up SLOP, deviate due weather, strip out some points to calcualte an arrival time at destination, etc., and it is easier for us to detect who is not following the route specified in the clearance.

Hope the above helps.

_________________________________
edit:

Having just looked at your initial question again, as far as the crew are concerned, ADS will downlink only when the aircraft crosses a waypoint on the route stored in the FMC or when the crew alter the route held in the FMC (once the aircraft is within oceanic airspace, e.g. for WX deviation).

However, ATC can at any time select a "Demand Contract" - which will downlink to ATC the aircraft's present position plus the ensuing waypoints.

Other ADS contracts can be set up, such as the "MET contract", which sends a report every 30 minutes, or the "R-LONGSM (Reduced longitudinal separation minima) Contract", which reports every 18 minutes, but these are as invisible to the crew as they are to ATC. (ATC can only see such reports in the flight's "History" and in any event they would be of limited use).

The data from ADS/FMC and HF reports are used at Shanwick to provide a picture on a 'pseudo radar' display (Graphic Data Display) showing the approximate position of aircraft. It is not (yet) used as a tool for separation purposes but simply to give the controller a real-time 'picture' of what is going on where and in relation to whom. (The system will 'plot' the aircraft position between waypoints on the basis of stored Met and aircraft speed, hence the aircraft symbols will move across the screen as the associated aircraft transit oceanic airspace, thereby making the display 'look' as though it were radar).

A couple of pix online of our own kit (top) and the Canadian kit upon which it is based.(bottom)


(bigger version here)


Last edited by rab-k; 30th Jan 2012 at 15:39.
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Old 29th Jan 2012, 13:52
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Thanks Rab-K. You answered my question exactly. Now I understand how it works. Appreciate the time you took for the answer.
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Old 30th Jan 2012, 15:40
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You're welcome.
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Old 6th Mar 2012, 17:09
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People under ADS contract do include non-official waypoints in the FMS routing?
In my airline I would be hanged, drawn and quartered if I did...

(but then again, if given a shortcut (Shanwick don't do that often, but Gander do, west of 50W) does ATC appreciate ADS reports abeam the flight planned reporting points? The Airbus FMS automatically creates those when going directly to a point down route...)
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Old 11th Mar 2012, 12:57
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Usually the only "short cuts" we (Shanwick) give are to those flights with an urgent requirement for such, i.e. somebody in hurry to get on the ground, for whatever reason.

If I can do so, without penalising anybody else, I might be able to shave off a couple of minutes by routing somebody coming east 48/20 DCT OMOKO as opposed to 48/20 48/15 OMOKO, for example. However, we have to stick to the exit/entry fixes at the boundary with Scottish, Shannon, Brest and Madrid.

If somebody going east calls Scottish, for example, early enough on VHF and the Scottish controller isn't too busy they may call Shanwick and ask that we approve a direct route whilst the flight is still within Shanwick airspace, but it doesn't happen very often. The procedural separation distances are so big in Oceanic that often we're unable to approve a direct route due to it infringing other traffic which Scottish, or whoever, can't yet see on radar; therefore a lot of the guys understandably don't ask and generally give "after GOMUP route direct IOM" for example, rather than "route direct IOM" from the point a flight is first I-D'd on radar.

Not sure how Gander operate but the Gander Oceanic guys may have a more seamless setup with their Gander Radar colleagues than we do with the Irish, French, etc. Perhaps they have an agreement that you're released to radar for vectors once west of 50W. Don't know TBH.

Back to your question. If we do give a direct route an ADS report wouldn't be essential, given how close to the exit boundary you would be, but would be "appreciated" none the less in as much as it updates our system which ensures a greater degree of accuracy.
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Old 15th Aug 2014, 03:01
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ADS-C reports

Very interesting Rab-k your comprehensive explanation.
It is clear that everythink you put into the FMS you guys at the ground will get to see it, but I was told there were some exception like a time-marker you put for a crewrest or a TOC/TOD. Can you confirm that.At least in my experience controlers never complaint about those time-markers nor required any explanation.

You said that you can set met-contracts that sends report every 20 mins or R-longSM every 18 mins. Is that a standard use? According to GOLD "normal" contracts are set for 304 secs. unless otherwise stated.

And one last question about the 3 min error revise estimate. How come you want in Shanwick a revise estimate via ADS-C or voice if you are getting,say every 304 secs , a position report?
KZWY doesnt want them.

Thanks very much
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Old 17th Aug 2014, 21:47
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Hi Ch

The time markers will indeed be seen by the controller. However, use of the 'Demand Contract' function can provide the controller with the necessary confirmation that the next significant waypoint beyond the crew rest/ETOPS time marker is correct. The controller may then elect not to seek confirmation of the route in the FMC where it can be seen that the Lat/Lon of the time marker will not result in any deviation from the cleared route.

The standard ADS-C waypoint event contract is 1 report per significant waypoint. The 'R-LONGSM' 18 minute reporting interval is established automatically by the ATC system/Aircraft, where that facility exists, and is in addition to the significant waypoint reports.

The 30 minute Met contract is rarely used but can be selected by the controller. For example, if there is a CPDLC log-on issue and the R-LONGSM separation becomes unavailable, due to a lack of CPDLC, the controller can cancel the R-LONGSM (18 minute) contract and issue a Met contract (30 minute) so that any unintended use of reduced separation in the absence of a CPDLC connection can be avoided.

The only other contract we use at Shanwick is the emergency contract, which, depending upon the aircraft manufacturer, will downlink a report every 2 or 10 minutes. (I've not read GOLD I'm afraid so I can't comment on the 304 seconds periodic contract you mention, but at Shanwick we don't use such for establishing periodic contracts).

The passing, by HF or CPDLC, of a 3 minute revised estimate applies to all aircraft, whether ADS-C equipped or not. Unless there is a credibility/conformance issue, significant and intermediate waypoint position reports do not refer to the controller but simply update the flight's profile in the ATC system.

However, by bringing to the attention of the controller the possibility of arriving over a significant waypoint >=3 minutes will enable the controller to intervene, (apply a time restriction and/or adjust speed), at the earliest opportunity to ensure that separation at the next significant waypoint will not be lost.

Why New York do not require the passing of >=3 minute revisions I do not know I'm afraid. Hopefully someone here may be able to inform us.

Hope the above helps.

RK
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Old 17th Aug 2014, 22:29
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Sorry if it's a stupid question, but why don't people use the fix pages for these extra points instead making them active route waypoints? Can't speak for the Airbus equivalent, but I've never needed to put anything extra on the legs page of a Boeing in normal cruise and was always taught not to for the reasons described.
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Old 17th Aug 2014, 23:20
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Dump it in the fix page as a Zulu time, or, if you really, really, really want a geographical position, enter it in as a route amend, don't execute it, pull up route data, get the waypoint crossing time, erase the amend and put that into the FMC as a Zulu time fix.

Never add waypoints to a cleared NATS route.
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Old 18th Aug 2014, 19:11
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Thanks rab-k for you plausible explanations.On Airbus we have only 2 (or 4 depending on the software) fix info options, sometimes not enough to deal with.

Copied about the 3 min revise estimate. Gander and Santa Marķa have pretty much your same rule. Still wondering about NY.

Ch.
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Old 2nd Sep 2014, 21:34
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A bit long, but may be of interest to those crossing the pond...

https://www.youtube.com/watch?v=EJTjwW5ZYas
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