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Trimeresurus
Topic Author
Posts: 117
Joined: Fri Jun 02, 2017 6:06 pm

Radar coverage over Atlantic and other oceanic zones

Wed Mar 03, 2021 1:48 pm

If there's no transponder radar coverage over Atlantic and other oceanic zones, how can we see the aircraft passing through via websites like flightradar24? Is it all satellite? And are ATC services provided over the ocean? What happens if there are two aircraft coming from two opposite directions on the same airway, right at each other? Is it just that they rely on the very big chance that wind and established routes etc wouldn't allow such a scenario?
 
GalaxyFlyer
Posts: 7461
Joined: Fri Jan 01, 2016 4:44 am

Re: Radar coverage over Atlantic and other oceanic zones

Wed Mar 03, 2021 2:51 pm

ADS-B, next. Yes, nearly all of the oceans have ATC services. Until recently with ADS, it was done procedurally— 10 minutes in trail, 60nm apart laterally, sort of, actually about 57 nm. That’s the NAT tracks which are very unidirectional due to flow. In the Pacific, it’s a mix of fixed and variable tracks.

If they’re coming right at each on the same airway, ATC had better have them at different levels. Which they do. The last mid-air was between a USAF and GAF transports in Class G airspace off Africa. IIRC, the GAF plane did not change level when the track changed from westbound to eastbound, by a few degrees.
 
RetiredWeasel
Posts: 838
Joined: Sat Jul 05, 2014 8:16 pm

Re: Radar coverage over Atlantic and other oceanic zones

Wed Mar 03, 2021 3:05 pm

My 2 cents (maybe dated):
The on-line flight tracker sites use ADS-B reception to determine the aircraft's position and altitude. Over the oceans, ADS-B reception is not available. So they use dead reckoning on their computers which is based on the flight planned route, and position reports (provided by an oceanic control center).

Actually that is how the centers determine an aircraft's position also. Position reports are generally done at least every hour and change of altitudes and routes have to be approved by the controlling center. They ensure aircraft separation using this method and have been for decades.

I believe ADS-B reception via satellites is still in the testing phase.
 
VSMUT
Posts: 5398
Joined: Mon Aug 08, 2016 11:40 am

Re: Radar coverage over Atlantic and other oceanic zones

Wed Mar 03, 2021 4:38 pm

Trimeresurus wrote:
If there's no transponder radar coverage over Atlantic and other oceanic zones, how can we see the aircraft passing through via websites like flightradar24?


FR24 has begun tracking with satellites. Aircraft tracked by satellite are displayed with a blue icon. The NAT takes aircraft fairly close to Iceland, Greenland and Newfoundland, so they aren't that far from potential ground stations.


Trimeresurus wrote:
And are ATC services provided over the ocean?


Yes, via HF radio.


Trimeresurus wrote:
What happens if there are two aircraft coming from two opposite directions on the same airway, right at each other? Is it just that they rely on the very big chance that wind and established routes etc wouldn't allow such a scenario?


A couple of basic rules.

- Flying west you fly at even levels, flying east you fly at uneven levels. That takes care of traffic coming in the opposite direction.
- The north atlantic track system only runs in one direction at a time, and swaps a couple of times a day. If you want to fly in the opposing direction outside hours, you can't use the track and have to fly somewhere else. It goes west at day, east at night.
- ATC will clear you for a certain level prior to entering the tracks.
- ATC can also tell aircraft to maintain or stay under a certain speed, or pass certain waypoints at specific times in order to keep aircraft separated.
 
Woodreau
Posts: 2056
Joined: Mon Sep 24, 2001 6:44 am

Re: Radar coverage over Atlantic and other oceanic zones

Wed Mar 03, 2021 4:42 pm

I’m not sure how CPDLC works/ if the text messages are going directly between the flight crew and the ATC controller

But when doing it via voice on HF. The controllers and flight crews aren’t talking directly with each other. Instead there is an intermediary ARINC radio operator that relays messages between the flight crews and ATC.

So if you need a weather deviation. You call the radio operator. The operator calls ATC. ATC approves the deviation. the operator calls you and then you get to deviate. At least that’s how it works in WATRS. Don’t know if NAT is similar.
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
 
GalaxyFlyer
Posts: 7461
Joined: Fri Jan 01, 2016 4:44 am

Re: Radar coverage over Atlantic and other oceanic zones

Wed Mar 03, 2021 4:53 pm

Most oceanic airspace now uses CPDLC and ADS-Contract where the plane sends near continuous positions and has a “contract” with the OAC to report at each 10 degrees and any deviations in track or level. HF is only a back to satellite CPDLC. Nearly no voice comms once in the airspace. Controller Pilot Datalink Communication goes direct to the controller. Having had a couple of emergencies on the NAT, declare MAYDAY on Gander or Shanwick and the radio operator patches you directly to the controller in an instant whose only question is “what do you need?”
.
The NATS were like that before CPDLC and the link for Gander, Shanwick or Santa Maria Radio, FSS essentially.
 
CosmicCruiser
Posts: 2493
Joined: Tue Feb 22, 2005 3:01 am

Re: Radar coverage over Atlantic and other oceanic zones

Wed Mar 03, 2021 10:58 pm

Woodreau wrote:
I’m not sure how CPDLC works/ if the text messages are going directly between the flight crew and the ATC controller

But when doing it via voice on HF. The controllers and flight crews aren’t talking directly with each other. Instead there is an intermediary ARINC radio operator that relays messages between the flight crews and ATC.

So if you need a weather deviation. You call the radio operator. The operator calls ATC. ATC approves the deviation. the operator calls you and then you get to deviate. At least that’s how it works in WATRS. Don’t know if NAT is similar.


During the HF days we just called Gander and Shanwick. I don't remember any relaying as they answered our question/ request as we asked.

Then came CPDLC...heaven!
 
GalaxyFlyer
Posts: 7461
Joined: Fri Jan 01, 2016 4:44 am

Re: Radar coverage over Atlantic and other oceanic zones

Wed Mar 03, 2021 11:32 pm

Gander and Shanwick were radio stations that sent your position reports and requests to the appropriate Oceanic Control Center for controllers to work and send the reply back to you. It was like sending to a FSS for forwarding to the ARTCC, which I’ve also done at one time.

Prior to 1966, there was a Prestwick and Shannon control centers with respective aeradio stations. To consolidate the two, the UK and Ireland ATC, created Shanwick—Shannon getting the Flight Services and Prestwick the traffic control portion. When you called “Shanwick Radio, NW xxx, position”; your position was sent to a radio operator on HF who electronically sent it on to Prestwick OAC.
 
26point2
Posts: 1112
Joined: Wed Mar 03, 2010 6:01 am

Re: Radar coverage over Atlantic and other oceanic zones

Fri Mar 05, 2021 5:23 am

GalaxyFlyer wrote:
Prior to 1966, there was a Prestwick and Shannon control centers with respective aeradio stations. To consolidate the two, the UK and Ireland ATC, created Shanwick—Shannon getting the Flight Services and Prestwick the traffic control portion. When you called “Shanwick Radio, NW xxx, position”; your position was sent to a radio operator on HF who electronically sent it on to Prestwick OAC.


A ground school instructor once asked the Int’l recurrent class “who here’s been to Shanwick?” Of course a couple of know it all types raised their hands.
 
CeddP
Posts: 45
Joined: Sat Feb 23, 2013 12:04 am

Re: Radar coverage over Atlantic and other oceanic zones

Sun Mar 07, 2021 1:59 pm

If there's no transponder radar coverage over Atlantic and other oceanic zones, how can we see the aircraft passing through via websites like flightradar24? Is it all satellite?

Yes. As said earlier, blue aircraft on flightradar24 map use space based ADS-B. The information comes from a company called Aireon which uses ADS receptors hosted on the Iridium Next constellation. Trials started early 2017, active and in use in different FIRs since 2019. Lots of info available from Aireon or Navcanada.
https://aireon.com/
https://www.navcanada.ca/en/air-traffic/space-based-ads-b.aspx

And are ATC services provided over the ocean?

As already explained yes. But here again satellites improved the communication part quite dramatically those last few years with CPDLC (provided by either Iridium or Inmarsat depending on the onboard equipment). We're also talking about sat based voice communication using VHF, but we're still very early in the process and I haven't heard about it for some time now (I think it was being tested in the Edmonton FIR if someone can confirm?).
As for HF, 95% of the time the only thing we still do with it is asking for a selcal check when entering a FIR...

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