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Topic: Ocean Radio Nav
Username: Ducker
Posted 2004-02-22 00:20:48 and read 4977 times.

I'm currently tracking a flight LH404, FRA-JFK on webtrax. The software showed the flight in progress up to the Irish coast, timed out and then reappears somewhere around Newfoundland. My question is how do crews use radio navigation over the ocean w/o VOR's, NDB's, etc. and which ATC follows any tracking reports to ensure correct spacing?
Ralph

Topic: RE: Ocean Radio Nav
Username: Futureualpilot
Posted 2004-02-22 00:29:55 and read 4958 times.

This might be better answered in the tech/ops forum, and I think they probably use GPS and some form of long-range radio navs or something along those lines.

Topic: RE: Ocean Radio Nav
Username: SlamClick
Posted 2004-02-22 00:42:12 and read 4940 times.

The transAtlantic navigation would mostly be with GPS. It can also be done without GPS using IRS/FMS. Since GPS is satellite based it is usable just about anywhere over the earth where planes are likely to be flying. Just need a couple of satellites above the horizon at any one time. IRS uses inertial guidance but also utilizes VOR/DMEs along the way to crosscheck. It can do this up until half an hour or so beyond coast-out and then again about half an hour before coasting in.

The truth is, on a clear night you could navigate the NAT tracks by following the plane in front of you both visually and on the TCAS. It is a solid stream of airliners across there on any given night.

Historically aircraft have given position reports on HF radio to Shanwick and Gander ATC facilities. These are normally given every ten degrees of longitude. Add to that we are all maintaining an assigned mach number and you have the means to track us. On some aircraft the ACARS can now do HF position reports automatically. If one is not received within a few minutes of the expected time Gander or Shanwick will contact the aircraft via SELCAL and advise them to resume doing the reports the old fashioned way.

Topic: RE: Ocean Radio Nav
Username: Mconway
Posted 2004-02-22 00:52:52 and read 4911 times.

I happen to work at Gander Radio, so this would be one area where I have half a clue what I'm talking about  Smile Most oceanic aircraft are cleared on the OTS (Organized Track Sytem). DLH404 was cleared today via NAT D, routing GIPER, DINIM, 50N020W, 49N030W, 49N040W, 49N050W, VIXUN. His oceanic clearance in all liklihood would have been received from Prestwick Centre. The coordinates would be then inputted into the aircraft's FMC and he would enter oceanic airspace. Shanwick radio would receive the handoff from Shannon control and the flight would receive a couple of HF frequencies for the crossing. Normaly the flight would be required to make routine position reports every 10 degrees of longitude via HF voice, but in this case DLH404 is CPDLC equipped (Controller Pilot Data Link Communications). As such voice reports are not required but are instead automatically transmitted by the aircraft's FMC to ARINC in New York who in turn forwards the reports to the applicable agencies. So after receiving his initial HF's, DLH404 would have been told by Shanwick to contact Gander at 30W which is the oceanic boundary. Upon contact with Gander and after receiving the exit point from the flight (in this case 49N050W), a VHF frequency (133.9) would have been assigned to the aircraft to contact Gander centre at 50W.

[Edited 2004-02-22 00:56:42]

Topic: RE: Ocean Radio Nav
Username: Myk
Posted 2004-02-22 00:54:56 and read 4893 times.

I heard that there are some areas over the sahara without NDB or VOR. Is it a kind of same as transoceanic flights ? Sorry if the question sounds silly, but I always wanted to know how ATC handle transoceanic flights and sahara flights.

Topic: RE: Ocean Radio Nav
Username: N79969
Posted 2004-02-22 01:18:03 and read 4857 times.

This is a very interesting thread and something I have wondered about as well. I flew LAX-HNL on United once and could not really comprehend the ATC calls. I do know that the pilots called in a position which was then confirmed by San Francisco Ctr. But I could not follow much else.

McConway,

Would you mind explaining your post some more using DLH 404 as an example?

Particularly these terms: "NAT D, routing GIPER, DINIM, 50N020W, 49N030W, 49N040W, 49N050W, VIXUN."

Topic: RE: Ocean Radio Nav
Username: Ducker
Posted 2004-02-22 01:28:28 and read 4843 times.

Geez, I'd forgotten about GPS! Probably b/c my wife and daughter are on LH404. Forgot about modern technology! It must have been really fun on the early Martin and Sikorsky flying boats, where the navigator had to shoot the stars and the sun to keep position. I wonder if the nav changed when the 377/DC-6/L049 started crossing in the late 1940's
Ralph

Topic: RE: Ocean Radio Nav
Username: Mconway
Posted 2004-02-22 01:58:35 and read 4811 times.

N79969, np. NAT D is short for North Atlantic Track Delta. The NAT tracks are issued daily, with the westbound tracks via Prestwick and the eastbound by Gander. The tracks are issued to try and take advantage of the jetstream. The eastbounds will try to follow the path of the jetstream while the wesbounds will try to avoid it for obvious reaons. Most oceanic flights will follow the tracks but others will fly north or south or even in between. In the example above, GIPER is the "entry point" onto the ocean via westbound track Delta. It's actual coordinates are 51N012W (51 degrees north latitude, 012 degrees west longitude), whereas VIXUN would be the clearance limit as received from Prestwick. Once the aircraft is in VHF cotact with Gander ATC at 50W, they will then receive their domestic routing to destination.

Topic: RE: Ocean Radio Nav
Username: N79969
Posted 2004-02-22 02:13:07 and read 4782 times.

Mconway,

Thank you. Are the rest of the lat/long simply reporting points? What does "DINIM" mean?

Topic: RE: Ocean Radio Nav
Username: Mconway
Posted 2004-02-22 02:39:05 and read 4770 times.

N79969,

Yes the rest of the lat/longs are simple reporting points. Whether done automatically or via voice, position reports are required every 10 degrees of longitude in oceanic airspace - 20W, 30W, etc. DINIM is just another ocean "fix" in Shanwick's airspace. There are literally hundreds of such fixes if you were to take in the whole Atlantic area.

Topic: RE: Ocean Radio Nav
Username: Myk
Posted 2004-02-22 04:15:36 and read 4746 times.

and what about such flight as those crossing over the sahara ???

Topic: RE: Ocean Radio Nav
Username: AZFAN777
Posted 2004-02-22 16:38:54 and read 4678 times.

Mconway,
What are good HF frequencies to monitor gander to listen to during the day on the us east coast for europe to NA bound traffic, based on the propagation factors.

Topic: RE: Ocean Radio Nav
Username: Mconway
Posted 2004-02-24 09:17:14 and read 4603 times.

AZFAN777,

The best HF frequencies to listen out on would be:

8864 KHz - reserved for aircraft of North American registry. We share this with Shanwick and Iceland.

8879 KHz - reserved for aircraft of European registry. Also shared with Shanwick and Iceland. This is an interesting frequency in that quite a few ground stations in the Indian Ocean/Oceania use it as well. Generally early in the evening (2000Z) we will start to pick up these ground stations and aircraft. Some of the ground stations we'll pick up are Mumbai, Melbourne, Dar es Salaam, Mauritius and Seychelles just to name a few. Quite a few times I've spoken to the likes of SAA, MAU, QFA, CPA and others. It's generally amusing to hear the flight crew reaction when they realize they are talking to Gander.

8831 KHz - independent of registry, shared with Shanwick.

These are the three "primary" daytime frequencies and as such are generally always used. During the peak traffic periods (from approximately 1400Z-1800z) we will also use a few others:

13291 KHz or 5616 KHz depending on propagation. We're in a cycle now where the higher frequencies are generally better so most likely 13 MHz. American registry.

11336 KHz - we use this most days but have a problem with an adjacent broadcast station causing splashover. 6622 KHz sometimes used instead.

8906 KHz or 8891 KHz depending on the location of the tracks. 8906 Khz is used for southerly traffic (shared with New York, Shanwick and Santa Maria - can be the proverbial zoo). 8891 KHz is generally for northerly traffic (shared with Shanwick, Iceland, Arctic and Bodo).

hth.

[Edited 2004-02-24 09:29:58]

Topic: RE: Ocean Radio Nav
Username: Iakobos
Posted 2004-02-24 12:13:21 and read 4565 times.

check http://www.grove-ent.com/mtwara.html
for a complete list of HF air frequencies, and
http://flugfunk.de/mwara.shtml
which lists all ground stations worlwide (click on VOLMET, and NEW YORK RADIO, and you will get real time meteo fm NY)

Topic: RE: Ocean Radio Nav
Username: B747Skipper
Posted 2004-02-24 12:51:22 and read 4555 times.

Those of you who want to listen to HF communications need to have USB capability on their sets. The "shortwave" radios normally sold are strictly receiving AM type broadcasts, and listening to USB type broadcast sounds like "Donald Duck" - I used to be a shortwave ham in the old days, and still practice that hobby from the airplane occasionally.
xxx
HF aircraft communications (oceanic position reports) coming from a few thousands of miles away, is certainly much more interesting than listening to your local VHF FBO jibberish...
xxx
Happy contrails  Smile
(s) Skipper


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