North Atlantic Navigation

[green-dot-speed]

Hello guys,
I'm courious to know if NAT routes are flown as GREAT CIRCLES or RHUMB LINES
thanx a lot
G-D-S

[Rainboe]

Do you long haul pilots out there know anything about this

Do we know about Great Circles and Rhumb Lines? Yessir! We can spell it as well without the need for capitals! My goodness have you come to the right place for this!

You fly Great Circles between every 10 degrees longitude, staying at nice round figure en route points like 51N 30W. This gives legs up to about 380 miles maximum on the N. Atlantic. Chief determining factor is the location of the jetstream winds which blow west to east across to Europe/N.Africa at up to 200kts. So the routes planned (which are currently set at 1 degree, or 60 nms apart) are arranged to either benefit from this or avoid as much as possible. It is planned by Shanwick (British Isles side) or Gander (Canada), and there are about 5 routes each way. The shortest route is usually not the most economical.
Plenty on N. Atlantic routes if you use Search.

[green-dot-speed]

Thank you very much Rainboe!! Yes, I knew I had come to the right place for my question ehehe ...

Anyway, let me better understand...rhumb lines cut merdiens with costant angles, while great circles are the shortests tracks from A to B.

So I assume that when you fly great circles your track costantly changes, isnt this right?
Well, does your track changes when you're flying a NAT going, for example, from 40N20W to 43N30W ??

Thank You very much!

[oncenterline]

The NAT-Routes are established taking into account wind and weather situation. This happens anew every day. They are designated with A and onward on westbound flights and Z and backward eastbound. The tracks are valid within a certain time interval in reference to time over 30W.
The tracks may be great circles or rhumb lines but most of the the time they are not.
And yes, long-haul-pilots have heard of great circles and rhumb lines...

[Rainboe]

Right, this gets complicated. On a Mercator map projection, Rhumb Lines are straight, Great Circles are curved towards the Equator. So you would think you would fly RLs. Notso. Think we're going to scrunch up the top of those meridians to a point on the map (North Pole)- what's it going to do to the tracks on it? In real life, because meridians converge to the Poles, RLs are really curved towards the Poles and Great Circles are straight lines. So a plane flying a GC is indeed altering course all the time whilst flying absolutely straight- that's why they are the shortest distance.

So pull yourself together man, this is the nation of Captain Cook, and if he had it sorted 240 years ago, we will get it knocked off now OK? Just be nice to the natives.

[Spitoon]

Forgive me if I wildly wrong here because I am a simple ground-bound controller, but I always thought that short-haul pilots got to know all about navigation and maps too.....because they have professional pilot licences.

BTW, even controllers know quite a lot about rhumb lines and great circles and projections.....well, they certainly had to learn about it when I went through the training.

[machone]

Far to complicated most of us just follow the little magenta line that is drawn nicely on the TV screen. The little black box that cost so much and tells us how fast, high we can does the rest. It even reminds us that we are short on fuel

[dick badcock]

Green dot and others.
The FMC always gives you great circle track between two points no matter the distance between them. So between 55N40W and 55N50W, on a rhumbline track you would stay at a constant 270 degrees, while on a great circle track (as per the FMC) your ITT (inital true track) will start somewhere greater than 270 (say 273) and end somewhere below 270 (perhaps 267). Sometimes the NAT tracks are very close to great circle tracks, but most often they are not. As has been pointed out earlier, however, this is not a concern, as they are planned to make use of (or avoid!) the prevailing winds as much as possible.
Rgds,

DB

PS! Rainboe, I'm sure you meant to say that on a Mercator chart, great circle tracks are curved upwards towards the North pole (in the northern hemisphere), not towards the equator.

[Rainboe]

PS! Rainboe, I'm sure you meant to say that on a Mercator chart, great circle tracks are curved upwards towards the North pole (in the northern hemisphere), not towards the equator.

Quite right to pick me up! Rereading it, it can be seen as wrong. I was meaning 'curved towards' as one would mean it if one was travelling along it (as I spend thousands of hours doing!), not that the curve is viewed as curved down towars the equator....... Still doesn't get much clearer- I should have used 'concave to' and 'convex to' the equator! I know what I mean anyway!

[411A]

Strange, no one has mentioned that superb bit of obtuse flying called pressure pattern navigation.

Oh yes, now I remember, this died out with Stratocruisers.
What a shame.
No 'button pushing' for the pilots, just change the heading once in awhile at the direction of that fine fellow in back, often called the Navigator.

[Old Smokey]

green-dot-speed,

Long Distance over water flying has always used Great Circle Navigation, but until INS, Omega, GPS/IRS etc. came along to enable constant maintainance of the Great Circle Track, The Great Circle was 'broken' into smaller sections, usually about 300 nm apart, and Navigators would fly a Rhumb line between these successive points. Such tracking was known as "Composite Tracking", and some tracks, such as Southern Indian Ocean from Australia to South Africa were published and named as such, i.e. Composite Great Circle / Rhumb Line Track. The advent of INS, Omega, GPS/IRS etc. enabled pilots to fly constant Great Circle Tracks, and forced the Navigators into retirement.

What can be fairly misleading on a great deal of the North Atlantic routes is that Magnetic Variation change fairly nicely disguises the actual constant change in True Track, making them APPEAR to be Rhumb Lines. For the example quoted earlier (40N20W to 43N30W), the Initial Track, Distance, and Final Tracks are -

295.1°(T) / 483.7 nm / 288.5°(T), clearly showing a 6.6° Track change, or a 1° Track change every 73 miles.

If you consider the Initial and Final Magnetic Variation to be applied (9.40°W and 14.26°W), the same track becomes -

304°(M) / 483.7 nm / 303°(M), which does look very close to being a Rhumb Line, but is NOT.

411A, the last time that I used Pressure Pattern Navigation was on a DC 4, I must be showing my age It did work well, wandering all over the sky from MPP to MPP, but magically arriving very close to the destination I suspect not so suitable for today's congested airways.

Regards,

Old Smokey

[madtrap]

Pressure pattern?!? That’s it; I’m jolted out of my trance.
In an earlier life and previous trade I used it on C-130s in the late 60s and early 70s, and it worked fine. That’s not to say that we wandered all over the Pond on the way east, Gander and Shanwick took a dim view of that. The technique simply involved comparing true and pressure altitudes every 15-20 minutes to maintain the pressure pattern log. You could check the accuracy of the Doppler drift (no really, honest)
Our antennae had an occasional tendency to lock or freeze in position. That was the type that turned to equalize the shift for the two forward-facing beams, then measured the angle between the AE and the mounting as drift angle.
Anyway, cross-checking that Doppler readout was prudent, especially if you were expecting to penetrate a front.
If the Loran A sky waves got tangled in twilight shifting ionosphere layers, and the high cirrus kept you from your celestial salvation, a plot from your last decent fix, combined with the calculations from the PP log, would give you a better position line than Quimper-Plonéis or Varhaug Consol stations.
I do prefer ring-laser gyros, FMCs and CPDLC though, the romance of the other stuff having faded with my youth and hairline.

[Rainboe]

You're a real pilot when:
you can remember counting the Consol beeps from Quimper or Vigo (was it Ploneis as well?), and getting a different total each time. A German wartime U-boat navaid still used in the 70s!

[stator vane]

reminds me of Guy Murchie!!!---

and his amazing books!!!!
so fascinating, but my retention level is so low!!!
there are some amazingly intelligent people in this world, but i am not a member of that club!!
but i appreciate them when i read their works, this thread included!
thanks for keeping it alive---

[Stuck_in_an_ATR]

Can you guys tell us, youngsters, a bit more about that pressure pattern stuff? Never heard of that before and it sounds interesting...

[forget]

....... a bit more about that pressure pattern stuff?

Here, you (I) learn something every day.

http://www.planeandpilotmag.com/cont...evisiting.html

[NRU74]

I used to fly with a Navigator called Ray Farmer and apparently he invented [ ?? discovered] a navigation method / system called the Farmer System ....anyone recall this - late 50's - 1960's ish ??

[galaxy flyer]

BTW, does anybody know the history of NAT navigation? The Ocean stations were is place until the early '70s, but when did the track system come into play? When was lateral separation reduced from 120 nm to 60 nm? How was the transition to INS nav with the introduction of the 747?

Yes, I have some questions.

GF

[IO540]

I must be missing something obvious here but surely all aircraft routes nowadays are GC routes between waypoints.

Rhumb lines (constant heading) are flown only during one's PPL training or when being vectored by ATC. All the time one is flying A to B to C under own navigation, the route is a GC. GC is what every GPS gives you (automatically, and with no other option) and I would imagine that's what every INS/FMS system gives you too.

[Rainboe]

Read post #2 boy! Rhumb lines are flown doing airplots where you just fly headings, note position when you can and deduce from that what the wind has been doing to you so you can work out what it is, and hence aply that wind to your next leg. Really only maritime search and rescue and 'find the submarine' flights pre-INS era.

The B747 started flying the Atlantic in 1971 with 3 Carousel or Litton INSs. It went very well, although they used to pick up significant inaccuracies until you could update with radial/DME on the other side. I recall on the 747 in the 70s, INS failures were quite regular. Considering all the flight instruments were fed off them and they provided artificial horizon information (except standby), they were essential equipment. I think we were flying NATs from when I started on the Atlantic in 1971.