Great Circle Routes and Progress Strips???

[AdamATC]

Hi Chaps,

I'm studying for my NATS technical interview and as you read this I'm probably scouring the internet for the info I need but to save some time I thought I'd ask on this forum too.

I'm trying to find out about what is on a flight progress strip (it has been recommended I know this) I have found an American site but it has 14 pages of text :eek: :o :p

I've also been prompted to find out what the Great Cirle Routes are? All the net throws up is Nautical Navigation Charts - I don't plan on getting wet:)

Any help would be most welcome - if anyone thinks knowing all this is a waste of time let me know as I wouldnt want to come over as a snotty little sh*t that knows it all in the interview either.

Thanks

Adam:) :)

[HEATHROW DIRECTOR]

Adam. Someone with more know-how than me is going to give you a few web sites to look at! However:

Great Circle is the shortest distance between any two places on the earth's surface. Get yourself a globe and then draw a line between any two points - that's a Great Circle.

Flight progress strips will contain varying information depending on which control sectors they are used by. However, much basic info is the same: A/c callsign, a/c type, filed airspeed, point of departure, point of destination and a very brief resume of the route taken. I don't think you should need to know much more...

Good luck!

[1261]

"Great Circle" route is a navigational term used to describe the shortest distance between two points on the earth's surface. This is really only an issue for aircraft on Oceanic tracks (or other very long-distance routes). I'll try to explain why it's important without getting too technical.....

Because the earth is a sphere (those cleverer than me will jump in at this point but ignore them!), it isn't possible to accurately reflect its surface on a flat chart (or FMS screen). So navigational charts are in fact a slightly distorted (the degree of distortion depends on the scale of the chart) view of the earth's surface. There are several different ways of representing this distortion, the most common are called "mercator" and "gnomonic". If you were to plot an aircraft's "great circle" flight path on a mercator chart it would appear as a curve.

Aircraft in flight are either following a (magnetic) radar heading (on the instructions of a controller) or a track (based on their nav charts). Aircraft headings/tracks are based on routes determined using navigational charts: in order to fly a true great circle track the aircraft's heading would be constantly changing, so they fly an approximation (sometimes called "composite great circle") with a waypoint (i.e. turn) every ten-or-so degrees of longitude.

I hope that hasn't confused you too much. If no-one else posts a simpler version (or if you want me to try and explain further) drop me an e-mail.

As for the flight progress strips, if you e-mail me your snail mail address I'll send you some real ones with some info!

[1261]

Aha! Whilst I was typing, HD's beaten me to it with a succinct explanation!

He's quite right, you probably don't need to know this in any detail....

[AdamATC]

Heathrow Director and 1261 THANK YOU VERY MUCH!!!:) :) :)

This all helps a great deal - as posted I'm finding loads of irrelevant stuff on the net so this is great!

1261 I shall be intouch about the flight progress strips.

Thanks again guys, Regards Adam :) :D :) :D :) :D :)

[2 six 4]

You might find this site useful on Great Circle routes. As a useful figure you might want an idea of how far from London to New York or Tokyo.

Great Circle plotter (http://gc.kls2.com/)

[AdamATC]

:) :) Thanks 2six4 - I would have been able to tell them its a long walk, know I'll have some figures to quote!

Cheers! Adam:) :D :)

[professor yaffle]

Before your interview, it might be a good idea to try and arrange a visit or 2 at an airfield or area unit.
Most are quite happy to show you round , but you must organise this in advance before pitching up and probably bring some id with you these days
Good luck!

[AdamATC]

Thnks Proffessor - I'm in Manchester, so if anyone knows any names or numbers for MACC then I would be most grateful!

Adam :) :)

[eyeinthesky]

Just a few further points about Great Circles:

1) The plane (i.e. if it were a disc, its surface) of the circle must pass though the centre of the Earth.

2) All Meridians of Longitude are Great Circles but lines of Latitude, with the exception of the Equator, are not.

3) Radio waves travel in great circles, so if you track a radial to or from a radio beacon you will fly a great circle track. (I THINK that's right...):confused:

[1261]

Eyeinthesky - that is entirely correct. In theory you should apply half-convergency to radio bearings before using them, but it's not accepted practice in the aviation industry, I assume because of the relatively short distances involved.

[j17]

Adam ATC

Ring Manchester Airport and ask for Atc. You should be connected to the ATC Watch Manager explain your situation and you will get should get a visit .

[matspart3]

oblate spheroid

[AdamATC]

Thanks guys this is all really helpful :D

I have contacted the Watch Manager at MACC this morning and have two names to contact in the training dept! My interview is on 3 July so I'd better get my finger out :p

The great circles are becoming clearer too - I'd better get a chance to mention them now in the interview!

If anyone has any other useful tips or hints please feel free to post them, thanks again guys!:) :) :)

Regards
Adam

[bulmers]

Hi Alan,

Try this site for the great circle and related info
http://mathforum.org/library/drmath/view/52318.html

On progress strips you should among other things see.
Callsign, type, speed, height, reporting points and estimated arrival times at these points, airport of departure oand arrival etc

Good luck

Bulmers

[AdamATC]

Hi Bulmers,

Thanks for the info - that website explanation is great and has made things crystal clear. Thanks too for the info on flight progress strips!:) :)

Life would be a lot more difficult without this forum and the help of you chaps so a big thank you to everyone who has posted help for me - CHEERS:D :) :D

[Hippy]

Lots of great definitions and explanations for 'great circles', but surely more important is knowing the relevence in an ATC context.
I hope I don't sound patronising, but I just thought it worth mentioning that putting the theory into practice, it explains why Trans-Atlantic flights head off towards Iceland and why Far East fights head off up towards Scandinavia.

Hippy.

[AdamATC]

Hi Hippy

Thanks for putting the info into context - I must admit I hadn't thought of applying the maths practically - if you know where I could find any literature on this I'd be grateful as it would save time trawling the web.

Thanks again - Adam:) :) :)