pilotaydin
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Great Circle Tracks And Flight Planning Q?

Mon Jan 31, 2005 12:00 am

Ok, most of us know the shortest route between two points it a straight line, and on the globe this corresponds to the great circle track, that cuts the earth in half.

I am wondering what software do airlines use to dispatch and create flight plans for calculating these routes. I am very curious as i will be flying for an airline very soon, these things interest me greatly.
Does the software find the best possible route with the winds and then transpose it to the closest airways? What sort of logic ?

any input would be great.

thanks
The only time there is too much fuel onboard, is when you're on fire!
 
SlamClick
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RE: Great Circle Tracks And Flight Planning Q?

Mon Jan 31, 2005 12:27 am

I cannot name any flight planning software for you but I am quite sure that computer-based flight planning does favor great circle.

Several years ago it was quite common for us to be offered a vector 3/4 of the way across the country during the climb out of the departure airport. Eventually flight ops sent out a memo telling us not to accept those clearances anymore because they were rhumb-line direct and actually were longer than the filed route.

Of course current winds aloft must be considered and it does not take much wind to wipe out the difference between great circle and some other logical routing.

Happiness is not seeing another trite Ste. Maarten photo all week long.
 
OPNLguy
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RE: Great Circle Tracks And Flight Planning Q?

Mon Jan 31, 2005 12:41 am

>>>I am wondering what software do airlines use to dispatch and create flight plans for calculating these routes.

There are a variety of flight planning "engines" used by various vendors and airlines, and Jeppesen is just one of them.

As far as routes go, it depends upon the ATC environment one is operating in. If I'm planning/releasing a flight in the northeast US, I'm not going via Great anything, and instead will be on DPs/airways/STARs, expecially on the shorter flights. On the longer flights, and flights from the Mississippi River westward, I'll still be on DPs/airways/STARs, but I can optimize my route to avoid headwinds, or take advantage of tailwinds.
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spencer
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RE: Great Circle Tracks And Flight Planning Q?

Mon Jan 31, 2005 3:31 am

I doubt either of these 2 websites are used professionally, however they may be of some assistance to you as a general guideline.
http://williams.best.vwh.net/avform.htm
http://gc.kls2.com/faq.html
Spencer.
EOS1D4, 7D, 30D, 100-400/4.5-5.6 L IS USM, 70-200/2.8 L IS2 USM, 17-40 f4 L USM, 24-105 f4 L IS USM, 85 f1.8 USM
 
timz
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RE: Great Circle Tracks And Flight Planning Q?

Mon Jan 31, 2005 9:17 am

"...because they were rhumb-line direct and actually were longer than the filed route."

Is that true? When the aircraft is flying "direct" to a fix 2000 miles away, it's flying a rhumb line?

I still suspect they were pulling your leg. I'm too lazy to calculate it, but offhand I'm guessing the rhumb line distance between, say, Mina and Wilkes-Barre wouldn't be longer than any airway distance between them.

As for calculating great circles, anyone who has a programmable calculator can do it, especially if you're willing to pretend the earth is a sphere.
 
nonrvsmdmf
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RE: Great Circle Tracks And Flight Planning Q?

Mon Jan 31, 2005 9:40 am

The flight planning engine we use is also used by some of the airlines
though I do not know which ones.

Great circle routes are great if all conditions are perfect. Our flight
planning engine is based off best winds first then it takes into account
the great circle distance. This is for random routes only.
I did not forget...I just misplaced the thought...
 
fxra
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RE: Great Circle Tracks And Flight Planning Q?

Mon Jan 31, 2005 2:51 pm

The system we use can be asked to find the Min Time Track, which willl factor in winds to find the shortest time (and lowest fuel burn in theory.. though i've beat the machine regularly). AN example, this time of year, we send the flights SEA-OSN up over southerns alaska the southwest parallel to the Kamchatka peninsula. Thats generally the quickest route (withouth overlfying Russia). The return flight , stays well south over the north pacific and gets a nice push from the jets. The distance is longer but its faster than doing the circle routing.

SImilar conditions are in place over the Atlantic. There are the tracks published daily for both u can use (or not) and they are generally the favorable routing, though sometimes you can shave tme not usuaing the tracks occasionally, mostly westbound.

later
jd
Visualize Whirled Peas
 
pilotaydin
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RE: Great Circle Tracks And Flight Planning Q?

Mon Jan 31, 2005 10:13 pm

hey everyone, thanks for all the productive inputs, im starting to get a much better idea of how it works, and a min time track would be logical for airlines with fuel as an issue obviously.


cheers
The only time there is too much fuel onboard, is when you're on fire!
 
spencer
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RE: Great Circle Tracks And Flight Planning Q?

Tue Feb 01, 2005 4:09 am

Timz said, Is that true? When the aircraft is flying "direct" to a fix 2000 miles away, it's flying a rhumb line?
Well, not exactly. 2000 miles away is quite a distance, and a Direct to that that fix would be something! Nonetheless, rhumb lines are tracks of constant true course with the exception of meridians and the equator, they are not the same as great circles.
Spencer.
EOS1D4, 7D, 30D, 100-400/4.5-5.6 L IS USM, 70-200/2.8 L IS2 USM, 17-40 f4 L USM, 24-105 f4 L IS USM, 85 f1.8 USM
 
timz
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RE: Great Circle Tracks And Flight Planning Q?

Tue Feb 01, 2005 5:40 am

"a Direct to that that fix [2000 miles away] would be something!"

Don't imagine it's unheard of, though. On overnight transcon nonstops particularly.

Turns out if you fly a rhumb line from 40N 120W to 40N 75W it's 1.1% longer than the "great circle". The rhumb line stays on latitude 40 and the "great circle" peaks at latitude 42.26 degrees.
 
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Buyantukhaa
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RE: Great Circle Tracks And Flight Planning Q?

Tue Feb 01, 2005 9:58 pm

So a rhumb line is what KAL007 was flying from ANC (At least, according to the official line of the story)? A constant heading?
I scratch my head, therefore I am.
 
timz
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RE: Great Circle Tracks And Flight Planning Q?

Wed Feb 02, 2005 7:05 am

I guess a rhumb line course is constant true direction, isn't it? But an aircraft's heading is always magnetic? Anyway, constant heading on the aircraft doesn't necessarily produce a constant-direction course, due to crosswinds.
 
SlamClick
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RE: Great Circle Tracks And Flight Planning Q?

Wed Feb 02, 2005 7:58 am

First, I would say that the vectors I was referring to were probably more like 1600nm than two thousand.

I would personally not plan to use a rhumb line more than about 500 miles or so, and not up in the tall latitudes. If you plot a northerly rhumb line it spirals around the pole in what is known as a loxodromic spiral. The thing is very difficult to plot on a flat chart of a round planet.

The letter we got from flight ops was quite serious. That does not mean that it was completely correct. For that we'd have to know how the vectors are generated for ATC.
Happiness is not seeing another trite Ste. Maarten photo all week long.

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