Dainan
Topic Author
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Joined: Sat Sep 17, 2005 10:39 pm

Why No Direct Rnav Flights Over Land?

Sat Nov 27, 2010 10:03 am

Hi forum!

Why arn't there any (or few) direct flights or great circle flights being flown over land?

When flying from Europe to the U.S and vice versa the North Atlantic Tracks are used. Of course consederation is taken to the prevailing winds aloft as well as ETOPS rules and such, but generaly they strive to stay as close to the great circle as possible.

When flying from Europe to Asia or from the U.S to Asia a flitghtpath along the great circle is chosen. So far so good, in RNAV we trust! =)

BUT when flying from Arlanda Airport in Stockholm to Portela Airport in Lisbon for example or from London to Rome, why on Earth isn't a direct route chosen? If the airplane is RNAV capable, why not? Europe is full of airports suitable for diversions, so I guess that can't be the reason. Why keep folowing routes/airways based on now obsolete navaids? Why no "NATs" between the various cities? I reckon that a lot of fuel could be saved here. I mean if airlines reduce the ZFW of their fleet by even making their cuttlery just a tad lighter, why wouldn't they push for more fuel efficient routes?

As long as safety, winds and airspace permits it I believe that a straight route RNAV route would make more sense than many of the routes that we have to day, so why hasn't anyone botherd to update them yet?


Dainan
 
Mir
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RE: Why No Direct Rnav Flights Over Land?

Sat Nov 27, 2010 10:13 am

Quoting Dainan (Thread starter):
As long as safety, winds and airspace permits it I believe that a straight route RNAV route would make more sense than many of the routes that we have to day

Problem is, the airspace really doesn't permit it. It's a lot easier to have more direct routes over the oceans because there's a relatively low amount of traffic, and everyone is headed in pretty much the same direction. Over Europe, you have a heck of a lot more traffic, and you've got airplanes headed every which way. You've also got military areas, restricted areas, etc. to deal with. In other words, it's a big mess, and separating by altitude only goes so far, so you need some airways and standard routes to sort things out a bit.

There are a lot of RNAV routes in Europe, which do cut out some distance as opposed to the VOR-based airways, but they are still airways in their own way, and I don't see that changing any time soon - it's just too crowded. Of course, ATC can always give planes shortcuts once they're in the air if traffic permits, and that accomplishes the same thing a direct RNAV route would.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
cloudyapple
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RE: Why No Direct Rnav Flights Over Land?

Sat Nov 27, 2010 10:24 am

Quoting Dainan (Thread starter):
in RNAV we trust! =)

First RNAV does not mean great circle and indeed RNAV has nothing to do with the flight plan route. It's a track keeping technology that allows more flexible and higher density (of routes, with RNP) design of routes.

Quoting Dainan (Thread starter):
why on Earth isn't a direct route chosen?

Because there are other aeroplanes in the sky. There are airspace and national boundaries. There are sectors and behind each sector there sits a controller (or 2) and each controller has finite capacity.

Try crossing the road at a busy crossing. Can you walk from 1 side to another in a straight line without bumping into other people? Same issue in the sky and that's why things are managed up there and the routes are designed like they are and flow rates are managed. Just to keep your aeroplane from crashing into other aeroplanes.

Now get a copy of Ireland's airspace map. Hopefully things will head that way with MTCD.
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Dainan
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RE: Why No Direct Rnav Flights Over Land?

Sat Nov 27, 2010 11:06 am

Quoting Mir (Reply 1):
Problem is, the airspace really doesn't permit it. It's a lot easier to have more direct routes over the oceans because there's a relatively low amount of traffic, and everyone is headed in pretty much the same direction.

Yeah I guessed it might be something like that. Do you reckon that the system could be made more efficient some way or do you think that we might at our wits limit?

Quoting cloudyapple (Reply 2):
First RNAV does not mean great circle and indeed RNAV has nothing to do with the flight plan route. It's a track keeping technology that allows more flexible and higher density (of routes, with RNP) design of routes.

Thanks for making my statement clearer =) I didn't mean that RNAV = great circle. Just that the NATs require RNAV capabilities, but some how I seem to have skipped that part =)

Quoting cloudyapple (Reply 2):
Try crossing the road at a busy crossing. Can you walk from 1 side to another in a straight line without bumping into other people? Same issue in the sky and that's why things are managed up there and the routes are designed like they are and flow rates are managed. Just to keep your aeroplane from crashing into other aeroplanes.

Yeah I see your point. I do however think that, as crowded as the skies are, that aerpspace should give us some more leeway. But as you and Mir pointed out, it's tricky since planes will come from various directions at all times.

I just can't shake of this feeling that if one were to come to a consensus about the usage of some of the airspace a lot of money and time could be saved by many European carriers. I guess that the ATCs are doing their best by giving direct routing when they can though =)
 
flyingalex
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RE: Why No Direct Rnav Flights Over Land?

Sat Nov 27, 2010 11:31 am

Quoting Dainan (Reply 3):

I just can't shake of this feeling that if one were to come to a consensus about the usage of some of the airspace a lot of money and time could be saved by many European carriers. I guess that the ATCs are doing their best by giving direct routing when they can though =)

Yeah, this is a big issue for European carriers, and they are quite anxious to get the problem resolved. For example Lufthansa's CEO Wolfgang Mayerhuber never misses an opportunity to talk about the Single European Sky project and how much money and CO2 emissions it would would save. The problem is that national authorities within the various European countries would have to give up a lot of their present rights and responsibilities to a pan-European body, and not all countries are comfortable with that. Time will tell.

Until then, it will be the patchwork we have today:



The area boundaries lead to the sometimes convoluted routings you see on a daily basis.
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Mir
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RE: Why No Direct Rnav Flights Over Land?

Sat Nov 27, 2010 11:37 am

Quoting Dainan (Reply 3):
I do however think that, as crowded as the skies are, that aerpspace should give us some more leeway.

And it does, because you can have airplanes pass right over one another without colliding, which you can't do on a road. But that still isn't enough.

Quoting Dainan (Reply 3):
Yeah I guessed it might be something like that. Do you reckon that the system could be made more efficient some way or do you think that we might at our wits limit?

It can be made better, and it is being made better, but in very small and gradual increments that tend not to get noticed by those who aren't actively involved in the system. You're not going to see any big changes in the way things work. There's no technology that's ready to go that will make a big difference - they're basically at the limits of what's out there (as opposed to the US, where there is a larger gap between what is possible and what is used). Advances will be made, and the system will be updated to reflect that, but it's not likely to be anything groundbreaking for a while.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
flyingalex
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RE: Why No Direct Rnav Flights Over Land?

Sat Nov 27, 2010 11:56 am

Speaking of convoluted routings in Europe, here's one case that I'm very familiar with:

I often travel to Spain, and flights leaving Frankfurt never take the shortest route right into France. Traffic is invariably routed via Switzerland, crossing into France near Geneva.

http://www.gcmap.com/mapui?P=fra-mad...C+fra-zrh-gva-tls-mad&MS=wls&DU=mi

I have no idea why there is no direct route into France, or why it is not used if there is one. I just know we've always gone that way on at least a dozen flights in the last two years.
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Mir
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RE: Why No Direct Rnav Flights Over Land?

Sat Nov 27, 2010 12:03 pm

Quoting flyingalex (Reply 6):
I have no idea why there is no direct route into France

IIRC, there's a big restricted area in that corner of France that has to be circumnavigated.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
cloudyapple
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RE: Why No Direct Rnav Flights Over Land?

Sat Nov 27, 2010 6:15 pm

Quoting flyingalex (Reply 6):
I have no idea why there is no direct route into France, or why it is not used if there is one. I just know we've always gone that way on at least a dozen flights in the last two years.

Sometimes it could be to do with route charges. If you can pay a lower rate per CSU then it may be worth taking a longer route. Or some states charge a flat rate so if the distance is short it may be worth going round an entire country to avoid an additional bill.

http://www.eurocontrol.int/crco/gall...ublic/docs/unit_rates/ur201010.pdf

Apparently the Swiss charges more than the French so this is probably not the reason for your detour. Perhaps there's a big military area in the way that preclude a more direct routing? I don't know.
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LAXintl
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RE: Why No Direct Rnav Flights Over Land?

Sat Nov 27, 2010 8:56 pm

As mentioned above RNAV has nothing to do with a direct or great-circle route.

RNAV is simply alternate navigation means and a RNAV routes can be everything from an arch, 3/4 of a box, or zig-zag for example.

So don't associate RNAV with direct, or shortest line distance necessarily.
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Fly2HMO
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RE: Why No Direct Rnav Flights Over Land?

Sat Nov 27, 2010 8:59 pm

Quoting Dainan (Thread starter):
If the airplane is RNAV capable, why not?

You are really overestimating the capability of current navigation systems. Everybody dreams of going direct point to point but you got to remember the current airspace navigation systems are based on pretty much 70 year old technology. And even then the amount of traffic in the skies is at unprecedented levels. If everyone was allowed to fly as they wanted it would be raining aluminum all over the world. And while many current planes are more than capable of flying direct-to anywhere on the planet, you still would have to update many ground based systems. So far, the implementation of ADS-B and other datalink technologies is slowly taking over radar facilities, but it won't fully replace them until two decades from now.

Quoting Dainan (Thread starter):
As long as safety, winds and airspace permits it I believe that a straight route RNAV route would make more sense than many of the routes that we have to day, so why hasn't anyone botherd to update them yet?

They are being updated as we speak, but the technology to fully implement self-spacing and direct routing system won't be here until at least 20 years from now.

You may want to read up on this:

http://www.faa.gov/nextgen/
 
Dainan
Topic Author
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RE: Why No Direct Rnav Flights Over Land?

Sat Nov 27, 2010 10:40 pm

Quoting LAXintl (Reply 9):
As mentioned above RNAV has nothing to do with a direct or great-circle route.

RNAV is simply alternate navigation means and a RNAV routes can be everything from an arch, 3/4 of a box, or zig-zag for example.

So don't associate RNAV with direct, or shortest line distance necessarily.

Never ment to imly that they are the same. Just ment that aircrafts capable of RNAV (i.e not bound by navaids and such) potentially should be able to fly more directly between destinations. But than again I should have expressed that more clearly =)

Quoting Fly2HMO (Reply 10):
And while many current planes are more than capable of flying direct-to anywhere on the planet, you still would have to update many ground based systems. So far, the implementation of ADS-B and other datalink technologies is slowly taking over radar facilities, but it won't fully replace them until two decades from now.

Good point, didn't take the limitations of the ground based equipment into consederation.

Quoting Fly2HMO (Reply 10):
You may want to read up on this:

http://www.faa.gov/nextgen/

Thank's for the link! Good to see that the wheels are indeed turning than =)
 
411A
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RE: Why No Direct Rnav Flights Over Land?

Sun Nov 28, 2010 2:48 am

Direct flight paths have been available for many years.
Example.
Circa, 1996.
Departing LosAngeles (LAX) and after turning left to proceed direct EED, the controller asks...
Are you RNAV equipped?
When the First Officer replies in the affirmative, we are then told....proceed direct Dover AFB.
We did so, no problems.
Type...Lockheed TriStar.

The L1011 had this capability from 1977, with Hamilton Sundstrand FMS equipment installed.
A moving map?
Yup, had one as well.
 
SPREE34
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RE: Why No Direct Rnav Flights Over Land?

Sun Nov 28, 2010 3:03 am

I was clearing aircraft direct point to point in the early 80s. When I retired a while back, we were clearing them direct anywhere in domestic airspace, and to oceanic transition fixes within RADAR coverage.

BTW, a "direct" clearance plots out to great circle routing.
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Fly2HMO
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RE: Why No Direct Rnav Flights Over Land?

Sun Nov 28, 2010 3:08 am

Quoting 411A (Reply 12):
A moving map?
Yup, had one as well.

Did it look like this?:

http://www.sonofthesouth.net/revolutionary-war/maps/old-world-map.jpg

    

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