contrails67
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Reason For Polar Route

Mon Sep 19, 2011 8:36 pm

While tracking UAE 215, a flight that my sister had been on, my father asked why the plane took the polar route. With my limited aviation knowledge, I had mentioned that it had something to do with the jet stream and that it is supposed to be a quicker way. Can someone fully explain it to me? Is it really faster and does weather condition necessitate this route? In addition, many airlines take what appears to be a circuitous route to their destination. I had always learned in math class that the quickest distance between two points is a straight line, but obviously this doesn't apply in aviation.


Thanks,
Contrails67
 
Flighty
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RE: Reason For Polar Route

Mon Sep 19, 2011 8:55 pm

Pretty simple, and yes jetstream plays a part. Polar route can be the shortest "still air distance" to travel. It is really all about shortest distance. With the caveat that, when air is moving, the shortest distance must take the air movement into account, to build a new shortest track. To save fuel and time, airlines get pretty close to ideal "as the crow flies" shortest route between longhaul cities, subject to adequate emergency landing runways along the way. So, for example, the shortest route from Boston to Beijing is this (assuming still air):

http://www.gcmap.com/mapui?P=BOS-PEK

They will try to save fuel (=money) and time (=money) by making a journey as short as safely possible. If there are no legal runways on the route, within necessary limits, then they will make a new route that is the shortest legal, and safe route to take.

[Edited 2011-09-19 13:57:31]
 
Fly2HMO
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RE: Reason For Polar Route

Mon Sep 19, 2011 9:02 pm

Quoting contrails67 (Thread starter):
I had always learned in math class that the quickest distance between two points is a straight line, but obviously this doesn't apply in aviation.

Of course it applies, that's part of the reason why planes go over the poles among others. Not too long ago we didn't have the capability of doing such routes reliably and safely but now we do

As a side note, one of the other reasons airplanes don't always go in straight direct routes is mainly because like cars, airplanes, for the most part, have to stick to airways (interstates in the sky), and those rarely offer a direct route. Many of those airways have been around since WW2 and the system is based on ground navigation systems, hence the convoluted routes taken in some cases.

However, before 2020 (in the US at least) when the NEXTGEN airspace system comes online, the airway system and ground NAVAIDS will be pretty much extinct as we know it, almost every flight will use direct navigation from point A to B. Most modern airliners already have the technology to do that already.

[Edited 2011-09-19 14:03:43]
 
26point2
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RE: Reason For Polar Route

Mon Sep 19, 2011 10:56 pm

Quoting contrails67 (Thread starter):
I had always learned in math class that the quickest distance between two points is a straight line

LAX-DXB via the N. Pole region IS the shortest distance. I don't understand why this route is in question. Run a piece of string between these points on a globe and you'll see.

As mentioned, earlier long haulers didn't have the range to so this so required a stop in LHR, for example, which is a substantial detour from Great Circle
 
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Starlionblue
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RE: Reason For Polar Route

Mon Sep 19, 2011 11:41 pm

The problem with most people's understanding is that the world maps displayed in class rooms and other places are all splayed out into flat projections that distort direction and distance. The world is a 3D place but maps are 2D. ANY flat projection will be distorted.


One common projection is Mercator, which straightens out all the meridians. This is why people think Greenland is so enormous, while in actual fact it is much smaller than the United States. With this projection, you'd think flights from, say, LAX to LHR should fly straight across the US and then the mid-Atlantic. The real route is much further north.


In actual fact the world looks more like this. Now you can see clearly how the polar routes make sense. However this projection only really works with one "center point" at a time.


The best thing to use if you want an intuitive understanding is of course a globe
Quoting 26point2 (Reply 3):
Run a piece of string between these points on a globe and you'll see.

That's your answer.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
n92r03
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RE: Reason For Polar Route

Tue Sep 20, 2011 12:25 am

Two weeks ago, UA had cancellations out of ORD for Asia due to "solar flares". UA put everyone up in hotels for the night, gave them $15 for food and then a choice of compensation/mileage credit, etc. I know this affected UA 895 and I believe there were 3 or 4 other flights that same day. September 6 or 7.

I always thought these "flares" happened mostly in the winter but I must be wrong. Strange that CO flew from EWR, CX flew from JFK and DL flew from DTW, but UA did not fly from ORD.
 
NoWorries
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RE: Reason For Polar Route

Tue Sep 20, 2011 12:50 am

The geometry of the plane is an example of Euclidean geometry -- the geometry we typically learn in high school. The geometry of a sphere's surface is an exampe of non-Euclidean geomtry -- which informally means that parallel lines don't behave the same as they do for Euclidean geometry. On a sphere, for example, a pair of longitudes appear parallel at the equator but intereset at the poles. Consider a triangle: on the plane, the sum of the angles is always 180 degrees; on the surface of a sphere the sum of the interior anglers must be greater than 180 degress. A right triangle with a vertex at the pole and two on the equator has angles that sum to 270 degrees. But, the shortest distance between two points is still a "straight" line.
 
Viscount724
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RE: Reason For Polar Route

Tue Sep 20, 2011 2:24 am

Quoting 26point2 (Reply 3):
Quoting contrails67 (Thread starter):
I had always learned in math class that the quickest distance between two points is a straight line

LAX-DXB via the N. Pole region IS the shortest distance. I don't understand why this route is in question. Run a piece of string between these points on a globe and you'll see.

LAX-DXB and especially SFO-DXB are two of the best examples of polar routings. The great circle route SFO-DXB passes almost directly over the Pole.

 
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Starlionblue
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RE: Reason For Polar Route

Tue Sep 20, 2011 3:15 am

Quoting n92r03 (Reply 5):
I always thought these "flares" happened mostly in the winter but I must be wrong.

Nope. The sun doesn't care about our seasons. 
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
tdscanuck
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RE: Reason For Polar Route

Tue Sep 20, 2011 4:34 am

Quoting Starlionblue (Reply 4):
The problem with most people's understanding is that the world maps displayed in class rooms and other places are all splayed out into flat projections that distort direction and distance.

Actually, the Mercator projection (the standard one with the horrible distortion) is widely used precisely because it does *not* distort directions in one very particular way...a constant heading is always a straight line on the map. It sacrifices everything else (scale, physical fidelity, etc.) to that end.

Tom.
 
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Starlionblue
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RE: Reason For Polar Route

Tue Sep 20, 2011 8:17 am

Quoting tdscanuck (Reply 9):
Actually, the Mercator projection (the standard one with the horrible distortion) is widely used precisely because it does *not* distort directions in one very particular way...a constant heading is always a straight line on the map. It sacrifices everything else (scale, physical fidelity, etc.) to that end.

Yeah. Sorry. I knew that! Total brainfart!!! 

Still, it doesn't really invalidate my point. if anyone looks at a Mercator World Map, the "obvious" route from JFK to HKG is hardly across the pole.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
nomadd22
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RE: Reason For Polar Route

Tue Sep 20, 2011 11:41 am

It would be a lot easier if you just looked at a globe.
Anon
 
simairlinenet
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RE: Reason For Polar Route

Tue Sep 20, 2011 11:59 am

Quoting Flighty (Reply 1):
They will try to save fuel (=money) and time (=money) by making a journey as short as safely possible.

A shorter (in time and fuel) flight is usually but not always cheaper. To add to the complexity, air navigation charges can be more expensive over some countries (read: Russia) than others.
 
tdscanuck
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RE: Reason For Polar Route

Tue Sep 20, 2011 1:50 pm

Quoting Starlionblue (Reply 10):
Still, it doesn't really invalidate my point. if anyone looks at a Mercator World Map, the "obvious" route from JFK to HKG is hardly across the pole.

Absolutely agreed...the "obvious" route on a Mercator will work (i.e. it will get you there if you follow that constant heading) but it will almost never be the shortest route unless you're working symmetrically around the equator (which few airlines do).

Tom.
 
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RE: Reason For Polar Route

Wed Sep 21, 2011 4:54 am

Quoting tdscanuck (Reply 13):

Absolutely agreed...the "obvious" route on a Mercator will work (i.e. it will get you there if you follow that constant heading) but it will almost never be the shortest route unless you're working symmetrically around the equator (which few airlines do).

Tom.

Mercator Projection will also give your Rhumb Line Tracks.
Lambert's Conical Conformal will give your Great Circle Tracks. That also makes a difference to start with.

Erich
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HAWK21M
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RE: Reason For Polar Route

Wed Sep 21, 2011 11:17 am

Flying Polar routes though faster & more Economical.
What are the risks involved in terms of Magnetic Influence & Icing?.
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Starlionblue
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RE: Reason For Polar Route

Wed Sep 21, 2011 11:41 am

Quoting HAWK21M (Reply 15):
What are the risks involved in terms of Magnetic Influence & Icing?.

You just have to be aware of icing and plan for it. Here's a good article about that: http://boeing.com/commercial/aeromagazine/aero_16/polar_story.html

The only magnetic influence I can think of is drift. Given GPS and inertial navigation it is hardly an issue. Again, awareness.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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HAWK21M
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RE: Reason For Polar Route

Wed Sep 21, 2011 11:56 am

Quoting Starlionblue (Reply 16):
The only magnetic influence I can think of is drift. Given GPS and inertial navigation it is hardly an issue. Again, awareness.

Considering in the abnormal event on only relying on Magnetic navigation.....The Polar route might not respond as other places around the globe.
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Starlionblue
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RE: Reason For Polar Route

Wed Sep 21, 2011 12:31 pm

Quoting HAWK21M (Reply 17):

Considering in the abnormal event on only relying on Magnetic navigation.....The Polar route might not respond as other places around the globe.

Well, sure. However the deviation can be calculated. Then again how likely is it that an airliner doing a long range flight in the polar regions does not have redundant inertial navigation and/or GPS?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Fly2HMO
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RE: Reason For Polar Route

Wed Sep 21, 2011 4:31 pm

Quoting HAWK21M (Reply 17):

Considering in the abnormal event on only relying on Magnetic navigation.....The Polar route might not respond as other places around the globe.

The old school magnetic compass would be useless once very close to the pole, but with the myriad of other instruments to back it up that are unaffected by the closely spaced magnetic flux lines it's hardly an issue.
 
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HAWK21M
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RE: Reason For Polar Route

Wed Sep 21, 2011 8:53 pm

What about fuel.......Specially treated I presume.....to prevent High Altitude Freezing.
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Starlionblue
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RE: Reason For Polar Route

Wed Sep 21, 2011 10:59 pm

Quoting HAWK21M (Reply 20):
What about fuel.......Specially treated I presume.....to prevent High Altitude Freezing.

Read all about it: http://boeing.com/commercial/aeromagazine/aero_16/polar_story.html

Not so much specially treated as carefully managed.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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Scooter01
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RE: Reason For Polar Route

Wed Sep 21, 2011 11:16 pm

Quoting Starlionblue (Reply 21):
Read all about it: http://boeing.com/commercial/aeromag....html

-beat me to it by 5 minutes.....

Quoting HAWK21M (Reply 17):
Considering in the abnormal event on only relying on Magnetic navigation.....The Polar route might not respond as other places around the globe.

Check out the gyro-compass...

Some older aircraft also carried a navigator, and this crewmember's skill in using a sextant was also wery helpful.
Astrodome at the navigator's station provided needed observation of the Sun or stars.

View Large View Medium
Click here for bigger photo!

Photo © Nils Rosengaard



Scooter01
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26point2
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RE: Reason For Polar Route

Wed Sep 21, 2011 11:32 pm

Fuel does get cold but it's more due to the amount of time spent at altitude on these flights. Hi altitude temps at these latitudes aren't substantially colder than at the equator. As a matter of fact the tropopause, where atmospheric cooling plateaus at about -57C, is at a much lower altitude near the poles than at the equator. In the FL300 range vs. FL600

Today's high altitude significant weather map illustrates this. 3 digit numbers in white boxes are the trop altitudes in hundreds of feet.



[Edited 2011-09-21 16:34:40]

[Edited 2011-09-21 16:40:43]

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