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dcaord
Topic Author
Posts: 66
Joined: Wed Nov 10, 2010 8:47 pm

Polar Routes

Sat Sep 26, 2015 10:52 pm

When flying polar routes from the US to Asia, is there a point in the flight when the compass suddenly switches from north to south? That of course happens without making a single turn but rather flying over the northernmost point of the planet.
 
covert
Posts: 1528
Joined: Sun Oct 21, 2001 1:02 am

RE: Polar Routes

Sat Sep 26, 2015 11:01 pm

I can't speak from personal experience, but in polar operations your magnetic compass becomes very unreliable so aircraft have to use true vs magnetic references to north.


http://code7700.com/high_latitude.html
http://www.boeing.com/commercial/aeromagazine/aero_16/polar_story.html
none
 
timz
Posts: 6581
Joined: Fri Sep 17, 1999 7:43 am

RE: Polar Routes

Sat Sep 26, 2015 11:05 pm

Why would the compass do anything sudden?
 
skyhawkmatthew
Posts: 480
Joined: Wed Oct 26, 2005 4:42 pm

RE: Polar Routes

Sat Sep 26, 2015 11:39 pm

Quoting timz (Reply 2):
Why would the compass do anything sudden?

If you track directly over the magnetic North Pole, the compass will switch from indicating N to S fairly rapidly as you pass over the top.
Qantas - The Spirit of Australia.
 
bourbon
Posts: 172
Joined: Sat Jan 03, 2015 3:35 pm

RE: Polar Routes

Sun Sep 27, 2015 2:40 am

I believe when United first started JFK-HKG or ORD-HKG ( I think it was ORD) they mentioned how the flight would go directly over the North Pole and would have to be hand flown for a period of time while crossing.
 
RetiredWeasel
Posts: 838
Joined: Sat Jul 05, 2014 8:16 pm

RE: Polar Routes

Sun Sep 27, 2015 5:17 am

Quoting bourbon (Reply 4):
I believe when United first started JFK-HKG or ORD-HKG ( I think it was ORD) they mentioned how the flight would go directly over the North Pole and would have to be hand flown for a period of time while crossing.

I'm pretty sure when UA started flying that route in 1996, they didn't fly a polar route. The overflight charges over Russia and China were extravagant back then, and the nav procedures over those countries were in their infancy. Those mid-late 90s routes ORD-HKG flown by UAs 747-200 sometimes bordered on 16 hours and in some winter months were impossible to make without a fuel stop in ANC. Later on I believe in early 2000s, polar routes became more common place and the 400s took over.

Never flew directly over the North Pole, but the 744 procedures besides ensuring the heading system was in the 'True' mode above approx 80 N, didn't require any switching off of the autopilot. I believe it was the same in the 200.
 
b747400erf
Posts: 3177
Joined: Wed Jun 19, 2013 4:33 am

RE: Polar Routes

Sun Sep 27, 2015 5:32 am

Heading NORM and TRUE


View Large View Medium
Click here for bigger photo!

Photo © Planecatcher

 
wingflex744
Posts: 139
Joined: Fri May 31, 2013 8:52 pm

RE: Polar Routes

Sun Sep 27, 2015 9:20 am

Inertial Navigation Systems (INS) and later Inertial Reference Systems (IRS) solved the direct reading magnetic compass errors a while back...especially when flying Polar routes whan the errors are most relevant. That's what commercial airliners are using today.

https://en.wikipedia.org/wiki/Inertial_navigation_system
Don't worry about the world coming to an end today...it's already tomorrow in Australia!
 
BravoOne
Posts: 4094
Joined: Fri Apr 12, 2013 2:27 pm

RE: Polar Routes

Sun Sep 27, 2015 12:46 pm

Here is a pretty good resource on polar operations.

http://www.boeing.com/commercial/aeromagazine/aero_16/polar_story.html

There have been a few revisions to this article over the last few years and keep in mind that some operators do not follow these procedures verbatim. The fact that the magnetic north pole is constantly moving along with updated MAG/VAR tables makes this subject a moving target. No pun intended,

Basically as others have said, you should be using True data when in the NCA or Northern Control Area which covers most of northern Canada up to around 80 degrees north. Suggest you look up the Polar keyhole for additional information, As for the initial question recall that when you're at the top of the world, aka, north pole everything is south from there. Some where I have a video of a 777 passing directly over the north pole. You can see the nav display swing rapidly to the new southern direction as it passes overhead. There is no requirement to hand fly the airplane during this event.

The term Polar has been thrown around loosely for years when in fact if you are not above 78 North you are not in the polar regions. Many flights transit very high latitude routes without actually being polar by definition.



[Edited 2015-09-27 05:59:17]

[Edited 2015-09-27 06:02:53]
 
BravoOne
Posts: 4094
Joined: Fri Apr 12, 2013 2:27 pm

RE: Polar Routes

Sun Sep 27, 2015 5:01 pm

Quoting B747400ERF (Reply 6):
Heading NORM and TRUE

Your picture does nothing (that I can see), to explain anything relevant to this subject?
 
Max Q
Posts: 8900
Joined: Wed May 09, 2001 12:40 pm

RE: Polar Routes

Sun Sep 27, 2015 9:50 pm

Quoting RetiredWeasel (Reply 5):
Those mid-late 90s routes ORD-HKG flown by UAs 747-200

Pretty sure those routes were flown by 400's RW.
The best contribution to safety is a competent Pilot.


GGg
 
skyhawkmatthew
Posts: 480
Joined: Wed Oct 26, 2005 4:42 pm

RE: Polar Routes

Sun Sep 27, 2015 10:04 pm

Quoting BravoOne (Reply 9):
Your picture does nothing (that I can see), to explain anything relevant to this subject?

B747400ERF is referencing the HDG NORM/TRUE switch (second from the right in the little row above the upper EICAS display), which would be used to force the navigation displays to display true heading as opposed to magnetic – an essential part of navigation in polar regions.
Qantas - The Spirit of Australia.
 
RetiredWeasel
Posts: 838
Joined: Sat Jul 05, 2014 8:16 pm

RE: Polar Routes

Sun Sep 27, 2015 11:40 pm

Quoting Max Q (Reply 10):
Pretty sure those routes were flown by 400's RW.

You're probably correct. I was going on memory which is suspect at my age. A rumor around our (a competitor) airline was that some of these winter flights were towed out to near the takeoff runway and engines started just prior to release time to save fuel. I think they still flew NOPAC routes and the traditional airways down to HKG in those early years.
 
b747400erf
Posts: 3177
Joined: Wed Jun 19, 2013 4:33 am

RE: Polar Routes

Mon Sep 28, 2015 3:37 am

Quoting BravoOne (Reply 9):

Your picture does nothing (that I can see), to explain anything relevant to this subject?

Maybe you shouldn't be posting in tech ops if this is your response.
 
KELPkid
Posts: 5247
Joined: Wed Nov 02, 2005 5:33 am

RE: Polar Routes

Mon Sep 28, 2015 5:24 am

Quoting skyhawkmatthew (Reply 3):
If you track directly over the magnetic North Pole, the compass will switch from indicating N to S fairly rapidly as you pass over the top.

Before you get to the Magnetic North Pole, if you are using a typical aircraft wet compass, you will experience significant compass misbehavior long before you get there due to the phenomenon of compass dip.
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
BravoOne
Posts: 4094
Joined: Fri Apr 12, 2013 2:27 pm

RE: Polar Routes

Mon Sep 28, 2015 9:20 am

Quoting skyhawkmatthew (Reply 11):
B747400ERF is referencing the HDG NORM/TRUE switch (second from the right in the little row above the upper EICAS display), which would be used to force the navigation displays to display true heading as opposed to magnetic – an essential part of navigation in polar regions.

I know where it's at and have forgotten more about what it does than most, but that picture is worthless. Just say'n 
 
BravoOne
Posts: 4094
Joined: Fri Apr 12, 2013 2:27 pm

RE: Polar Routes

Mon Sep 28, 2015 9:23 am

Quoting KELPkid (Reply 14):
Before you get to the Magnetic North Pole, if you are using a typical aircraft wet compass, you will experience significant compass misbehavior long before you get there due to the phenomenon of compass dip.

I think he was referring to the nav display (ND) and not the compass which is seldom reference unless one is doing a nav accuracy check...for some reason.
 
BravoOne
Posts: 4094
Joined: Fri Apr 12, 2013 2:27 pm

RE: Polar Routes

Mon Sep 28, 2015 9:32 am

Quoting B747400ERF (Reply 13):
Maybe you shouldn't be posting in tech ops if this is your response.

Childish. That is a poor picture at best.
 
Caryjack
Posts: 416
Joined: Tue May 08, 2007 9:45 am

RE: Polar Routes

Thu Oct 01, 2015 5:43 am

Quoting BravoOne (Reply 8):
The term Polar has been thrown around loosely for years when in fact if you are not above 78 North you are not in the polar regions. Many flights transit very high latitude routes without actually being polar by definition.

On the SEA to DXB route according to the IFE we go over or very near the pole. Just looking I see SFO as being a bit closer. I simply added the longitude of the city pairs (177:38 for the SEA trip). Anyone have a closer pair?
Obviously many factors determine the actual track.
Thanks,   
Cary
 
skyhawkmatthew
Posts: 480
Joined: Wed Oct 26, 2005 4:42 pm

RE: Polar Routes

Thu Oct 01, 2015 12:01 pm

Quoting Caryjack (Reply 18):
On the SEA to DXB route according to the IFE we go over or very near the pole. Just looking I see SFO as being a bit closer. I simply added the longitude of the city pairs (177:38 for the SEA trip). Anyone have a closer pair?
CX's HKG-BOS great circle is a little further from the pole than EK's DXB-SEA, but SQ's SIN-EWR service was a little closer at 178º9' dLong.

If Canada changes their bilateral to allow Emirates to expand their Canadian operations and open YVR, that would result in a dLong of 178º33' – that's the closest realistic city pair I can find!

If you want to go more unlikely, BKK-YYZ is 180º23'.

http://www.gcmap.com/mapui?P=90N0E%2...2C+sin-ewr%2C+dxb-yvr&MS=wls&DU=mi

[Edited 2015-10-01 05:02:11]

[Edited 2015-10-01 05:06:05]
Qantas - The Spirit of Australia.
 
BravoOne
Posts: 4094
Joined: Fri Apr 12, 2013 2:27 pm

RE: Polar Routes

Thu Oct 01, 2015 4:01 pm

Quoting Caryjack (Reply 18):
On the SEA to DXB route according to the IFE we go over or very near the pole. Just looking I see SFO as being a bit closer. I simply added the longitude of the city pairs (177:38 for the SEA trip). Anyone have a closer pair?
Obviously many factors determine the actual track.

As you have noted there are many factors that determine the actual route flown on any one day. Darn few actually mirror a great circle route. On route like this the difference ground miles flown and air miles flown can be significant at certain times of the year. The last time I checked ther was only one airway that went over the pole while many other simply came close.
 
CosmicCruiser
Posts: 2495
Joined: Tue Feb 22, 2005 3:01 am

RE: Polar Routes

Tue Oct 06, 2015 12:31 pm

I did one polar flight and was disappointed to see the magnetic compass just lazily wobble around. Keep in mind the mag. N pole was far to the south but the compass didn't really point that way. We passed about 90nm from the geo. N. pole and as others pointed out the FMS did a great job. Left Narvick Norway and came down the length of Alaska to ANC.
 
Max Q
Posts: 8900
Joined: Wed May 09, 2001 12:40 pm

RE: Polar Routes

Tue Oct 06, 2015 8:09 pm

Quoting RetiredWeasel (Reply 12):
You're probably correct. I was going on memory which is suspect at my age. A rumor around our (a competitor) airline was that some of these winter flights were towed out to near the takeoff runway and engines started just prior to release time to save fuel. I think they still flew NOPAC routes and the traditional airways down to HKG in those early years.

Interesting, on a route that long I can see how every drop helps.
The best contribution to safety is a competent Pilot.


GGg
 
BravoOne
Posts: 4094
Joined: Fri Apr 12, 2013 2:27 pm

RE: Polar Routes

Wed Oct 07, 2015 9:18 am

Quoting CosmicCruiser (Reply 21):
I did one polar flight and was disappointed to see the magnetic compass just lazily wobble around.

That's why they call it the AMU or Area of Magnetic Unreliability, thus you need to be in True as opposed to Magnetic.
 
CosmicCruiser
Posts: 2495
Joined: Tue Feb 22, 2005 3:01 am

RE: Polar Routes

Wed Oct 07, 2015 2:11 pm

I was quite up to speed on what the FMS would do and actually made it all the way to a normal ldg. I just expected to see the mag compass point to my left towards the mag. N. Pole and thus still AMU.
 
kalvado
Posts: 3103
Joined: Wed Mar 01, 2006 4:29 am

RE: Polar Routes

Thu Oct 08, 2015 9:58 pm

Quoting CosmicCruiser (Reply 24):
I was quite up to speed on what the FMS would do and actually made it all the way to a normal ldg. I just expected to see the mag compass point to my left towards the mag. N. Pole and thus still AMU.

You may want to take a look at magnetic field maps - http://ngdc.noaa.gov/geomag/WMM/image.shtml
"H" one is for horizontal field intensity. Unfortunately they have north magnetic pole cut off, but they have south pole on a map. Horizontal field, which would be picked up by the compass, is pretty weak around the pole
Another one which covers Arctic region, but has less readable maps: http://geomag.nrcan.gc.ca/mag_fld/arctics-en.php
Looking at actual inclination map (5th from the top), if that one uses same 2 deg spacing as the upper set, looks like there is a very big region to the north of magnetic pole where field is almost vertical. Probably that is what your compass tried to say by it's lazily wobble around - you didn't allow that needle to point downwards as it desired.
 
BravoOne
Posts: 4094
Joined: Fri Apr 12, 2013 2:27 pm

RE: Polar Routes

Fri Oct 09, 2015 12:59 am

Just to add a little more fuel to the conversation, Boeing provides a "Grid" option the their Nav Display for those that opt to back up the navigation while in the polar regions. To my knowledge KAL is the only carrier that utilizes this feature on their 777 and 747's.

Back in the good old days Gris was the only way you could operate with a degree of certainty while in the polar regions. First used by the USAF and followed shortly there after by SAS, then Pan Am and TWA along with other European airlines.
These were navigator duties so as the nav was replaced by doppler, and INS these procedures were no used as much as before.

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