Polar navigation paradoxon

[Holger Wende]

...are there any photos or drawings of this ND layout when grid north is up? What happens to the compass rose then? ...

In the "PilotsEye.tv" video "Sonderflug 01.Mai2007 Nordpol" the compass rose on the ND is clearly visible while they circle the north pole (A330).
It seems Grid-South is alighed with the 0deg meridian and Grid-North aligned with the 180deg meridian. Thus they fly Grid-North (or South) as long as they fly parallel to this Grid-meridian.
It's difficult to explain, but I hope its clear though.

I tried to make a snapshot but failed using Windows standard tools.

The captain also explains a few things about grid navigation, if you are interested I will try to translate and summarize it here.

In January 2001 Andrea Fontana published 3 PS1 videos and a PDF explaining grid navigation

Regards, Holger

P.S. This video offers amazing views to Spitzbergen, Northpole and Greenland!

[Hardy Heinlin]

I think I misunderstood the term "ND is aligned to grid north" in that quote.

I thought the map is fixed with grid north up then.

It's probably just the compass rose that indicates grid heading. This way the airplane symbol keeps pointing at the cockpit roof and the radar image will always remain on the upper half of the ND as usual.

Yes, the 0-meridian, in the southpole-to-northpole direction, points at grid north.
And the 180-meridian, in the northpole-to-southpole direction, points at grid north.


Cheers,

|-|ardy

[Holger Wende]

Hello,


This ND map display seems to show grid heading.

Regards, Holger

[Hardy Heinlin]

Yep, definetely :-) Clear now, thanks!

I think this "compass-shows-grid-heading" feature was a good idea from Airbus (or Honeywell's idea?).


Cheers,

|-|ardy

[Zinger]

From B747-400 AOM:
Grid heading (W) MAP, MAP
CTR, PLAN
Displays grid heading when
Heading Reference switch
NORM and IRU magnetic
information not available
due to airplane latitude.

[Hardy Heinlin]

From B747-400 AOM:
Grid heading (W) MAP, MAP
CTR, PLAN
Displays grid heading when
Heading Reference switch
NORM and IRU magnetic
information not available
due to airplane latitude.

I think this refers to the boxed digital grid heading indicator on the right hand side of the regular longitudinal heading indicator in the middle. I don't think the 744 applies grid heading to the compass rose.

Interesting, however: Is the digital grid heading indicator a software option that shows whenever the aircraft is in polar regions, regardless of the TRU/NORM switch position? (NORM automatically uses TRU in polar regions anyway.) Or is the indicator not an option, and the reason why it's only sometimes visible on photos always lies in the current TRU/NORM switch position?

(The latitudes and longitudes at which TRU heading is forced, are known. The region at which the mag var database ends may be closer to the poles, though.)


|-|

[masselli]

Here is a link to some info from Boeing about Polar Navigation.

http://www.boeing.com/commercial/aeromagazine/aero_16/polar_nav_by_model.pdf

[Zinger]

[Hardy Heinlin]

Lufthansa says nearly the same:

"Displays grid heading when heading reference switch is in NORM and airplane position is north of 73N or south of 60S."

That's roughly the area where the magvar database ends.

[Hardy Heinlin]

Here is a link to some info from Boeing about Polar Navigation.

http://www.boeing.com/commercial/aeromagazine/aero_16/polar_nav_by_model.pdf

Glad to see it all agrees with PSX Alpha 41 :-)