Mag, Grid & True North Align

[ORAC]

https://twitter.com/myoutdoors/status/1587854152402702338?s=61&t=euWgWAmrWtPVK9YPzCTiCA


Magnetic north, true north and grid north align over Great Britain for the first time in history.

Our calculations have discovered the three 'norths' will combine for the first time in history this week🧭

True north, magnetic north and grid north will combine at a single point - starting at Langton Matravers, a village just west of Swanage

https://www.ordnancesurvey.co.uk/newsroom/blog/magnetic-true-grid-north-align-over-great-britain?fbclid=IwAR35Zekr-NXZQTg1-E_VUkZ1adtTErUn_CtVllJfS8IG6PnhKNGR2fvNN_o


https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/1120x2000/image_c97d7354d060f25b445c3ff46ef366e7551190f2.jpeg

[Timelord]

True N and Grid N don’t change do they, so I presume they have always coincided at that village?

True equals Mag, Local equals Zulu. What a day to be a navigator!

[Lyneham Lad]

So the 'add for mag, get rid for grid' beloved of hillwalkers etc becomes redundant?

[DaveReidUK]

True N and Grid N don’t change do they, so I presume they have always coincided at that village?

Yes, True N = Grid N for anywhere in the UK on the 2W meridian.

[Wensleydale]

Don't tell the BBC: they will start to blame it on Global Warming.

[reds & greens]

Ruddy Brexit

[SRFred]

Is there an equivalent situation 180 degrees removed, eg the southern hemisphere?

[Wensleydale]

I remember being informed at a morning brief that due to the reduction in magnetic variation, Waddington's runway was no longer "two one" but "two zero": a co-pilot put up his hand and asked if the other end was still zero three.

[Wensleydale]

Is there an equivalent situation 180 degrees removed, eg the southern hemisphere?

Same as the Northern Hemisphere: along the 2W line - because compasses always point to magnetic north.

[[email protected]]

Bring back the LightWeightNavAid from the AH1 Gazelle so we can use it without doing Grivation calculations........

[Asturias56]

Don't tell the BBC: they will start to blame it on Global Warming.


well magnetic North has been moving somewhat faster than usual recently I understand

of course we're also getting closer to the point when the earth's field will flip and North becomes south - "it's grim up South " doesn't have the same ring to it

[Timelord]

Same as the Northern Hemisphere: along the 2W line - because compasses always point to magnetic north.
The significance of 2W is that it is the central meridian (?) of the particular transverse Mercator projection used by OSGB. That is why TN and OS GN coincide along that line.

[ShyTorque]

well magnetic North has been moving somewhat faster than usual recently I understand

of course we're also getting closer to the point when the earth's field will flip and North becomes south - "it's grim up South " doesn't have the same ring to it

Just hold the chart upside down….easy.

[911slf]

well magnetic North has been moving somewhat faster than usual recently I understand

of course we're also getting closer to the point when the earth's field will flip and North becomes south - "it's grim up South " doesn't have the same ring to it

If you want to be ultra-pessimistic read Jim Al Khalili's book "Sunfall" which postulates a coronal mass ejection hitting Earth just at the point when the magnetic field passes through a temporary zero. Not likely but not impossible. Very nasty.

[63000 Triple Zilch]

With the ever changing magnetic North does this mean that at any time in the near future we will see 27R and 27L revert to 28R and 28L? I remember it changing sometime in the 1970s and surely with the ever changing magnetic North it should change back at some point.

[ORAC]

With the proliferation of GPS/PNR equipment, and the weakening and variability of Mag, at what stage will everything switch to True at all levels rather than just the upper air?

Its been a joke for years at places such as Goose Bay to watch FJs fly the approach patterns 30+ degrees out till nudged….

kinda like the QFE/QNH thing….

[DaveReidUK]

With the ever changing magnetic North does this mean that at any time in the near future we will see 27R and 27L revert to 28R and 28L? I remember it changing sometime in the 1970s and surely with the ever changing magnetic North it should change back at some point.

Heathrow's runways are closer to 260°T than to 280°T, so don't hold your breath.

[RetiredBA/BY]

I remember being informed at a morning brief that due to the reduction in magnetic variation, Waddington's runway was no longer "two one" but "two zero": a co-pilot put up his hand and asked if the other end was still zero three.

As an ex V force copilot that seems to me a sensible question as magnetic variation changes with geographic location as well as time !
Hat, coat !

[RetiredBA/BY]

Anyone ?

[reynoldsno1]

Down here in the Antipodes variation varies between 18 to 25E, the isogonals lying roughly east-west across NZ. During my time as an instrument flight procedure designer we had to change runway designators on a number of occasions.

[Asturias56]

"f you want to be ultra-pessimistic read Jim Al Khalili's book "Sunfall" which postulates a coronal mass ejection hitting Earth just at the point when the magnetic field passes through a temporary zero. "

highly nlikley - the mag field reversal is quite common (in geological terms ) often less than 100,000 years apart

[deltahotel]

Do other countries have national grids? I’ve got some rather beautiful 50thou maps of the Pyrenees by the IGN (French OS equivalent). They match the OS as maps of quality. The only grid overlay is WGS84 with 4 km squares and no info on magnetic North and not an isogonal in sight. It’s obviously designed to be used with GPS (Compatible GPS/WGS84) gives that away!

[India Four Two]

Nice video from OSGB, explaining the concepts:

https://youtu.be/18kQrt3KCbM

https://m.youtube.com/watch?time_continue=65&v=18kQrt3KCbM&feature=emb_logo

As Timelord pointed out earlier, on the UK National Grid, True North and Grid North are only coincident at 2° W, because this is the Central Meridian of the projection.

For most of the last 400 years, the North Magnetic Pole has been wandering around the Canadian Arctic, but 30 years ago it started moving fast towards Russia.


https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/888x1024/0c1b3d8c_2a28_45cd_a937_32a0cad8c820_09949f6f7b6cc3a591d7eb3 d96772043220bde18.jpeg

PS Having posted a video link, it turns out I can’t see it in my post. This is a common complaint on PPRuNe these days.

A quick way to see the link is to click on the Quote button below, which will allow you to see and copy the video link.

[Timelord]

Do other countries have national grids? I’ve got some rather beautiful 50thou maps of the Pyrenees by the IGN (French OS equivalent). They match the OS as maps of quality. The only grid overlay is WGS84 with 4 km squares and no info on magnetic North and not an isogonal in sight. It’s obviously designed to be used with GPS (Compatible GPS/WGS84) gives that away!

Hello DH, how are you?

I think most other countries’ 50k s have a UTM grid.

TL

[pilotmike]

Is there an equivalent situation 180 degrees removed, eg the southern hemisphere?
Not really, because oddly, Aussies tend not to use the OSGB36 datum for grid alignment that we use in the UK.

[pilotmike]

With the ever changing magnetic North does this mean that at any time in the near future we will see 27R and 27L revert to 28R and 28L? I remember it changing sometime in the 1970s and surely with the ever changing magnetic North it should change back at some point.
As local variation in the UK has been steadily decreasing West for a few hundred years, and continues to do so, and it is now passing through zero degrees variation to become Easterly variation, the runways' magnetic alignment will continue to decrease, and at some point it will make sense to rename them 26R and 26L. Variation certainly ain't going more Westerly, at least not in the UK for now.

[pilotmike]

"f you want to be ultra-pessimistic read Jim Al Khalili's book "Sunfall" which postulates a coronal mass ejection hitting Earth just at the point when the magnetic field passes through a temporary zero. "

highly nlikley - the mag field reversal is quite common (in geological terms ) often less than 100,000 years apart
Possibly you missed the point that it is the close-to-zero magnetic field that is the concern, not the reversal of the magnetic poles, per se. As these pole reversals can take many thousands of years, Earth could be exposed to damaging radiation for a very long time.

And given the long duration of reversals, this present faster movement of the magnetic poles and the weakening of the magnetic filed are likely indicators that the end of this chron is nigh, and reversal is already starting to take place.

[Mogwi]

Hello DH, how are you?

I think most other countries’ 50k s have a UTM grid.

TL

The 1:50k maps first issued to us during the 1982 fracas down South had no grid overlay at all. Made plotting a bit trick but we managed!

One snag that took a bit of working out was that if you did a radar update using a ground feature, the NAVHARS always gave a position error of 360/999nm and if you accepted the fix, the kit immediately went TU. We discovered that it hadn’t been programmed to cope with the southern hemisphere and always updated to the corresponding position in the northern hemisphere!

Made us larf!

Mog

[kiwi grey]

Down here in the Antipodes variation varies between 18 to 25E, the isogonals lying roughly east-west across NZ. During my time as an instrument flight procedure designer we had to change runway designators on a number of occasions.
https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/594x795/screenshot_2022_11_06_160043_ccfcdb0db9e8ca0d498f129ea74dc04 e4607f039.jpg


https://teara.govt.nz/en/map/9217/magnetic-declination-in-new-zealand

[Asturias56]

"As these pole reversals can take many thousands of years,"

Some seem pretty short - less than 2000 years IITC - as humanoids have existed on earth through several reversals without disappearing I'd guess it's a low risk - tho we may see more in the way of cancers caused by higher radiation levels

[Asturias56]

Hello DH, how are you?

I think most other countries’ 50k s have a UTM grid.

TL

National grids vary a great deal - the Romanian one used to be NORTHINGS then Eastings - the opposite of just about everywhere else............. The Russian one is famously skewed

[PPRuNeUser0211]

National grids vary a great deal - the Romanian one used to be NORTHINGS then Eastings - the opposite of just about everywhere else............. The Russian one is famously skewed
Soviet grids are northings/eastings as well. They're in common usage in Eastern Europe incl Ukraine.

[Fortissimo]

There is a team actively working on moving the entire aviation system to True. Canada is shifting its entire airspace to True in 2030 and ICAO has just surveyed state responses to the idea of a global change.

Industry spends ~$2Bn per 5 year magnetic model on keeping up with the movement of the N pole. It used to be a 10 year epoch but the pole is moving too fast now. Cost of change is about $10K per stop bar.

IFPs are designed in True and converted to Mag for display because that is what ICAO decided in 1948, when an inertial navigation system was someone who slept in the rear cockpit. PNT information is derived in True, very accurately, then converted to Mag by using declination values that could be 5 or more years old.

Nav Canada has already done proving flights to show that zeroing the aircraft INS look up tables works seamlessly. The alternative is to simply select True on the relevant switch.

Fewer runways and aids need updating in Europe than could be left as is. Agreed, there is a one time cost for the infrastructure but then nothing for changes TFN.

Why aren’t we doing this now?

[fitliker]

The global axis is wobbling , hence the increase in daylight in the Arctic . One of the hunters we flew mentioned the extra daylight in the North . We thought he was just displaying cabin fever . The increase in wobble may be caused by the weight shift caused by mining and moving billions of tons of ore around the world since industrialization began . Like changing the lead balance weights on a wheel . The movement of all those weights may have an effect of the harmonic resonance of this spinning oblique spheroid . To counter the effects of these changes I would humbly suggest we all stand on one foot for twenty minutes per day . Standing on one foot for twenty minutes a day might not mitigate the effects of harmonic resonance change , but might have the same effect as carbon trading has in preventing climate changes :)

[deltahotel]

Good thanks. Still freighting away

[PAXboy]

May I point out spell check error? The earth is an Oblate Spheroid.

[India Four Two]

As PAXboy noted the earth is an oblate spheroid - but only just. ;)

WGS-84, used as the default spheroid by GPS, has an equatorial diameter of 12,756 km. The polar diameter is 43 km less - a difference of 0.3%.

We discovered that it hadn’t been programmed to cope with the southern hemisphere and always updated to the corresponding position in the northern hemisphere!

Made us larf!

Mog

I remembered a similar problem with a flight of F-22s crossing the dateline on their way to Japan:

https://www.pprune.org/military-aviation/265757-f-22-software-glitch.html

I once worked for a Canadian oil company that started doing exploration work in places other than North America. Their computer-mapping system not only couldn't cope with anywhere south of the equator, but it assumed, for convenience, that all positive Longitudes were west of Greenwich!

A colleague of mine who was assigned to fix this problem, created a test file to make sure the new program was always correct, even after modifications. It consisted of four short seismic lines with True azimuths of 360, 045, 090 and 135. They intersected each other, at the Equator and the Greenwich Meridian.

[Ninthace]

May I point out spell check error? The earth is an Oblate Spheroid.
Since the Earth has an inclined axis of rotation, it is an oblique, oblate spheroid?

Hat, coat, gone.

[Asturias56]

" The increase in wobble may be caused by the weight shift caused by mining and moving billions of tons of ore around the world since industrialization began"

No its a long term effect that seems to originate in the Earth's core -

[Ninthace]

Originally Posted by Mogwi View Post (https://www.pprune.org/military-aviation/649671-mag-grid-true-north-align-2.html#post11325892)
We discovered that it hadn’t been programmed to cope with the southern hemisphere and always updated to the corresponding position in the northern hemisphere!

Made us larf!

Mog
In the days of Flight Systems training at Cosford, we taught the basic theory of inertial navigation. All examples involved ac flying E or N or even NE. Any other direction involved negative numbers which the would-be techies, being products of the then educational system, had trouble coping with.

[Fitter2]

I42
As PAXboy noted the earth is an oblate spheroid - but only just. https://www.pprune.org/images/smilies/wink2.gif

WGS-84, used as the default spheroid by GPS, has an equatorial diameter of 12,756 km. The polar diameter is 43 km less - a difference of 0.3%.

WGS-84 actually treats the Earth as an ellipsoid (a body of rotation defined by an ellipse rotated about its minor axis). A more accurate model flattens the South pole end rather more, and makes the North pole end a bit pointier (hence, 'everything has gone pear shaped') but that make the spherical trig calculations far too difficult and the ellipsoid is good enough for government work.

[ORAC]

To just elucidate a bit further, WGS-84 is a gravity model, so the density of the different components (mantle, core etc)
is modelled rather than just the shape.

Then, of course, the Barycentre has to be taken into account..

[pilotmike]

Oblique! Maybe last week... but rather more oblate of late.

[DaveReidUK]

In the days of Flight Systems training at Cosford, we taught the basic theory of inertial navigation. All examples involved ac flying E or N or even NE. Any other direction involved negative numbers which the would-be techies, being products of the then educational system, had trouble coping with.

Slightly OT, but related - I'm reminded that for many years one of the first of the enthusiast ADS-B receivers (RadarBox) suffered from a 5 million square mile equatorial "black hole", whereby it was incapable of decoding coordinates between 2°S and 2°N, so if you wanted to use your shiny new box to track aircraft in Singapore, Nairobi, etc you were in for a nasty surprise.

[OK4Wire]

There is a team actively working on moving the entire aviation system to True. Canada is shifting its entire airspace to True in 2030 and ICAO has just surveyed state responses to the idea of a global change.
....
Why aren’t we doing this now?

Couldn't agree more! Spent all of my time in the Navy flying on True.

[brakedwell]

I took an RAF Britannia into Resolute Bay, Northern Canada in 1972 when the Magnetic North Pole was only 30 NM northwest of the airfield. I remember the compasses were all over the place on the ILS/visual approach!


https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/2000x1230/resolute_bay_sept_73_early_am_85354ace874f9689e815aece114a1d 310c3c5185.jpeg

https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/2000x1227/resolute_bay_dawn_d357bf6ec75d2cd21e45c214ad23cb115f4d256f.j peg

[India Four Two]

I remember the compasses were all over the place!

As a consequence of that, headings on airways and approach plates in the Canadian Arctic (the "Area of Compass Unreliability" - shown on charts as the Northern Domestic Airspace) are True bearings.


https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/1020x1021/taa_2017_02_figure_1_051991adabd0d0305dc6fa04332acf3218084fb 0.jpg

https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/630x1080/11_2_copy_7e410041c8bb8fa689fe67c1b1e9ae44b54954fb.jpg

[brakedwell]

India Four Two, we did the approach and landing on what was Rwy 35. I am sure we used an ILS with broken cloud giving some contact with Resolute and the Smiths Flight System compasses were showing almost 90 degrees out. The runway was packed ice and snow. Being October it was also very cold!


https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/2000x1309/resolute_bay_18_9_1973_a5267a322ac014a82ca4c1941e6122ce4a561 d16.jpeg

[Fortissimo]

https://skybrary.aero/bookshelf/accident-report-a11h0002-b732-cfit-resolute-bay-canada-20-aug-2011

A sad example of the confusion that can come from high declination values.

[deltahotel]

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/2000x1504/image_c05e35463118aae2a2525b7a35f5fc1000f98db7.jpg
Just bought a truly beautiful 25000 of part of Italy with this panel.

[albatross]

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/1020x2000/68a20f3c_bc53_42ce_9c24_3c3305d7f6d3_8aba1b8a9691fe7f96abf9e 373fb57e3c2c0c2c6.jpeg
These are very useful.

[brakedwell]

I agree, we used to carry navigators with sextants on the RAF Britannias. I did a polar trainer in 1971, with SpecN navs at the end of their Manby Course and a Litton 51 on board. We flew from Thule to the North Pole, orbited for about 20 minutes while checking compasses etc then set off for Brize Norton and landed 9 hours later.. One thing that came out well was the Smiths Flight System and our magnetic compass.

[reynoldsno1]

The NZ Antarctica enroute charts (Transverse Mercators) have tracks in True & Grid (Grid is aligned with 180E/W) - or they used to!