True Navigation! Part 1

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True Navigation! Part 1

#1 Post by TheGreenGoblin » Mon Oct 25, 2021 8:48 am

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Calling occupants of interplanetary, most extraordinary craft
Really interesting article from Flight International...
While professional mariners stopped using the earth’s magnetic field as their primary directional reference some 50 years ago, civil aviation did not, because at that time accurate inertial navigation systems (INS) were too heavy and bulky for aircraft use.

Today, however, navigation by global navigation satellite systems (GNSS) – backed up by ring laser gyro-stabilised INS/attitude and heading reference system platforms, radio beacons and air traffic control surveillance using multiple technologies – means that aviation has no real need to use a magnetic reference.

The debate about changing from Magnetic to True navigation is now moving towards how to change, and when, with March 2030 as the proposed date.

Modern civil and military aircraft have the capability to fly to a True North reference at the push of a button: the flight management system (FMS) is designed to identify True North at start up, and when a magnetic reference is required it is computed from True by applying local magnetic variation via embedded look-up tables.

With the ubiquitous use of GNSS, impressive capability of modern inertial reference systems, and the steady decommissioning worldwide of surface-based radio navigation aids, the decision to rely on the earth’s constantly changing magnetic field is increasingly hard to justify.

The International Association of Institutes of Navigation (IAIN), which has meticulously studied all the issues, comments: “The biggest single problem in trying to implement this change worldwide would be inertia – the large number of countries involved and the difficulty of finding the will to all change at once.”

To work out how best to overcome this inertia, the IAIN set up a specialist working group, the Aviation Heading Reference Transition Action Group (AHRTAG), which has been meeting monthly since early 2021.

A Canadian-led multinational team of navigation experts from Australia, France, the Netherlands, the UK and the USA, the AHRTAG is chaired by Anthony MacKay, Nav Canada’s director of operational safety. The group includes representatives from several national aviation authorities (NAAs), major aircraft manufacturers, pilot associations, and also the commercial air navigation charting and aviation information provider Jeppesen.

UPDATING SYSTEMS
The migration of the geographic magnetic poles has accelerated in recent years, adding to the relentless task of updating systems and distributing the associated flight information.

The AHRTAG points out that updating aircraft declination look-up tables is a specialist and expensive maintenance activity that has no effect on the way an aircraft derives its directional information. It merely ensures the result is displayed as a magnetic value that is normally less accurate than the originally determined True heading.

And, if a future variation shift is sufficient to affect airport assets – like runway and taxiway signage and markings, plus instrument procedures, landing aids documentation, and FMS coding – at a major hub, the cost can top $20-30 million.

Moving from Magnetic to True reference is no more challenging than, for example, the periodic task of re-orientating VHF omnidirectional radio range (VOR) and TACAN radio navigation beacons for local magnetic variation changes. Across the industry, staff have the necessary skills and knowledge to make the move.

Canada is now actively concentrating on implementing the change: it already references True North in nearly half of its airspace because of its proximity to the (moving) surface location of the magnetic North pole.

Aviators in the northern Canadian airspace have employed tried and tested procedures for both traditional radio navigation beacons and all types of performance-based navigation (PBN) systems. The country’s air navigation service provider (ANSP), Nav Canada, working with the AHRTAG, has almost completed drawing up its concept of operations (CONOPS) for the switch.

ICAO has shown great interest in Nav Canada’s “Mag2True” work, particularly since Canada presented a White Paper on the subject to its 13th Air Navigation Conference in 2018, seeking agreement and proposing adoption by 2030. The conference agreed that a further study of Mag2True’s cost/benefit should go ahead.

IMPLEMENTATION PLANS
The agency is hoping to be presented with “ready-made SARPS [standards and recommended practices] and implementation plans to move issues forward”. Canada was due to present a formal Mag2True update during ICAO’s high-level conference in October 2021, and a presentation by the AHRTAG on True North is on the agenda of ICAO’s European PBN Task Force/Navigation Steering Group meeting in early December.

Assisting ICAO to overcome global inertia might work like this: one state – Canada – unilaterally files a difference from international heading reference standards, successfully transitions to True North within its entire airspace, and demonstrates that the new system works.

The US Federal Aviation Administration (FAA) is also warming to the idea. According to FAA sources, the body’s thinking is moving in much the same direction as Canada’s, recognising that pilots are accustomed to operating despite differences that come into play at a border. For example, most of the world measures flight altitude in feet, but China, the Russian Federation and a few other states use the metric system.

To sceptics reluctant to abandon any heading reference system – especially one as familiar as the magnetic compass – despite the existence of proven alternatives, AHRTAG member Dai Whittingham points out that modern aviation rulemaking is risk-based. Risk can never be reduced to zero, but the introduction of any new system must be proven to be extremely low-risk.

Comparisons between the existing and proposed regimes are inevitable, but Whittingham – who is also chief executive of the UK Flight Safety Committee – believes it is wise when playing “what if” games with the proposed system to admit that the existing one has its faults, and to enumerate those.

Meanwhile, the AHRTAG, which continually seeks feedback from all parts of the industry, has been able to report that anticipated resistance to change in sectors like general aviation (GA) is softening to the point of disappearance, especially as GA is a now big user of GNSS systems, whether employing installed avionics, hand-held GPS devices specified for aviation, or tablet-computer electronic flight bags.
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Re: True Navigation! Part 2

#2 Post by TheGreenGoblin » Mon Oct 25, 2021 8:49 am

PROPOSED CHANGEOVER
Similarly, airline pilot associations and the airlines themselves seem generally happy about the proposed changeover, for which the accepted shorthand has become Mag2True.

Canada’s draft CONOPS offers a good indication of how the Mag2True task might be rolled out. There are three aviation arenas affected: aircraft operations, which implies inclusion of the airlines and original equipment manufacturers; aerodromes; and, finally, ANSPs. Overseeing this will be the NAAs, with ICAO keeping an eye on standardisation.

Questions remain about timing, though. Should the switch to True be global and simultaneously made on a single date, or managed regionally, or by hemisphere?

Canada’s proposed 2030 transition year would require NAAs, ANSPs and states to trigger the change. If an implementation date can be agreed, it would be entered in ICAO’s Aeronautical Information Regulation and Control calendar in the normal way for promulgating changes.

The draft CONOPS proposes that, in the six to eight months ahead of Mag2True adoption, the state would not action any changes to its aeronautical information publication (AIP), freezing all but emergency changes to procedures. The only changes promulgated would be those needed to convert Magnetic to True.

During this time, the state would also need to enact a plan to rotate its VORs and ensure that surveillance systems and air traffic controllers are all ready for the change.

All states have a procedure in place for crews to adjust VOR radials (+/- bearing values) until publication of the corrected values once the VOR is rotated and calibrated. The Mag2True transition date would be the last such rotation, because once set to “0” – or True – they would never need to be adjusted again.

The ARINC 424 database that the state AIP feeds could be maintained with its current structure, with all magnetic variation values being set to “0”. Jeppesen has successfully tested this conversion method, demonstrating it via a Bombardier CRJ200 flight test conducted with Nav Canada.

The draft CONOPS proposes a way of staging the changeover. For those regions of the world where existing magnetic declination is small, VORs could safely be aligned today to within +/-4° of True North – a move that would still fall within the current tolerance of many states.

Canada uses +/-2° as a tolerance, but given the amount of magnetic variation change from coast to coast, the nation would have to rotate its VORs anyway.


For many aerodromes in areas where the variation is less than +/-10° of True North, no immediate change to runway numbering – or to airport manuals – would be required. Indeed, the draft CONOPS notes, it could be argued that no change would ever be required.

Change would have to be more carefully managed in other areas, which are predominantly either oceanic, or cover Brazil, Canada, Russia and the USA: the states most accustomed to having to implement updated variation values.

Since most carriers already use True tracks during oceanic operations, there would be little or no change for the ANSPs managing oceanic areas, or those bordering them.

Admittedly, there would be other small but important details that would need attending to. For example, airport air traffic services would need to ensure that adjusted vector headings for common procedures were included in any memory aids for controllers.

With the exception of NDB approaches and vector headings, most other conventional and PBN procedures are now track-based anyway, allowing correct tracks over the ground to continue during the change period. However, the heading error would appear as apparent wind drift, which could be misleading to aircrew.

Crew confusion also could arise from changes to routines, especially to oft-flown procedures. However, there is arguably already plenty of potential for confusion in a system that continues to use two heading references, one of which is variable.

Examples exist of repeated heading reference problems that are endemic to the existing magnetic navigation system.

In one incident, a Boeing 757’s pilots were flying a CAT II approach to runway 29 at St John’s, Newfoundland, Canada. When it intercepted the localizer, the aircraft rolled back and forth across the localiser trying to maintain the centreline. The cause was that the magnetic variation (mag var) of the published procedure differed from the out-of-date mag var tables in the aircraft’s inertial reference unit (IRU).

MISALIGNED IMAGE
Also in Canada, a crew was testing the CAT III approach to Calgary’s new runway 17L, when they observed that the synthetic runway image in the head-up guidance system was misaligned by 7° versus the actual runway. The crew ran the same test again after the aircraft had been fitted with new IRUs for which the tables had been updated from 2010 to 2015 information, and the synthetic and actual world aligned perfectly.

In the months that followed this event, many crews conducting autolands on 17R at Calgary reported their aircraft moving off the centreline when transitioning to autonomous flare mode. In all cases, their aircraft were found to have out-of-date mag var tables in their IRUs.

Canada’s CONOPS for 2030 offers a route to modernity and the avoidance of needless costs for the aviation industry. Moreover, the case for embracing the Mag2True shift is likely to become unstoppable as the numbers of remotely piloted air systems and autonomous platforms – which navigate in True – increase globally.

As such, why would aviation want to persist with two systems of reference?
https://www.flightglobal.com/flight-int ... 63.article
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Re: True Navigation! Part 1

#3 Post by prospector » Sun Nov 07, 2021 11:32 pm

Another interesting article from AirFacts.

https://airfactsjournal.com/2021/11/fly ... _source=li

" Flying a Cirrus VFR across Russia"

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Re: True Navigation! Part 1

#4 Post by Pontius Navigator » Mon Nov 08, 2021 9:09 am

A side issue from the OP.

On the V bombers we used mercator charts whereas on the Nimrod we used Lambert plotting charts.

Why?

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Re: True Navigation! Part 1

#5 Post by Boac » Mon Nov 08, 2021 9:20 am

Just think of the employment prospects for runway number painters. (-|

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Re: True Navigation! Part 1

#6 Post by TheGreenGoblin » Mon Nov 08, 2021 10:59 am

prospector wrote:
Sun Nov 07, 2021 11:32 pm
Another interesting article from AirFacts.

https://airfactsjournal.com/2021/11/fly ... _source=li

" Flying a Cirrus VFR across Russia"
+1

Thanks for posting.
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Re: True Navigation! Part 1

#7 Post by TheGreenGoblin » Mon Nov 08, 2021 11:10 am

Pontius Navigator wrote:
Mon Nov 08, 2021 9:09 am
A side issue from the OP.

On the V bombers we used mercator charts whereas on the Nimrod we used Lambert plotting charts.

Why?
I was taught that one used Polar for high latitudes, the Lambert Conformal Conic projection, most likely in aviation where one might choose Lambert for a map's projection when the area represented by the map has more East-West extent than North-South extent, for mid latitudes, and the Mercator projection, which displays extreme distortion at higher latitudes, for low latitudes.

The bloke that taught me this was an ex-RAF navigator, so I assume he knew of what he spake!

The reasons for the variation between the use in aircraft types may have been as prosaic as differing opinions between senior officers! ;)))

https://map-projections.net/index.php
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Re: True Navigation! Part 1

#8 Post by Pontius Navigator » Mon Nov 08, 2021 11:53 am

TGG, correct as far as you go except for the final paragraph regarding aircraft types. 😉

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Re: True Navigation! Part 1

#9 Post by TheGreenGoblin » Mon Nov 08, 2021 12:38 pm

Pontius Navigator wrote:
Mon Nov 08, 2021 11:53 am
TGG, correct as far as you go except for the final paragraph regarding aircraft types. 😉
Well please elucidate on the aircraft type question for this naïve gentleman... ;)))

I am intrigued!
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Re: True Navigation! Part 1

#10 Post by Pontius Navigator » Mon Nov 08, 2021 1:31 pm

The Vulcan navigation system depended on straight line tracks. A Mercator chart was thus ideal for rhumb line tracks.
The Nimrod, with a slightly more modern system, could fly great circle tracks and thus used the Lamberts.
As it happens, the UK Air Defence people defined the Air Defence Region using Mercator charts and thus caused difficulties in plotting on a Lamberts projection. Radar range and bearings were not straight lines on the Mercator.

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Re: True Navigation! Part 1

#11 Post by TheGreenGoblin » Mon Nov 08, 2021 1:42 pm

Pontius Navigator wrote:
Mon Nov 08, 2021 1:31 pm
The Vulcan navigation system depended on straight line tracks. A Mercator chart was thus ideal for rhumb line tracks.
The Nimrod, with a slightly more modern system, could fly great circle tracks and thus used the Lamberts.
As it happens, the UK Air Defence people defined the Air Defence Region using Mercator charts and thus caused difficulties in plotting on a Lamberts projection. Radar range and bearings were not straight lines on the Mercator.
Thanks for that interesting insight! ^:)^
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Re: True Navigation! Part 1

#12 Post by Boac » Mon Nov 08, 2021 2:05 pm

The Vulcan navigation system depended on straight line tracks.
Waddington to Moscow - shirley better great circle?

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Re: True Navigation! Part 1

#13 Post by Pontius Navigator » Mon Nov 08, 2021 2:28 pm

Obviously. So where you you put the SAM Sites?
🤔

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Re: True Navigation! Part 1

#14 Post by Undried Plum » Mon Nov 08, 2021 2:57 pm

The Vulcan navigation system depended on straight line tracks.
I am not understanding.

A rhumb line is not a straight track. Sure, the heading (+/- drift) remains the same, but it's not a straight line over the ground as a GC track would be.

Was it for simplicity? Surely with two pilots and two navs a tweaking of the hdg every ten or fifteen minutes or whatever would not have been much of a chore?

I seem to recall that the Vulcans used the INS in the Blue Steel for outbound navigation. Did that system not have a waypoint capability? Is that why they used a rhumb instead of a GC?

Did the crews plan jinks and feinted tracks to confuse the defences as to the intended target? Or was the idea to minimise time en-route on the grounds that the defenders knew bloody well what the targets were?

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Re: True Navigation! Part 1

#15 Post by Boac » Mon Nov 08, 2021 3:35 pm

PN wrote:Obviously. So where you you put the SAM Sites?
I I chose Waddington purely as an example............ I was led to believe the tracks might start somewhere else, and putting Sam sites on all options............ ?? No. I had always hoped the Int guys would have some idea of where the fixed SAM sites were.........
UP wrote:Did the crews plan jinks and feinted tracks to confuse the defences as to the intended target? Or was the idea to minimise time en-route on the grounds that the defenders knew bloody well what the targets were?
More likely to confuse the navs................ minimal time to anywhere is GC.

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Re: True Navigation! Part 1

#16 Post by Pontius Navigator » Mon Nov 08, 2021 4:31 pm

The simple question first, a straight line, constant heading, essential for astro navigation. Our night fix would take about 9 minutes if we went for a simple 5 shot sandwich, longer if we went for 7. A further 5 minutes or so for reduction, plotting, and calculating the wind and new heading.

On the question of target tracks. The planner used a number of techniques to simplify the war plan. He would use an arc 100nm radius on Flamborough Head, then a line on 5 degrees East and another at 8 or 10 East (can't remember the exact line). Next an arc, 260 nm radius based on the most westerly hostile radar site.

Aircraft departing from the main bases would fan out to a point on the Flamborough arc. Similarly, if flying from English or Welsh bases they would use the same points.

From Flamborough tracks were parallel to 5 East, turn to near due East remaining parallel, and then to the 260 mile early warning arc and top of descent.

Most tracks would fly over Gotland before funnelling through about 3 gaps on the Baltic Coast. So far so good.

The first strikes might be on coastal targets. Spacing through the gaps was not time based but by concentrating 6 or 7 or more through one gap it was hoped that a SAM site would be momentarily shot out.

Then came the cunning plan. A single line might run directly toward Moscow. An aircraft might be sent down that track but in a blind area branch off to a different target. Then another aircraft might join and set off down the same track. On being detected it was hoped the Air Defence would calculate an incorrect ground speed.

In the confusion of nuclear strikes this might have worked.

There were other ploys to saturate the defences such as near simultaneous attacks from different directions. Fratricide, assuming successful penetration to the target was a certainty. For obvious reasons this was neither briefed to crews nor discussed by them.

The master planning chart was a 3 million scale Mercator and no track segment was longer than the side of a Douglas Protractor. Someone had knicked his straight edge.

His other rule of thumb for fuel calculation was to take the distance from take off to top of drop, three times the distance from TOD to final climb point, and the distance from FCP to overhead recovery. He would then apply this distance to the appropriate high level cruise graphs and got a good estimate of fuel required.

Obviously quite a lot more factors but that should give an idea.

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Re: True Navigation! Part 1

#17 Post by Undried Plum » Mon Nov 08, 2021 5:23 pm

A cracking good post, PN.

His other rule of thumb for fuel calculation was to take the distance from take off to top of drop, three times the distance from TOD to final climb point, and the distance from FCP to overhead recovery. He would then apply this distance to the appropriate high level cruise graphs and got a good estimate of fuel required.

And would then land the thing like a cat pissing on wet glass in Yorkshire.

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Re: True Navigation! Part 1

#18 Post by TheGreenGoblin » Mon Nov 08, 2021 6:27 pm

Pontius Navigator wrote:
Mon Nov 08, 2021 4:31 pm
The simple question first, a straight line, constant heading, essential for astro navigation. Our night fix would take about 9 minutes if we went for a simple 5 shot sandwich, longer if we went for 7. A further 5 minutes or so for reduction, plotting, and calculating the wind and new heading.

On the question of target tracks. The planner used a number of techniques to simplify the war plan. He would use an arc 100nm radius on Flamborough Head, then a line on 5 degrees East and another at 8 or 10 East (can't remember the exact line). Next an arc, 260 nm radius based on the most westerly hostile radar site.

Aircraft departing from the main bases would fan out to a point on the Flamborough arc. Similarly, if flying from English or Welsh bases they would use the same points.

From Flamborough tracks were parallel to 5 East, turn to near due East remaining parallel, and then to the 260 mile early warning arc and top of descent.

Most tracks would fly over Gotland before funnelling through about 3 gaps on the Baltic Coast. So far so good.

The first strikes might be on coastal targets. Spacing through the gaps was not time based but by concentrating 6 or 7 or more through one gap it was hoped that a SAM site would be momentarily shot out.

Then came the cunning plan. A single line might run directly toward Moscow. An aircraft might be sent down that track but in a blind area branch off to a different target. Then another aircraft might join and set off down the same track. On being detected it was hoped the Air Defence would calculate an incorrect ground speed.

In the confusion of nuclear strikes this might have worked.

There were other ploys to saturate the defences such as near simultaneous attacks from different directions. Fratricide, assuming successful penetration to the target was a certainty. For obvious reasons this was neither briefed to crews nor discussed by them.

The master planning chart was a 3 million scale Mercator and no track segment was longer than the side of a Douglas Protractor. Someone had knicked his straight edge.

His other rule of thumb for fuel calculation was to take the distance from take off to top of drop, three times the distance from TOD to final climb point, and the distance from FCP to overhead recovery. He would then apply this distance to the appropriate high level cruise graphs and got a good estimate of fuel required.

Obviously quite a lot more factors but that should give an idea.

What a fascinating post and an apocalyptic, depressing, Strangelovian plan. A grimly gripping piece of Cold War aviation navigation history there, and thanks for that PN. ☢️
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Re: True Navigation! Part 1

#19 Post by Hydromet » Thu Nov 18, 2021 11:08 am

Thanks for your posts, PN, most interesting and enlightening.

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Re: True Navigation! Part 1

#20 Post by Boac » Thu Nov 18, 2021 11:56 am

From Flamborough tracks were parallel to 5 East,
Where were these tracks aiming? Why not fly direct to the Gotland area?

PS For fratricide read suicide, as with the Air Defence force in the event of a Russian attack. We DID discuss this and had a laugh about it :))

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