Safety

September 19, 2019

Switching to TRUE: Pulling away from magnetic north

NAV CANADA is leading industry efforts to move away from magnetic north to true north, improving safety and saving millions of dollars annually for the aviation industry. As Anthony MacKay, Assistant Vice President, ATS Service Delivery, NAV CANADA, explains, issues with magnetic variation persist largely because “that’s the way we have always done it”. In this guest blog by CANSO, we get more insight into NAV CANADA’s “attraction” to true north.

(A longer version of this story was originally published in CANSO’s Airspace journal on August 26, 2019. Read the full story here.)

Magnetic variation has always posed a problem for the design and operation of instrument procedures from the enroute through to terminal and approach phases of flight. Not only that but a working paper presented at the 13th ICAO Air Navigation Conference noted that “air carriers, air navigation service providers (ANSPs) and avionics original equipment manufacturers (OEMs) spend millions annually managing magnetic variation.” The problem has continued into the digital age even though aviation doesn’t need the original magnetic reference anymore.

The background

The use of magnetic north dates back to the earliest days of flight. As soon as aircraft were developed, a heading reference system was required. And the fragile nature of the early aircraft meant that the system needed to be small, lightweight and simple. “Nothing is more simple than a magnetic compass,” says MacKay. “It doesn’t need any power and it always works.”

As navigation systems developed, a heading instrument or directional gyro was used to account for small errors in the magnetic compass caused by dips in the Earth’s magnetic field. Periodically, the pilot would reset the heading instrument to align with the magnetic compass.

In the jet age, the heading instrument was tied to a magnetic sense system eliminating that one step of the pilot reading the magnetic compass and then setting the heading instrument.

“Unless you were flying north or south of 70 degrees latitude, the difference between the moving magnetic poles and the true north and south poles that form the anchors between the latitude and longitude lines around earth were easily handled,” MacKay explains. “Small directional errors in an analogue system were not that critical and the analogue human in the middle could easily adjust and compensate.”

But as aircraft systems became more tightly integrated and digital systems developed, those small errors have become more than a mere distraction, driving a mismatch between the various navigation systems. As MacKay puts it: “If a computer is expecting to see a one and instead it is given a zero, it doesn’t like it very much.”

Today, all modern aircraft with Inertial Reference Systems or Attitude Reference Systems that use cost-effective Inertial technology actually function in true north (TRUE).

“All the systems, all the math under the hood is done in TRUE,” says MacKay. “Then the aircraft systems convert it to magnetic north to show it to the pilot. Today, instrument procedures are built in TRUE and then converted to magnetic prior to publication. Our surveillance systems use latitude and longitude in TRUE and then adjust to magnetic prior to showing the tracks/targets to controllers.”

Advantages

There are many advantages in moving to TRUE, including simplifying technical processes.

Because Magnetic North is always moving, all the procedures and systems built upon magnetic north need to be constantly updated and amended. Switching to TRUE will therefore remove the cost involved for airlines in updating magnetic variation in Inertial Reference Units (usually two or three per aircraft), flight management systems and, if installed, Synthetic Vision Systems.

“Basically, while using magnetic north, every computer system on the aircraft requires updates to maintain the current magnetic value,” he says. “And they all have to match – which sometimes they don’t, depending on the model and the implementation.”

Similarly, for air navigation service providers, switching to TRUE removes the time devoted to updating IFR approach and enroute procedures with the latest magnetic values. The system would be frozen on TRUE.

Airports, meanwhile, would never need to change runway numbering again. Given the documentation involved in that process, it would be a significant gain. “Essentially, switching to TRUE removes a large and costly time and money burden for all segments of modern aviation,” MacKay insists.

Select the switch

Perhaps the biggest advantage to TRUE is that it can be implemented by simply stopping a process – the conversion to magnetic north. As noted, Inertial Reference Systems on modern aircraft already function in TRUE. Most aircraft have a Mag/True switch that would just need to be selected.

Of course, this solution works for the larger aircraft used in scheduled commercial aviation. General aviation planes that still only have and can only have a magnetic compass or sense system on board would need to either manually do a small plus/minus conversion on what was read off the magnetic compass prior to setting the directional gyro or use a device that would convert from magnetic to TRUE for them. But these systems for light aircraft are much cheaper than those required to go from TRUE to magnetic on a large aircraft fleet.

Most importantly, however, there needs to be a desire to change. The next step, therefore, is working with ICAO to accept the change and help the industry move towards TRUE. Those meetings have started. NAV CANADA anticipates a lead time to enact the change of 10 or more years.

“It would be more than manageable,” concludes MacKay. “There are millions of dollars lying on the table for the aviation industry to save.”

 

4 Comments

As always Nav Canada likes to try to “diminish” the effect on GA. Fact is it will cost those in GA more money to switch systems so that Nav Canada can save Money and improve its bottom line — similar to antenna diversity.

This saves Nav Canada lots and lots of money but does not mean that the commercial consumer will get a reduction in Nav Canada fees or a decrease in Air port improvement fees.

That said I do completely agree that a move to TRUE only would be fantastic for the non monetary reasons. Flight planning and training alone would benefit enormously.

There is no “magic box” that directly measures true north. Inertial reference systems still have to initialize to a known direction, usually by magnetometers measuring the Earth’s magnetic field, so an accurate magnetic field model of the Earth is still required, and needs to be kept up to date. Plus, inertial systems drift and need to be realigned by external reference (again, usually via magnetometers). And don’t think an accurate GPS will help – it can only detect direction while moving, and measures track (affected by wind), not heading. The bottom line is that while the drifting magnetic poles cause expensive updates to runway designations, charts, databases, etc., we can’t just wish them away by “flipping a switch” and start using true headings. It would be nice to not have to contend with the difference between magnetic and true north, but that’s the world we were given and we still have to work within it.

As mentioned, a GPS can determine a true *track*, so maybe a case could be made for redesignating runway designations as they do in the far north (when approaching a runway, a pilot flies a track, not a heading, anyway to compensate for a cross wind). But if one of the reasons to do so is to reduce possibility for confusion, Canada had better realize that the only way it will do so is if all countries did as well. In the far north, there isn’t much choice with the magnetic dip being so high, but can you imagine the mess if all of Canada’s runways were designated as true but the rest of the world as magnetic?

Conceptually, yes, it would be great if we could do away with magnetic headings. But the reason we do so is not largely because “that’s always the way we’ve done it”, but instead because “that’s about the only way we can do it”. That is, until someone invents a magic box that directly measures true north.

Personally, very glad to see that MAG v.s. TRUE is on the table. While working in ICAO as Chief, Aeronautical Information and Charts (AIS/MAP) Section, I was the secretary of the AIS/MAP Divisional Meeting in March 1998. (ICAO Doc 9733). At that meeting, ICAO Secretariat presented under Agenda Item 1.3 TRUE vs. MAG bearing issue. There was a considerable discussion on that interesting topic and the meeting made the following Recommendation 1.3/1 – True vs. Magnetic bearing issue.
“That ICAO introduces as the new operations (OPS) task “True vs. Magnetic bearing issue” into the regular programme of the Organization for the detailed consideration that should cover all the aspects of the possible change including the technical, operational, human factors, training as well as economic effects.”
Unfortunately, the ICAO OPS section did not have manpower to pursue this very important matter further and it got “lost’ in the Organization. As the originator of the intent to make the change to TRUE at that meeting and at that time, I never lost the hope that this will have to happen. Also I read the working paper presented by Canada at the 13th AN Conference last year. After 21 years from the initial intent to make the change to TRUE, it seems that it is about the time to do so. If you would like to read the discussions at this topic at the AIS/MAP DIV Meeting, I could provide you with the copy of the meeting report (Doc 9733).
Kind regards, Aleks

The problem is that there still needs to be a directional reference for the aircraft instruments.

A GPS knows position, not direction. A moving GPS can determine true track, but it cannot determine true heading. That’s why even modern aircraft still have a flux valve or magnetometer to align the gyros. It’s more practical than sighting stars or the sun… the only other natural reliable directional references.

Swapping from MAG to TRUE actually goes backwards, adding or subtracting the magnetic variation from the magnetic tracks in the database to get the TRUE numbers, and is still subject to the drift of the magnetic pole. The only other option is to set your gyros to free and slew them yourself to a TRUE runway heading or known direction.

And what will be the savings? VORs are being decommissioned rapidly so no need to rotate them. Runway painting and signage, maybe; but many are almost ten degrees off already and almost all would have to be repainted and re signed upon the switch to TRUE.

And as always, light general aviation is forgotten… where all we have is a whisky compass for directional information. To install an INS or integrated GPS with an AHRS system and current database would be cost-prohibitive… or is that the point?

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