Spin axis

The global industry is preparing to change its navigational heading reference from Magnetic North to True North. This article examines the issues involved, and provides an update on the progress of research into options for managing the transition process.

David Learmount Private pilot Former pilot and Qualified Flying Instructor in the Royal Air Force Independent aviation journalist, London, UK

It may seem unlikely that any full-time aviation professionals still do not know that the global industry is preparing to change its navigational heading reference from Magnetic North to True North (Mag2True). In reality, however, there may be many such people, employed by airlines, airports, air navigation service providers, and even some at national civil aviation authorities.

Using data gathered by a working party of the International Association of Institutes of Navigation – known as the Attitude and Heading Reference Transition Action Group (AHRTAG) – this article examines the issues involved, and provides an update on the progress of research into options for managing the transition process. AHRTAG’s work is being overseen by the International Civil Aviation Organization (ICAO). Magnetic North, aviation’s traditional heading reference, has always been shifting but, for reasons unknown, the shift has accelerated in the last three decades. The industry has long coped with the navigational anomalies that arise from measurable variations in the earth’s magnetic field, but having to cope with this uncertainty has now become an expensive distraction. This is ironic considering that modern navigation technologies already enable an alternative – using True North as the heading and azimuth reference – that eliminate the problems, the inaccuracies, and the associated ongoing costs of this constantly shifting reference.

Canada’s air navigation service provider (ANSP), Nav Canada, is the world’s expert in coping with navigation difficulties resulting from massive local variations between Magnetic and True North. This is because the geographical location of Magnetic North has traditionally been in its far north domestic territory, but this has recently changed, with the magnetic pole now lying in the eastern hemisphere. Rates of change may now become more of a European problem, and Mag/True variation can change significantly when aviators are operating in the vicinity of the geographic magnetic north pole.

The maximum possible value of the variation between the two norths – 180deg – occurs on the line between the geographic surface positions of Magnetic North and True North: anywhere on that line, an aircraft’s magnetic compass will show north as south, and vice versa. For these reasons, Canada divides its domestic airspace into two sectors: Northern Domestic Airspace (NDA) and Southern Domestic Airspace. In the NDA the heading reference is True North, and the ANSP and all ground-based navigational aids and PBN procedures, along with charts and airports, reflect this fact. Meanwhile in Canada’s SDA, where changes in Mag/ Tue variation are less pronounced, the heading reference used is Magnetic.

If this sounds like a problem peculiar to Canada that others could happily ignore, a chart of global Mag/True variations shows burying one’s head in the sand is not an approach that would work everywhere. And the crews of long-haul flights in particular cannot ignore the inevitable changes in variation during a journey if they are navigating by Magnetic.

Canada’s example provides a useful study for the rest of the world in how aviators, including general aviation pilots, can – and do – cope, routinely operating with the two different heading references, and managing the transition from one to the other.

Canada’s aviators cope by a variety of means according to their aircraft’s equipment. Basically, the crews of aircraft with the latest avionics – including the latest triplex inertial reference units (IRU) as well as GPS – have no problems. Pilots flying classics, on the other hand, have to be familiar with the techniques of flying in an area where variation can change considerably on a single leg, especially flying across lines of longitude rather than along them. But this can be done, even with old equipment, and traditional navigation skills prevail.

Because of this long experience of managing airspace encompassing huge differences between Magnetic and True North, Nav Canada leads the multinational AHRTAG which has been engaged for more than three years in a detailed study of the Mag2True transition and all its implications, technical and operational. Indeed, with AHRTAG taking on the research role, ICAO’s specialist resources like the Air Navigation Commission (ANC) are freed to oversee the proposals and processes.

Nav Canada has its own True North SubWorking Group, and it has produced a Concept of Operations (ConOps) for transitioning the whole of Canadian airspace onto True North as employed in its NDA. This ConOps is, effectively, a blueprint for the methodology that the rest of the world could adopt during transition to True North. Nav Canada has used the year 2030 in the ConOps simply as a target, because it needs a proposed transition date for costing purposes.

The ConOps rationale for the change to True North reference is spelled out with stunning simplicity in this statement: “After the 1980s, as aircraft systems became more tightly integrated and digital systems developed, minor magnetic variation errors have become more than a mere distraction, driving a mismatch between the various navigation systems.” Whatever risks might be involved in transitioning to True, the growing risks just described by Nav Canada’s ConOps will outweigh them. Meanwhile the multinational AHRTAG – which has met monthly via webinars for several years – recently conducted a face-to-face meeting at the Royal Institute of Navigation (RIN) in London, England (5 June 2023), and the Group reports a growing international awareness of the desirability of change.

Indeed, Dai Whittingham, a member of AHRTAG and chair of the UK Flight Safety Committee, observed at the RIN meeting that failure to transition would be to ignore the definition of the duty to ensure flight safety adopted by the UK Civil Aviation Authority (CAA). The CAA says organisations have a duty to make aviation “as safe as reasonably practicable”. Whittingham points out that, by staying with the Magnetic heading reference, “We are accepting errors that we can easily eliminate.”

There are still voices expressing reluctance, but they are becoming fewer and, rather than stating outright opposition, they are mostly posing questions to bodies like AHRTAG about how to overcome anticipated transition problems and costs.

Some academic bodies are starting from fundamentals in considering the transition to True. For example, the Polytechnic University of Bucharest’s Faculty of Aerospace Engineering has proposed an examination of whether the recent acceleration in the rate of migration of the geographic Magnetic North pole might be a precursor to a reversal of the earth’s magnetic poles, stating that contingency planning for such an event must be carried out. Existing geological evidence that the University is studying suggests that such a polar “flip” might take about 100 years at the rate of 3deg per year. Depending on the outcome of the Bucharest study, the case for a move to True in advance of such a historic reversal would seem compelling. And no-one, even among the assembled experts, knows how soon such a cataclysmic event might happen.

Factors that have to be considered in the event of the Mag2True transition include aircraft equipage, airport signage, ground navigation beacon orientation, ANSP/ATC procedures, meteorological reporting, and aviation information service (AIS) updating.

Changes, where necessary, may often be adopted in advance, or switch-over prepared beforehand. Nav Canada, which has carried out airborne trials of options for transitioning to True, makes this observation: “In its simplest form, changing from Magnetic to True could be done in many aircraft avionic systems by setting the magnetic variation or declination to ‘0’. Since all procedures and systems have been built by original equipment manufacturers (OEM) to a stable common reference (TRUE NORTH) and then converted to magnetic for end use, setting the correction to ‘0’ will set the reference to TRUE. Databases for navigation now using standard 424-23 have recognized this concept since the publication of ARINC 424-20 many years ago.”

Speaking at the RIN meeting, Susan Cheng of Boeing paints a picture of the potential for data mismatches that exists within all modern commercial air transport category aircraft when they use the Magnetic heading reference for navigation. As the Nav Canada ConOps paper has already stated, there is a potential for “mismatch between the various navigation systems”. Cheng, who is a flight deck crew operations engineer at Boeing, points out that the main sources of potential mismatch are the magnetic variation (MagVar) tables that are part of both the inertial reference system (IRS) and the flight management computer system (FMCS). There is a need for the operator to update the MagVar tables regularly in both these complex interacting systems, so if they are updated late – or not at all – or if one table is updated and the other is not, the outputs can differ, confusing the autoflight systems. Also, other pilot tools like synthetic vision systems can be affected by mismatches. Nav Canada reports that it has investigated several operational incidents caused by just such inputs, but fortunately – so far – they have not led to accidents.

Operators of older aircraft with less sophisticated navigation systems clearly worry about the Mag2True transition challenge, but rather than threatening to veto it they have appealed for time and consultation to work out how best to cope. No-one is demanding that they – nor indeed the major airlines – give up their standby magnetic compasses, but organisations like GAMA (General Aviation Manufacturers’ Association) and AOPA (Aircraft Owners and Pilots’ Association) warn against forcing GA pilots – while flying – to read their standby compass, apply the local magnetic variation, and set their gyrodriven directional indicators (DI) to True. The potential for error, they argue, is high. Both are also nervous about GA aircraft fitted with horizontal situation indicators (HSI) slaved to flux valves that provide Magnetic headings. Their concern is the expense of fitting converters to make the HSI read True. Indeed, like other organizations, GAMA and AOPA say they would want to see a proper ConOps from ICAO for transition well before the Mag2True transition phase, to enable the industry to prepare. Meanwhile there are also those who accuse detractors of exaggerating the problems, and of ignoring input from Global Navigation Satellite Systems (GNSS), widely used by all sectors of GA.

ICAO has, meanwhile, conducted a survey to measure the support for a Mag2True change. The Organisation reported that it received a robust response from more than half the contracting states. Among these respondents – which ICAO confirms came from all sectors of industry, including regulators – less than 10% were resolutely opposed to it. Those most in favour included ANSPs and flight procedure designers. Air operators provided varied levels of support, but less than 15% actually opposed change. Interestingly, the particularly high reported level of appreciation of “forseen benefits” and “additional forseen benefits” appeared to be at odds with the level of nervousness about managing the transition.

ICAO also confirmed that many air operators report already operating True North procedures in remote and oceanic airspace, and also in polar regions.

Given this chance to voice their concerns to ICAO, the industry’s two most important demands were for a clear transition plan supported by regulation and guidance, and for the transition to be wellcoordinated across states, stakeholders and the military. In terms of timescale for implementation, most respondents said five to ten years to prepare is acceptable.

Right now a set of four objectives to prepare for transition have been mooted: development of a global ConOps; development of strategies for implementing True North; analysing the potential safety risks and identifying mitigations; and finally identifying the ICAO Air Navigation Commission Panels that will be impacted and propose tasks accordingly.

Nav Canada’s own ConOps argues that the move to True is unquestionably beneficial – indeed essential – for aviation’s future: “The case for converting to True as the datum for aviation instructions, procedures, and surveillance is clear, and the only problems would be those of practically implementing it. Whilst it would be a large-scale undertaking, it would also be a one-off operation which, once completed, would be final, unlike the present situation, which is also costly and constantly with us, requiring resources to manage it.”

Chairman of the AHRTAG, Nav Canada’s Anthony MacKay, sums up the Group’s conclusion: “The risks of change are known and manageable. The transition will require careful planning and implementation, most likely through ICAO. To remain on magnetic continues to allow a latent threat to safety to reside within our aviation safety system.” Finally, ICAO’s survey found that there is a very high understanding of the many benefits of a True North reference, including more accurate navigation and “eliminating errors caused by MAGVAR”