By David Learmount While professional mariners stopped using the Earths magnetic field as their primary directional reference 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 inertial navigation/attitude and heading reference systems (INS/AHRS), radio beacons and air traffic control surveillance using multiple technologies enables aviation to navigate perfectly without any magnetic reference. The debate about changing from Magnetic to True is no longer about whether to change, but how to manage the change, and when. March 2030 is the proposed date. Modern civil and military aircraft have the capability to fly to a True North reference at the push of a button: a flight management system (FMS) based on an inertial reference system (IRS) is designed to identify True North at startup. When a magnetic reference is required, the FMS computes it from True by applying local magnetic variation from embedded look-up tables. Airways and approach procedures within the FMS, however, may use up to four different sources of magnetic variation (FMS, Procedure Design, Airport, or Station Declination) from either the FMS or an ARINC 242 navigation database, and errors occur when these do not match. With the ubiquitous use of GNSS and the impressive capability of the modern IRS, plus the steady decommissioning worldwide of surface-based radio navigation aids, the decision to rely on Earths 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. Finding a solution 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. The AHRTAG is a Canadian-led multinational team of navigation experts from the USA, UK, France, the Netherlands and Australia, and is chaired by Nav Canadas Director of Operational Safety, Anthony MacKay. The group includes representatives from several national aviation authorities (NAAs), major aircraft manufacturers, pilot associations, and the commercial air navigation charting and aviation information provider Jeppesen. 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. AHRTAG points out that updating aircraft magnetic variation look-up tables is a specialist and expensive maintenance activity that has no effect on the way the aircraft derives its directional information. It merely ensures the result is displayed as a magnetic value, which will incorporate any uncorrected system errors and add them to the originally determined True heading. If a future variation shift is sufficient to require correction to airport assets such as runway and taxiway signage and markings, plus instrument procedures, landing aids documentation, and FMS coding at a major hub, the cost can top $20-30m. The one-off act of moving from Magnetic to True reference is no more challenging than, for example, the periodic task of reorientating VOR and TACAN radio navigation beacons to take account of local magnetic variation changes. Across the industry, stakeholders 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 its airspace because its farnorthern territories contain the (slowly moving) surface location of the magnetic North Pole. Aviators in northern Canadian airspace have employed tried-and-tested procedures for traditional radio navigation beacons and all types of performance-based navigation (PBN) systems. The countrys air navigation service provider (ANSP) Nav Canada, working with the AHRTAG, has almost completed drawing up its concept of operations (CONOPS) for the switch to True within the whole of Canadas airspace. The International Civil Aviation Organization (ICAO) has shown great interest in Nav Canadas Mag2True work, particularly since Canada presented a white paper on the subject to ICAOs 13th Air Navigation Conference (2018), seeking agreement and proposing adoption by 2030. The conference agreed further study of Mag2True cost/benefit should go ahead which it has. The agency is hoping to be presented with ready-made Standards & Recommended Practices (SARPs), and implementation plans to move issues forward. Meanwhile, Canada, together with the IAIN, presented a formal Mag2True information paper at the ICAO High-Level Conference on COVID-19 in October 2021. Questions remain about timing. Should the switch to True be global and simultaneously on a single date, managed regionally, or by hemisphere? 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. Its thinking is moving in much the same direction as Canadas, recognising that pilots are already accustomed to incorporating differences that come into play at airspace borders. For example, the use of metres instead of feet below transition altitude in China, the Russian Federation and a few other states. 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 such as General Aviation (GA) is softening to the point of disappearance, especially as GA is now a big user of GNSS systems, whether employing installed avionics, hand-held GPS devices specified for aviation, or electronic flight bags. Similarly, airline pilot associations and airlines themselves seem generally happy about the proposed changeover, for which the accepted shorthand has become Mag2True. Canadas CONOPS Canadas 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 (OEM); aerodromes; and, finally, ANSPs. Overseeing this will be the NAAs, with ICAO keeping an eye on standardisation. But questions remain about timing. Should the switch to True be global and simultaneously on a single date, managed regionally, or by hemisphere? Canada proposes 2030 as a target transition year, with NAAs and ANSPs and states triggering the change. If a target date can be agreed, it would be entered in ICAOs Aeronautical Information Regulation and Control (AIRAC) calendar in the normal way for promulgating changes. The draft CONOPS proposes that, in the six months ahead of Mag2True transition, the state would not action any changes to its aviation information publications (AIP), freezing all but emergency changes to procedures. The only changes promulgated would be changes to convert Magnetic to True. During this time, the state would also need to enact a plan to rotate its VORs and ensure surveillance systems and air traffic controllers were all ready for the change. All states have a procedure in place for crews to adjust VOR radials (plus or minus bearing values) until publication of the corrected values once the VOR is rotated and calibrated. The Mag2True transition date would be the last rotation of VORs, because once set to 0 or True they would never need to be rotated 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 successfully tested this conversion method, which was demonstrated via a CRJ 200 flight test with Nav Canada. The draft CONOPS proposes a way of staging the changeover. The yellow areas of the image below designate the places where existing magnetic variation is small. VORs in those areas could be aligned safely today to within plus or minus 4 degrees of True North, and would still fall within the current tolerance of many states. Canada uses plus or minus 2 degrees as a tolerance, but, given the amount of magnetic variation change from coast to coast, Canada would have to rotate its VORs anyway. US/UK World Magnetic Model Epoch 2020.0 Main Field Declination (D) For many aerodromes in areas within the magenta and yellow zones where the variation is less than plus or minus 10 degrees 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. Areas shaded in green are the regions where True North is already in use today. For the remaining areas, change would have to be more carefully managed. But these areas are predominantly either oceanic, or cover Canada, USA, Russia, and Brazil, the states most accustomed to having to implement updated variation values. As many carriers already use True tracks during oceanic operations, there would be little or no change for the ANSPs managing oceanic areas, or for 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 adjusted vector headings for common procedures were included in any memory aids for controllers. With the exception of NDB approaches and vector headings, however, most other conventional and PBN procedures are now track-based anyway, allowing correct tracks over the ground to continue during the change period. The heading error would appear as apparent wind drift, however, and that could be misleading to aircrew. Crew confusion could indeed arise from changes to routines, especially to oft-flown procedures. On the other hand, there is plenty of potential for confusion in a system that continues to use two heading references, especially where one is variable. Here are just two examples of repeating heading reference problems that are endemic to the existing system: A Boeing 757 was flying a CAT II approach to runway 29 at St Johns, Newfoundland, Canada. When it intercepted the localiser, the aircraft rolled back and forth across the localiser trying to maintain the centreline. The cause was that the magnetic variation of the published procedure differed from the out-of-date magnetic variation tables in the aircrafts IRU. At Calgary, Canada, a crew was testing the CAT III approach to the new runway 17L. The crew observed that the synthetic runway image in the head-up guidance system was misaligned by 7 degrees compared with 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, and suddenly the synthetic and actual world aligned perfectly. In the months that followed, many crews conducting autolands on 17R at Calgary reported the aircraft moving off the centreline when transitioning to autonomous flare mode. In all cases, those aircraft were found to have out-of-date magnetic variation tables in their IRUs. Canadas CONOPS offers a route to modernity and the avoidance of needless costs for the aviation industry. Moreover, the case for Mag2True will probably become unstoppable as the numbers of RPAS and autonomous platforms increase they already navigate in True. Why would aviation want to persist with two systems of reference, where True generates stability and Magnetic has to be constantly managed for error? NAVIGATION Aviation prepares to reorientate