Mag2True: Aviation prepares to reorientate


Whilst professional mariners stopped using the earth’s magnetic field as their primary directional reference some fifty 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 GNSS (global navigation satellite systems) – backed up by ring laser gyro-stabilized 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, and 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 424 navigation database, and errors occur when these do not match.

With the ubiquitous use of GNSS and the impressive capability of modern inertial reference systems (IRS), plus the steady decommissioning worldwide of surface-based radio navigation aids, the decision to rely on the constantly changing earth’s 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. The AHRTAG is a Canadian-led multinational team of navigation experts from the USA, UK, France, the Netherlands, Croatia and Australia, and is chaired by Nav Canada’s Director of Operational Safety, Anthony MacKay. The group includes representatives from several national aviation authorities (NAA), major aircraft manufacturers, pilot associations, and also 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. And if a future variation shift is sufficient to require correction to 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.

The one-off act of moving from Magnetic to True reference is no more challenging than, for example, the periodic task of re-orientating 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 far-northern territories contain the (slowly 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 to True within the whole of Canada’s airspace.

The International Civil Aviation Organization (ICAO) has shown great interest in Nav Canada’s “Mag2True” work, particularly since Canada presented a White Paper on the subject to ICAO’s 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. Meanwhile, Canada presented a formal Mag2True information paper at the HLCC in October 2021, and a presentation by AHRTAG on True North was already on the agenda of ICAO’s European PBN Task Force/Navigation Steering Group meeting in early December 2021.

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 is also warming to the idea. According to FAA sources, the agency’s thinking is moving in much the same direction as Canada’s, recognizing 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, or thousands of feet, but in China, the Russian Federation and a few other states, altitudes below the transition level are in meters.

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 – also chief executive of the UK Flight Safety Committee – 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 believes it is wise – when playing “what if” games with the proposed system – to admit the existing one has many 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 electronic flight bags (EFB tablet computers). Similarly, airline pilot associations and the airlines themselves, seem generally happy about the proposed changeover, for which the accepted shorthand has become Mag2True.