Slowly, the old rules of navigation are changing, and one of the oldest, which dates back before the days of sailing ships, is the rule about magnetic variation and compasses: “Variation East, Magnetic Least; Variation West, Magnetic Best.” That means, for example, that if you’re flying out of Presque Isle, Maine, and want to fly due west, you need to turn onto a compass heading of 290 degrees, because up there, the local variation is 20 degrees West and the variation rule says “West is best.” That is, adding magnetic to true makes it a bigger number, or “best.” But to fly due west out of, say, Seattle, where the variation is around 20 degrees East, you’ll need to head 250 degrees, because when the variation is East, you subtract magnetic from true, making your compass heading a smaller number, or “least.”
By now most of us have forgotten the East/West rule because we rarely need to apply it. Just about every heading we fly, such as VOR radials, ILS localizers, holding patterns, airway centerlines, runway headings and so forth have already been corrected to the local magnetic variation values on aeronautical charts, approach plates and other flight information data. But at ICAO’s Air Navigation Conference (ANC) last November, Nav Canada proposed that aviation should cease using magnetic references and use only directions relative to the geographic, or true, North Pole.
That proposal offers three distinct benefits and appears to have few, if any, disadvantages. First, all satellite and inertial navigation system basic calculations are made relative to True North, and each system’s navigation computer must then convert the true data to magnetic for the specific convenience of the aircraft crew, using its built-in true/mag world conversion tables, and then goes the opposite way to allow crew inputs of heading changes and so on.
Second, it removes a potential, but rare, source of mainly human error in those conversions. But the third and overwhelmingly compelling reason is that the North and South Magnetic Poles are constantly moving slowly below the earth’s surface, and actually at different speeds; the North Magnetic Pole currently moves more quickly, at around 40 nm per year. That is enough to produce changes in local magnetic variation patterns around the world, which in some places can be as much as one degree in three years, and that could necessitate the re-issue of all navigation data and publications covering the affected areas and, in some cases, the repainting of runway headings, all of which can be a significant cost burden for both service providers and (many of which produce many of their own documents) operators.
But the aviation industry’s conversion to a True North standard certainly won’t happen quickly, however desirable it appears. At the ICAO ANC, Nav Canada simply stated its eventual intent to move in that direction and requested comments from attending national representatives.