Magnetic Variation, commonly abbreviated as MAG VAR, is a critical concept in aviation that pilots and navigators must understand to ensure accurate course plotting and navigation. Essentially, magnetic variation refers to the angular difference between True North (geographic north) and Magnetic North (the direction a magnetic compass points). This variation affects compass readings and must be accounted for in all navigational calculations.
In aviation, ignoring Magnetic Variation can result in significant navigational errors, especially over long distances. Since the Earth’s magnetic field is not fixed and varies geographically, the magnetic variation changes depending on location and time. This article will delve into the fundamentals of Magnetic Variation, its importance in aviation, how it is calculated, and how pilots compensate for it during flight operations.
Understanding Magnetic Variation in Aviation
Magnetic Variation is defined as the angle on the horizontal plane between magnetic north and true north. It is expressed in degrees east or west depending on whether magnetic north lies east or west of true north at a particular location. For example, a variation of 10°E means magnetic north is 10 degrees east of true north, whereas 15°W means magnetic north is 15 degrees west.
The Earth’s magnetic field originates from the molten iron in the Earth’s outer core and changes over time due to geomagnetic variations. These changes lead to shifts in the position of Magnetic North, which in turn alter the magnetic variation values around the globe. The variation can range anywhere from 0° to as much as 30° or more depending on the geographic location. For instance, near the agonic line—where true north and magnetic north align—the variation is zero.
To help pilots, aviation charts such as sectional charts and enroute charts provide magnetic variation values for different regions, often along with annual rates of change. These charts are essential for updating flight plans and ensuring accuracy in compass readings. The National Geospatial-Intelligence Agency (NGA) regularly updates magnetic variation data, available through online resources like the [World Magnetic Model](https://www.ngdc.noaa.gov/geomag/WMM/).
How Pilots Use Magnetic Variation for Navigation
In practical aviation navigation, pilots convert between True Heading, Magnetic Heading, and Compass Heading, using Magnetic Variation as a key correction factor. True Heading is the direction relative to True North, Magnetic Heading is relative to Magnetic North, and Compass Heading is the heading indicated by the aircraft’s magnetic compass, which can be further influenced by compass deviation.
The conversion formula frequently used is:
- Magnetic Heading = True Heading ± Magnetic Variation
When the variation is east, it is subtracted from the true heading, and when west, it is added. This ensures the compass reading aligns correctly with the Earth’s magnetic field. For instance, a true heading of 090° with 5°E magnetic variation results in a magnetic heading of 085°. Conversely, a 090° true heading with 10°W variation yields 100° magnetic heading.
Failure to correctly adjust for Magnetic Variation can lead to deviations from the intended flight path. Over long flights, even a small error of 2-3 degrees can cause a significant off-course situation, potentially leading to hazardous circumstances. Modern GPS-based navigation minimizes reliance on magnetic compasses, but backups and cross-checks with magnetic headings remain mandatory in aviation.
Factors Affecting Magnetic Variation and Its Future in Aviation
Several factors influence the Magnetic Variation experienced at any particular point on Earth. These include the slow drift of the magnetic poles, solar activity, and local magnetic anomalies. The movement of the North Magnetic Pole has accelerated in recent decades, shifting approximately 55 kilometers per year towards Russia. This dynamic nature requires constant updates to aviation maps and instruments.
Magnetic variation changes approximately 0.1° to 0.2° per year in many regions, though this rate is higher near the poles and very low near the equator. Aviation authorities recommend pilots check the latest information from updated charts before flight planning and adjust navigation computations accordingly. Aircraft certified with Magnetic Heading systems include the capability to input updated magnetic variation figures so flight instruments reflect current magnetic conditions.
Looking ahead, increasing adoption of satellite navigation systems such as GPS, GLONASS, and Galileo may eventually reduce dependence on magnetic compasses. However, magnetic compasses remain an essential backup navigation tool. Understanding and properly applying Magnetic Variation is fundamental knowledge for all aviators to maintain safe and accurate navigation.
For detailed, up-to-date magnetic variation data and aviation guidance, consult official resources such as the [FAA Aeronautical Information Manual (AIM)](https://www.faa.gov/air_traffic/publications/atpubs/aim_html/), which provides comprehensive definitions and instructions relevant to MAG VAR use in aviation operations.
For More: What is ADIRS in Aviation? (Air Data And Inertial Reference System)
