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Magnetic Variation in Aviation: What Pilots Need to Know

Updated: Dec 19, 2025

Every pilot learns early that headings and courses are based on magnetic north, not true north. But behind that simple rule lies a constantly changing phenomenon that affects navigation, charts, runways, and even instrument approaches: magnetic variation.


Understanding magnetic variation—and how it’s applied in aviation—is critical for accurate navigation, situational awareness, and regulatory compliance. This article explains what magnetic variation is, why it exists, how it’s depicted, and how pilots use it every day.



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What Is Magnetic Variation?

Magnetic variation (also called declination) is the angular difference between:

  • True North (the direction toward the geographic North Pole), and

  • Magnetic North (the direction a magnetic compass points)


This difference exists because the Earth’s magnetic field does not align perfectly with its rotational axis.


Variation is expressed as:

  • East variation, or

  • West variation


For example:

  • 10° East variation means magnetic north lies 10 degrees east of true north.

  • 7° West variation means magnetic north lies 7 degrees west of true north.


Why Magnetic Variation Exists

The Earth’s magnetic field is generated by molten iron moving within the outer core. This field:

  • Is irregular

  • Shifts over time

  • Does not originate at the geographic poles


As a result:

  • Magnetic north moves every year (tens of miles annually)

  • Variation changes slowly but continuously

  • Charts, runways, and navigation systems must be periodically updated


True North vs. Magnetic North in Aviation

True North

  • Used for:

    • Sectional and enroute chart grid references

    • Long-range navigation

    • Satellite-based systems (GPS)


Magnetic North

  • Used for:

    • Magnetic compasses

    • Heading indicators

    • Runway numbers

    • ATC headings

    • IFR navigation procedures


Aviation primarily operates in magnetic references to remain compatible with onboard magnetic instruments.


How Magnetic Variation Is Depicted on Charts

Isogonic Lines

On aeronautical charts, magnetic variation is shown using isogonic lines, which:

  • Connect areas of equal magnetic variation

  • Are labeled with degrees east or west

  • Include an annual rate of change


Example:

  • “10°W (2025) Annual Change 0.2°E”


This tells pilots:

  • The current variation

  • How quickly it is changing over time


Applying Magnetic Variation: True vs. Magnetic

Pilots frequently convert between true and magnetic directions.

A common memory aid is:

  • “East is least, West is best”

  • Subtract easterly variation

  • Add westerly variation


Example

  • True course: 090°

  • Variation: 10° West

  • Magnetic course: 100°


This conversion is essential for:

  • Dead reckoning

  • VOR navigation

  • Cross-checking GPS data

  • IFR flight planning


Magnetic Variation and Runway Numbers

Runway numbers are based on magnetic heading, rounded to the nearest 10 degrees.


Example:

  • A runway aligned to 183° magnetic → Runway 18

  • Reciprocal runway → Runway 36


Why Runway Numbers Change

As magnetic north drifts:

  • Runway magnetic headings shift

  • Eventually exceed rounding tolerances

  • Airports must renumber runways


This has occurred at many airports worldwide and requires:

  • New signage

  • Updated charts

  • Revised approach procedures


Magnetic Variation in IFR Operations

Instrument Approaches

  • Published courses are magnetic

  • Final approach courses are aligned with magnetic north

  • Missed approach instructions use magnetic headings


VOR Navigation

  • VOR radials are oriented to magnetic north

  • Station declination is periodically updated

  • Older VORs may have slight discrepancies if not recently aligned


ATC Instructions

  • Headings assigned by ATC are magnetic

  • Radar displays are referenced to magnetic north

  • Pilots should not attempt to “correct” ATC headings for variation


Variation vs. Deviation (Important Distinction)

These two terms are often confused.


Magnetic Variation

  • Difference between true north and magnetic north

  • Depends on geographic location

  • Shown on charts


Magnetic Deviation

  • Error caused by aircraft magnetic interference

  • Depends on aircraft electrical systems and structure

  • Corrected using a compass deviation card


Both must be accounted for to get accurate compass headings.


Why Pilots Still Learn Variation in the GPS Age

Modern avionics automate most conversions, but pilots must still understand variation because:

  • Charts are still true-referenced

  • ATC operates magnetically

  • Partial-panel or equipment failures require raw navigation skills

  • Checkrides and knowledge tests require understanding

  • Situational awareness improves with deeper knowledge


A pilot who understands variation is less likely to be confused when instruments disagree.


Real-World Example

You’re flying an IFR cross-country:

  • GPS shows a true track

  • Chart course is true

  • Heading indicator is magnetic

  • ATC assigns a magnetic heading

  • Approach plate shows magnetic courses


Knowing which reference applies prevents costly errors.


Final Thoughts

Magnetic variation is an invisible but ever-present factor in aviation. While technology has reduced the mental workload involved in applying it, pilots must still understand:

  • What variation is

  • Why it exists

  • Where it appears

  • How it affects navigation, runways, and procedures


Aviation is built on consistency and shared references—and magnetic variation is one of the quiet systems that makes that consistency possible.


Master it, and you’ll be a more confident, accurate, and professional pilot—whether flying VFR, IFR, steam gauges, or glass.



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