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PilotSchool Knowledge Base

Magnetic Variation and Direction

In aviation navigation, accurately applying magnetic variation is essential for converting true direction into magnetic direction. Ground navigation charts typically align with true north, while most aircraft compass systems align with magnetic north. Understanding and applying magnetic variation is crucial for precise navigation and operational safety.

Understanding Magnetic Variation

Definition

Magnetic Variation (Declination): The angular difference between true north (geographic north) and magnetic north. This variation depends on both geographical location and changes over time due to shifts in the Earth’s magnetic field.

Causes of Magnetic Variation

  • Earth’s Magnetic Field: Variations occur because the Earth’s magnetic field does not perfectly align with its geographic poles.
  • Polar Wandering and Earth’s Core Flows: Both cause changes in magnetic declination over time.
  • Local Influences: Earth’s crustal composition, such as iron ore deposits, can affect local magnetic variation.

Measurement

  • Isogonic Lines: Indicate areas of equal magnetic variation on navigation charts.

  • Agonic Lines: Indicate where the magnetic declination is zero.

  • Direct Measurement: Declinometers or aeronautical charts measure and display local magnetic variation.

  • World Magnetic Model (WMM): Provides a standardized approach to measure and predict magnetic variation globally.

  • Magnetic Variation | SKYbrary Aviation Safety

  • Magnetic declination | Wikipedia

Converting True Direction to Magnetic Direction

Importance in Navigation

Converting between true and magnetic headings is critical for aligning navigational systems, including aircraft compasses, with ground-based references.

The Adjustment Rule

To convert a true direction to a magnetic direction, apply the magnetic variation as follows:

  • Variation East: Subtract from true heading to get magnetic heading (“East is least”).
  • Variation West: Add to true heading to get magnetic heading (“West is best”).

Practical Example

  1. Given: True heading of 090° and a magnetic variation of 5° West.
  2. Calculation: 090° (true) + 5° (variation west) = 095° (magnetic).

This mnemonic—“East is least, West is best”—assists pilots with quick conversions and is a crucial part of pilot training.

Practical Applications

Compass Adjustments

Regular adjustments to the compass are necessary for ensuring the navigational systems remain aligned with magnetic north. This impacts runway numbering and flight planning activities, significantly affecting the accuracy of aviation operations.

Systematic Calibration

Frequent updates and calibrations of instruments, references, and charts involving magnetic variation ensure alignment with the current conditions of the Earth’s magnetic field.

Understanding and effectively applying magnetic variation is integral to achieving accuracy in both flight planning and execution, thereby promoting aviation safety.