The Earth
The Solar System & Time
Charts
Using Aeronautical Charts
Basics of Navigation
Distance, Speed & Time
Vertical Navigation
Fuel Planning
Practical Navigation Techniques
Radio Navigation
Practice Exam

Compass Deviation & Errors

Magnetic Dip

The magnet suspended in our compass aligns with Earth’s magnetic field. However, as we move away from the equator, the magnetic field is not parallel to the Earth’s surface. This causes the magnet to ‘dip’ towards the pole.

At the equator, magnetic dip is 0°
At the poles, magnetic dip is 90°

This means that at latitudes greater than 60° North or 60° South the magnetic compass is less accurate.

Dip Angle

The magnetic force (from the Earth’s magnetic field) that the magnet aligns itself to is known as the Total Magnetic Force (T). This can be divided into the Horizontal Component (H) and the Vertical Component (V).

The Dip Angle is the angle between the Horizontal Component (H) and the Total Magnetic Force (T).

In other words, the dip angle is how far ‘down’ the magnet has dipped from horizontal.

As latitude increases, the Horizontal Component (H) decreases, the Vertical Component (V) increases and Dip Angle increases.

Compass Errors

Some aircraft components create their own, weaker magnetic fields which interfere with the ability of the compass to align with the Earth’s magnetic field. This causes slight errors in the compass. Components that create their own magnetic fields include:

Aircraft electrical systems
Aircraft metal components
Headsets and other electrical devices (phones, iPads etc.)

The effects of the aircraft’s electrical and metal components cause the compass to point towards Compass North (°C) instead of Magnetic North (°M). The difference should only be slight and will vary in each aircraft. A compass deviation card is placed in the aircraft which advises you of the Compass Deviation. It will state, for example, “For North, Steer 001” This means that to fly a heading of magnetic north, you should steer towards 001° on the compass.

A typical compass deviation card