In the Northern Hemisphere, if an aircraft is accelerated or decelerated, the magnetic compass will normally indicate correctly when on which heading?

• A. North or South heading
• B. East heading
• C. West heading
• D. Any heading

Answer: (A)

When accelerating or decelerating, the magnetic compass in the Northern Hemisphere can show a temporary error due to acceleration effects. This is often described as the acceleration error: speeding up tends to pull the reading toward the north, while slowing down tends to pull it toward the south. This disturbance is most noticeable on east or west headings, where the misreading can make you think you’re slightly turned toward a different direction.

On a north or south heading, however, the acceleration-induced deflection aligns with the direction you’re already facing, so the compass continues to indicate the actual heading. In other words, the influence of speeding up or slowing down does not cause a significant left-right error when you’re pointing along the north-south meridian, so the reading remains reliable there.