During acceleration or deceleration, the magnetic compass will normally indicate correctly on which headings?

• A. North or South headings
• B. East heading only
• C. West heading only
• D. All headings

Answer: (A)

Acceleration or deceleration can cause a temporary error in the magnetic compass because the needle has inertia and the aircraft is moving through Earth's magnetic field. This inertial effect alters the reading most noticeably when the airplane is on east–west headings, so the compass can momentarily mislead you on those tracks. When you’re flying toward the poles, the orientation of the Earth's field relative to the mast and pivot means the inertial lag doesn’t produce a noticeable deflection, so the compass tends to read correctly. In other words, during acceleration or deceleration the compass is most reliable on north or south headings.