Acceleration error affects which instrument on certain headings?

• A. Magnetic compass
• B. Airspeed indicator
• C. Altimeter
• D. Attitude indicator

Answer: (A)

Acceleration error is a quirk of the magnetic compass. When the airplane speeds up or slows down, the compass needle doesn’t respond instantly because of inertia and the damping fluid inside the instrument. This causes a temporary deflection in the displayed heading. The effect is most noticeable on east or west headings, where a rapid acceleration can make the compass read a slightly different direction than the actual track. Specifically, accelerating tends to pull the reading toward a northerly indication, while decelerating pulls it toward a southerly one, until the compass settles. So, on certain headings, the magnetic compass reading can be misleading due to this acceleration error.