Compass errors: acceleration and deceleration

On an east or west heading, speeding up or slowing down makes the compass show a turn that isn't happening.

MAGNETIC COMPASS
HEADING INDICATOR (actual heading)

1 · Pick a heading

2 · Change speed

Steady speed
The compass matches the heading indicator.
Airspeed 100 ktActual 090°Compass 090°
Key points +
ANDS: Accelerate North, Decelerate South
  • Northern Hemisphere. Largest on east and west headings, no error on north or south headings.
  • The compass shows a turn toward north when you speed up, and toward south when you slow down.
  • The airplane isn't turning. When the speed settles, the compass swings back to the correct heading.
  • Only read the compass in straight, level, unaccelerated flight.