The heading indicator experiences drift errors due to gyroscopic precession. What is this drift error called?

• A. Nutation
• B. Precession
• C. Lag
• D. Drift

Answer: (B)

Gyroscopic precession is what causes that kind of slow drift on a heading indicator. When the spinning gyro is subjected to a torque to change heading, the axis moves in a direction 90 degrees to the torque due to precession. That motion shows up as a gradual misreading of heading even though the airplane’s real heading hasn’t changed. Nutation would be a brief wobble right after a disturbance, not a sustained drift. Lag is just a delayed response to a real heading change, and drift alone is too generic to name the specific gyroscopic behavior. So the drift you’re seeing from the heading indicator is called precession.