Which instrument's readings can be affected by gyro precession and mounting conditions, requiring periodic alignment with the magnetic compass?

• A. Airspeed Indicator
• B. Vertical Speed Indicator
• C. Heading Indicator
• D. Attitude Indicator

Answer: (C)

Heading information is provided by a gyro-based instrument that tracks the aircraft’s horizontal direction. Because its gyro isn’t tied to the Earth's magnetic field, it drifts due to gyro precession and any mounting misalignment. Over time this causes the indicated heading to wander from the actual magnetic heading, so pilots periodically set or align this instrument with the magnetic compass to keep it accurate. The airspeed and vertical speed indicators rely on pitot-static pressures and aren’t affected by gyroscopic precession, while the attitude indicator is gyro-based but references an artificial horizon rather than the magnetic field, so it’s not aligned with the magnetic compass during normal operation.